A Sandwich Structure Sensor Based on Ag-Silk Fibroin-Ag Co-Modification for Trace Water Determination in Visible Light Band

A sensor based on silver- Silk Fibroin -silver sandwich structure is proposed to detect trace water in organic solvents. The side Section of D-shaped optical fiber is coated with silver, silk fibroin, and silver film in turn. The inherent nanopores in the top silver membrane allow water molecules to penetrate the middle layer, then the middle silk fibroin layer absorbs water and expands, resulting in the shift of the surface plasmon resonance peak. The sensitivity of the sensor is improved by the strong local electric field enhancement effect between the double-layer metals. The simulation results show that when the initial thickness of silk is 140 nm, the upper silver thickness is 30 nm, the lower silver thickness is 21 nm and the air hole spacing is
$0.55 \mu \text{m}$
, the sensing effect is the best, final sensitivity can reach 1.92 nm/ppt. In the visible band, the sensor proposed in this paper has the potential to be used for high sensitivity and rapid detection in organic solvents.