Tube Glass Waveguides Modified With Gold Nanoparticles for Application as a Simple Chemical and Biological Sensor

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.