An Optical Au Sensor Based on layer-by-layer PEI/PAA-Rho thin Films on ITO.

This study presents the development of a sensitive and selective gold ion (Au) sensor utilizing layer-by-layer (LbL) assembled thin films composed of polyethylenimine (PEI) and poly (acrylic acid) (PAA) conjugated with rhodamine (Rho). The first study revealed that the polymeric sensors (PAA-Rho) demonstrated significant selectivity and sensitivity in their colorimetric and fluorescence responses to Au compared to other metal ions. In their spirolactam form, the polymeric sensors were non-fluorescent but could selectively transform into the fluorescent ring-opened amide form upon interaction with Au ions, resulting in fluorescence enhancement and observable color changes. Common co-existing metal ions showed negligible interference in the detection of Au. The LbL sensor exhibited a linear increase in absorbance with the addition of bilayers, confirming successful film deposition. Surface morphology analysis using SEM, along with structural confirmation via ATR-FTIR and XRD, further validated the sensor's capability to detect cation. Results demonstrated that the LbL sensor exhibited selectivity for Au ions within the range 1 × 10 to 1 × 10 M. This approach offers an easily understandable and intrinsically sensitive means for detecting Au ions in both environmental and biological applications.