IE84482B1

IE84482B1 - An optical detector

Info

Publication number: IE84482B1
Application number: IE2005/0558A
Authority: IE
Inventors: Mathewson Alan; Alderman John; Carlton Jackson John
Original assignee: University College Cork National University Of Ireland Cork
Filing date: 2005-08-22
Publication date: 2007-01-10

Description

An Optical Detector INTRODUCTION Field of the Invention The invention relates to optical detection for analysis of samples.

Prior Art Discussion Capillary electrophoresis, or CE, describes a family of techniques used to separate a variety of compounds. These analyses, all driven by an electric ﬁeld, are performed in narrow tubes and can result in the rapid separation of many hundreds of different compounds. The versatility and number of ways that CE can be used means that almost all molecules, and even whole organisms can be separated.

UV-visible absorption is the most common detection method because it is simple to use and most analytes can be observed with it. It is also a tested method for other chromatographic analyses and can be used quantitatively. When using fused silica capillaries it is possible to use detection wavelengths down to about 200nm. A window is burnt in the polyamide protecting the capillary and UV light can be shone through and absorbed by passing analytes.

However a problem with the use of CE capillaries for a detection cell comes about because of the very narrow nature of the capillary. This means that the optical beam must be very tightly focused in order to get the best sensitivity. Another problem is that the capillary being thin results in a very short path length for the light. This can lead to CE being somewhat insensitive with some analytes.

Some molecules cannot be observed by UV detectors. They may lack a chromophore and be unsuitable for use with phosphate and borate buffers. This is quite common with carbohydrates and peptides for example. In order to visualize these one must use alternative methods. A common approach is ﬂuorescence. Before analysis the molecules of interest are chemically labelled with a ﬂurophore, and then separation is performed as normal. A light source which excites the ﬂurophore is used as a source of radiation, and as the analytes move past the detection window the ﬂurophores excite and emit radiation at a different wavelength. This can then be detected, once again in a quantitative fashion. This fonn of detection is useful for analytes present at low concentrations as a powerful ﬂurophore can be chosen, increasing the limit at which they can be detected.

A common method of detection is known as indirect UV detection. This involves using a buffer in the capillary, which actually absorbs the radiation from the lamp along with analytes, which do not absorb UV radiation. As analytes move past the detector the amount of light passing through the capillary increases as UV absorbing buffer is excluded. Indirect UV detection is commonly used for inorganic ions, which do not absorb UV radiation.

The invention is directed towards providing a miniaturised and improved optical detector for analysis applications.

SUMMARY OF THE INVENTION According to the invention, there is provided an optical detector comprising: an emitter for emitting incident radiation for a sample; a sensor for detecting response radiation from a sample, the sensor comprising a guide for the incident radiation and being mounted on a substrate; the emitter is mounted for emitting incident radiation for a sample through the guide; and wherein the sensor substrate comprises material aligned with the guide which is transparent to the incident radiation; and said material is opaque to the expected response radiation.

Thus, the incident radiation is directed particularly accurately for optimum sensing of the response radiation. This is particularly advantageous for applications involving low radiation intensities and physically-constrained situations such as inside the body for medical analysis.

In one embodiment, the sensor substrate allows said incident radiation to pass through it. This allows a particularly compact conﬁguration.

In another embodiment, the detector comprises a ﬁlter to pass the response radiation through to the sensor.

In one embodiment, the sensor comprises a plurality of sensor devices, and said devices surround the guide. This allows very effective sensing or response radiation spread over a relatively large cross-sectional area compared with the cross-sectional area of the incident radiation.

In one embodiment, said devices are photo-diodes. In one embodiment, the devices are mounted in an array, and the guide is central within the array.

In one embodiment, the sensor comprises an integrated circuit incorporating the sensor devices. This is a particularly compact and effective arrangement. In one embodiment, the guide passes through the integrated circuit. This allows particularly good accuracy.

In one embodiment, the emitter is located normal to the guide.

In one embodiment, the emitter is a laser device such as a VCSEL.

In one embodiment, the emitter emits radiation with a wavelength of 650nm.

In one embodiment, the sensor substrate comprises an opening for the incident radiation aligned with the guide.

In one embodiment, said ﬁlter is transparent to the response radiation and opaque to the incident radiation. This allows excellent integrity in the sensing of radiation.

In another embodiment, the ﬁlter comprises a thin ﬁlm layer on the sensor surface.

In one embodiment, the sensor comprises a plurality of sensor devices, and different ﬁlters for at least two devices.

In one embodiment, said ﬁlters have different ﬁlter characteristics. In this embodiment, said ﬁlters may have characteristics for passing ﬂuorescence of different ﬂuorophors.

In one embodiment, the emitter is mounted on a substrate, and said substrate and the sensor substrate are parts of an integral multi-purpose substrate which is folded over between the emitter and the sensor so that the emitter emits incident radiation through the guide.

In one embodiment, the multi-purpose substrate is folded at a ﬂexible part of the substrate.

In one embodiment, the detector further comprises a locating means for locating and mounting the optical detector as a discrete unit on a sample system.

In another aspect, the invention provides an optical detector comprising: an emitter mounted on a substrate for emitting incident radiation for a sample; a sensor mounted on the same substrate for detecting response radiation from a sample; and the substrate being folded over between the emitter and the sensor so that the emitter is located for directing incident radiation at a sample, and the sensor is located to receive response radiation.

In one embodiment, the detector further comprising an emitter drive circuit and a detector sensing circuit mounted on said substrate.

In one embodiment, the substrate is folded over at a ﬂexible part so that it is continuous and curved.

In one embodiment, the substrate supports the emitter so that it is maintained in alignment with a guide in the sensor.

In one embodiment, the substrate is retained in the fo1ded—over conﬁguration by encapsulation.

DETAILED DESCRIPTION OF THE INVENTION Brief Description of the Drawings The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings in which:- Fig. 1 is a diagrammatic perspective view from above of an optical detector of the invention, and Fig. 2 is an underneath plan view; Fig. 3 is a general side view, before encapsulation, showing the arrangement of a substrate of the detector; Fig. 4 is a cross—sectional diagram illustrating the detector in more detail and showing how it is coupled with a microﬂuidic system to detect a sample in a channel of the microﬂuidic system; Fig. 5 is a cross—sectional diagram illustrating an alternative embodiment in a similar manner; and Fig. 6 is a cross-sectional diagram showing a further optical detector of the invention.

Description of the Embodiments Referring to Figs. 1 to 4 there is shown an optical detector 1 which acts as a modular detection unit. It may be mounted on a separate microﬂuidic device 2 for detection of species within a channel 3 of the device 2. The detector 1 has mounting lugs 4 for mounting on the microﬂuidic device 2 for exact registry with the charmel 3.

The detector 1 comprises a signal port 10 and this is the only part which connects with an external circuit. The components of the detector 1 are encapsulated in epoxy 1], so that the overall construction is modular and robust. As shown in Fig. 2, the only parts of the detector 1 which protrude are the lugs 4.

Overall construction of the detector 1 is illustrated in Fig. 3. A substrate 15 is folded over at a ﬂexible part 25 through 180° and, at the top, supports a vertical emitting laser device 16. The lower branch of the substrate 15 supports an integrated circuit photo— diode array sensor 17 having chip bumps l8.The substrate 15 also supports emitter drive circuitry 26 and detector circuitry 27. Thus, the single substrate 15 supports all active components, allowing very simple manufacture. Also, alignment of the emitter 16 and sensor 17 is very simple and accurate. The folding—over and alignment is perfonned by bringing the light source 16 in approximate alignment with the guide aperture l7(c) in the sensor 17, and ensuring the alignment is sufﬁcient for accurate alignment of light through the guide aperture l7(c). Epoxy is then applied while holding the whole assembly ﬁxed. .

Referring to Fig. 4, the sensor 17 is a silicon integrated circuit, having an array of integrated photo-diodes l7(a) in a silicon wafer l7(b). There is a vertical through-hole l7(c) in the wafer, to act as a guide for incident radiation emitted by the emitter 16 (arrows IR). Because of the single folded-over substrate arrangement the emitter 16 can be particularly easily and accurately aligned with the guide aperture l7(c). The substrate is transparent so that the incident radiation IR passes through the guide aperture l7(a) through the wafer and between the diodes l7(a), and through the substrate 15. It then exits the optical detector 1, and when the detector is mounted on the microﬂuidic device 2 the incident radiation IR impinges on a ﬂuid capillary 3.

Light (“response radiation”, R) from particles in the channel 3 passes through the substrate 15 and a ﬁlter 90 and is detected by the array of diodes l7(a) on their undersides. The IR wavelength is 650nm. The ﬁlter 90 is a high pass ﬁlter in the form of a thin ﬁlm coating applied directly to the sensor 17. The cut-off wavelength of the ﬁlter 90 is 660nm, and so it passes the ﬂuorescence RR above this wavelength, while blocking any unwanted reﬂections or scatter of the (650 nm) incident radiation IR.

The response radiation RR may alternatively be reﬂected radiation. The ﬁlter may alternatively be a discrete glass ﬁlter mounted onto the sensor Referring to Fig. 5 a sensor 30 has a substrate 31 supporting a top laser emitter 32 in alignment with a central guide aperture 33(0) of an IC diode array sensor 33. The sensor 33 is mounted by chip bumps 35 onto a ﬁlter 34 mounted over an aperture 36 in the substrate 31. Different ﬁlters 91 are mounted under different diodes 33(a) to prevent light from the emitter from being detected by the diodes (possibly after reﬂection) and only light of a speciﬁc wavelength, ie. that emitted by the ﬂuorophore will be transmitted through the ﬁlter. Thus for each diode 33(a) light of different wavelengths for different ﬂuorophors in the same analyte mixture are detected. The ﬁlters 91 are high pass ﬁlters in the fonn of thin ﬁlm coatings applied directly to the sensor 33, and operate in a manner similar to the ﬁlter 90 of the detector 1.

The sensor guide aperture and alignment of the emitter allow particularly accurate excitation of the sample and detection of the ﬂuorescence. This level of accuracy achieves single-photon operation.

Referring to Fig. 7 another optical detector, 80, is shown. The detector 80 has a cylindrical conﬁguration and is 17mm long and only 2mm in diameter. A cylindrical housing 81 supports the components inside. These include a ceramic substrate 82, a VCSEL 83 mounted over a guide aperture 84 through an IC diode array sensor having diodes 85. A ﬁlter 86 overlies the diodes 85, and collimating lenses 87 overlie the ﬁlter 86. In this case the body of the IC of the diodes 85 supports the VCSEL emitter 83.

The sensor 80 may ﬁnd application implanted inside the body and intended to be used with labelled cancer drugs enabling the monitoring of their uptake by tumours ( a tumour T is shown diagrammatically in Fig. 6).. It is a full-ﬂuorescence platform and is sensitive to single photons. The VSCEL die 83 is mounted on the back of the sensor die 87. The guide 84 is a hole etched through the sensor die 88, and it allows perfect alignment of the laser light onto the target material relative to the sensors. In this embodiment the ﬁlter 86 is mounted onto the sensors and on top of the ﬁlter a micro- lens is mounted — ensuring that only collimated light is detected by the diodes 85.

In this embodiment, the VSCEL 83 excitation wavelength is 650nm. The diodes 85 detect reﬂected response radiation of greater than 660 nm, the high pass ﬁlter cut—off wavelength of the ﬁlter 86.

In the detector 81 there is an ASIC to interface with the diodes 85 for photon counting and to read the data. /hi RF module relays the data to the outside world and an inductive coil is used to power the system.

It will be appreciated that the invention provides a simple, inexpensive, modular, and robust detector for sample analysis applications.

The invention is not limited to the embodiments described but may be varied in construction and detail. For example, where there is a single folded-over substrate this may have a hinge instead of a ﬂexible part or folding over with a curved configuration.

Claims

1. Claims An optical detector comprising: an emitter for emitting incident radiation for a sample; a sensor for detecting response radiation from a sample, the sensor comprising a guide for the incident radiation and being mounted on a substrate; the emitter is mounted for emitting incident radiation for a sample through the guide; and wherein the sensor substrate comprises material aligned with the guide which is transparent to the incident radiation; and said material is opaque to the expected response radiation. An optical detector as claimed in claim 1, wherein the sensor substrate allows said incident radiation to pass through it. An optical detector as claimed in claims 1 or 2, wherein the detector comprises a filter to pass the response radiation through to the sensor. An optical detector as claimed in any preceding claim, wherein the sensor comprises a plurality of sensor devices, and said devices surround the guide. An optical detector as claimed in claim 4, wherein said devices are photo-diodes. An optical detector as claimed in claims 4 or 5, wherein the devices are mounted in an array, and the guide is central within the array. An optical detector as claimed in any of claims 4 or 6, wherein the sensor comprises an integrated circuit incorporating the sensor devices. An optical detector as claimed in claim 7, wherein the guide passes through the integrated circuit. An optical detector as claimed in any preceding claim, wherein the emitter is located normal to the guide. An optical detector as claimed in any preceding claim, wherein the emitter is a laser device. An optical detector as claimed in claim 10, wherein the laser device is a VCSEL. An optical detector as claimed in any preceding claim, wherein the emitter emits radiation with a wavelength of 650mn. An optical detector as claimed in any preceding claim, wherein the sensor substrate comprises an opening for the incident radiation aligned with the guide. An optical detector as claimed in any of claims 3 to 13, wherein said ﬁlter is transparent to the response radiation and opaque to the incident radiation. An optical detector as claimed in claim 14, wherein the ﬁlter comprises a thin film layer on the sensor surface. An optical detector as claimed in any of claims 3 to 15, wherein the sensor comprises a plurality of sensor devices, and different ﬁlters for at least two devices. An optical detector as claimed in claim 16, wherein said ﬁlters have different ﬁlter characteristics. An optical detector as claimed in claim 17, wherein said ﬁlters have characteristics for passing ﬂuorescence of different ﬂuorophors. An optical detector as claimed in any preceding claim, wherein the emitter is mounted on a substrate, and said substrate and the sensor substrate are parts of an integral multi-purpose substrate which is folded over between the emitter and the sensor so that the emitter emits incident radiation through the guide. An optical detector as claimed in claim 19, wherein the multi-purpose substrate is folded at a ﬂexible part of the substrate. An optical detector as claimed in any preceding claim, further comprising a locating means for locating and mounting the optical detector as a discrete unit on a sample system.