Abstract
A low-cost, simple, and stable optical chemical and biological sensor was prepared using a U-shaped glass tube, whose 200-μm-thick wall coated with a colored layer serves as a sensitive waveguide. Light from a LED is launched into the glass wall of the tube from an endface and emits from the other endface to be detected with a silicon photodetector. The refractive-index (RI) sensitivity of the sensor is mainly attributed to the clad-RI-induced enhancement of evanescent field that results in the increased absorption of the colored layer. The sensor's sensitivity can be effectively improved by hydrofluoric acid etching of the bent portion of the U-shaped tube before deposition of the colored layer. The gold-nanoparticle (GNP) monolayer was used as the colored layer in this paper, and the GNP self-assembly process that took more than 12 h was in situ monitored with the sensor. The resulting sensor can easily detect a small change of 1 wt% in sucrose concentration, and is also applicable for real-time detection of bimolecular adsorption and immunoreaction.
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