GB2455351A - Planar air amplifier on substrate - Google Patents

Abstract

An air amplifier jet pump is formed by etching channels in a planar substrate 212 and closing with a lid 211. Secondary or induced gas is introduced into a converging section of a main channel 204 and primary gas is introduced through slots 209a,b in the walls of the channel at a waist in the channel and adheres to the walls 206a,b of a diverging section by the Coanda effect. The primary gas induces secondary gas flow by a Venturi effect pressure drop. The secondary gas may contain an analyte in the form of ions from an electrospray to provide an increased analyte signal in sensor and analysis systems e.g. a mass or and ion mobility spectrometer. May be formed using different combinations of photolithography and etching, and an example is presented of a microengineered air amplifier integrated with a microengineered electrospray ionization source on common substrates e.g. metallic or semiconductor.

Description

Air amplifier

Field of the Invention

This invention relates to mass spectrometers and ion mobility spectrometers and in particular to a method of increasing signal sensitivity in such sensors.

Background

An air amplifier (otherwise known as an airflow amplifier or an air ejector) is a well-known device, used to increase the flow of a gas by a combination of the Coanda effect and the Venturi effect. The former is a phenomenon in which a gas flow can adhere to a convex boundary [Panitz 1972]. The latter is a phenomenon in which increased velocity in a gas flow causes a reduction in pressure. Air amplifiers have no moving parts, and hence require low maintenance. They have a variety of applications including fan replacements, spray guns, cleaning equipment and devices for removal of fumes or sawdust.

Air amplifiers use the discharge of a small volume of a primary gas at high speed near the walls of a shaped channel to increase the flow of a much larger volume of a secondary gas moving more slowly through the centre of the channel. The channel commonly has cylindrical symmetry, with a convergent tapered input and a divergent tapered output.

The secondary gas is inserted through the convergent input and leaves through the divergent output. The primary gas is inserled through an annular slot in the channel wall at the junction of the two tapered sections where there is a convex wall. The slot has a lip to deflect the primary flow towards the output, parallel to the walls of the channel, where it adheres by the Coanda effbct. The rapid flow of the primary gas results in a reduction in pressure along the centreline of the secondary gas channel by the Venturi effect, which in turn incivases the flow of the secondary gas [GB 863,124, US 3,047,208].

Air amplifiers arc conventionally constructed by machining or moulding three-dimensional shaped metal parts. Considerable effort has been expended on their design, particularly with regards to simple methods of providing the shaped slot and manufacturing removable parts [US 2,965,312; US 3,806,039; US 4,046,492].

Figure 1 a shows in sectional schematic the main features of a typical prior art air amplifier formed by conventional methods [adapted from US 4,046,492]. The device has two main parts, an input part 101 carrying a strongly convergent conical tapered input hole 102 and a concentric lip 103, and an output part 104 carrying a shallow conical input hole 105 connecting to a weakly divergent conical tapered output hole 106. The features 102, 103, 105 and 106 are cylindrically symmetric about a central axis 107. The two parts 101 and 102 are held together by screws 108. The holes 102, 105 and 106 combine to form a channel for the secondary gas with a convergent entrance and a divergent exit. At the waist between the sections 105 and 106 the channel wall is convex. The lip 103, the shallow conical hole 105, a concentric channel 109 and a threaded input pipe 110 form the input for the primary gas that enters the secondary gas channel by a slot 111 at the waist.

Figure lb shows the operation of the air amplifier in Figure la. The primary gas 112 is injected from a pressurised supply through the threaded input pipe 110. The primary gas is distributed around the circumference of the secondary gas channel by the concentric channel 109, and enters the secondary gas channel by the slot 111, where it is deflected by the lip 103. Through the Coanda effect, the primary gas forms a flow layer 113 adhering to the convex walls of the divergent section of the secondary gas channel 106.

Through the Venturi effect, the velocity of the primary gas flow then causes a pressure drop in the secondary gas channel, increasing the flow of a gas 114 passing through this channel.

Recently, a new application has been described in which air amplifiers are used to increase the flow of a gas carrying analyte ions by electrospray ionization towards an analytical instrument such as a mass spectrometer [US 6,992,299]. Electrospray ionization is a method of generating ions at atmospheric pressure from a liquid source [Fenn 1989]. The liquid is typically a dilute solution of analyte in a solvent. The spray is induced by the action of a strong electric field at the end of capillary containing the liquid. The electric field draws the liquid out from the capillary into a Taylor cone, which emits a spray at a threshold field that depends on the physical properties of the liquid and the diameter of the capillary. Increasingly, capillaries with internal diameters below 50 microns known as nano-electrospray capillaries or nanospray capillaries are used to reduce the threshold electric field and the volume of spray [1 lannis 1998]. however, maximum use must then be made of the ions generated in a subsequent analytical instrument.

In recent experiments involving air amplifiers and electrospray, a conventional air amplifier was placed between an electrospray source and an atmospheric pressure ionization mass spectmmetcr [Zhou 2003; Hawkridge 2004]. A mass spectrometer is a vacuum instrument that separates ions of different species according to their charge-to-mass ratio. When the ions are created at atmospheric pmssure, they are coupled into the high vacuum chamber of the mass spectmmcter via a differentially pumped interface chamber whose inlet is known as a sampling cone. Increased ion signals were obtained from a combination of increased secondary gas flow, aerodynamic focusing of the spray and electrostatic focusing of the ions, which resulted in a more concentrated ion stream passing into the mass spectmmeter.

It can be expected that similar benefits will be obtained using an alternative analysis technique such as ion mobility spectromeiry (also known as plasma chromatography or gaseous electrophoresis). An ion mobility spectmmeter separates ions according to their mobility in an electric field when travelling in a background gas with a pressure close to atmospheric pressure [Cohen 1970]. Ion mobility spectrometers can again operate using an clectrospray ion source [Wittmer 1994], and systems that combine electrospray with both ion mobility separation and mass spectmmetry have also been developed [Wu 1998].

It is desirable to exploit this cfilct in applications where the ion signal is inherently limited, for example in a miniaturised system that might allow a low cost identification of different chemical species. Applications for such systems lie in portable sensors for the detection of chemical and biochemical weapons and low cost analysis for pharmaceutical chemists. Some advances have been made in miniaturised mass spectrometers. For example, small quadrupole electrostatic mass filters have been constructed by stacking together multilayer silicon substrates containing etched mounting features for cylindrical electrode rods and used as quadrupole mass spectrometers [Geear 2005]. Electrospray sources have also been miniaturised, either as planar devices containing etched channels [Ramsay 1997; Licklider 2000] or as planar devices that mount nanospray capillaries [Syms 2007; GBO5 19439.4]. Ion mobility spectrometers have also been miniaturised as planar devices, using either printed circuit boards [Eiceman 2007] or microfabricated electrodes [Miller 2002].

Existing designs of air amplifiers are large, involved complex three-dimensional features, and cannot easily be combined with such sources in the form of a planar integrated device. Consequently, there is a barrier to miniaturisation of an overall system involving the use of an air amplifier to increase ion signals generated by electrospray or nanospray ionization.

Summary

These and other problems are addressed in accordance with the teaching of the present invention by a miniature air amplifier provided in a planar integrated form that may easily be combined with a miniature atmospheric pressure ionization source such as for example a nanospray source. Such a latter device may also be provided in integrated form.

This invention also pmvides a method for forming miniature air amplifiers on planar substrates, to achieve an increased flow of a secondary gas through a channel by the action of a primary gas flow. The device may be fabricated by a combination of photolithography and etching, and can also be integrated with other microengineered components such as a nanospray ionization source. Using such a device it is possible to provide an increased analytc signal in mass spcctmmetry and ion mobility spectrometry.

Accordingly there is provided an air assembly according to claim 1. Advantageous embodiments are provided in the dependent claims. An assembly according to claim 22 is also provided with advantageous embodiments thereof provided in the dependent claims thereto.

The construction and operation of thc micmenginecred air amplifier can be befter understood with reference to Figures 2 -10.

Brief Description of the Drawings

Figure 1 shows an air amplifier according the prior art, a) in schematic and b) in operation.

Figure 2 shows a schematic of a planar microengineered air amplifier a) in plan and b) in section, according to the present invention; Figure 2c shows an alternative section.

Figure 3 shows the operation of a planar microengineered air amplifier a) in plan and b) in section, according to the present invention.

Figure 4 shows a schematic in plan of a planar electrospray ionization source based on a

nanospray capillaiy according to the prior art.

Figure 5 shows a fabrication pmcess for forming a planar clectmspray ionization source based on a nanospray capillary according to the prior art.

Figure 6 shos the operation ola planar electrospray ionization source based on a nanospray capillaiy

according to the prior art.

Figure 7 shows a planar microengineered air amplifier used in combination with a planar electrospray ionization source, according to the present invention.

Figure 8 shows the operation of the Coanda-assisted electrospray source of Figure 7.

Figure 9 shows an alternative configuration of a planar microengineered air amplifier and a planar electrospray ionization source according to the present invention Figure 10 shos the operation of' the C'oanda-assisted clectrospray source of Figure 9.

Detailed Description of the Drawings

Main components of a known prior art arrangement for provision of an air amplifier have already been discussed with refrcncc to Figure 1. It will be appreciated that the construction of the two parts shown in Figure 1 involves complex three-dimensional machining operations. Although these are easy to carry out for macroscopic components such as the context of Figure 1, below a certain size scale, typically between ten and a hundred microns in feature size, conventional machining methods such as milling, slotting and drilling become inappropriate for fabricating complex structures.

The present invention addresses these pmblcms by employing alternative techniques and specifically microengineering or microfabrication methodologies. These processes are known, for example in the manufacture of micro-electro-mechanical structures(MEMS) and are generally carried out on planar substrates, which are often silicon or multilayers containing silicon. The most important of the processes considered here include: * Patterning methods such as photolithography, especially on a non-planar surface or using a resist that may act as a structural material * Etching methods such as crystal plane etching of silicon, deep reactive ion etching of silicon and powder-blasting of glass * Bonding methods such as thermocompression bonding of gold and bonding of silicon * Coating methods such as sputtering of metals, and electroplating of metals These methods are well known to those skilled in the art, and can be employed in many different combinations to achieve a given microstructured object.

Using such methods, it is still difficult to form three-dimensional structures containing features with the rotational symmetry of Figure 1. However, the present inventor has realised that it is possible to form quasi three-dimensional structures based on pmjections of two-dimensional patterns that embody many of the main features of the desired structure while employing MEMS type techniques. For example, Figure 2 shows an approximation of the air amplifier of Figure 1, according to the teaching of the present invention. here, features corresponding to those of a conventional air amplifier are provided on the two sidewalls of a channel with a rectangular cross-section, but not on its upper and lower walls.

The device is constructed from two parts: a base part 212 and a lid part 211, which are assembled to form the complete structure of the amplifier. Provided between each of the base and lid parts are a number of channels which are formed from for example a combination of photolithography and etching techniques. Figure 2a shows a base part 212, which is a multilayer formed from an upper layer attached to a substrate. The substrate 201 carries two holes 202a, 202b, which arc provided to enable a gas to be intmduced into the channels. These holes will be discussed later with regard to the provision of a primary gas for the amplifier. The upper layer is structured into two raised portions 203 a, 203b surrounding the holes 202a, 202b and separated by a channel 204 which forms a throughput channel for the amplifier and within which a secondary gas of the amplifier may flow. The two portions 203 a, 203b are outlined by features whose perimeters are formed as vertical walls in the upper layer. In this way the portions 203a, 203b define sidewalls for the throughput channel 204. The sidewalls are not straight or co-planar in that each wall may be sub-divided into a number of different regions whose relative orientation to each other is different.. Looking left to right on the plan view of Figure 2, it will be noted that the sidewalls define a pair of strongly tapered input features 205a, 205b and a pair of weakly tapered output features 206a, 206b and an intermediate pair of substantially parallel features. The throughput channel 204 may therefore be considered as having a strongly tapered entrance and a weakly tapered exit. A gas flowing through the throughput channel will therefore pass through an initial convergent input where it undergoes a constriction, passes through a convex waist provided by the parallel side walls and then undergoes expansion as it passes through the divergent output.

A primary gas may be introduced into the main or throughput channel 204 through a feed channel defined in the side walls. It will be understood that each of the side walls have a feed channel such that the primary gas can be introduced on both sides of the thnughput channel. It will be understood that if only one side wall was provided with a feed channel that an element of amplification would be provided but this effect is improved by having a primary gas along each side of the secondary gas, as is provided by having a feed channel on both sides of the main channel. Each feed channel may be considered as having a number of segments. Inlet regions arc provided by two gas flow channels defined by holes 207a, 207b in the upper layer that surround or overlay the holes 202a, 202b in the substrate. A gas can then be introduced through the holes 202a, 202b into the inlet region 207a, 207b. The gas will then how from the inlet regions along passage regions provided by two channels 208a, 208b leading to exits 209a, 209b into the main throughput channel 204 adjacent to two lips 210a, 210b. It will be appreciated that the exits 209a, 209b provide first and second outlets in the sidewalls for the primary gas to be fed into the main channel 204. It will be understood that when travelling along the passage regions the gas is travelling in a direction substantially perpendicular to the direction of flow of the secondary gas within the main channel 204. At the lips 21 Oa, 2 lOb, the primary gas is deflected sidewardly such that the primary gas enter the main channel in a direction along the direction of flow of the secondary gas.

These features all may be provided using planar processing. However, it is generally difficult to form a monolithic structure containing completely closed channels by planar processing methods. Instead, the channels may be closed as shown in Figure 2b, by attaching a lid part 211 to the base part 212 containing the features shown in Figure 2a, taking care to minimise gas leaks through any joints thus formed. The lid and base cooperate to define upper and lower surlüces for the channels such that fluid (be that in the gaseous or liquid) phase is contained within the channels.

The lid part 211 may be featureless or a simple planar surface, and simply designed to provide a surface that seals all the channels in the base part simultaneously. In this case, the axis of the secondary gas flow will lie at a distance of half the upper layer thickness above the substrate. Alternatively, the lid part may be a bilayer structure 213 containing all the features shown in Figure 2a except the holes 202a, 202b through the substrate-in other words a mirror image of the construct of the base. In this case, a device with twice the overall channel height will be formed, as shown in Figure 2c, and the axis of the secondary gas flow will lie approximately at the interface between the two assembled components. 11 will be appreciated that the axis of the secondary gas flow has a significance in the operation of the device, and consequently that the choice of construction will depend on the desired location of this axis.

It will also be appreciated that many of the features of the micmengineered air amplifier in Figure 2 correspond directly to those in the prior art device in Figure 1. For example, the holes 202a, 202b are analogous to the primary gas input 110. The strongly tapered input features 205a, 205b are analogous to the strongly convergent tapered input hole 102 for the secondary gas, and the weakly tapered output features 206a, 206b arc analogous to the weakly divergent tapered output hole 106. The connecting channels 208a, 208b are analogous to the surrounding concentric channel 109, the exits 209a, 209b are analogous to the exit Ill and the lips 210a, 210b are analogous to the concentric lip 103. However, the features in the microengincered air amplifier are arranged in pairs on either side of a rectangular channel, rather than concentrically around a circular channel-they are provided in a planar structure.

Thus in providing quasi two-dimensional analogues to these earlier three-dimensional features the microengineered air amplifier can provide a similar function, as shown in Figures 3a and 3b. Here two primary gas streams 3Ola, 301b that are injected through the holes 302a, 302b in the substrate follow the primary gas delivery channels until they are deflected by the lips 303a, 303b. The primary gas streams then adhere to the convex walls 304a, 304b of the secondary gas channel through the Coanda effect to form output streams 305a, 305b. The velocity of the primary gas then causes a pressure drop in the secondary gas channel, increasing the flow 306 of a secondary gas passing through this channel. It will be appreciated that the flow line 306 defines a longitudinal axis of the main throughput channel 204.

The two primary gas streams 301a, 301b may be conveniently provided from a single input 307 by holding or providing the air amplifier on a mount 308 containing drilled gas lines, which may be formed by conventional machining. A gasket 309 formed for 1) example in an elastomer may provide a suitable gas-tight seal between the air amplifier and the mount.

It will be appreciated that there arc many different combinations of materials and processes that may be used to form a planar microengineered air amplifier as described here. For example, the base part may be formed from two identical materials or from two different materials. The upper layer will typically be a conductor or a metallised semiconductor to prevent charging by the ion stream and allow application of a voltage to assist in transferring ions through the secondary gas channel. An example of a suitable metal is nickel and an example of a suitable semiconductor is silicon. Both these materials may easily be structured. The silicon will desirably be coated in metal to allow an electrical contact.

Depending on the application, the substrate layer may be a conductor, a semiconductor or an insulator. An insulating substrate may be used if it is desired to combine a microengineered air amplifier with another electrical device in monolithic form.

Examples of suitable insulating materials are plastics, glasses and ceramics. If an insulating substrate is used it may be desirable to cover the substrate with a conducting layer in the vicinity of the secondary gas channel, to prevent charging by the ion stream and allow application of voltages. Alternatively, a residual thickness of the upper layer material may be retained in the vicinity of the secondary gas channel 204 between the blocks 203a and 203b in Figure 2a.

Although the layout of the two layers will be defmed using lithography, the features will be constructed by removing or adding material. Material removal may involve processes such as etching or powder blasting. Plasma etching methods such as deep reactive ion etching [Hynes 1999] are appropriate for structuring an upper layer of silicon, since they may define deep features with vertical sidewalls. Powder blasting methods arc appropriate for structuring a base layer of glass, since they may easily define features such as via holes and gas inlets. Material addition may involve electroplating of a metal such as nickel in a mould. Such methods are again appropriate for structuring the upper layer, since they may define deep conducting katures with vertical sidewalls. Alternative methods of material addition include the use of thick epoxy photoresist. Such methods arc appropriate for structuring the base layer, since they may provide insulating features with high aspect ratio.

The lid part may again be formed from a similar material to the base layer or a different material. Different bonding methods may be used to attach the lid to the base, including soldering, bonding and the usc of an epoxy resin, which maybe of a conductive type. It will be apparent that the use of such methods can easily provide an electrical contact between the lid part and the upper layer of the base part.

In selecting the fabrication process, major requirements will be provision of mechanical, electrical and thermal functionality and compatibility with other integrated components.

Here, we describe a process (which is intended to be exemplary rather than exclusive) that allows co-integration with our co-assigned prior art nanospray source [GBO5 19439.4; Syms 2007].

Figure 4 shows the construction of the prior art nanospray source, which consists of two parts, a base part 401 and a lid part 402. Each part consists of two layers: a base layer 403 with through holes and a structural layer 404 carrying component mounts and electmdes.

Because the base layer 403 provides electrical isolation (and hence withstand the voltages of around 1 kV that are applied between elcctmdcs during nanospray) it is formed in an insulating material. Mechanical constraints will be appreciated as providing a determination of the exact choice of insulator.

For example, because the base layer 403 in the base part 401 carries an inlet 405 to allow gas to be passed through for nebulization of the spray, together with a drain 406, the insulator used may be an epoxy-based photoresist, SU-8 [Lorcnz 1997]. This material may be patterned in layers several hundred microns thick, and allows the outline of the base layer and any additional through-holes to be defined in a single patterning step.

Because the structural layer 404 provides a locating mount for the nanospray capillary, together with conducting electrodes set up normal to the base layer, it is formed from a metallised semiconductor. The semiconductor used in this arrangement is (100) oriented silicon, since this material can be patterned by a combination of crystal plane etching [Bean 1978] and deep reactive ion etching [1-lynes 1999] to form V-shaped grooves and vertical electrodes.

For example, the structural layer 404 in the base part 401 carries a mount for a nanospray capillary 405 in the form of a raised block 406 carrying an etched V-shaped groove 407.

The groove is continued along the stmcture to provide a groove 408 in a nebulizer block 409, and a groove 410 etched into an ion extraction electrode 411. The electrode 411 may be a thin diaphragm containing an orifice, or an extended element containing a tubular opening as shown here. The capillary mounting-block 406 also contains a plenum 412 connecting to the hole 405 in the base layer 403. Further raised blocks 41 3a, 41 3b, 41 3c, 413d and 414a, 414b, 414c, 414d provide contact pads for electrical connection to the capillary mounting block 406, the nebulizer block 409 and either end of the ion extraction electrode 411.

The lid part 402 carries a similar set of features, but the holes 405 and 406 through the baselayerandthecontactpads4l3a,4l3b, 413c,4I3dand4l4a,414b,414c,4l4dinthe structural layer are omitted. Additionally the capillary mounting-block 415 is somewhat shorter than the corresponding feature 406 in the base part.

To assemble the device the lid part 402 is stacked on top of the base part 401 so that the structural layers 404 are in contact. The grooved and etched structural features on the two parts then combine to form a parallelogram-shaped alignment feature for the nanospray capillary, a concentric tube nebulizer with a parallelogram-shaped cross-section and an ion extraction electrode with a parallelogram-shaped orifice.

Mechanical and electrical connections between the two parts arc then made using conductive epoxy. The epoxy is placed around the edge of the lid part in the regions of the contact pads 413a, 413b, 413c, 413d and 414a, 414b, 414c, 414d. The device is located on a printed circuit board, which has holes located in the regions of the holes 405 and 406 in the base part to allow a flow of gas. Wire bond connections arc made between the contact pads 413a, 413b, 413c, 413d and 414a, 414b, 414c, 414d and suitable drive electronics. A nanospray capillary 405 is then placed in the mounting groove, and slid forward so that the tip of the capillary is located between the nebulizer block 409 and the ion extraction electrode 411.

Figure 5 shows a process for fabrication of a nanospray ionization source according to this prior art [GBO5 19439.4; Syms 2007]. The process is based on crystalline silicon substrates on which plastic substrates are subsequently formed. The individual process steps are indicated by a set of evolving wafer cross-sections containing typical features.

In step 1, a (100)-oriented silicon substrate 501 is first oxidiscd to form an Si02 layer 502 on both sides. The Si02 is patterned and etched to form a channel-shaped opening 503, by photolithography and reactive ion etching. In step 2, the underlying silicon substrate is anisotropically etched down (ill) crystal planes to form a V-shaped groove 504.

Commonly an etchant consisting of potassium hydroxide (KOI-I'), water and isopropanol (IPA) may be used for this purpose [Bean 1978]. This step defines all capillary-mounling grooves and electrode pupils. The front side oxide is removed, and the wafer is turned over.

In step 3, the wafer is spin coated with a thick layer of the epoxy-based photoresist SU-8 505 [Lorenz 1997]. This resist maybe coated and exposed in layers of up to 0.5 mm thickness, has excellent adhesion, and is extimely rugged after curing, allowing it to be used as a substrate material after processing. The resist is lithographically patterned to form a dicing groove 506 around each die, together with any drain holes 507 and gas inlets.

In step 4, the front side of the wafer is metallised to inciase conductivity, typically with an adhesion layer ofCr metal and a thicker layer of Au 508. In step 5, the front of the wafer is coated in a photoresist 509. Since the wafer is non-planar, an electrodeposited resist is used [Kersten 19951. The resist is patterned to define the electrodes and alignment blocks 510, and the pattern is transferred through the metal. In step 6, the pattern is transferred through the silicon by deep reactive ion etching [Ilynes 1999], to form features 511 separating the elements. The photoresist is then removed, and individual dies are separated in step 7.

In step 8, two dies arc stacked together to ibrm a complete nanospray chip, by soldering or bonding the metal layers 512 together. Alternatively, a conducting epoxy may be used.

The chip is mounted on a circuit board, and wirebond connections 513 are made to features on the lower substrate. A nanospray capillary is then inserted in the alignment groove.

Figure 6 shows operation of the device as a nanospray source. In this figure, the lid part is omitted for clarity. The nanospray capillary 601 is connected to a suitable source of an analyte fluid to provide an analyte flow 602. Suitable sources include syringe pumps, liquid chromatographs and capillary electrophoresis separators. The flow rate of the source must be adjusted to suit the diameter of the chosen capillary.

Electrical connection to the analyte fluid may be by a variety of means, depending on the type of capillary. In the configuration here, the capillary is coated externally and at the tip with an electrically conducting layer and electrical connection is made by pressure contact between the capillary 601 and the mount 603. To generate a spray, a suitably high voltage V1 obtained from a first voltage source 604 is applied between the tip of the capillary 601 and the ion extraction electrode 605 via wirebond connections to the pads 606a and 606b.

The spray 607 passes axially through the orifice in the ion extraction clectmde 605 and then into an analytical instrument. In the example here, the anaytical instrument is an clectrospray ionization mass spectrometer, and the spray passes into the sampling cone 608 of the instrument. Coupling of the spray is promoted using a voltage V2 applied between the ion extraction electrode 605 and the sampling cone 608 by a second voltage source 609. Additional contacts may be used to pass a current through the nebulizer block so that the nebulizer gas is heated, and to pass currents through the ion extraction electrode so that the ion stream is heated. In each case, the result is to promote the removal of solvent.

To enhance the spray, a nebulizer gas (typically nitrogen) is passed through the PCB and then through the hole 610 in the base part. On entering the plenum 611 the gas flow is diverted out through the nebulizer block 612 to form a concentric flow of a nebulizer gas 613 around the tip of the nanospray capillary 601.

It will be appreciated that the microengineered air amplifier of Figures 2-3 contains features that are substantially similar to those of the microengineered nanospray source of Figures 4-6. In each case, structural features are defined as blocks in a layer lying on a substrate, and a complete device is assembled from two parts. Furthermore the spray axis of the source lies in the junction plane of the two assembled parts. The construction of Figure 2c will therefore locate the axis of a microengineered air amplifier in the same plane.

It will also be appreciated that the major difference between the two devices is that the nanospray source contains additional V-shaped grooves, which are not required in the air amplifier. I lowever, such features are incorporated only by their location in a two-dimensional pattern. Consequently, a microengineercd air amplifier may be realised using the process shown in FigureS and co-integrated with a microengineered nanospray source.

Figure 7 shows one example arrangement. Here a base part 701 and a lid part 702 are again combined with a nanospray capillary 703 to form a sequential arrangement of a nanospray source 704 and an air amplifier 705. It will be evident that the element 705 is substantially the same as the air amplifier shown in Figures 2 and 3, and that the element 704 is substantially the same as the nanospray source shown in Figures 4 and 6. The operation of the separate elements may therefore be understood from the description given heretofore.

Figure 8 shows the operation of the combined system in Figure 7. Tn this figure, the lid part is again omitted for clarity. Here a first voltage source 801 is used to generate an ion spray. A second voltage source 802 is used to couple the spray from the lens element into the air amplifier. A third voltage source 803 is used to couple the spray from the air amplifier into an analytical instrument, for example the sampling cone 804 of an atmospheric pressuic ionization mass spectrometer. Similar electrical connections may be made to the opposite side of the die, in the case of any unconnected electrical parts. Gases are passed into the electrospray source and the air amplifier to increase nebulization and flow respectively.

Figure 9 shows an alternative arrangement. Here a base part 901 and a lid part 902 arc again combined with a nanospray capillary 903 to form a more compact arrangement of a nanospray source and an air amplifier 904 by omitting the separate ion extraction electrode. Figure 10 shows the operation of the combined system in Figure 9. In this figure, the lid part is again omitted for clarity. Here a first voltage souite 1001 is used to generate an ion spray, which is now drawn between the nanospray capillary and the air amplifier itself. A second voltage source 1002 draws the spray from the air amplifier into the sampling cone 1003 of an atmospheric pressure ionization mass spectrometer. Similar electrical connections may again be made to the opposite side of the die if necessary.

It will be appreciated that in the above examples, the aim is to provide an increased flux of analyte ions, and that the mass spectrometer inlet shown for illustrative purposes may be replaced by the inlet of an ion mobility spectrometer with similar advantage. It will further be appreciated that the invention is applicable to other methods of ionization at atmospheric pressulc, for example using a radioactive source or a corona discharge.

It will be understood that what has been described herein are exemplary embodiments of a micro-engineered amplifier that may be used to achieve acceleration of a gas through use of the Coanda and Venturi effects. Such an amplifier has application in a number of different fields, exemplary applications having been described with reference to mass spectrometry. it will however be understood that it is not intended to limit the present invention in any way except as may be deemed necessary in the light of the appended claims.

Within the context of the present invention the term microengineered or microengineering or microfabricated or micro fabrication is intended to define the fabrication of three dimensional structures and devices with dimensions in the order of microns. It combines the technologies of microelectronics and micromachining.

Microelectronics allows the fabrication of integrated circuits from silicon wafers whereas micromachining is the production of three-dimensional structures, primarily from silicon wafers. This may be achieved by removal of material from the wafer or addition of material on or in the wafer. The attractions of microcngineering may be summarised as batch fabrication of devices leading to reduced production costs, miniaturisation resulting in materials savings, miniaturisation resulting in faster response times and reduced device invasiveness. Wide varieties of techniques exist for the microengineering of wafers, and will be well known to the person skilled in the art. The techniques may be divided into those related to the removal of material and those pertaining to the deposition or addition of material to the wafer. Examples of the former include: * Wet chemical etching (anisotropic and isotropic) * Electrochemical or photo assisted electrochemical etching * Dry plasma or reactive ion etching * Ion beam milling * Laser machining * Excimer laser machining Whereas examples of the latter include: * Evaporation * Thick film deposition * Sputlering * Electroplating * Electroforming * Moulding * Chemical vapour deposition (CVD) * Epitaxy These techniques can be combined with wafer bonding to produce complex three-dimensional, examples of which are the interface devices provided by the present invention.

Where the words "upper", "lower", "top", bottom, "interior", "exterior" and the like have been used, it will be understood that these are used to convey the mutual arrangement of the layers relative to one another and are not to be interpreted as limiting the invention to such a configuration where for example a surface designated a top surce is not above a surface designated a lower surface.

Furthermore, the words comprises/comprising when used in this specification are to specify the presence of staled features, integers, steps or components but does not preclude the presence or addition of one or more other ii,atures, integers, steps, components or groups thereof.

References Panitz T., Wasan D.T. "Flow attachment to solid surfaces: the Coanda effect" AIChE J. 18,51-57(1972) Sebac Nouvelle "New arrangement for putting gases into movement" GB 863,124 Sept 13(1956) SEBAC NOUVELLE Coanda 11. "Device for imparting movement to gases" US 3,047,208 July 31 (1962)

SEBAC NOUVELLE

Hale L. "Spray gun" US 2,965,312 Dec20 (1960) REFRACT-ALL Mocarski Z.R. "Coanda type nozzle with discontinuous slot" US 3,806,039 April 23 (1974) SRC Inglis L.R. "Air flow amplifier" US 4,046,492 Sept 6 (1977) VORTEC Lee E.D., Lee M., Rockwood A., Zhou Li "Method and apparatus Ibr aerodynamic ion focusing" US 6,992,299 Jan 31(2006) BRIGI-IAM YOUNG Fenn J.B., Mann M., Meng C.K., Wong S.F., Whitehouse C.M. "Electrospray ionization for the mass spectrometry of large biomolecules" Science 64-71(1989) Hannis J.C., Muddiman D.C. "Nanoelectrospray mass speclrometiy using nonmetallized, tapered (50 3 10 tm) fused silica capillaries" Rapid Comm. in Mass Spec j., 443-448(1998) Thou L., Yue B., Dearden D.V., Lee E.D., Rockwood A.L., Lee M.L. "Incorporation of a Venturi device in electrospray ionization" Anal. Chcm. 2., 5978-5983 (2003) Hawkridge A.M., Zhou L., Lee M., Muddiman D.C. "Analytical perfbrmance of a Venturi device integrated into an electrospray ionization Fourier transform ion cyclotron resonance mass spectrometer for analysis of nucleic acids" Anal. Chem. 76,4118-4122 (2004) Cohen M.J., Karasek F.W. "Plasma chromatography -a new dimension for gas chromatography and mass spectrometly" J. Chromatog. Sci. , 330-337 (1970) Witimer D., Chen Y.H., Luckenbill B.K., Hill H.H. "Electrospray ionization ion mobility spcctrometry" Anal. Chem. , 2348-2355 (1994) Wu C., Siems W.F., Reid Asbury G., Hill H.H. "Electrospray ionization high-resolution ion mobility spcctromctry-mass spcctromctry" Anal. Chem. 7Q., 4929-4938 (1998) GeearM., Syms R.R.A., Wright S., Holmes A.S. "Monolithic MEMS quadrupole mass spectrometers by deep silicon etching" IEEE/ASME J. Microelectromech. Syst. 14, 1156-1166 (2005) Ramsey R., Ramsey J."Generating electrospray from microchip devices using electro-osmotic pumping" Anal. Chem. 2, 1174-1178 (1997) Licklider L., Wang X.Q., Desai A., Tai Y.C., Lee T.D. "A micromachined chip-based electrospray source for mass spectrometry" Anal Chem. 7, 367-75 (2000) Syms R.R.A., Zou H., Bardwell M., Schwab M.-A. "Microcnginccrcd alignment bench for a nanospray ionisation source" J. Micromech. Microcng. 17., 1567-1574 (2007) Syms R.R.A. "Microengineered nanospray electrode system" UK Patent Application 0514843.2 July20 (2005); refiled as GB0519439.4 Eiceman G.A., Schmidt H., Rodriguez J.E., White C.R., Krylov E.V., Stone J.A. "Planar drift tube for ion mobility spcctrometry" Inst. Sci. and Tech. , 365-3 83 (2007) Miller R.A., Nazarov E.G., Eiceman G.A., King A.T. "A MEMS radio-frequency ion mobility spectrometer for chemical vapor detection" Sensors and Actuators A91, 301-3 12 (2001) Kersten P., Bouwstra S., Petersen J.W. "Photolithography on micromachined 3D surfaces using electrodeposited photoresists" Sensors and Actuators 51-54 (1995) Lorenz H., Despont M., Fahmi N., LaBianca N., Renaud P., Vettinger P. "SU-8: a low-cost negative resist for MEMS" J. Micromech. Microeng. 7, 121-124 (1997) Bean K.E. "Anisotropic etching of silicon" IEEE Trans. Electron Devices ED-25, 1185- 1193 (1978) Hynes A.M., Ashraf H., Bhardwaj J.K., Hopkins J., Johnston I., Shepheiü J.N. "Recent advances in silicon etching for MEMS using the ASEIM process" Sensors and Actuators 74,13-17(1999) Air amplifier

Field of the Invention

This invention relates to mass spectrometers and ion mobility spectrometers and in particular to a method of increasing signal sensitivity in such sensors.

Background

An air amplifier (otherwise known as an airflow amplifier or an air ejector) is a well-known device, used to increase the flow of a gas by a combination of the Coanda effect and the Venturi effect. The former is a phenomenon in which a gas flow can adhere to a convex boundary [Panitz 1972]. The latter is a phenomenon in which increased velocity in a gas flow causes a reduction in pressure. Air amplifiers have no moving parts, and hence require low maintenance. They have a variety of applications including fan replacements, spray guns, cleaning equipment and devices for removal of fumes or sawdust.

Air amplifiers use the discharge of a small volume of a primary gas at high speed near the walls of a shaped channel to increase the flow of a much larger volume of a secondary gas moving more slowly through the centre of the channel. The channel commonly has cylindrical symmetry, with a convergent tapered input and a divergent tapered output.

The secondary gas is inserted through the convergent input and leaves through the divergent output. The primary gas is inserled through an annular slot in the channel wall at the junction of the two tapered sections where there is a convex wall. The slot has a lip to deflect the primary flow towards the output, parallel to the walls of the channel, where it adheres by the Coanda effbct. The rapid flow of the primary gas results in a reduction in pressure along the centreline of the secondary gas channel by the Venturi effect, which in turn incivases the flow of the secondary gas [GB 863,124, US 3,047,208].

Air amplifiers arc conventionally constructed by machining or moulding three-dimensional shaped metal parts. Considerable effort has been expended on their design, particularly with regards to simple methods of providing the shaped slot and manufacturing removable parts [US 2,965,312; US 3,806,039; US 4,046,492].

Figure 1 a shows in sectional schematic the main features of a typical prior art air amplifier formed by conventional methods [adapted from US 4,046,492]. The device has two main parts, an input part 101 carrying a strongly convergent conical tapered input hole 102 and a concentric lip 103, and an output part 104 carrying a shallow conical input hole 105 connecting to a weakly divergent conical tapered output hole 106. The features 102, 103, 105 and 106 are cylindrically symmetric about a central axis 107. The two parts 101 and 102 are held together by screws 108. The holes 102, 105 and 106 combine to form a channel for the secondary gas with a convergent entrance and a divergent exit. At the waist between the sections 105 and 106 the channel wall is convex. The lip 103, the shallow conical hole 105, a concentric channel 109 and a threaded input pipe 110 form the input for the primary gas that enters the secondary gas channel by a slot 111 at the waist.

Figure lb shows the operation of the air amplifier in Figure la. The primary gas 112 is injected from a pressurised supply through the threaded input pipe 110. The primary gas is distributed around the circumference of the secondary gas channel by the concentric channel 109, and enters the secondary gas channel by the slot 111, where it is deflected by the lip 103. Through the Coanda effect, the primary gas forms a flow layer 113 adhering to the convex walls of the divergent section of the secondary gas channel 106.

Through the Venturi effect, the velocity of the primary gas flow then causes a pressure drop in the secondary gas channel, increasing the flow of a gas 114 passing through this channel.

Recently, a new application has been described in which air amplifiers are used to increase the flow of a gas carrying analyte ions by electrospray ionization towards an analytical instrument such as a mass spectrometer [US 6,992,299]. Electrospray ionization is a method of generating ions at atmospheric pressure from a liquid source [Fenn 1989]. The liquid is typically a dilute solution of analyte in a solvent. The spray is induced by the action of a strong electric field at the end of capillary containing the liquid. The electric field draws the liquid out from the capillary into a Taylor cone, which emits a spray at a threshold field that depends on the physical properties of the liquid and the diameter of the capillary. Increasingly, capillaries with internal diameters below 50 microns known as nano-electrospray capillaries or nanospray capillaries are used to reduce the threshold electric field and the volume of spray [1 lannis 1998]. however, maximum use must then be made of the ions generated in a subsequent analytical instrument.

In recent experiments involving air amplifiers and electrospray, a conventional air amplifier was placed between an electrospray source and an atmospheric pressure ionization mass spectmmetcr [Zhou 2003; Hawkridge 2004]. A mass spectrometer is a vacuum instrument that separates ions of different species according to their charge-to-mass ratio. When the ions are created at atmospheric pmssure, they are coupled into the high vacuum chamber of the mass spectmmcter via a differentially pumped interface chamber whose inlet is known as a sampling cone. Increased ion signals were obtained from a combination of increased secondary gas flow, aerodynamic focusing of the spray and electrostatic focusing of the ions, which resulted in a more concentrated ion stream passing into the mass spectmmeter.

It can be expected that similar benefits will be obtained using an alternative analysis technique such as ion mobility spectromeiry (also known as plasma chromatography or gaseous electrophoresis). An ion mobility spectmmeter separates ions according to their mobility in an electric field when travelling in a background gas with a pressure close to atmospheric pressure [Cohen 1970]. Ion mobility spectrometers can again operate using an clectrospray ion source [Wittmer 1994], and systems that combine electrospray with both ion mobility separation and mass spectmmetry have also been developed [Wu 1998].

It is desirable to exploit this cfilct in applications where the ion signal is inherently limited, for example in a miniaturised system that might allow a low cost identification of different chemical species. Applications for such systems lie in portable sensors for the detection of chemical and biochemical weapons and low cost analysis for pharmaceutical chemists. Some advances have been made in miniaturised mass spectrometers. For example, small quadrupole electrostatic mass filters have been constructed by stacking together multilayer silicon substrates containing etched mounting features for cylindrical electrode rods and used as quadrupole mass spectrometers [Geear 2005]. Electrospray sources have also been miniaturised, either as planar devices containing etched channels [Ramsay 1997; Licklider 2000] or as planar devices that mount nanospray capillaries [Syms 2007; GBO5 19439.4]. Ion mobility spectrometers have also been miniaturised as planar devices, using either printed circuit boards [Eiceman 2007] or microfabricated electrodes [Miller 2002].

Existing designs of air amplifiers are large, involved complex three-dimensional features, and cannot easily be combined with such sources in the form of a planar integrated device. Consequently, there is a barrier to miniaturisation of an overall system involving the use of an air amplifier to increase ion signals generated by electrospray or nanospray ionization.

Summary

These and other problems are addressed in accordance with the teaching of the present invention by a miniature air amplifier provided in a planar integrated form that may easily be combined with a miniature atmospheric pressure ionization source such as for example a nanospray source. Such a latter device may also be provided in integrated form.

This invention also pmvides a method for forming miniature air amplifiers on planar substrates, to achieve an increased flow of a secondary gas through a channel by the action of a primary gas flow. The device may be fabricated by a combination of photolithography and etching, and can also be integrated with other microengineered components such as a nanospray ionization source. Using such a device it is possible to provide an increased analytc signal in mass spcctmmetry and ion mobility spectrometry.

Accordingly there is provided an air assembly according to claim 1. Advantageous embodiments are provided in the dependent claims. An assembly according to claim 22 is also provided with advantageous embodiments thereof provided in the dependent claims thereto.

The construction and operation of thc micmenginecred air amplifier can be befter understood with reference to Figures 2 -10.

Brief Description of the Drawings

Figure 1 shows an air amplifier according the prior art, a) in schematic and b) in operation.

Figure 2 shows a schematic of a planar microengineered air amplifier a) in plan and b) in section, according to the present invention; Figure 2c shows an alternative section.

Figure 3 shows the operation of a planar microengineered air amplifier a) in plan and b) in section, according to the present invention.

Figure 4 shows a schematic in plan of a planar electrospray ionization source based on a

nanospray capillaiy according to the prior art.

Figure 5 shows a fabrication pmcess for forming a planar clectmspray ionization source based on a nanospray capillary according to the prior art.

Figure 6 shos the operation ola planar electrospray ionization source based on a nanospray capillaiy

according to the prior art.

Figure 7 shows a planar microengineered air amplifier used in combination with a planar electrospray ionization source, according to the present invention.

Figure 8 shows the operation of the Coanda-assisted electrospray source of Figure 7.

Figure 9 shows an alternative configuration of a planar microengineered air amplifier and a planar electrospray ionization source according to the present invention Figure 10 shos the operation of' the C'oanda-assisted clectrospray source of Figure 9.

Detailed Description of the Drawings

Main components of a known prior art arrangement for provision of an air amplifier have already been discussed with refrcncc to Figure 1. It will be appreciated that the construction of the two parts shown in Figure 1 involves complex three-dimensional machining operations. Although these are easy to carry out for macroscopic components such as the context of Figure 1, below a certain size scale, typically between ten and a hundred microns in feature size, conventional machining methods such as milling, slotting and drilling become inappropriate for fabricating complex structures.

The present invention addresses these pmblcms by employing alternative techniques and specifically microengineering or microfabrication methodologies. These processes are known, for example in the manufacture of micro-electro-mechanical structures(MEMS) and are generally carried out on planar substrates, which are often silicon or multilayers containing silicon. The most important of the processes considered here include: * Patterning methods such as photolithography, especially on a non-planar surface or using a resist that may act as a structural material * Etching methods such as crystal plane etching of silicon, deep reactive ion etching of silicon and powder-blasting of glass * Bonding methods such as thermocompression bonding of gold and bonding of silicon * Coating methods such as sputtering of metals, and electroplating of metals These methods are well known to those skilled in the art, and can be employed in many different combinations to achieve a given microstructured object.

Using such methods, it is still difficult to form three-dimensional structures containing features with the rotational symmetry of Figure 1. However, the present inventor has realised that it is possible to form quasi three-dimensional structures based on pmjections of two-dimensional patterns that embody many of the main features of the desired structure while employing MEMS type techniques. For example, Figure 2 shows an approximation of the air amplifier of Figure 1, according to the teaching of the present invention. here, features corresponding to those of a conventional air amplifier are provided on the two sidewalls of a channel with a rectangular cross-section, but not on its upper and lower walls.

The device is constructed from two parts: a base part 212 and a lid part 211, which are assembled to form the complete structure of the amplifier. Provided between each of the base and lid parts are a number of channels which are formed from for example a combination of photolithography and etching techniques. Figure 2a shows a base part 212, which is a multilayer formed from an upper layer attached to a substrate. The substrate 201 carries two holes 202a, 202b, which arc provided to enable a gas to be intmduced into the channels. These holes will be discussed later with regard to the provision of a primary gas for the amplifier. The upper layer is structured into two raised portions 203 a, 203b surrounding the holes 202a, 202b and separated by a channel 204 which forms a throughput channel for the amplifier and within which a secondary gas of the amplifier may flow. The two portions 203 a, 203b are outlined by features whose perimeters are formed as vertical walls in the upper layer. In this way the portions 203a, 203b define sidewalls for the throughput channel 204. The sidewalls are not straight or co-planar in that each wall may be sub-divided into a number of different regions whose relative orientation to each other is different.. Looking left to right on the plan view of Figure 2, it will be noted that the sidewalls define a pair of strongly tapered input features 205a, 205b and a pair of weakly tapered output features 206a, 206b and an intermediate pair of substantially parallel features. The throughput channel 204 may therefore be considered as having a strongly tapered entrance and a weakly tapered exit. A gas flowing through the throughput channel will therefore pass through an initial convergent input where it undergoes a constriction, passes through a convex waist provided by the parallel side walls and then undergoes expansion as it passes through the divergent output.

A primary gas may be introduced into the main or throughput channel 204 through a feed channel defined in the side walls. It will be understood that each of the side walls have a feed channel such that the primary gas can be introduced on both sides of the thnughput channel. It will be understood that if only one side wall was provided with a feed channel that an element of amplification would be provided but this effect is improved by having a primary gas along each side of the secondary gas, as is provided by having a feed channel on both sides of the main channel. Each feed channel may be considered as having a number of segments. Inlet regions arc provided by two gas flow channels defined by holes 207a, 207b in the upper layer that surround or overlay the holes 202a, 202b in the substrate. A gas can then be introduced through the holes 202a, 202b into the inlet region 207a, 207b. The gas will then how from the inlet regions along passage regions provided by two channels 208a, 208b leading to exits 209a, 209b into the main throughput channel 204 adjacent to two lips 210a, 210b. It will be appreciated that the exits 209a, 209b provide first and second outlets in the sidewalls for the primary gas to be fed into the main channel 204. It will be understood that when travelling along the passage regions the gas is travelling in a direction substantially perpendicular to the direction of flow of the secondary gas within the main channel 204. At the lips 21 Oa, 2 lOb, the primary gas is deflected sidewardly such that the primary gas enter the main channel in a direction along the direction of flow of the secondary gas.

These features all may be provided using planar processing. However, it is generally difficult to form a monolithic structure containing completely closed channels by planar processing methods. Instead, the channels may be closed as shown in Figure 2b, by attaching a lid part 211 to the base part 212 containing the features shown in Figure 2a, taking care to minimise gas leaks through any joints thus formed. The lid and base cooperate to define upper and lower surlüces for the channels such that fluid (be that in the gaseous or liquid) phase is contained within the channels.

The lid part 211 may be featureless or a simple planar surface, and simply designed to provide a surface that seals all the channels in the base part simultaneously. In this case, the axis of the secondary gas flow will lie at a distance of half the upper layer thickness above the substrate. Alternatively, the lid part may be a bilayer structure 213 containing all the features shown in Figure 2a except the holes 202a, 202b through the substrate-in other words a mirror image of the construct of the base. In this case, a device with twice the overall channel height will be formed, as shown in Figure 2c, and the axis of the secondary gas flow will lie approximately at the interface between the two assembled components. 11 will be appreciated that the axis of the secondary gas flow has a significance in the operation of the device, and consequently that the choice of construction will depend on the desired location of this axis.

It will also be appreciated that many of the features of the micmengineered air amplifier in Figure 2 correspond directly to those in the prior art device in Figure 1. For example, the holes 202a, 202b are analogous to the primary gas input 110. The strongly tapered input features 205a, 205b are analogous to the strongly convergent tapered input hole 102 for the secondary gas, and the weakly tapered output features 206a, 206b arc analogous to the weakly divergent tapered output hole 106. The connecting channels 208a, 208b are analogous to the surrounding concentric channel 109, the exits 209a, 209b are analogous to the exit Ill and the lips 210a, 210b are analogous to the concentric lip 103. However, the features in the microengincered air amplifier are arranged in pairs on either side of a rectangular channel, rather than concentrically around a circular channel-they are provided in a planar structure.

Thus in providing quasi two-dimensional analogues to these earlier three-dimensional features the microengineered air amplifier can provide a similar function, as shown in Figures 3a and 3b. Here two primary gas streams 3Ola, 301b that are injected through the holes 302a, 302b in the substrate follow the primary gas delivery channels until they are deflected by the lips 303a, 303b. The primary gas streams then adhere to the convex walls 304a, 304b of the secondary gas channel through the Coanda effect to form output streams 305a, 305b. The velocity of the primary gas then causes a pressure drop in the secondary gas channel, increasing the flow 306 of a secondary gas passing through this channel. It will be appreciated that the flow line 306 defines a longitudinal axis of the main throughput channel 204.

The two primary gas streams 301a, 301b may be conveniently provided from a single input 307 by holding or providing the air amplifier on a mount 308 containing drilled gas lines, which may be formed by conventional machining. A gasket 309 formed for 1) example in an elastomer may provide a suitable gas-tight seal between the air amplifier and the mount.

It will be appreciated that there arc many different combinations of materials and processes that may be used to form a planar microengineered air amplifier as described here. For example, the base part may be formed from two identical materials or from two different materials. The upper layer will typically be a conductor or a metallised semiconductor to prevent charging by the ion stream and allow application of a voltage to assist in transferring ions through the secondary gas channel. An example of a suitable metal is nickel and an example of a suitable semiconductor is silicon. Both these materials may easily be structured. The silicon will desirably be coated in metal to allow an electrical contact.

Depending on the application, the substrate layer may be a conductor, a semiconductor or an insulator. An insulating substrate may be used if it is desired to combine a microengineered air amplifier with another electrical device in monolithic form.

Examples of suitable insulating materials are plastics, glasses and ceramics. If an insulating substrate is used it may be desirable to cover the substrate with a conducting layer in the vicinity of the secondary gas channel, to prevent charging by the ion stream and allow application of voltages. Alternatively, a residual thickness of the upper layer material may be retained in the vicinity of the secondary gas channel 204 between the blocks 203a and 203b in Figure 2a.

Although the layout of the two layers will be defmed using lithography, the features will be constructed by removing or adding material. Material removal may involve processes such as etching or powder blasting. Plasma etching methods such as deep reactive ion etching [Hynes 1999] are appropriate for structuring an upper layer of silicon, since they may define deep features with vertical sidewalls. Powder blasting methods arc appropriate for structuring a base layer of glass, since they may easily define features such as via holes and gas inlets. Material addition may involve electroplating of a metal such as nickel in a mould. Such methods are again appropriate for structuring the upper layer, since they may define deep conducting katures with vertical sidewalls. Alternative methods of material addition include the use of thick epoxy photoresist. Such methods arc appropriate for structuring the base layer, since they may provide insulating features with high aspect ratio.

The lid part may again be formed from a similar material to the base layer or a different material. Different bonding methods may be used to attach the lid to the base, including soldering, bonding and the usc of an epoxy resin, which maybe of a conductive type. It will be apparent that the use of such methods can easily provide an electrical contact between the lid part and the upper layer of the base part.

In selecting the fabrication process, major requirements will be provision of mechanical, electrical and thermal functionality and compatibility with other integrated components.

Here, we describe a process (which is intended to be exemplary rather than exclusive) that allows co-integration with our co-assigned prior art nanospray source [GBO5 19439.4; Syms 2007].

Figure 4 shows the construction of the prior art nanospray source, which consists of two parts, a base part 401 and a lid part 402. Each part consists of two layers: a base layer 403 with through holes and a structural layer 404 carrying component mounts and electmdes.

Because the base layer 403 provides electrical isolation (and hence withstand the voltages of around 1 kV that are applied between elcctmdcs during nanospray) it is formed in an insulating material. Mechanical constraints will be appreciated as providing a determination of the exact choice of insulator.

For example, because the base layer 403 in the base part 401 carries an inlet 405 to allow gas to be passed through for nebulization of the spray, together with a drain 406, the insulator used may be an epoxy-based photoresist, SU-8 [Lorcnz 1997]. This material may be patterned in layers several hundred microns thick, and allows the outline of the base layer and any additional through-holes to be defined in a single patterning step.

Because the structural layer 404 provides a locating mount for the nanospray capillary, together with conducting electrodes set up normal to the base layer, it is formed from a metallised semiconductor. The semiconductor used in this arrangement is (100) oriented silicon, since this material can be patterned by a combination of crystal plane etching [Bean 1978] and deep reactive ion etching [1-lynes 1999] to form V-shaped grooves and vertical electrodes.

For example, the structural layer 404 in the base part 401 carries a mount for a nanospray capillary 405 in the form of a raised block 406 carrying an etched V-shaped groove 407.

The groove is continued along the stmcture to provide a groove 408 in a nebulizer block 409, and a groove 410 etched into an ion extraction electrode 411. The electrode 411 may be a thin diaphragm containing an orifice, or an extended element containing a tubular opening as shown here. The capillary mounting-block 406 also contains a plenum 412 connecting to the hole 405 in the base layer 403. Further raised blocks 41 3a, 41 3b, 41 3c, 413d and 414a, 414b, 414c, 414d provide contact pads for electrical connection to the capillary mounting block 406, the nebulizer block 409 and either end of the ion extraction electrode 411.

The lid part 402 carries a similar set of features, but the holes 405 and 406 through the baselayerandthecontactpads4l3a,4l3b, 413c,4I3dand4l4a,414b,414c,4l4dinthe structural layer are omitted. Additionally the capillary mounting-block 415 is somewhat shorter than the corresponding feature 406 in the base part.

To assemble the device the lid part 402 is stacked on top of the base part 401 so that the structural layers 404 are in contact. The grooved and etched structural features on the two parts then combine to form a parallelogram-shaped alignment feature for the nanospray capillary, a concentric tube nebulizer with a parallelogram-shaped cross-section and an ion extraction electrode with a parallelogram-shaped orifice.

Mechanical and electrical connections between the two parts arc then made using conductive epoxy. The epoxy is placed around the edge of the lid part in the regions of the contact pads 413a, 413b, 413c, 413d and 414a, 414b, 414c, 414d. The device is located on a printed circuit board, which has holes located in the regions of the holes 405 and 406 in the base part to allow a flow of gas. Wire bond connections arc made between the contact pads 413a, 413b, 413c, 413d and 414a, 414b, 414c, 414d and suitable drive electronics. A nanospray capillary 405 is then placed in the mounting groove, and slid forward so that the tip of the capillary is located between the nebulizer block 409 and the ion extraction electrode 411.

Figure 5 shows a process for fabrication of a nanospray ionization source according to this prior art [GBO5 19439.4; Syms 2007]. The process is based on crystalline silicon substrates on which plastic substrates are subsequently formed. The individual process steps are indicated by a set of evolving wafer cross-sections containing typical features.

In step 1, a (100)-oriented silicon substrate 501 is first oxidiscd to form an Si02 layer 502 on both sides. The Si02 is patterned and etched to form a channel-shaped opening 503, by photolithography and reactive ion etching. In step 2, the underlying silicon substrate is anisotropically etched down (ill) crystal planes to form a V-shaped groove 504.

Commonly an etchant consisting of potassium hydroxide (KOI-I'), water and isopropanol (IPA) may be used for this purpose [Bean 1978]. This step defines all capillary-mounling grooves and electrode pupils. The front side oxide is removed, and the wafer is turned over.

In step 3, the wafer is spin coated with a thick layer of the epoxy-based photoresist SU-8 505 [Lorenz 1997]. This resist maybe coated and exposed in layers of up to 0.5 mm thickness, has excellent adhesion, and is extimely rugged after curing, allowing it to be used as a substrate material after processing. The resist is lithographically patterned to form a dicing groove 506 around each die, together with any drain holes 507 and gas inlets.

In step 4, the front side of the wafer is metallised to inciase conductivity, typically with an adhesion layer ofCr metal and a thicker layer of Au 508. In step 5, the front of the wafer is coated in a photoresist 509. Since the wafer is non-planar, an electrodeposited resist is used [Kersten 19951. The resist is patterned to define the electrodes and alignment blocks 510, and the pattern is transferred through the metal. In step 6, the pattern is transferred through the silicon by deep reactive ion etching [Ilynes 1999], to form features 511 separating the elements. The photoresist is then removed, and individual dies are separated in step 7.

In step 8, two dies arc stacked together to ibrm a complete nanospray chip, by soldering or bonding the metal layers 512 together. Alternatively, a conducting epoxy may be used.

The chip is mounted on a circuit board, and wirebond connections 513 are made to features on the lower substrate. A nanospray capillary is then inserted in the alignment groove.

Figure 6 shows operation of the device as a nanospray source. In this figure, the lid part is omitted for clarity. The nanospray capillary 601 is connected to a suitable source of an analyte fluid to provide an analyte flow 602. Suitable sources include syringe pumps, liquid chromatographs and capillary electrophoresis separators. The flow rate of the source must be adjusted to suit the diameter of the chosen capillary.

Electrical connection to the analyte fluid may be by a variety of means, depending on the type of capillary. In the configuration here, the capillary is coated externally and at the tip with an electrically conducting layer and electrical connection is made by pressure contact between the capillary 601 and the mount 603. To generate a spray, a suitably high voltage V1 obtained from a first voltage source 604 is applied between the tip of the capillary 601 and the ion extraction electrode 605 via wirebond connections to the pads 606a and 606b.

The spray 607 passes axially through the orifice in the ion extraction clectmde 605 and then into an analytical instrument. In the example here, the anaytical instrument is an clectrospray ionization mass spectrometer, and the spray passes into the sampling cone 608 of the instrument. Coupling of the spray is promoted using a voltage V2 applied between the ion extraction electrode 605 and the sampling cone 608 by a second voltage source 609. Additional contacts may be used to pass a current through the nebulizer block so that the nebulizer gas is heated, and to pass currents through the ion extraction electrode so that the ion stream is heated. In each case, the result is to promote the removal of solvent.

To enhance the spray, a nebulizer gas (typically nitrogen) is passed through the PCB and then through the hole 610 in the base part. On entering the plenum 611 the gas flow is diverted out through the nebulizer block 612 to form a concentric flow of a nebulizer gas 613 around the tip of the nanospray capillary 601.

It will be appreciated that the microengineered air amplifier of Figures 2-3 contains features that are substantially similar to those of the microengineered nanospray source of Figures 4-6. In each case, structural features are defined as blocks in a layer lying on a substrate, and a complete device is assembled from two parts. Furthermore the spray axis of the source lies in the junction plane of the two assembled parts. The construction of Figure 2c will therefore locate the axis of a microengineered air amplifier in the same plane.

It will also be appreciated that the major difference between the two devices is that the nanospray source contains additional V-shaped grooves, which are not required in the air amplifier. I lowever, such features are incorporated only by their location in a two-dimensional pattern. Consequently, a microengineercd air amplifier may be realised using the process shown in FigureS and co-integrated with a microengineered nanospray source.

Figure 7 shows one example arrangement. Here a base part 701 and a lid part 702 are again combined with a nanospray capillary 703 to form a sequential arrangement of a nanospray source 704 and an air amplifier 705. It will be evident that the element 705 is substantially the same as the air amplifier shown in Figures 2 and 3, and that the element 704 is substantially the same as the nanospray source shown in Figures 4 and 6. The operation of the separate elements may therefore be understood from the description given heretofore.

Figure 8 shows the operation of the combined system in Figure 7. Tn this figure, the lid part is again omitted for clarity. Here a first voltage source 801 is used to generate an ion spray. A second voltage source 802 is used to couple the spray from the lens element into the air amplifier. A third voltage source 803 is used to couple the spray from the air amplifier into an analytical instrument, for example the sampling cone 804 of an atmospheric pressuic ionization mass spectrometer. Similar electrical connections may be made to the opposite side of the die, in the case of any unconnected electrical parts. Gases are passed into the electrospray source and the air amplifier to increase nebulization and flow respectively.

Figure 9 shows an alternative arrangement. Here a base part 901 and a lid part 902 arc again combined with a nanospray capillary 903 to form a more compact arrangement of a nanospray source and an air amplifier 904 by omitting the separate ion extraction electrode. Figure 10 shows the operation of the combined system in Figure 9. In this figure, the lid part is again omitted for clarity. Here a first voltage souite 1001 is used to generate an ion spray, which is now drawn between the nanospray capillary and the air amplifier itself. A second voltage source 1002 draws the spray from the air amplifier into the sampling cone 1003 of an atmospheric pressure ionization mass spectrometer. Similar electrical connections may again be made to the opposite side of the die if necessary.

It will be appreciated that in the above examples, the aim is to provide an increased flux of analyte ions, and that the mass spectrometer inlet shown for illustrative purposes may be replaced by the inlet of an ion mobility spectrometer with similar advantage. It will further be appreciated that the invention is applicable to other methods of ionization at atmospheric pressulc, for example using a radioactive source or a corona discharge.

It will be understood that what has been described herein are exemplary embodiments of a micro-engineered amplifier that may be used to achieve acceleration of a gas through use of the Coanda and Venturi effects. Such an amplifier has application in a number of different fields, exemplary applications having been described with reference to mass spectrometry. it will however be understood that it is not intended to limit the present invention in any way except as may be deemed necessary in the light of the appended claims.

Within the context of the present invention the term microengineered or microengineering or microfabricated or micro fabrication is intended to define the fabrication of three dimensional structures and devices with dimensions in the order of microns. It combines the technologies of microelectronics and micromachining.

Microelectronics allows the fabrication of integrated circuits from silicon wafers whereas micromachining is the production of three-dimensional structures, primarily from silicon wafers. This may be achieved by removal of material from the wafer or addition of material on or in the wafer. The attractions of microcngineering may be summarised as batch fabrication of devices leading to reduced production costs, miniaturisation resulting in materials savings, miniaturisation resulting in faster response times and reduced device invasiveness. Wide varieties of techniques exist for the microengineering of wafers, and will be well known to the person skilled in the art. The techniques may be divided into those related to the removal of material and those pertaining to the deposition or addition of material to the wafer. Examples of the former include: * Wet chemical etching (anisotropic and isotropic) * Electrochemical or photo assisted electrochemical etching * Dry plasma or reactive ion etching * Ion beam milling * Laser machining * Excimer laser machining Whereas examples of the latter include: * Evaporation * Thick film deposition * Sputlering * Electroplating * Electroforming * Moulding * Chemical vapour deposition (CVD) * Epitaxy These techniques can be combined with wafer bonding to produce complex three-dimensional, examples of which are the interface devices provided by the present invention.

Where the words "upper", "lower", "top", bottom, "interior", "exterior" and the like have been used, it will be understood that these are used to convey the mutual arrangement of the layers relative to one another and are not to be interpreted as limiting the invention to such a configuration where for example a surface designated a top surce is not above a surface designated a lower surface.

Furthermore, the words comprises/comprising when used in this specification are to specify the presence of staled features, integers, steps or components but does not preclude the presence or addition of one or more other ii,atures, integers, steps, components or groups thereof.

References Panitz T., Wasan D.T. "Flow attachment to solid surfaces: the Coanda effect" AIChE J. 18,51-57(1972) Sebac Nouvelle "New arrangement for putting gases into movement" GB 863,124 Sept 13(1956) SEBAC NOUVELLE Coanda 11. "Device for imparting movement to gases" US 3,047,208 July 31 (1962)

SEBAC NOUVELLE

Hale L. "Spray gun" US 2,965,312 Dec20 (1960) REFRACT-ALL Mocarski Z.R. "Coanda type nozzle with discontinuous slot" US 3,806,039 April 23 (1974) SRC Inglis L.R. "Air flow amplifier" US 4,046,492 Sept 6 (1977) VORTEC Lee E.D., Lee M., Rockwood A., Zhou Li "Method and apparatus Ibr aerodynamic ion focusing" US 6,992,299 Jan 31(2006) BRIGI-IAM YOUNG Fenn J.B., Mann M., Meng C.K., Wong S.F., Whitehouse C.M. "Electrospray ionization for the mass spectrometry of large biomolecules" Science 64-71(1989) Hannis J.C., Muddiman D.C. "Nanoelectrospray mass speclrometiy using nonmetallized, tapered (50 3 10 tm) fused silica capillaries" Rapid Comm. in Mass Spec j., 443-448(1998) Thou L., Yue B., Dearden D.V., Lee E.D., Rockwood A.L., Lee M.L. "Incorporation of a Venturi device in electrospray ionization" Anal. Chcm. 2., 5978-5983 (2003) Hawkridge A.M., Zhou L., Lee M., Muddiman D.C. "Analytical perfbrmance of a Venturi device integrated into an electrospray ionization Fourier transform ion cyclotron resonance mass spectrometer for analysis of nucleic acids" Anal. Chem. 76,4118-4122 (2004) Cohen M.J., Karasek F.W. "Plasma chromatography -a new dimension for gas chromatography and mass spectrometly" J. Chromatog. Sci. , 330-337 (1970) Witimer D., Chen Y.H., Luckenbill B.K., Hill H.H. "Electrospray ionization ion mobility spcctrometry" Anal. Chem. , 2348-2355 (1994) Wu C., Siems W.F., Reid Asbury G., Hill H.H. "Electrospray ionization high-resolution ion mobility spcctromctry-mass spcctromctry" Anal. Chem. 7Q., 4929-4938 (1998) GeearM., Syms R.R.A., Wright S., Holmes A.S. "Monolithic MEMS quadrupole mass spectrometers by deep silicon etching" IEEE/ASME J. Microelectromech. Syst. 14, 1156-1166 (2005) Ramsey R., Ramsey J."Generating electrospray from microchip devices using electro-osmotic pumping" Anal. Chem. 2, 1174-1178 (1997) Licklider L., Wang X.Q., Desai A., Tai Y.C., Lee T.D. "A micromachined chip-based electrospray source for mass spectrometry" Anal Chem. 7, 367-75 (2000) Syms R.R.A., Zou H., Bardwell M., Schwab M.-A. "Microcnginccrcd alignment bench for a nanospray ionisation source" J. Micromech. Microcng. 17., 1567-1574 (2007) Syms R.R.A. "Microengineered nanospray electrode system" UK Patent Application 0514843.2 July20 (2005); refiled as GB0519439.4 Eiceman G.A., Schmidt H., Rodriguez J.E., White C.R., Krylov E.V., Stone J.A. "Planar drift tube for ion mobility spcctrometry" Inst. Sci. and Tech. , 365-3 83 (2007) Miller R.A., Nazarov E.G., Eiceman G.A., King A.T. "A MEMS radio-frequency ion mobility spectrometer for chemical vapor detection" Sensors and Actuators A91, 301-3 12 (2001) Kersten P., Bouwstra S., Petersen J.W. "Photolithography on micromachined 3D surfaces using electrodeposited photoresists" Sensors and Actuators 51-54 (1995) Lorenz H., Despont M., Fahmi N., LaBianca N., Renaud P., Vettinger P. "SU-8: a low-cost negative resist for MEMS" J. Micromech. Microeng. 7, 121-124 (1997) Bean K.E. "Anisotropic etching of silicon" IEEE Trans. Electron Devices ED-25, 1185- 1193 (1978) Hynes A.M., Ashraf H., Bhardwaj J.K., Hopkins J., Johnston I., Shepheiü J.N. "Recent advances in silicon etching for MEMS using the ASEIM process" Sensors and Actuators 74,13-17(1999)

Claims (32)

1. Claims 1. An air amplifier constructed in planar form having a base portion and lid portion separated by first and second channel side walls, the dimensions and relative positions of the channel side walls to one another defining a main channel within the amplifier, the walls further defming first and second outlets for introduction of a primary gas into the main channel along an axis substantially parallel to a longitudinal axis of the main channel, and wherein the main channel also provides for thc passage of a secondary gas thenthrough such that operably the primary and secondary gases travel side by side along the main channel, the primary gas being biased towards the side walls of the main channel and effecting an increase in the flow of the secondary gas through a combination of the Coanda effect and the Venturi effect.
2. 2. The air amplifier as in Claim 1 wherein each of the side walls define a feed channel for the primary gases, the feed channels including an inlet region, a passage region and an exit region, the first and second outlets in the side walls being provided at the exit regions and wherein the passage region extends substantially perpendicular to the longitudinal axis of the main channel.
3. 3. The amplifier of claim 2 wherein the side walls defme lips at the exit regions of the feed channel such that operably the primary gas is deflected sidewardly at the lips prior to exiting the feed channel in a direction along the direction of flow of the secondary gas.
4. 4. The amplifier of claim 3 wherein at the exits of the feed channel the side walls of the main channel are configured to taper outwardly from the longitudinal axis of the main channel.
5. 5. The amplifier of any preceding claim wherein the side walls define within the main channel a convergent input, a divergent output and a convex waist, the feed channels intersecting with the main channel at or about the waist of the main channel.
6. 6. The amplifier of any preceding claim constructed in a multi-layer construct, the base portion including a substrate having at least one layer provided thereon, the a layer including thc side walls defining the feed and main channels defined therein, the lid portion also being formed from a substrate, the lid and base portion being coupled to one another to provide the amplifier.
7. 7. The amplifier of claim 6 wherein the lid portion has at least one layer provided on the substrate thereof, the layer of the lid portion also defining side walls of the amplifier such that on assembly of the lid and base portions together the height of the side walls provided in each of the lid and base portion collectively define the height of the channels.
8. 8. The amplifier of claim 6 wherein the lid portion provides a planar surface which abuts against the top of the side walls of the base portion to seal the channels at the top.
9. 9. The amplifier ofany one of claims 6 to 8 wherein the channels are exposed to the substrate of each of the lid and base portions at the top and bottom of the channels.
10. 10. The amplifier of any one of claims 6 to 9 wherein the base portion includes at least one aperture through which gas for the primary gas channel may be introduced into the amplifier.
11. 11. The amplifier of claim 10 wherein the at least one aperture extends through the substrate of the base portion in a direction substantially transverse to the longitudinal axis of the main channel.
12. 12. The amplifier ofclaim 10 wherein the feed channels includes an inlet region coincident with the location of the at least one aperture such that the gas introduced through the at least one aperture is fed directly into the feed channels.
13. 13. The amplifier of claim 12 wherein the feed channel is dimensioned such that operably on introduction of the gas into the inlet region it is deflected perpendicularly so as to travel in the same plane as the main channel.
14. 14. The amplifier of any one of claims 71o 13 in which the substrates forming each of the base and lid portions arc provided in a glass, a plastic or a ceramic material.
15. 15. The amplifier of any preceding claim wherein the side walls are provided in a silicon or nickel material.
16. 16. The amplifier of any preceding claim wherein the side walls are subjected to a Th lithography process or an etching process to define the channels.
17. 17. The amplifier ofany one of claims I to 13 wherein the channels are formed in silicon and are fabricated through a plasma etching of the silicon.
18. 18. The amplifier of any one of claims ito 13 wherein the channels are Ibrmed by electroplating of nickel.
19. 19. The amplifier of claim 6, in which the substrate is formed by paueming of an epoxy photoresist.
20. 20. The amplifier of claim 10 or 11 in which the at least one aperture is Ibrmed by powder blasting.
21. 21. The amplifier as claimed in any preceding claim wherein the primary gas is provided at a higher pressure than the secondary gas.
22. 22. An assembly including an air amplifier as claimed in any preceding claim used in conjunction with an atmospheric pressure ionization source.
23. 23. The assembly of claim 22 in which the atmospheric pressure ionization source is an electrospray or nanospray ionization souite.
24. 24. The assembly of claim 22 wherein the air amplifier and atmospheric pressure ionization source are provided as a monolithic object.
25. 25. The assembly of claim 22 wherein the air amplifier is provided downstream of an ion extraction electrode of the nanospray source.
26. 26. The assembly of claim 22 or 25 wherein the air amplifier provides an ion extraction electmde of the nanospray source.
27. 27. An assembly including an air amplifier as claimed in any one of claims ito 21 used in conjunction with a mass spectrometer or an ion mobility spectrometer.
28. 28. An assembly including an air amplifier as claimed in any one of claims 1 to 21 used in conjunction with an electrospray source and a mass spectTometer or an ion mobility spectrometer.
29. 29. An integrated assembly including an electrospray source and an air amplifier claimed in any one of claims 1 to 21 in communication with a mass spectrometer or an ion mobility spectrometer.
30. 30. Use of an amplifier as claimed in any one of claims ito 21 to increase the flow of an analyte ion stream.
31. 31. The use as claimed in claim 30 wherein application of a voltage to at least a portion of the side walls of the air amplifier provides for an increase in the flow of an analyte ion stream.
32. 32. A device substantially as hereinbefore described with reference to any one of Figures 2 to 10.

    32. A device substantially as hereinbefore described with reference to any one of Figures 2 to 10.

    Claims 1. An air amplifier constructed in planar form having a base portion and lid portion separated by first and second channel side walls, the dimensions and relative positions of the channel side walls to one another defining a main channel within the amplifier, the walls further defming first and second outlets for introduction of a primary gas into the main channel along an axis substantially parallel to a longitudinal axis of the main channel, and wherein the main channel also provides for thc passage of a secondary gas thenthrough such that operably the primary and secondary gases travel side by side along the main channel, the primary gas being biased towards the side walls of the main channel and effecting an increase in the flow of the secondary gas through a combination of the Coanda effect and the Venturi effect.

    2. The air amplifier as in Claim 1 wherein each of the side walls define a feed channel for the primary gases, the feed channels including an inlet region, a passage region and an exit region, the first and second outlets in the side walls being provided at the exit regions and wherein the passage region extends substantially perpendicular to the longitudinal axis of the main channel.

    3. The amplifier of claim 2 wherein the side walls defme lips at the exit regions of the feed channel such that operably the primary gas is deflected sidewardly at the lips prior to exiting the feed channel in a direction along the direction of flow of the secondary gas.

    4. The amplifier of claim 3 wherein at the exits of the feed channel the side walls of the main channel are configured to taper outwardly from the longitudinal axis of the main channel.

    5. The amplifier of any preceding claim wherein the side walls define within the main channel a convergent input, a divergent output and a convex waist, the feed channels intersecting with the main channel at or about the waist of the main channel.

    6. The amplifier of any preceding claim constructed in a multi-layer construct, the base portion including a substrate having at least one layer provided thereon, the a layer including thc side walls defining the feed and main channels defined therein, the lid portion also being formed from a substrate, the lid and base portion being coupled to one another to provide the amplifier.

    7. The amplifier of claim 6 wherein the lid portion has at least one layer provided on the substrate thereof, the layer of the lid portion also defining side walls of the amplifier such that on assembly of the lid and base portions together the height of the side walls provided in each of the lid and base portion collectively define the height of the channels.

    8. The amplifier of claim 6 wherein the lid portion provides a planar surface which abuts against the top of the side walls of the base portion to seal the channels at the top.

    9. The amplifier ofany one of claims 6 to 8 wherein the channels are exposed to the substrate of each of the lid and base portions at the top and bottom of the channels.

    10. The amplifier of any one of claims 6 to 9 wherein the base portion includes at least one aperture through which gas for the primary gas channel may be introduced into the amplifier.

    11. The amplifier of claim 10 wherein the at least one aperture extends through the substrate of the base portion in a direction substantially transverse to the longitudinal axis of the main channel.

    12. The amplifier ofclaim 10 wherein the feed channels includes an inlet region coincident with the location of the at least one aperture such that the gas introduced through the at least one aperture is fed directly into the feed channels.

    13. The amplifier of claim 12 wherein the feed channel is dimensioned such that operably on introduction of the gas into the inlet region it is deflected perpendicularly so as to travel in the same plane as the main channel.

    14. The amplifier of any one of claims 71o 13 in which the substrates forming each of the base and lid portions arc provided in a glass, a plastic or a ceramic material.

    15. The amplifier of any preceding claim wherein the side walls are provided in a silicon or nickel material.

    16. The amplifier of any preceding claim wherein the side walls are subjected to a Th lithography process or an etching process to define the channels.

    17. The amplifier ofany one of claims I to 13 wherein the channels are formed in silicon and are fabricated through a plasma etching of the silicon.

    18. The amplifier of any one of claims ito 13 wherein the channels are Ibrmed by electroplating of nickel.

    19. The amplifier of claim 6, in which the substrate is formed by paueming of an epoxy photoresist.

    20. The amplifier of claim 10 or 11 in which the at least one aperture is Ibrmed by powder blasting.

    21. The amplifier as claimed in any preceding claim wherein the primary gas is provided at a higher pressure than the secondary gas.

    22. An assembly including an air amplifier as claimed in any preceding claim used in conjunction with an atmospheric pressure ionization source.

    23. The assembly of claim 22 in which the atmospheric pressure ionization source is an electrospray or nanospray ionization souite.

    24. The assembly of claim 22 wherein the air amplifier and atmospheric pressure ionization source are provided as a monolithic object.

    25. The assembly of claim 22 wherein the air amplifier is provided downstream of an ion extraction electrode of the nanospray source.

    26. The assembly of claim 22 or 25 wherein the air amplifier provides an ion extraction electmde of the nanospray source.

    27. An assembly including an air amplifier as claimed in any one of claims ito 21 used in conjunction with a mass spectrometer or an ion mobility spectrometer.

    28. An assembly including an air amplifier as claimed in any one of claims 1 to 21 used in conjunction with an electrospray source and a mass spectTometer or an ion mobility spectrometer.

    29. An integrated assembly including an electrospray source and an air amplifier claimed in any one of claims 1 to 21 in communication with a mass spectrometer or an ion mobility spectrometer.

    30. Use of an amplifier as claimed in any one of claims ito 21 to increase the flow of an analyte ion stream.

    31. The use as claimed in claim 30 wherein application of a voltage to at least a portion of the side walls of the air amplifier provides for an increase in the flow of an analyte ion stream.