Integrated optical sensor for chemical analysis based on near-infrared evanescent wave absorbance measurements

Details Integrated optical sensor for chemical analysis based on near-infrared evanescent wave absorbance measurements Integrated optical sensor for chemical analysis based on near-infrared evanescent wave absorbance measurements

Publishing date

Sep 1995

URL

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995spie.2508..243b&link_type=abstract

Journals

Proc. SPIE Vol. 2508, p. 243-252, Chemical, Biochemical, and Environmental Fiber Sensors VII, Annamaria V. Scheggi; Ed.

Science

Physics

Additional info 2

1

Type

Scientific paper

Abstract

Investigations into the optimization of a long-path integrated optical evanescent field absorbance sensor for the detection of nonpolar organic substances in water are described. The sensor is based on a multimode strip waveguide produced by Na+Ag+ ion- exchange in a borosilicate glass substrate and a hydrophobic silicone sensing layer deposited on the IO structure, that reversibly enriches organic contaminants from water or air. Light from a tungsten-halogen lamp in launched into the planar structure and evanescent wave absorption measurements of the organic species in the silicone superstrate are performed with a near-infrared diode array spectrograph. Polymethyl(phenyl)siloxanes with varying refractive index were prepared and tested as sensitive coating for the IO structure. The light transmission through the sensor may decrease up to 90% if the coated sensors come in contact with water. These losses caused by light scattering effects due to the formation of H2O micro- emulsions in the silicone superstrate can be minimized by using polysiloxanes with a higher degree of cross-linkage. Measurements of aqueous trichloroethene samples were successfully performed in the region of the C-H first overtone vibration band. The sensitivity of the measurement can be raised distinctively by using polymethylphenylsiloxanes, which have a higher refractive index than polydimethylsiloxane. Kinetic experiments with aqueous trichloroethene samples showed a reversible sensor response with t90 values in the range from 7-20 minutes.

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