Fiber-Optic SPR pH Sensor Based on MMF–NCF–MMF Structure and Self-Assembled Nanofilm

A fiber-optic pH sensor, based on layer-by-layer (LBL) self-assembly and surface plasmon resonance (SPR) technology, is proposed and experimentally confirmed. This article proposes poly (diallyldimethylammonium chloride) (PDDA) as the pretreatment solution for the surface of the gold film and the highly sensitive polyacrylic acid/chitosan (PAA/CS) self-assembled nanomembrane as the pH-sensitive film. It has been experimentally verified that the sensor can detect pH from 3.18 to 11.84 and it exhibits a high average sensitivity of 32.31 nm/pH in this range. In addition, experiments have confirmed that the sensor has attractive stability, repeatability, and hysteresis characteristics.