Silver nanoparticles doped silica nanocomposites coated on an optical fiber for ammonia sensing

Silver doped silica nanocomposite was synthesized via a sol–gel technique combined with a nanoparticle preparing method using a thiol stabilizer ((3-mercaptopropyl)trimethoxysilane). The freshly prepared sol sample of Ag-doped silica nanocomposite was investigated by transmission electron microscope (TEM). Determined from the TEM image, the sizes of the Ag nanoparticles are around 25 nm. The Ag-doped silica nanocomposite was coated as a membrane on the surface of a bent silica optical fiber by using a dip-coating technique. The response of this coated bent optical fiber probe to trace ammonia in a gas sample was investigated by using a fiber optic spectrometric method. It was found that the exposure of the nanocomposite coated bent optical fiber probe to an ammonia containing gas sample enhances the attenuation of light power guided through the fiber probe. This response is reversible. Ammonia in a gas sample down to sub-ppm level can be continuously monitored with this sensing technique.