Method and apparatus for chemical imaging in a microfluidic circuit

The instant application relates to U.S. patent application Ser. No. 10/922,006, filed simultaneously herewith, entitled “Water Quality Monitoring by Raman Spectral Analysis” and U.S. patent application Ser. No. 10/920,533, filed simultaneously herewith, entitled “Tunable Spectral Imaging Filter Configured for UV Spectral Ranges” and U.S. patent application Ser. No. 10/882,082, filed Jun. 30, 2004 and entitled “System and Method for Dynamic Chemical Imaging”. Each of the above-identified applications is assigned to the assignee of the present application. Each of the above-referenced applications is incorporated herein in its entirety.

Spectroscopic imaging combines digital imaging and molecular spectroscopy techniques, which can include Raman scattering, fluorescence, photoluminescence, ultraviolet, visible and infrared absorption spectroscopies. When applied to the chemical analysis of materials, spectroscopic imaging is commonly referred to as chemical imaging. Instruments for performing spectroscopic (i.e. chemical) imaging typically comprise image gathering optics, focal plane array imaging detectors and imaging spectrometers.

In general, the sample size determines the choice of image gathering optic. For example, a microscope is typically employed for the analysis of sub micron to millimeter spatial dimension samples. For larger objects, in the range of millimeter to meter dimensions, macro lens optics are appropriate. For samples located within relatively inaccessible environments, flexible fiberscopes or rigid borescopes can be employed. For very large scale objects, such as planetary objects, telescopes are appropriate image gathering optics.

Conventional imaging system include a slide for receiving the sample, a light source for illuminating the sample with a plurality of photons, a lens for receiving the photons scattered (or emitted) by the sample, a tunable filter and an image sensor for forming a three dimensional image of the sample. During operation, the sample is placed on a microscopic slide or a Petri dish and placed at a designated location where photons emitted or scattered from the sample can be collected by an objective lens. The conventional imaging spectrometers are configured to obtain an image of a sample in a homeostasis. That is, the conventional imaging systems are directed to detecting an image from a samples in a state of physical and/or chemical equilibrium with a tendency to remain in such state. There is a need for a method and apparatus for chemical imaging of a dynamic system.

In one embodiment, the disclosure relates to a system for detecting a change in an attribute of a substance. The system may include a photon source for a first of a plurality of photons which interact with the substance while an attribute of the substance changes to thereby produce a second plurality of photons; a filter for receiving the collected photons and providing therefrom filtered photons; a photon detector for receiving the filtered photons and obtaining therefrom a spectrum of the substance; and a processor for detecting an aspect of the filtered photons wherein the aspect of the filtered photons is the function of the attribute of the substance.

In another embodiment, the disclosure relates to a system for detecting a change in attribute of a substance in a dynamic system. The system can include a photon source for providing a first plurality of photons which interact with the substance and produce a second plurality of photons; a microfluidic circuit for collecting said second plurality of photons; a microfluidic circuit through at least a portion of which the substance passes while the attribute of the substance changes; an optical lens for collecting the second plurality of photons; a filter for receiving the collected photons and providing therefrom filtered photons; a photon detector for receiving the filtered photons and obtaining therefrom a spectrum of the substance; and a processor for determining an aspect of the filtered photons wherein the aspect of the filtered photons is a function of the attribute of the substance, to thereby determine a change in the attribute of the substance.

In a method according to an embodiment of the disclosure, a change in the attribute of a substance is determined by illuminating the substance with a first plurality of photons which interact with the substance while an attribute of the substance changes to thereby produce a second plurality of photons; collecting said second plurality of photons; receiving the collected photons and providing therefrom filtered photons; detecting the filtered photons and obtaining therefrom a spectrum of the substance and determining an aspect of the filtered photons wherein the aspect of the filtered photons is a function of the attribute of the substance to thereby determine a change in the attribute of the substance.

According to another embodiment, a method for detecting a change in an attribute of a substrate includes illuminating the substance with a first plurality of photons which interact with the substance while an attribute of the substance changes to thereby produce a second plurality of photons; collecting said plurality of photons; receiving the collected photons and providing therefrom filtered photons; detecting the filtered photons to obtain a spectrum of the substance and determining an aspect of the filtered photons. The aspect of the filtered photons can be a function of the attribute of the substance to thereby determine a change in the attribute of the substance.

FIG. 1 is a schematic representation of a microfluidic circuit;

FIG. 2 shows another embodiment of a microfluidic circuit;

FIG. 3 shows a system according to one embodiment of the disclosure; and

FIG. 4 is a detection system according to one embodiment of the disclosure.

FIG. 1 is a schematic representation of a microfluidic circuit. The microfluidic circuit 100 is shown to have reservoirs or receptacles 110 and 120 communicating with channels 112 and 120 , respectively. Channels 112 and 120 merge to form channel 130 . Channel 130 is received by reservoir 140 . Although not shown, reservoir 140 can include an exit channel for taking the mixture away from the reservoir. In addition, reservoir 140 maybe replaced by extending channel 130 or by forming a serpentine channel to provide additional time for the reactants to admix. Each of reservoirs 110 and 120 can receive different reactants or reagents. When using a microfluidic circuit, the reaction dynamic may be a function of the microfluidic circuit as well as the rate of reaction. Thus, the circuit can be designed to receive a plurality of reagents, provide extended reaction time for some of the reagents or provide additional for controlling the rate of reaction. Microfluidic circuits have complex structures. As a result, the provide spatially-dependent chemical changes within the circuit that need to be monitored. In one embodiment, the disclosure enables monitoring and understanding such changes despite the complex spatial arrangement of the fluids within the microfluidic circuit.

FIG. 2 shows another embodiment of a microfluidic circuit. In the embodiment shown in FIG. 2 , receptacles 201 and 202 receive a first and a second reagent and, respectively, communicate the reagent through embedded channels 205 and 207 to region 208 of circuit 200 . Region 208 can be a reservoir or a plurality of channels specifically designed to enhance mixing of the reagents. Illumination is shown as arrows 210 , 220 and 230 directed to the mixing region 208 . The mixture can be carried out though channel 240 .

FIG. 3 shows a system according to one embodiment of the disclosure. Referring to FIG. 3 , microfluidic circuit 300 includes reservoirs 310 and 320 each receiving a reactant (or a reagent). The reactants are directed to channels 312 and 322 prior to adjoining at region 332 . In one embodiment, the substance under detection will enters and passes through at least a portion of detection region 332 while the attribute of the substance is changing. In other words, detection region 332 can be selected such that the substance is undergoing an attribute change while passing therethrough. Alternatively, detection region 332 can be selected further downstream or upstream to monitor and detect an attribute of the composition.

The substance can be one of a single molecule, a group of molecules, a chemical reagent or a fluid containing pathogens. In one embodiment, the substance is one of a single cell, an element, a compound, a molecule, a reactant, a solvent, a solute, a fluid or a biological substance. The attribute of the substance can relate to one or more of the following characteristics: a physical property, a chemical property, an electrical property, a magnetic property, an optical property or a biological property. For example, the attribute can define a physical structure, a physical orientation, a chemical structure, a chemical composition, a chemical state or an index of refraction. In one embodiment, the attribute is a combination of several identifiable characteristics.

Although not shown in the exemplary embodiment of FIG. 3 , one or more radiation source (interchangeably, photon source) can be positioned about microfluidic circuit 300 to direct photons to detection region 332 . The radiation used to illuminate the sample need not pass through optical lens 360 to illuminate the sample. For example, one or more light source can be positioned below circuit 300 so as to direct photons to detection region 332 . Alternatively, one or more light source can be positioned above circuit 300 or at an oblique angle to circuit 300 so as to direct photons to detection region 332 . This results is reduced internal scattering and attenuation of the incident exciting photons. The multitude of photons reaching detection region 332 can be absorbed by the sample, scatter upon reaching the sample or be emitted by the substance present at this region. The scattered or emitted photons are schematically shown by arrows 358 .

In one embodiment, the photons source is selected from the group consisting of a laser and a light emitting diode. In another embodiment, the photon source can have a wavelength in one of the infrared, the near infrared, the visible, ultraviolet or x-ray wavelength range. In still another embodiment, the photon sources is selected from the group consisting of electro-generated luminescence and chemi-luminescence. In still another embodiment, a plurality of photon sources are provided where each source provides photons in one or more of the above-cited exemplary wavelength ranges. In still another embodiment, a brad band photons sources is passed through a narrow-pass filter and then used as an illumination source. Thus, an exemplary spectrum can be one of a Raman, luminescence (e.g., fluorescence), near infrared, an infrared, ultraviolet or an x-ray spectrum. In one embodiment, the wavelength of the source is in the range of about 15-25 cm −1.

Lens 360 is positioned above a region of the microfluidic circuit to receive optical emitted or scattered light by detection region 332 . Lens 360 can be a single objective lens or it can be an objective train as used in microscopic or macroscopic devices. The color and the resolution of the viewed sample can be determined by the tunable filter and the resolution of the imaging detector. Thus, in one embodiment, the system can use a conventional high resolution, low aberration lens. Indeed, a simpler reduced resolution/aberration lens can be designed with larger numeral aperture to increase system throughput (light delivery and collection efficiency) while providing the same quality resolution as the conventional systems.

The photons received by lens 360 are then processed through one or more rejection filter 364 . The rejection filter enables spectral filtering of light at the illuminating wavelength. Filter 364 can be selected from the group consisting of a notch filter, a bandpass filter or a spectral filter. Additionally, a laser rejection filter (not shown) can be positioned prior to rejection filter 364 to filter out scattered illumination light represented and to optimize the performance of the system.

Photons passing through rejection filter 364 are received by a wavelength imaging analyzer 368 . The analyzer receives the plurality of photons from rejection filter 364 and produces an image therefrom. The image can be a 3-D image. A conventional tunable filter (including electro-optical tunable filters) including liquid crystal tunable filter (“LCTF”) or acusto-optical tunable filter (“AOTF”), Evans split element filter, a Lyot filter, a Solc filter, and a photonic crystal filter can be used as analyzer 368 . The electro-optical filters (interchangeably, tunable filters) allow specific wavelengths or ranges of wavelengths of light to pass through as an image, depending on the control signals placed on the device by a controller (not shown). The wavelengths that can be passed through tunable filter 368 may range from 200 nm (ultraviolet) to 2000 nm (i.e., the far infrared). The choice of wavelength depends on the desired optical region and/or the nature of the sample being analyzed.

Referring again to FIG. 3 , photon detector 368 relays the images of the wavelength imaging analysis to wavelength detector 370 . Wavelength detector 370 can be a charge-coupled device, a complementary metal oxide semiconductor, a charge injection device, an intensified charge injection device, an electron multiplying charge-coupled device, a photo diode, a silicon photo diode, a silicon avalanche diode or a camera. In one embodiment of the disclosure, the photon detector determines a change in the attributes of the substance by detecting an identifying an aspect of the received photons where an aspect of the received photons is a function of the attribute of the substance. By way of example, the aspect of the received photons can be, among others, a wavelength, frequency, phase, polarization, and intensity.

In another embodiment, detector 370 can be a two-dimensional, image focal plane array (“FPA”). The optical region employed to characterize the sample of interest governs the choice of FPA detector. For example, silicon charge-coupled device (“CCD”) detectors can be employed with visible wavelength fluorescence and Raman spectroscopic imaging, while gallium arsenide (GaAs) and gallium indium arsenide (GaInAs) FPA detectors can be employed for image analyses at near infrared wavelengths. The choice of such devices depends on the type of sample being analyzed. Photon detector 370 produces digital images of the entire view of the sample as processed by analyzer 368 . The digital images can be communicated to display devices or electronically transmitted to another network for further processing.

FIG. 4 is a detection system according to one embodiment of the disclosure. More specifically, FIG. 4 shows an exemplary system for detecting pathogens in water. Referring to FIG. 4 , microfluidic circuit 400 is shown to have input channels 402 , 404 , 406 and 408 . The input channels 402 , 406 and 408 may be used for introducing the various reagents into the system. Input channel 404 can be used to transmit laser, among others, through the system. In other words, input channel 404 can be coupled to a radiation source for illuminating to circuit 400 . Valves 403 , 405 and 407 are interposed in channels 402 , 406 and 408 , respectively, to regulate the flow of reagents into the system. In the embodiment of FIG. 4 , the valves are controlled by controller 480 so as to meter the flow of each reagent.

Channels 410 , 411 and 412 show the path traveled by each of the reagents prior to mixing. The layout of channels 410 , 411 and 412 is exemplary in nature. Channel 410 is shown to have a serpentine path while channels 411 and 412 are shown with a relatively direct path to detection region 432 . Detection region 432 is also the region where the reagents comes in contact with each other to form a reaction mixture. In the exemplary embodiment of FIG. 4 , reagent A admixes with reagent B and the resulting mixture which then reacts with reagent N. Thus, imaging region 432 represents a chemically dynamic region such that the imaging system of FIG. 4 can detect and report the attribute changes of the system as the reactants come in contact with each other.

To illuminate detection region 432 , radiation sources 450 and 452 are respectively positioned below and above microfluidic circuit 400 . The additional radiation source 404 is strategically positioned to illuminate the circuit from within by using a microfluidic channel that acts as a light pipe. A light pipe can arise from the different indexes of refraction between the fluid and the channel material in order to transport, and in some cases, focus the light to particular regions within the microfluidic circuit. The channels used as light pipes may have optical coating or carry special fluids to optimize the internal channeling of light to regions o interest. The regions of interest may lie inside the microfluidic circuit. The positioning of radiation source 404 can be particularly beneficial as it can provide radiation frequency different from those of sources 450 and 452 . For example, radiation source 404 can be used to provide laser or fluorescence illumination while radiation sources 450 and 452 provide different radiation.

As in FIG. 3 , the photons reaching the sample at the detection region can be scattered and/or emitted. The scattered and emitted photons are schematically shown as 458 . The scattered and emitted photons are collected by lens 460 and are directed to rejection filter 464 , analyzer 468 and detector 470 .

In the exemplary embodiment of FIG. 4 , analyzer 468 and detector 470 are shown to communicate with each other and with controller 480 . The controller can be an integrated circuit programmed to execute instructions from a memory. The controller can be a stand-alone system (not shown) or can be coupled to a computer 488 . Computer 488 can be a handheld device, a desktop computer or a network. In the exemplary embodiment of FIG. 4 , computer 488 is coupled to databases 481 and display 490 . In an alternative embodiment, computer 488 may be integrated with database 481 and display 490 .

Database 481 can provide a data library to computer 488 . Computer 488 can use data received from detector 470 , controller 480 and database 481 not only to provide an output in the form display 490 , but to also direct controller 480 . In turn, controller 480 can optimize the operation of analyzer 468 and detector 470 . In addition, controller 480 can provide follow control by metering fluid flow through each of valves 403 , 405 and 407 . For illustration, controller 480 is shown to be coupled to valve 403 through connection line 482 . Although not shown controller 480 can be independently coupled to each of valves 405 and 407 .

Display 490 , as shown in FIG. 4 , is exemplary as it depicts detection region 432 with each of reagents A ( 491 ), reagent B ( 492 ) and reagent N ( 493 ). The region identified as 494 shows the reaction dynamics of the reagents A, B and N. In one embodiment, the image shown is a function of dimensions (x, y) and time. In other words, the images can depict a reaction as a function of time. The images can be saved for future viewing by computer 488 . In an alternative embodiment, the images can be compared against the images in database 481 to identify or quantify the displayed reaction. In still another embodiment, computer 488 can record and display the images as a continuous stream of data.

The configurations disclosed herein are suitable for Raman imaging of micro fluid circuits or biological samples undergoing change. The disclosed configuration can also be used with multiple detection system simultaneously. For example, the detection system shown in FIG. 4 can be configured to receive and analyze Raman and fluorescent images simultaneously.

Although the principles disclosed herein have been described in relation with the non-exclusive exemplary embodiments provided herein, it should be noted that the principles of the disclosure are not limited thereto and include permutations and variations not specifically described.