RU2792724C2 - Integrated micro-photoionization detector with ultra-thin uv transmission window - Google Patents

Abstract

FIELD: chromatography.

SUBSTANCE: integrated microfluidic photoionization detector (PID), containing a microfluidic ionization chamber and a microfluidic ultraviolet radiation chamber capable of generating ultraviolet photons. An ultra-thin transmission window is located between the microfluidic ionization chamber and the microfluidic ultraviolet radiation chamber for the passage of ultraviolet photons from the microfluidic ultraviolet radiation chamber to the microfluidic ionization chamber. Also, the system for detecting one or more VOC analytes is proposed, which includes a gas chromatography (GC) block containing at least one gas chromatography column, and an integrated microfluidic photoionization detector (PID) located after the gas chromatography (GC) block.

EFFECT: integrated microfluidic photoionization detector (PID), containing a microfluidic ionization chamber and a microfluidic ultraviolet radiation chamber capable of generating ultraviolet photons.

20 cl, 5 dwg

Description

Governmental support

The present invention was made with government support in accordance with RD-83564401-0 issued by the US Environmental Protection Agency. The government has certain rights to the invention.

Link to related applications

The present application claims the priority of U.S. Provisional Application No. 62/740,583 dated October 3, 2018. The entire contents of the above application are incorporated herein by reference.

The field of technology to which the invention belongs

The present invention relates to an integrated photoionization microdetector with an ultra-thin UV transmission window.

State of the art

This section provides background information regarding the present invention, which is not necessarily prior art.

Gas chromatography (GC) is widely used for the analysis of volatile organic compounds (VOCs) and other analyzed compounds. When used for analysis, GC systems also typically include an analyte detector. Flame ionization detectors (FIDs) are commonly used as vapor detectors for benchtop GC instruments. However, PIDs and microPIDs (micro-PIDs) are destructive and therefore limited in use. For example, FIDs and microFIDs cannot be placed in the middle of a vapor flow path to control multidimensional gas chromatography separations. Instead, they can only be used at the end of the GC instrument. In addition, FIDs require the use of hydrogen, which prevents their widespread use in gas chromatography microdevices. Thermal conductivity detectors (TCD) and µTCD (micro-TCD) have also been used as vapor detectors in conjunction with gas chromatographs. They are non-destructive and have a flow-through design. However, TCDs suffer from low sensitivity (nanograms) and require helium. Electron capture detectors (ECDs) are another type of non-destructive vapor detector. Although they are very sensitive, they have a limited dynamic range and require the use of radioactive materials to ionize the analyte.

A photoionization detector (PID) is another type of vapor detector. PIDs are sensitive (picogram), non-destructive and applicable to a wide range of vapors. In a PID, vapor molecules are ionized inside an ionization chamber by exposure to ultraviolet (UV) radiation generated by a UV lamp. The ions generated in the ionization chamber are then sent to the electrodes to generate current. The UV lamp is usually filled with low pressure argon, krypton, or other gases to produce UV light when externally electrically excited. In UV lamps, sealing windows (i.e., windows that let in UV radiation) are formed from special materials such as calcium fluoride, magnesium fluoride, or lithium fluoride. Such materials have a relatively high transmittance in the UV wavelength range of interest. However, such materials are relatively expensive and susceptible to water etching, crystal solarization, and yellowing effects due to UV damage, which degrade the performance of the UV lamp (and hence the PID) and shorten lamp life. In addition, such conventional UV lamps are incompatible with micromanufacturing processes. Therefore, it is difficult to manufacture a PID using such conventional UV lamps.

The essence of the invention

This section provides the essence of the invention, and it is not an all-inclusive description of its entire scope and all its features.

In some aspects, the present invention provides an integrated microfluidic photoionization detector (PID) that includes a microfluidic ionization chamber having an inlet that receives a fluid sample and an outlet through which the fluid sample exits the microfluidic ionization chamber. The integrated microfluidic PID also includes a first electrode and a separate second electrode electrically connected to the microfluidic ionization chamber. The ultraviolet microfluidic chamber is configured to generate ultraviolet photons. The integrated microfluidic PID also includes an ultra-thin transmission window located between the microfluidic ionization chamber and the ultraviolet microfluidic chamber, which allows ultraviolet photons to pass from the ultraviolet microfluidic chamber to the microfluidic ionization chamber. In some embodiments, the ultra-thin transmission window transmits more than or about 5% of ultraviolet photons.

In one aspect, the ultra-thin transmission window comprises a material selected from the group consisting of silica, fused silica, quartz, sapphire, magnesium fluoride, calcium fluoride, lithium fluoride, and combinations thereof.

In one aspect, an ultrathin transmission window is defined as one or more selected areas on a wafer.

In one aspect, an ultra-thin transmission window is located on the base plate, and the ultra-thin transmission window is defined in certain regions of the base plate.

In one aspect, the integrated microfluidic photoionization detector (PID) also includes a layer stack containing a first layer and a second layer. An ultra-thin transmission window is set in the first layer, and one or more regions of the second layer corresponding to the ultra-thin transmission window are missing.

In one aspect, the ultrathin transmission window has a thickness less than or equal to about 20 microns and is configured to transmit more than or about 5% of ultraviolet photons.

In one aspect, the ultra-thin transmission window has a thickness greater than or equal to about 250 nm to less than or equal to about 500 nm.

In one aspect, the ultraviolet microfluidic chamber has an inlet to which ultraviolet generating fluid is supplied.

In one aspect, the ultraviolet microfluidic chamber comprises an ultraviolet generating fluid selected from the group consisting of krypton, argon, helium, and combinations thereof.

In one aspect, the microfluidic ionization chamber is one or more microfluidic channels.

In one aspect, one or more microfluidic channels have a total volume of less than about 10 μl.

In one aspect, the first electrode and a separate second electrode are formed in a layer of electrically conductive material, and one or more microfluidic channels are located in the layer to electrically isolate the first electrode from the second separate electrode.

In some other aspects, the present invention provides a detection system for one or more VOC analytes, comprising a gas chromatography (GC) unit that includes at least one gas chromatography column and an integrated microfluidic photoionization detector (PID) located after the gas chromatography (GC) unit . An integrated microfluidic photoionization detector (PID) comprises a microfluidic ionization chamber having an inlet that receives a fluid sample and an outlet through which the fluid sample exits the microfluidic ionization chamber. The integrated microfluidic photoionization detector (PID) also includes a first electrode and a separate second electrode electrically connected to the microfluidic ionization chamber. The integrated microfluidic photoionization detector (PID) also contains a microfluidic ultraviolet radiation chamber that is configured to generate ultraviolet photons. The integrated microfluidic photoionization detector (PID) also contains an ultra-thin transmission window located between the microfluidic ionization chamber and the microfluidic ultraviolet radiation chamber, which allows more than or about 5% of ultraviolet photons to pass from the microfluidic ultraviolet radiation chamber to the microfluidic ionization chamber. A microfluidic photoionization detector (PID) analyzes a sample processed in a gas chromatography (GC) unit.

In one aspect, the ultra-thin transmission window comprises a material selected from the group consisting of silica, fused silica, quartz, sapphire, magnesium fluoride, calcium fluoride, lithium fluoride, and combinations thereof.

In one aspect, an ultrathin transmission window is defined as one or more selected areas on a wafer.

In one aspect, an ultra-thin transmission window is located on the base plate, and the ultra-thin transmission window is defined in certain regions of the base plate.

In one aspect, the integrated microfluidic photoionization detector (PID) also includes a layer stack containing a first layer and a second layer. An ultra-thin transmission window is set in the first layer, and one or more regions of the second layer corresponding to the ultra-thin transmission window are missing.

In one aspect, the ultrathin transmission window has a thickness less than or equal to about 20 microns and is configured to transmit more than or about 5% of ultraviolet photons.

In one aspect, the microfluidic ionization chamber is one or more microfluidic channels.

In one aspect, the first electrode and a separate second electrode are formed in a layer of electrically conductive material, and one or more microfluidic channels are located in the layer to electrically isolate the first electrode from the second separate electrode.

Additional areas of applicability will become apparent from the description presented in this document. The description and specific examples in this section are for illustration only and are not intended to limit the scope of the present invention.

Description of drawings

The drawings described herein are provided to illustrate only selected embodiments, not all possible implementations, and are not intended to limit the scope of the present invention.

In FIG. 1 schematically shows an example of a detection system including a gas chromatography (GC) unit that includes at least one gas chromatography column and an integrated microfluidic photoionization detector (PID) located after the gas chromatography (GC) unit.

In FIG. 2 is an illustration of an integrated microfluidic photoionization detector (PID) having an ultra-thin transmission window, in accordance with certain aspects of the present invention.

In FIG. 3 is a cross-sectional view of the integrated microfluidic photoionization detector (PID) shown in FIG. 2, the section being drawn along line 3-3.

In FIG. 4 is a photograph of an ultra-thin ultraviolet (UV) transmission window imaged on a silicon substrate coated with thermal oxide.

In FIG. 5 is a graph comparing the ultraviolet transmission capability of an ultra-thin ultraviolet (UV) transmission window prepared in accordance with certain aspects of the present invention compared to an air window.

Corresponding reference numerals designate corresponding parts in several of the drawings.

Detailed description of the invention

The exemplary embodiments of the invention are provided so that the description of the invention is exhaustive and fully conveys the scope of the invention to those skilled in the art. Numerous specific details are set forth in the form of examples of specific formulations, components, devices, and methods in order to provide a thorough understanding of the embodiments of the present invention. It will be apparent to those skilled in the art that the specific details need not be used, that the embodiments may be embodied in many different forms, and that they do not limit the scope of the invention. In some embodiments, well-known processes, well-known device designs, and well-known technologies are not described in detail.

The terminology used in this document is only intended to describe specific examples of the invention and is not meant to be limiting. As used herein, the singular forms may include plural forms, unless the contrary is clear from the context. The terms "comprises", "comprising", "comprising" and "having" are inclusive and therefore describe the presence of certain features, elements, compositions, steps, integers, operations and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, processes, elements, components and/or groups thereof. Although the unrestricted term "comprising" should be understood as a non-limiting term used to describe and endorse the various embodiments set forth herein, in certain aspects, this term, and in the alternative, can be understood as a more limiting and restrictive term, for example, "consisting of of" or "consisting essentially of". Thus, for any given embodiment containing compositions, materials, components, elements, characteristics, integers, operations and/or process steps, the present disclosure specifically also includes embodiments consisting of or consisting essentially of such listed compositions, materials, components, elements, functions, integers, operations and/or process steps. In the case of "consisting of" the alternative embodiment excludes any additional compositions, materials, components, elements, properties, integers, operations and/or process steps, while in the case of "consisting essentially of" any additional compositions, materials , components, elements, characteristics, integers, operations and/or process steps that significantly affect the main and new characteristics are excluded from such an implementation, but any compositions, materials, components, elements, features, integers, operations and/ or process steps that do not significantly affect the core and new features may be included in the embodiment.

It should not be assumed that the steps of the methods, processes and operations described in this document are necessarily required to be performed in a particular described or discussed order, unless specifically indicated the order of execution. It is also understood that additional or alternative steps may be used unless otherwise indicated.

If a component, element or layer is said to be "on", "attached to", "attached to", or "docked to" another element or layer, then it can be directly on another component, element or layer, be directly linked to them, attached to it or docked to it, or there may be intermediate elements or layers. By contrast, if an element is said to be "directly on", "directly coupled to", "directly attached to", or "directly attached to" another element or layer, then there should be no intervening elements or layers. Other words used to describe relationships between elements should be interpreted similarly (eg, "between" and "immediately between", "adjacent" and "immediately adjacent", etc.). As used herein, the term "and/or" includes any and all combinations of one or more of the respective listed elements.

Although the terms first, second, third, etc., may be used in this document to describe various steps, elements, components, regions, layers, and/or sections, these steps, elements, components, layers, and/or sections should not be limited to these terms, unless otherwise indicated. These terms may only be used to distinguish one step, element, component, region, layer, or section from another step, element, component, region, layer, or section. Terms such as "first", "second", and other numeric terms used in this document do not imply sequence or order unless explicitly indicated in the context. Thus, a first step, element, component, region, layer, or section discussed below may be referred to as a second step, element, component, region, or section without departing from the inventive spirit of the embodiments.

Relative spatial or temporal terms such as before, after, inside, outside, below, below, below, above, above, etc. may be used to simplify the description to describe the relationship of one element or feature to another element(s) or feature(s), as shown in the figures. The relative spatial or temporal terms may be intended to encompass various orientations of the device or system in use or operation in addition to the orientation depicted in the figures.

In this description, the numerical values are approximate measures or range limits to cover minor deviations from the given values, and embodiments having approximately the value mentioned, as well as those having the precisely specified value. With the exception of working examples provided at the end of the detailed description, all numerical values of parameters (e.g., amounts or conditions) in this description, including the appended claims, should be understood as modified in all cases by the term "about", regardless of whether " approximately" precedes a numeric value or not. "About" means that the specified numerical value allows for some slight inaccuracy (with some approximation to precision in value; approximately or close enough to value; almost). If the imprecision provided by the expression "about" is not understood in the art in this conventional sense, then "about" as used herein indicates at least the variations that may result from conventional methods of measuring and using such parameters. For example, "about" may include a variation less than or equal to 5%, optionally less than or equal to 4%, optionally less than or equal to 3%, optionally less than or equal to 2%, optionally less than or equal to 1%, alternatively, less than or equal to 0.5%, and in some aspects, alternatively, less than or equal to 0.1%.

Further, expanding ranges includes expanding all values and further subdivided ranges within the entire range, including the endpoints and subranges specified for the ranges.

Now with reference to the accompanying drawings will be more fully described embodiments.

Detection systems using gas chromatography can be used to detect the presence of certain analytes such as VOCs or other compounds. In such systems, a microfluidic PID vapor detector, such as those prepared in accordance with certain aspects of the present invention, is used in conjunction with a gas chromatography (GC) column. The vapor sample for analysis is first injected into the GC column. In some aspects, the GC column may be miniaturized in the form of micro-GC (μGC). The sample is then transported through the column with an inert carrier gas, and the sample is separated on a GC column according to the physical properties of each compound (analyte) in the sample. Each eluted compound exits the GC column and enters the vapor detector assembly, which can be a photoionization detector (PID) or a microfluidic PID (µPID), as described below. In other PID or microPID designs, vapor detector units can be used at intermediate positions within the GC column to detect analytes. As discussed herein, unless otherwise noted, PID and microPID are used interchangeably.

PIDs typically use high energy photons (eg, ultraviolet (UV) wavelengths) to dissociate eluted analyte molecules into positively charged ions. Often a PID uses a discharge gas, such as an inert gas (eg krypton and argon), which is ionized in a discharge lamp chamber. External energy (for example, high frequency energy) can be absorbed by the discharge gas, so that the atoms in the discharge gas become excited. In the discharge chamber of a UV lamp, each ion can combine with another atom to emit one or more photons. Eluted compounds enter the PID device in the ionization chamber. The ionization chamber and the discharge lamp chamber are usually separated from each other by an optically transparent window which allows high energy photons to pass into the ionization chamber. A typical transmission window is formed from a material such as magnesium fluoride, calcium fluoride, or lithium fluoride and has a thickness of from about 0.1 mm (about 100 microns) to about 10 mm. The ionization chamber containing the eluted compounds is then bombarded with photons generated by ionized discharge gas from the discharge lamp chamber.

The photons/energy are then absorbed by the analyte molecules, which become excited and ionized in a separate ionization chamber, eventually forming positively charged ions. Thus, based on the relative retention time in the GC column, different analyte molecules in the sample are separated, eluted at different times, and then enter the chamber where they are ionized by photons emitted by the ionized discharge gas.

The gas thus becomes electrically charged and the ions produce an electrical current which becomes an output signal related to the concentration of ionized analyte molecules. As each ionized compound passes through one or more collecting electrodes near the ionization chamber, an electrical current is generated. Thus, analyte compounds can be identified based on their retention time and quantified using the PID signal (or current generated by the PID).

In various aspects, the present disclosure contemplates an integrated photoionization detector (PID), which in some embodiments may be a microfluidic PID (microfluidic PID), as discussed further below. The microfluidic ionization chamber contains a microfluidic ionization chamber for receiving and processing a liquid sample. The first electrode and a separate second electrode are electrically connected to the microfluidic ionization chamber. The McPID also contains an integrated ultraviolet microfluidic chamber that is capable of generating ultraviolet photons. An ultra-thin transmission window is located between the microfluidic ionization chamber and the ultraviolet microfluidic chamber, which allows ultraviolet photons to pass from the ultraviolet microfluidic chamber to the microfluidic ionization chamber.

The present disclosure provides, in certain aspects, a system 20 for detecting one or more volatile organic compounds (VOCs) or other target analytes, such as that shown in FIG. 1. In the detection system 10, the gas chromatography (GC) unit 20 contains at least one gas chromatography column 22. As used herein, the term "column" is intended to broadly include various flow paths through which fluids may flow, such as a structured flow field from microstructures defined on one or more substrates, or other fluid flow paths known to those skilled in the art. this field of technology. Downstream of the gas chromatography (GC) unit 20 is an integrated microfluidic photoionization detector (μPID) 30.

In some aspects, the GC unit 20 is a microfluidic GC (μGC) and the PID 30 is a microfluidic PID (μFID). In various aspects, the invention provides shaping methods and devices having microscale features or channels and therefore being microfluidic. In some aspects, the feature, such as a channel or chamber, is optionally smaller than the microscale, such as being a nanoscale structure. As used herein, the term "microscale" refers to a structure having at least one dimension that is less than about 500 microns, alternatively less than about 400 microns, alternatively less than about 300 microns, alternatively less than about 200 microns, alternatively, less than about 150 microns, and in some embodiments, alternatively, less than about 100 microns. The "nanoscale" structure has at least one size that is less than or equal to about 50 µm, alternatively less than or equal to about 10 µm (10000 nm), alternatively less than or equal to about 1 µm (1000 nm), alternatively, less than or equal to about 0.1 μm (100 nm), optionally less than about 50 nm, and optionally less than about 10 nm. In this context, reference to a microscale, microchannel, microfluidic channel, or microstructure encompasses smaller structures such as equivalent nanoscale structures.

A microfluidic channel is a microchannel formed within or on a substrate that has a cross-sectional area and volume sufficient to enable the microfluidic channel to receive, transfer and/or store materials, including fluids. Fluids include gases, vapors, liquids, and the like. Thus, the microfluidic channel is typically sized such that the length of the structure forms the largest dimension, such as a groove (open shape) or a channel (structurally closed geometry). In some embodiments, the microfluidic channels may be completely enclosed structures that define an empty area that allows fluid communication through itself, as described later in this document. The microfluidic channels may have various cross-sectional shapes, including annular, circular or oval (tube-forming or cylindrical), rectangular, and the like.

Detection systems 20 based on gas chromatography typically include at least five components: (1) carrier gas source 24; (2) a fluid sample injection system 26; (3) one or more columns 22 gas chromatography; (4) a detector such as a microfluidic PID 30; and (5) a data processing system (not shown). The carrier gas (also called the mobile phase) is a relatively inert, high purity gas such as helium, hydrogen, nitrogen, argon, or air. The carrier gas may flow through the 22 GC column simultaneously with the test fluid sample (during the entire separation process). The fluid sample injection system 26 injects a predetermined volume of a sample mixture containing one or more target analytes to be tested (eg, in gaseous form) into the column by combining it with a flowing carrier gas from a source of carrier gas. Typically, separations are achieved within the chromatographic column 22 because the interior surfaces of the column are covered (or the interior of the column is filled) with material that acts as the stationary phase. The stationary phase adsorbs various target analytes in the sample mixture to varying degrees. Differences in adsorption lead to different delays and thus mobility coefficients for different chemicals as they pass through the column, thereby affecting the physical separation of the target analytes in the sample mixture. Notably, although gas chromatography (GC) unit 20 is shown as only one GC column 22, it may contain multiple columns through which a fluid sample may pass. In addition, such detection systems may include various other components such as modulators and the like.

A detector, such as a microfluidic PID 30, is located after the exit 32 of one or more GC columns 22. The microFID 30 is integrated with the gas chromatography (GC) unit 20 and serves to detect different chemicals or target analytes in the sample leaving or eluting from the column 22 at different times. The microfluidic ionization chamber 40 comprises a microfluidic ionization chamber 40 having an inlet 42 which receives a fluid sample and an outlet 44 through which the fluid sample exits the microfluidic ionization chamber 40. The first electrode and a separate second electrode (not shown) are also electrically connected to the microfluidic ionization chamber. chamber 40. The ultraviolet microfluidic chamber 50 is configured to generate ultraviolet photons. A transmission window 60 is located between the microfluidic ionization chamber 40 and the ultraviolet microfluidic chamber 50, which allows ultraviolet photons to pass from the ultraviolet microfluidic chamber 50 to the microfluidic ionization chamber 40. Thus, the microfluidic ionization chamber 40 analyzes the sample processed in the gas chromatography (GC) unit 20. Although not shown, the data processing system is also typically associated with the microPID 30 to be able to store, process and record separation test results.

In FIG. 2 and 3 show a schematic and cross-sectional view of a typical integrated microfluidic photoionization detector (µPID) 100 prepared in accordance with some aspects of the present invention. The MCFID 100 includes a substrate 110. One or more microfluidic channels 118 may be formed in or on the substrate 110. FIG. 2 and 3, a wall structure 112 is formed on a substrate 110 to define one or more microfluidic channels 118. The substrate 110 may be formed from an inorganic material or a polymer. In some aspects, substrate 110 may be glass (eg, silicon dioxide or borosilicate). In some embodiments, substrate 110 includes a plurality of layers.

In some embodiments, wall structure 112 may be a layer or selected regions of electrically conductive material (e.g., conductive silicon material) formed on substrate 110. Thus, in certain embodiments, when wall structure 112 is electrically conductive, wall structure 112 may act as positive electrode and/or negative electrode. Thus, at least one layer of the wall structure 112 may comprise an electrically conductive material. The electrically conductive material may be formed from a conductive material or a semiconductor material (such as a doped semiconductor material). In some aspects, the electrically conductive material comprises a material selected from the group consisting of: silicon (Si) (e.g. doped silicon), aluminum (Al), indium tin oxide (ITO), gold (Au), silver (Ag), platinum (Pt), iridium (Ir), palladium (Pd), tungsten (W), stainless steel (SS), zinc (Zn), titanium (Ti), their alloys and oxides, and combinations thereof. At least two of the plurality of layers may have different compositions. For example, the first layer on substrate 110 may comprise a doped semiconductor material, such as doped silicon, and the second layer overlaying the first layer may comprise an electrically conductive metal. Alternatively, electrically conductive materials may be incorporated into the wall structure 112 as electrodes and are in contact with one or more microfluidic channels 118.

The wall structure 112 may be selectively formed in certain areas or alternatively removed in selected areas in a pattern that forms one or more microfluidic channels 118. In some aspects, one or more microfluidic channels 118 may form a helical pattern. Thus, one or more microfluidic channels 118 may define a sinuous pattern on the substrate. By "tortuous" is meant that the fluid passage is a flow-through structure that bends and has at least two 180° changes of direction along the fluid path. The fluid path defined by one or more microfluidic channels 118 is thus curved and avoids direction changes that result in dead zones or reduced fluid flow. Such a tortuous path may define a helical structure or an interlaced type structure. In one embodiment, one or more microfluidic channels 118 may define an Archimedes spiral. One or more microfluidic channels 118 may be etched or formed into a conductive silicon wafer or layer, such as an Archimedes spiral channel formed in such material. In other embodiments, one or more microfluidic channels may have other flow path configurations, including straight flow paths.

In some embodiments, the total volume of one or more microfluidic channels 118 (or ionization chamber) is less than or equal to about 10 μl. In some preferred aspects, less than or equal to about 9 μl, alternatively, less than or equal to about 8 μl, alternatively, less than or equal to about 7 μl, alternatively, less than or equal to about 6 μl, optionally less than or equal to about 5 μl , optionally less than or equal to about 4 µl, optionally less than or equal to about 3 µl, optionally less than or equal to about 2 µl, and in some embodiments, optionally less than or equal to about 1.5 µl For example, in one In an embodiment, one or more microfluidic channels 118 limit the volume of the ionization chamber to only about 1.3 μl.

In addition, in some aspects, the microfluidic device 100 has a negligible total dead volume in the microfluidic channel. The total dead volume of one or more microfluidic channels 118 may be less than or equal to about 1% of the total microfluidic channel volume, for example, when the total volume of one or more microfluidic channels is 5 µl, a dead volume of less than or equal to 1% would be a dead volume, less than or equal to approximately 0.05 μl or 50 nl. In some other embodiments, the total dead volume of one or more microfluidic channels 118 may be less than or equal to about 0.9% of the total volume of one or more microfluidic channels, alternatively, less than or equal to about 0.7% of the total volume of one or more microfluidic channels. channels, optionally less than or equal to about 0.6% of the total volume of one or more microfluidic channels, and in some embodiments, less than or equal to about 0.5% of the total volume of one or more microfluidic channels. In some other embodiments, the dead volume of one or more microfluidic channels may be less than or equal to about 30 nl, alternatively less than or equal to about 25 nl, alternatively less than or equal to about 15 nl, alternatively less than or equal to about 10 nl, alternatively less than or equal to about 5 nl, alternatively less than or equal to about 4 nl, alternatively less than or equal to about 3 nl, and in some embodiments, alternatively less than or equal to about 2 nl.

The microfluidic channel may have a width greater than or equal to about 50 μm to less than or equal to about 200 μm, optionally greater than or equal to about 100 μm to less than or equal to about 200 μm, and in some aspects, alternatively greater than or equal to about 125 µm to less than or equal to about 175 µm. In some other embodiments, the microfluidic channel has a height or depth greater than or equal to about 100 microns to less than or equal to about 600 microns, alternatively greater than or equal to about 200 microns to less than or equal to about 500 microns, alternatively greater than or equal to from about 300 microns to less than or equal to about 400 microns, and in some aspects, optionally from greater than or equal to about 350 microns to less than or equal to about 400 microns. The total length of the microfluidic channel may be greater than or equal to about 0.5 cm, but less than or equal to about 10 cm, optionally greater than or equal to about 1 cm and less than or equal to about 5 cm, and in some aspects, alternatively greater than or is about 2 cm and less than or equal to about 3 cm. The wall thickness (e.g., between respective passages adjacent to each other in the microfluidic channels) can be greater than or equal to about 10 μm to less than or equal to about 100 μm, alternatively from greater than or equal to about 25 microns to less than or equal to about 75 microns, and in some aspects optionally greater than or equal to about 40 microns to less than or equal to about 60 microns. In one embodiment, the microfluidic channel has a cross section of 150 µm (width) × 380 µm (depth), a wall thickness of 50 µm, and a length of 2.3 cm.

As noted above, the microfluidic photoionization detector (PID) 100 also includes a first electrode and a second electrode of opposite polarity. For example, the wall structure 112 may define a first electrode region 114 and a separate second electrode region 116. The first electrode region 114 and the second electrode region 116 may be formed in selected regions of one or more layers of the wall structure 112 on the substrate 110. The wall structure 112 may have one or more non-conductive regions 108. In some embodiments, the substrate 110 includes selected regions having a first layer of doped silicon and a second layer of electrically conductive metal, the selected regions being separate regions that correspond to the respective region 114 of the first electrode and the region 116 of the second electrode. The first electrode region 114 may be separated and electrically isolated from the second electrode region 116 by one or more microfluidic channels 118. The microfluidic channel 118 may be formed in the wall structure 112 and thus may separate and delimit the first electrode region 114 and the second electrode region 116 . In some aspects, the bottom of the microfluidic channel 118 may be the substrate 110, or alternatively, although not shown, one or more microfluidic channels may be completely formed in the wall structure 112 such that the side walls and the bottom/bottom are defined therein. .

The first electrode region 114 and the second electrode region 116 may be connected to an external positive and negative terminal of a power supply (not shown). Although not shown, the first electrode area 114 and the second electrode area 116 with opposite polarity can be connected to a power drive circuit connected to a power source. The first and second electrode regions 114, 116 may be connected to an amplifier (not shown) to form a closed circuit. In some aspects, the power supply may be a low voltage power supply having a maximum voltage less than or equal to about 20 volts direct current (VDC). Thus, the electrodes defined by the first electrode region 114 and the second electrode region 116 allow measurement of electrical signals generated by ionized analytes in one or more microfluidic channels 118 when they are bombarded and excited by photons.

The microfluidic device 100 also includes an inlet 122 for one or more microfluidic channels 118 that serve as a microfluidic ionization chamber. There is also an outlet 124 for one or more microfluidic channels 118. Thus, a carrier gas containing one or more target analytes can exit the GC column and enter the inlet 122, where it passes through one or more microfluidic channels 118. As discussed above, analytes in fluid flowing through a microfluidic ionization chamber (one or more microfluidic channels 118) can be ionized and charge can be measured. The first electrode region 114 and the second electrode region 116 can detect the current generated by the target analyte(s) upon UV ionization. Fluid may then exit the microfluidic ionization chamber (from one or more microfluidic channels 118) through outlet 124.

The microFID device 100 also includes an electromagnetic radiation or light source, which may be a microfluidic ultraviolet light chamber or a microfluidic discharge chamber 130 that is configured to generate ultraviolet photons. The microfluidic discharge chamber 130 may have an inlet 132 and may be filled with an ultraviolet generating fluid such as krypton, argon, helium, and other pure or mixed gases known in the art to generate ultraviolet light. In one aspect, the ultraviolet generating fluid may be selected from the group consisting of krypton, argon, helium, and combinations thereof. Inlet 132 may be closed after being filled with ultraviolet generating fluid. Alternatively, the microfluidic discharge chamber 130 may have an outlet 134 such that ultraviolet generating fluid may flow into the inlet 132 and exit the microfluidic discharge chamber 130 through an outlet 134. The microfluidic discharge chamber 130 may also have a non-conductive cover 136 located at the edges of the open cameras.

The integrated microfluidic discharge chamber 130 generates light or electromagnetic radiation within the integrated lamp, and hence photons, which are directed to the contents of one or more microfluidic channels 118. As shown, the first excitation electrode 140 and the second excitation electrode 142 of opposite polarity are arranged in a pattern in overburden 144, which typically matches the pattern of one or more microfluidic channels 118 below. Thus, when a current or potential is applied to the first excitation electrode 140 and the second excitation electrode 142, the ultraviolet generating fluid is excited and generates photons in regions corresponding to one or more microfluidic channels 118.

Particularly suitable light falls within the ultraviolet electromagnetic spectrum. In some embodiments, the light may be ultraviolet (UV) radiation (including ultraviolet A, ultraviolet B, ultraviolet C, near ultraviolet, mid ultraviolet, far ultraviolet, extreme ultraviolet, and vacuum ultraviolet) with a wavelength greater than or equal to about 10 nm to less or equal to about 400 nm. In other embodiments, the light may be ultraviolet radiation in the wavelength range from greater than or equal to about 100 nm to less than or equal to about 400 nm (including ultraviolet A, ultraviolet B, ultraviolet C). In particular, the light may be filtered light, light focused, polarized light, or may be non-spectral or a mixture of different wavelengths.

In some embodiments, as further described below, the UV transmission window may be ultrathin, and thus, in certain embodiments, may be submicron thick. Thus, the ultra-thin transmission window 150 is located between the microfluidic ionization chamber in the form of one or more microfluidic channels 118 and the ultraviolet microfluidic chamber in the form of a microfluidic discharge chamber 130. The ultra-thin transmission window 150 allows a sufficient amount of ultraviolet photons to pass from the microfluidic discharge chamber 130 to one or a plurality of microfluidic channels 118 that serve as a microfluidic ionization chamber to excite one or more target analytes to a detectable level. In some aspects, the term "transmission" means that the ultrathin window is transparent to the target wavelength range of electromagnetic energy, such as the ultraviolet wavelength ranges described above. Thus, in certain aspects, the transmission window transmits greater than or equal to about 5% of electromagnetic energy in a predetermined wavelength range, alternatively greater than or equal to about 10%, alternatively greater than or equal to about 20%, alternatively greater than or equal to about 30% as an option, greater than or equal to about 40%, as an option, greater than or equal to about 50%, as an option, greater than or equal to about 60%, as an option, greater than or equal to about 70%, as an option, greater than or equal about 80%, alternatively, greater than or equal to about 90%, and in some aspects, alternatively, greater than or equal to about 95% of electromagnetic energy in a predetermined wavelength range (for example, in the ultraviolet ranges of the spectrum). In some embodiments, the ultrathin transmission window has a thickness of less than or equal to about 20 microns and is configured to transmit more than or about 5% of ultraviolet photons or any of the levels of ultraviolet photon transmission noted above.

The thickness of the ultrathin transmission window 150 may be less than or equal to about 20 micrometers (μm), optionally, less than or equal to about 10 microns, optionally, less than or equal to about 5 microns, optionally, less than or equal to about 4 microns, optionally, less than or equal to about 3 μm, optionally less than or equal to about 2 μm, and in some embodiments, optionally less than or equal to about 1 μm. In some embodiments, the thickness of the ultrathin transmission window 150 may be less than or equal to about 500 nm, alternatively, less than or equal to about 450 nm, alternatively, less than or equal to about 400 nm, alternatively, less than or equal to about 350 nm, alternatively , less than or equal to about 300 nm, optionally less than or equal to about 250 nm, optionally less than or equal to about 200 nm, optionally less than or equal to about 150 nm, optionally less than or equal to about 100 nm, and in some alternatively less than or equal to about 50 nm. In some embodiments, the thickness of the ultrathin transmission window 150 may be greater than or equal to about 50 nm, but less than or equal to about 20 microns, alternatively greater than or equal to about 50 nm, but less than or equal to about 10 microns, alternatively greater than or equal to about 50 nm, but less than or equal to about 5 µm, optionally, greater than or equal to about 50 nm, but less than or equal to about 4 µm, optionally, greater than or equal to about 50 nm, but less than or equal to about 3 µm, optionally, greater than or equal to about 50 nm, but less than or equal to about 2 µm, optionally greater than or equal to about 50 nm, but less than or equal to about 1 µm, optionally greater than or equal to about 50 nm, but less than or equal to about 500 nm alternatively greater than or equal to about 50 nm but less than or equal to about 250 nm alternatively greater than or equal to about 50 nm but less than or equal to about 250 nm alternatively greater than or equal to about 50 nm but less than or equal to about 200 nm, optionally greater than or equal to about 50 nm, but less than or equal to about 150 nm, and in some embodiments, alternatively, greater than or equal to about 50 nm, but less than or equal to about 100 nm.

As discussed below, the ultra-thin transmission window 150 may be an ultra-thin plate, or may be one or more selected ultra-thin regions or layers provided in a thicker plate or layers of material. In some aspects, the ultrathin window 150 may be located over one or more microfluidic channels 118. In some embodiments, the ultrathin window 150 is placed over at least a portion of one or more microfluidic channels 118, thereby forming a top wall (e.g., the fourth side of a three-way channel). ) to enclose the microfluidic channel(s) 118. However, the ultra-thin transmission window 150 does not have to be in contact with one or more microfluidic channels 118, but instead may be located adjacent to the microfluidic channel(s) and may leave a small gap, for example, located at a distance from less than a few millimeters to less than about 10 microns from one or more microfluidic channels 118. Thus, the ultraviolet light source in the form of a microfluidic discharge chamber 130 is positioned and configured to direct photons towards fluid samples that may be present in one or more microfluidic channels. Thus, one or more microfluidic channels 118 serve as an ionization chamber for the analyzed compounds present and flowing therein.

In particular, in some embodiments, the ultra-thin transmission window may be microfabricated from a material like silica, which has generally been considered unsuitable for such applications because such a material is considered opaque to UV radiation. Silica is known to have extremely low transmittance (or extremely high attenuation) in the UV spectrum of interest (for example, for wavelengths from about 140 nm to about 70 nm, corresponding to UV photon energies from 9 eV to 17.5 eV). Therefore, silica has traditionally not been considered as a material that could be used as a UV window for a PID device. However, using certain microfabrication techniques described in this document, silica can be formed as part of a transmission window that has an ultra-thin thickness and therefore becomes transparent in the target UV spectrum. More specifically, the fraction of the transmitted UV photon flux is defined as (1-A×t), where A is the attenuation coefficient of silicon dioxide, and t is the thickness of the transmission window. Despite the large value of A, A×t becomes relatively small (which means that it becomes transparent to ultraviolet light) when the value of t is very small (for example, when t has a submicron thickness). However, the present invention involves the formation of ultra-thin transmission windows not only from silicon-containing materials such as silicon dioxide (for example, silica), fused silica, silicon, but also from various other materials such as magnesium fluoride (MgF ₂ ), calcium fluoride ( CaF ₂ ), lithium fluoride (LiF) and the like. In some embodiments, the ultrathin transmission window comprises a material selected from the group consisting of silica, fused silica, silicon, quartz, sapphire, magnesium fluoride, calcium fluoride, lithium fluoride, and combinations thereof.

In some embodiments, to maintain mechanical integrity, the transmission window is designed as a plate having one or more selected areas of ultra-thin thickness for UV/photon transmission, while remaining areas of the plate outside of one or more selected areas may remain relatively thick. because they are not transparent. The thicker opaque regions are thicker than the ultrathin transmission regions. In some embodiments, the ratio of the average first thickness of the ultrathin transmission region to the average second thickness of the remaining opaque thicker regions may be less than or equal to about 1:2, alternatively less than or equal to about 1:3, alternatively less than or equal to about 1:4 , alternatively less than or equal to about 1:5, and in some embodiments, alternatively less than or equal to about 1:5.

In some embodiments, the thicker regions have a thickness greater than about 500 nm, alternatively greater than or equal to about 600 nm, alternatively greater than or equal to about 700 nm, alternatively greater than or equal to about 750 nm, alternatively greater than or equal to about 800 nm, optionally greater than or equal to about 900 nm, optionally greater than or equal to about 1 µm, optionally greater than or equal to about 2 µm, optionally greater than or equal to about 3 µm, optionally greater than or equal to about 4 µm, optionally greater than or equal to about 5 µm, optionally greater than or equal to about 10 µm, and in some embodiments, optionally greater than or equal to about 20 µm.

In other aspects, the transmission window may be an assembly including multiple layers, for example, one layer may be an ultra-thin layer and the other layer may be one or more thicker layers. Thus, the transmission window can be formed as a layer pack containing the first layer and the second layer. An ultra-thin transmission window is set in the first layer, and one or more regions of the second layer corresponding to the ultra-thin transmission window are missing. Therefore, selected areas of one or more thicker layers can be removed to allow UV light to pass through the ultrathin layer in selected areas. Removal can be achieved using nanostructure shaping, etching, lithography or photolithography techniques. In some aspects, the material forming the transmission window may be one that can be processed using such lithography, photolithography, or nanostructuring techniques, such as silicon dioxide, silicon, quartz, fused silica, and the like.

In FIG. 4 shows an image of an ultra-thin transmission window made in accordance with some aspects of the present disclosure. A window that transmits ultraviolet radiation, made of silicon dioxide of submicron thickness (for example, 500 nm), is formed on a silicon wafer having a thermal oxide coating. Thermal oxidation occurs after a silicon wafer is exposed to a combination of oxidants (and possibly heat) to create a thermal oxide layer containing silicon dioxide (SiO ₂ ) or silica. In order to preserve its mechanical integrity, the silica-containing transmission window can be designed so that some parts are extremely thin (eg, less than or equal to about 500 nm thick), while other parts can remain relatively thick. To provide mechanical strength, a periodic pattern with a small open area is created and etched from the silicon side (ie, the side opposite the side having the thermal oxide coating). The thermal oxide layer (ie the silicon dioxide layer) serves as an anti-etch layer. The thickness of the silicon dioxide transmission window is controlled by a thermal oxide layer on a silicon wafer. Thus, the etch pattern creates a pattern of selected areas of silica that limit the UV/photon transmission window. As a non-limiting example, such transmission windows can be formed by standard cleanroom photolithography techniques.

Examples

Testing the ability of an ultra-thin quartz window to transmit UV radiation. In this study, a UV lamp used in a conventional PID was purchased from Baseline-Mocon and used as a UV source (UV photon energy 10.6 eV, wavelength approximately 120 nm). The lamp was placed directly on top of an ultra-thin, UV-transmitting silica window formed in accordance with some aspects of the present invention. Toluene was used as the analyte and passed through a microfluidic ionization chamber under a silica window. We received a signal of ~ 0.01 V (column on the right in Fig. 5). For comparison, in the column on the left in Fig. 5, the silica window is replaced by a silicon wafer having an air window (meaning that part of the silicon wafer is completely etched through) with the same UV transmission area as the silica window. A signal of 0.05 V was obtained under the same test conditions as for the silica window. The above comparison shows that the ultra-thin silica window can effectively transmit UV light.

The above description of the embodiments has been provided for purposes of illustration and description. It is not intended to be all inclusive or to limit the invention. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but where appropriate, they may be interchangeable and may be used in the selected embodiment even if not specifically shown or described. They can also be modified in many ways. Such changes should not be construed as a departure from the invention, and all such modifications are intended to be included within the scope of the invention.

Claims (20)

1. An integrated microfluidic photoionization detector (PID) comprising: a microfluidic ionization chamber having an inlet that receives a fluid sample and an outlet through which the fluid sample exits the microfluidic ionization chamber; a first electrode and a separate second electrode electrically connected to the microfluidic ionization chamber; an integrated ultraviolet microfluidic chamber for generating ultraviolet photons; and a transmission window located between the microfluidic ionization chamber and the microfluidic ultraviolet radiation chamber, wherein the transmission window defines one or more ultrathin transmission regions having a thickness less than or equal to about 500 nm, which allow transmission of ultraviolet photons from the microfluidic ultraviolet radiation chamber into the microfluidic ionization chamber. camera. 2. An integrated microfluidic photoionization detector (PID) according to claim 1, wherein the transmission window comprises a material selected from the group consisting of silicon dioxide, fused silica, silicon, quartz, sapphire, magnesium fluoride, calcium fluoride, lithium fluoride, and their combinations. 3. An integrated microfluidic photoionization detector (PID) according to claim 1 or 2, wherein the ultrathin transmission regions are formed as one or more selected regions on the wafer. 4. Integrated microfluidic photoionization detector (PID) according to any one of paragraphs. 1-3, in which the transmission window is located on the base plate, and ultra-thin transmission regions are formed as one or more selected areas on the base plate. 5. Integrated microfluidic photoionization detector (PID) according to any one of paragraphs. 1-4, wherein the transmission window also comprises a layer stack comprising a first layer and a second layer, said one or more ultrathin transmission regions being formed in the first layer where the second layer is absent. 6. Integrated microfluidic photoionization detector (PID) according to any one of paragraphs. 1-5, in which the transmission window has a thickness less than or equal to about 20 microns, and is configured to transmit more than or about 5% of ultraviolet photons. 7. Integrated microfluidic photoionization detector (PID) according to any one of paragraphs. 1-6, wherein said one or more ultrathin transmission regions comprise a material selected from the group consisting of silica and fused silica and have a thickness greater than or equal to about 250 nm to less than or equal to about 500 nm. 8. Integrated microfluidic photoionization detector (PID) according to any one of paragraphs. 1-7, wherein the ultraviolet radiation microfluidic chamber has an inlet for supplying an ultraviolet radiation generating fluid. 9. Integrated microfluidic photoionization detector (PID) according to any one of paragraphs. 1-8, wherein the ultraviolet microfluidic chamber contains an ultraviolet radiation generating fluid selected from the group consisting of krypton, argon, helium, and combinations thereof. 10. Integrated microfluidic photoionization detector (PID) according to any one of paragraphs. 1-9, in which the microfluidic ionization chamber is one or more microfluidic channels, while the integrated microfluidic photoionization detector (PID) further comprises a third electrode and a separate fourth electrode formed in a layer located on top of the microfluidic ultraviolet radiation chamber and electrically connected to it wherein the third electrode and the fourth electrode form a second pattern that corresponds to a first pattern of said one or more microfluidic channels of the microfluidic ionization chamber below the ultraviolet microfluidic chamber. 11. Integrated microfluidic photoionization detector (PID) according to any one of paragraphs. 1-10, wherein the microfluidic ionization chamber has a total volume less than or equal to about 10 microliters (μl) and the ultraviolet microfluidic chamber has a total volume of less than about 10 μl. 12. Integrated microfluidic photoionization detector (PID) according to any one of paragraphs. 1-11, wherein the first electrode and a separate second electrode are formed in a layer of electrically conductive material, and said one or more microfluidic channels are located in said layer to electrically isolate the first electrode from the second separate electrode. 13. System for detecting one or more analytes of volatile organic compounds (VOC), containing: (i) a gas chromatography (GC) unit containing at least one gas chromatographic column; and (ii) an integrated microfluidic photoionization detector (PID) located after the gas chromatography (GC) unit, comprising: a microfluidic ionization chamber having an inlet for receiving a fluid sample and an outlet for exiting a fluid sample from the microfluidic ionization chamber; a first electrode and a separate second electrode electrically connected to the microfluidic ionization chamber; an integrated ultraviolet microfluidic chamber for generating ultraviolet photons; and a transmission window located between the microfluidic ionization chamber and the microfluidic ultraviolet radiation chamber, wherein the transmission window defines one or more ultrathin transmission regions having a thickness less than or equal to about 500 nm, which allow transmission of ultraviolet photons from the microfluidic ultraviolet radiation chamber to the microfluidic ionization chamber. chamber, wherein the microfluidic photoionization detector (PID) is configured to analyze the sample processed in the gas chromatography (GC) unit. 14. The detection system of claim 13 wherein the transmission window comprises a material selected from the group consisting of silica, fused silica, quartz, silicon, sapphire, magnesium fluoride, calcium fluoride, lithium fluoride, and combinations thereof. 15. The detection system according to claim 13 or 14, wherein the transmission window is formed in the form of one or more selected areas on the plate. 16. The detection system according to any one of paragraphs. 13-15, in which the transmission window is located on the base plate, and one or more ultra-thin transmission regions are formed in selected areas of the base plate. 17. The detection system according to any one of paragraphs. 13-16, wherein the integrated microfluidic ionization detector (PID) transmission window also comprises a layer stack comprising a first layer and a second layer, with one or more ultrathin transmission regions formed in the first layer where the second layer is absent. 18. The detection system according to any one of paragraphs. 13-17, in which the transmission window has a thickness less than or equal to about 20 microns and is configured to transmit more than or about 5% of ultraviolet photons. 19. The detection system according to any one of paragraphs. 13-18, in which the microfluidic ionization chamber is one or more microfluidic channels, while the integrated microfluidic photoionization detector (PID) further comprises a third electrode and a separate fourth electrode formed in a layer located on top of the microfluidic ultraviolet radiation chamber and electrically connected to it wherein the third electrode and the fourth electrode form a second pattern that corresponds to a first pattern of said one or more microfluidic channels of the microfluidic ionization chamber below the ultraviolet microfluidic chamber. 20. The detection system of claim 19, wherein the first electrode and the separate second electrode are formed in a layer of electrically conductive material, and said one or more microfluidic channels are located in said layer to electrically isolate the first electrode from the second separate electrode.

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