Ambient light assisted spectroscopy
A spectroscopic device, which may be a handheld spectroscopic light source, which uses ambient light as a primary broadband light source, but which may be supplemented with an auxiliary light source to supplement band regions which may be deficient in the broad band source. The spectroscopic device makes use of a number of parallel control channels to monitor for sufficient light and to compensate for variations in the input light levels.
1. A device for detecting a target substance in a solution, comprising:
a light source that processes and filters the ambient light to emit substantially monochromatic light;
a sample container configured to contain the solution that contains one or more types of target substances, said solution having a refractive index different from a refractive index of said one or more types of target substances;
a reference container containing no substance therein or a reference for the target substances;
a substantially planar diffraction element optically coupled to the light source to receive the light originating from the light source, the diffraction element having a top surface and a bottom surface and having one or more of openings that are empty or filled with a dielectric to generate plasmon waves upon receipt of the light from the light source, the top surface of the diffraction element being configured to be in contact with the solution in the sample container and with the reference container and configured to be chemically treated to attach surface-immobilized receptors thereon that will bind said one or more types of target substances in the solution so that a change in refractive index occurs in the vicinity of said top surface when the target substance binds to said top surface;
a two-dimensional image sensor disposed under the diffraction element to detect a first diffraction pattern projected onto the two-dimensional image sensor by the light from the light source that has interacted with a portion of the diffraction element that is in contact with the solution in the sample container and to detect a second diffraction pattern projected onto the two-dimensional image sensor by the light from the light source that has interacted with another portion of the diffraction element that is in contact with the reference container, the two-dimensional image sensor having a plurality of pixels to detect the diffraction patterns; and
a processor connected to the two dimensional image sensor to process signals representing the first diffraction pattern with signals representing the second diffraction pattern, outputted from the two-dimensional image sensor, so as to compensate for fluctuations of said ambient light for determining the presence or absence of the target substance on the diffraction element,
wherein the diffraction element and the two-dimensional image sensor are configured and arranged such that, upon receipt of the light from the light source, the plasmon waves are generated on the diffraction element so as to generate the diffraction pattern that includes a plurality of distinct diffraction spots or lines on the two-dimensional image sensor, properties of which are dependent on the refractive index in the vicinity of the top surface of the diffraction element.
2. The device according to claim 1 , wherein the diffraction element and the two-dimensional image sensor are configured and arranged such that said change in refractive index that occurs when the target substance binds to the top surface of the diffraction element causes at least one of the plurality of diffraction spots or lines to shift its position by a distance greater than a pitch of the pixels.
3. The device according to claim 1 , wherein the device is configured to detect a single target substance and the processor uses a single threshold to determine the presence or absence of the target substance on the surface of the top layer of the diffraction element in processing signals from the image sensor.
4. The device according to claim 1 , wherein the processor processes the signals from the two-dimensional image sensor to detect a pattern formed by at least some of the plurality of distinct diffraction spots or lines, and determines the presence or absence of the target substance in accordance with a two-dimensional spatial change in the pattern.
5. The device according to claim 1 , wherein the processor uses a subpixel interpolation algorithm to determine two-dimensional coordinates representing a position of at least one of the plurality of distinct diffraction spots or lines.
6. The device according to claim 1 , wherein the processor uses a subpixel interpolation algorithm to determine two-dimensional coordinates representing respective peak positions of the plurality of distinct diffraction spots or lines at a resolution greater than a resolution of the two-dimensional image sensor, and detects a pattern formed by the determined peak positions of the plurality of distinct diffraction spots or lines using a pattern recognition algorithm, and wherein the processor determines the presence or absence of the target substance in accordance with a two-dimensional spatial change in the pattern.
7. The device according to claim 1 , wherein the diffraction element has a detection site defined by a two-dimensional area on the top surface thereof that includes said one or more of openings and a vicinity thereof, and
wherein when the target substance covers only partially the detection site of the diffraction element, the processor processes the signals from the image sensor to determine an area percentage at which the target substance occupies the detection site.
8. The device according to claim 1 , wherein the light emitted from the light source is directed to the sample container so that the light passes through the sample container containing solution to interact with the diffraction element.
9. The device according to claim 1 , further comprising an optical modulator that modulates at least one of phase, polarization, and intensity of the light emitted from the light source, wherein the processor demodulates the signals from the image sensor to improve a signal-to-noise ratio.
10. The device according to claim 1 , further comprising a polarizer to polarize the light emitted from the light source so that the light impinging upon the top surface of the diffraction element is linearly polarized.
11. The device according to claim 1 , wherein the diffraction element is made of a metal and the opening is filled with a dielectric.
12. The device according to claim 1 , wherein the diffraction element has a periodic array of a plurality of the openings.