An integrated optical multisensor for organic pollutants has been realised, and characterised for a single analyte. The sensor exploits fluorescence immunoassay in the evanescent field of channel waveguides to enable rapid, simultaneous and high-sensitivity fluorescence detection of up to 32 pollutants in water. The chemical modification used to render the surface specific to analytes allows automatic regeneration for immediate reuse. The system has been demonstrated for the key pollutant estrone and a detection limit below 1 ng/L has been achieved.
Intensity transmission measurements of biological tissue with light in the wavelength range from 600 am to 1000nm yields limited resolution due to strong scattering. The resolution can be improved using time gated methods. These measurements are technically complicated and require a long detection time. A different approach is the measurement of the phase shift of transmitted light using a radio frequency modulated light source. We have investigated the influence of the modulation frequency on the intensity distribution and on the phase shift both theoretically and experimentally. Further the dependence on the scattering and absorption coefficients of the illuminated medium has been examined. The theoretical calculations have been carried out using analytical and numerical solutions of the diffusion equation. Results are given for the modulation frequency range from 60 MHz to 500 MHz. They show that the modulation frequency has an effect mainly on the phase shift and only to a small degree on the intensity distribution.
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