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Abstract: In this study, a sensitive optical waveguide (OWG) sensor for the detection and identification of volatile organic compounds (VOCs) was reported. The sensing membrane is constructed by immobilization of peroxopolytungsten acid (PTA) thin film over a single-mode potassium ion (K+) exchanged glass OWG by spin-coating method. A laser beam was coupled into and out of the glass optical waveguide using prism couplers, and dry air functioned as a carrier gas. The sensor was tested for various volatile organic compounds (VOCs), and it showed higher response to the chlorobenzene gas compared to other VOCs. Therefore, we used the OWG sensor to detect chlorobenzene gas as a typical example of VOCs. The sensor exhibits a linear response to chlorobenzene gas in the range of 0.4–1000ppm with rapid response and good reversibility. The constructed sensor is easy to fabricate and it has some unique qualities which can be characterized as inexpensive, sensitive, and reusable. [Copyright &y& Elsevier]

The light traveling in the COWG along the path of the TE 0 mode (Fig. 1), the light streak in the region of COWG was wider and brighter than that in the region of K+ ion-exchanged glass OWG. The composite OWG layer can produce a much strong evanescent wave field, which makes the sensor's sensitivity higher. The ZnO film/K+ ion-exchanged glass COWG structure thus enhances the OWG sensor's sensitivity. Fig. 1. Structure of TMP-coated ZnO film COWG sensor and schematic diagram of light propagation in the COWG. • A highly sensitive two-layer composite waveguide is prepared. • High-refractive-index ZnO film is deposited on a K+ ion-exchanged glass OWG surface. • The ZnO film was coated with thin-film TMP via spin-coating or immersion method. • The composite OWG layer improves the sensor properties. • The TMP–ZnO interaction affects the OWG sensor performance. A highly sensitive and selective optical sensor device based on a porphyrin-coated ZnO thin film/K+ ion-exchanged glass composite optical waveguide (COWG) layer was developed. The surface of the ZnO film was coated with a thin film of 5,10,15,20-tetrakis-(4-methoxyphenyl) porphyrin by the spin-coating or immersion method. The optical properties of the films were probed by UV–vis and Fourier-transform infrared spectroscopies. The gas sensing performance was also examined in detail. The high sensitivity, room temperature operation, good selectivity, and reproducibility of the sensor render it a promising candidate for industrial use and in environmental monitoring. [ABSTRACT FROM AUTHOR]