METHOD OF PERFORMING WAVELENGTH MODULATED DIFFERENTIAL LASER PHOTOTHERMAL RADIOMETRY WITH HIGH SENSITIVITY
First Claim
1. A method of calibrating a wavelength modulated differential photothermal radiometry system for detecting the presence of an analyte within a substance, said method comprising the steps of:
- providing a first optical beam and a second optical beam, wherein said first optical beam is characterized by a first wavelength and said second optical beam is characterized by a second wavelength, and wherein said first wavelength is selected so that analyte concentrations within a concentration range of interest will cause sufficient absorption of said first optical beam to produce detectable thermal-wave emission, and wherein an absorption coefficient of said analyte at said first wavelength exceeds that at said second wavelength;
producing a first modulated beam and a second modulated beam by modulating an intensity of said first optical beam and an intensity of said second optical beam, respectively;
wherein said first modulated beam and said second modulated beam are modulated at a substantially equal modulation frequency, and wherein a phase difference between said first modulated beam and said second modulated beam is approximately 180 degrees;
providing a reference sample substantially free of analyte;
directing and substantially overlapping said first modulated beam and said second modulated beams onto said reference sample;
measuring a first photothermal signal produced by said first modulated beam;
measuring a second photothermal signal produced by said second modulated beam;
obtaining a relative photothermal phase between said first photothermal signal and said second photothermal signal; and
controlling a relative phase of said first modulated beam and said second modulated beam so that said relative photothermal phase is approximately 180 degrees.
0 Assignments
0 Petitions
Accused Products
Abstract
Methods are provided for the detection of an analyte in a sample using wavelength modulated differential photothermal radiometry with enhanced sensitivity. A wavelength modulated differential photothermal radiometry system, comprising two optical modulated beams, where each beam experiences different absorption by the analyte, is calibrated by controlling the relative phase difference between the modulated beams so that individual photothermal signals corresponding to each modulated beam are 180° out of phase, corresponding to peak sensitivity to analyte concentration. The system may be further calibrated by varying the relative intensities of the two modulated beams and measuring standards containing known analyte concentration in order to determine an optimal relative intensity for a given concentration range of interest.
-
Citations
29 Claims
-
1. A method of calibrating a wavelength modulated differential photothermal radiometry system for detecting the presence of an analyte within a substance, said method comprising the steps of:
-
providing a first optical beam and a second optical beam, wherein said first optical beam is characterized by a first wavelength and said second optical beam is characterized by a second wavelength, and wherein said first wavelength is selected so that analyte concentrations within a concentration range of interest will cause sufficient absorption of said first optical beam to produce detectable thermal-wave emission, and wherein an absorption coefficient of said analyte at said first wavelength exceeds that at said second wavelength; producing a first modulated beam and a second modulated beam by modulating an intensity of said first optical beam and an intensity of said second optical beam, respectively;
wherein said first modulated beam and said second modulated beam are modulated at a substantially equal modulation frequency, and wherein a phase difference between said first modulated beam and said second modulated beam is approximately 180 degrees;providing a reference sample substantially free of analyte; directing and substantially overlapping said first modulated beam and said second modulated beams onto said reference sample; measuring a first photothermal signal produced by said first modulated beam; measuring a second photothermal signal produced by said second modulated beam; obtaining a relative photothermal phase between said first photothermal signal and said second photothermal signal; and controlling a relative phase of said first modulated beam and said second modulated beam so that said relative photothermal phase is approximately 180 degrees. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
-
-
15. A method of calibrating a wavelength modulated differential photothermal radiometry system for detecting the presence of an analyte within a substance, said method comprising the steps of:
-
providing a first optical beam and a second optical beam, wherein said first optical beam is characterized by a first wavelength and said second optical beam is characterized by a second wavelength, and wherein said first wavelength is selected so that analyte concentrations within a concentration range of interest will cause sufficient absorption of said first optical beam to produce detectable thermal-wave emission, and wherein an absorption coefficient of said analyte at said first wavelength exceeds that at said second wavelength; producing a first modulated beam and a second modulated beam by modulating an intensity of said first optical beam and an intensity of said second optical beam, respectively; wherein said first modulated beam and said second modulated beam are modulated at a substantially equal modulation frequency, and wherein a phase difference between said first modulated beam and said second modulated beam is approximately 180 degrees; providing a reference sample comprising a known concentration of analyte; directing and substantially overlapping said first modulated beam and said second modulated beams onto said reference sample; obtaining a differential photothermal signal by detecting emission radiated by said reference sample with a phase-sensitive detection system; and varying an intensity ratio of said first modulated beam and said second modulated beam to minimize said differential photothermal signal. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23)
-
-
24. A method of calibrating a wavelength modulated differential photothermal radiometry system for detecting the presence of an analyte within a substance, said method comprising the steps of:
-
a) providing a first optical beam and a second optical beam, wherein said first optical beam is characterized by a first wavelength and said second optical beam is characterized by a second wavelength, and wherein said first wavelength is selected so that analyte concentrations within a concentration range of interest will cause sufficient absorption of said first optical beam to produce detectable thermal-wave emission, and wherein an absorption coefficient of said analyte at said first wavelength exceeds that at said second wavelength; b) producing a first modulated beam and a second modulated beam by modulating an intensity of said first optical beam and an intensity of said second optical beam, respectively;
wherein said first modulated beam and said second modulated beam are modulated at a substantially equal modulation frequency, and wherein a phase difference between said first modulated beam and said second modulated beam is approximately 180 degrees;c) selecting an intensity ratio of said first modulated beam and said second modulated beam; d) providing a reference sample comprising a known concentration of analyte; e) directing and substantially overlapping said first modulated beam and said second modulated beams onto said reference sample; f) obtaining a differential photothermal signal by detecting emission radiated by said reference sample with a phase-sensitive detection system; g) repeating steps d) to f) one or more times to measure differential photothermal signals for one or more additional standard samples, wherein each said additional standard samples comprise different known analyte concentrations; h) obtaining a calibration curve by relating said differential photothermal signals to said known analyte concentrations; i) repeating steps c) to h) to obtain an additional calibration curve corresponding to a different intensity ratio; and j) selecting a preferred calibration curve having a desired sensitivity over a predetermined range of analyte concentration, and placing said system into a configuration corresponding to said preferred calibration curve. - View Dependent Claims (25, 26, 27)
-
-
28. An apparatus for performing wavelength modulated differential photothermal radiometry for detecting the presence of an analyte within a substance, said apparatus comprising:
-
a first optical source and a second optical source, wherein said first optical source is characterized by a first wavelength and said second optical source is characterized by a second wavelength, and wherein said first wavelength is selected so that analyte concentrations within a concentration range of interest will cause sufficient absorption of said first optical source to produce detectable thermal-wave emission, and wherein an absorption coefficient of said analyte at said first wavelength exceeds that at said second wavelength; modulation means for producing a first modulated beam and a second modulated beam by modulating an intensity of said first optical source and an intensity of said second optical source, respectively, wherein said modulation means is configured to modulate said first modulated beam and said second modulated beam at a substantially equal modulation frequency, phase control means for controlling a relative phase between said first modulated beam said second modulated beam; intensity control means for controlling a relative intensity of said first modulated beam and said second modulated beam; optical means for directing and spatially overlapping said first modulated beam and said second modulated beam onto a sample; collection means for collecting photothermal radiation emitted from said sample; and a phase-sensitive detector for obtaining a signal related to said photothermal radiation. - View Dependent Claims (29)
-
Specification