System and method for non-invasive photothermal radiometric measurement
First Claim
1. A method of detecting an analyte within a material, said method comprising the steps of:
- a) directing and overlapping first and second intensity modulated optical beams onto a surface of said material;
wherein an absorption spectrum of said material comprises a spectral region substantially free of spectral features in the absence of said analyte, and wherein the presence of said analyte produces a spectral peak within said spectral region;
wherein said first and second optical beams are provided with substantially equal intensity, and wherein said first and second optical beams are modulated at a substantially equal frequency with a phase difference of approximately 180 degrees; and
wherein wavelengths of said first and second optical beams are selected to lie within said spectral region so that the presence of said analyte produces increased absorption of said first optical beam relative to absorption of said second optical beam;
b) obtaining a signal by detecting photothermal emission radiated in response to differential absorption of said first and second optical beams, wherein said photothermal emission is detected with a phase-sensitive detection apparatus provided with a reference signal related to a phase of said modulated optical beams; and
c) correlating said signal with an amount of said analyte in said material.
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Abstract
There is provided a glucose monitoring method and apparatus based on the principle of Wavelength-Modulated Differential Laser Photothermal Radiometry (WM-DPTR). Two intensity modulated laser beams operating in tandem at specific mid-infrared (IR) wavelengths and current-modulated synchronously by two electrical waveforms 180 degrees out-of-phase, are used to interrogate the tissue surface. The laser wavelengths are selected to absorb in the mid infrared range (8.5-10.5 μm) where the glucose spectrum exhibits a discrete absorption band. The differential thermal-wave signal generated by the tissue sample through modulated absorption between two specific wavelengths within the band (for example, the peak at 9.6 and the nearest baseline at 10.5 μm) lead to minute changes in sample temperature and to non-equilibrium blackbody radiation emission. This modulated emission is measured with a broadband infrared detector. The detector is coupled to a lock-in amplifier for signal demodulation. Any glucose concentration increases will be registered as differential photothermal signals above the fully suppressed signal baseline due to increased absorption at the probed peak or near-peak of the band at 9.6 μm at the selected wavelength modulation frequency. The emphasis is on the ability to monitor blood glucose levels in diabetic patients in a non-invasive, non-contacting manner with differential signal generation methods for real-time baseline corrections, a crucial feature toward precise and universal calibration (independent of person-to-person contact, skin, temperature or IR-emission variations) in order to offer accurate absolute glucose concentration readings.
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Citations
27 Claims
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1. A method of detecting an analyte within a material, said method comprising the steps of:
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a) directing and overlapping first and second intensity modulated optical beams onto a surface of said material; wherein an absorption spectrum of said material comprises a spectral region substantially free of spectral features in the absence of said analyte, and wherein the presence of said analyte produces a spectral peak within said spectral region; wherein said first and second optical beams are provided with substantially equal intensity, and wherein said first and second optical beams are modulated at a substantially equal frequency with a phase difference of approximately 180 degrees; and wherein wavelengths of said first and second optical beams are selected to lie within said spectral region so that the presence of said analyte produces increased absorption of said first optical beam relative to absorption of said second optical beam; b) obtaining a signal by detecting photothermal emission radiated in response to differential absorption of said first and second optical beams, wherein said photothermal emission is detected with a phase-sensitive detection apparatus provided with a reference signal related to a phase of said modulated optical beams; and c) correlating said signal with an amount of said analyte in said material. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. An apparatus for detecting an analyte within a material, said apparatus comprising:
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a) first and second sources of radiation producing first and second optical beams for irradiating a surface of said material; wherein an absorption spectrum of said material comprises a spectral region substantially free of spectral features in the absence of said analyte and wherein the presence of said analyte produces a spectral peak within said spectral region; and wherein wavelengths of said first and second optical beams are selected to lie within said spectral region so that the presence of said analyte produces increased absorption of said first optical beam relative to absorption of said second optical beam when said beams are directed onto said surface; b) modulation means for modulating an intensity of said first beam and an intensity of said second beam, wherein said modulation means modulates said first and second beams at a substantially equal frequency, said modulation means further producing a difference in phase between said first and second modulated beams of approximately 180 degrees; c) equalizing means for substantially equalizing a power of said first modulated beam and said second modulated beam; d) optical means for directing and overlapping first and second optical beams onto said surface; e) collection means for collecting photothermal power radiated from said surface in response to differential absorption of said first and second optical beams; and f) a phase-sensitive detection apparatus for detecting said collected photothermal power, said phase-sensitive detection system receiving as an input a reference signal related to a phase of said first and second modulated beams. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27)
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Specification