RESUMO
This study presents the development of a sensitive and selective gold ion (Au3+) 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 Au3+ 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 Au3+ ions, resulting in fluorescence enhancement and observable color changes. Common co-existing metal ions showed negligible interference in the detection of Au3+. 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 Au3+ ions within the range 1 × 10-6 to 1 × 10-3 M. This approach offers an easily understandable and intrinsically sensitive means for detecting Au3+ ions in both environmental and biological applications.