A Self-Calibrating Flexible SERS Substrate Incorporated PB@Au Assemblies for Reliable and Reproducible Detection

Precise quantitative analysis of surface-enhanced Raman spectroscopy (SERS) in uncontrollable environment still faces a significant obstacle due to the poor reproducibility of Raman signals. Herein, we propose a facile method to fabricate self-calibration substrate based on flexible Polyvinyl Alcohol (PVA) film comprising assemblies of Prussian blue (PB) and Au NPs (PB@Au) for reliable detection. The PB cores were coated with Au shell through a simple electrostatic interaction, forming the core-shell nanostructure PB@Au assemblies within the PVA. The Au outer layer provided identical trends in enhancement for both PB core and neighboring targets, while PB cores served as internal standard (IS) to correct the signal fluctuations. The prevention of competitive adsorption on the metal surface between targets and ISs was achieved. The proposed PVA/PB@Au film exhibited enhanced stability of Raman signals after IS correction, resulting in improved spot-to-spot and batch-to-batch reproducibility with significantly reduced standard deviation (RSD) values from 11.42% and 25.02% to 4.43% and 9.39%, respectively. Simultaneously, higher accuracy in quantitative analysis of 4-mercaptobenzoic acid (4-MBA) and Malachite green (MG) were achieved with the fitting coeffcient (R²) values improving from 0.9675 and 0.9418 to 0.9974 and 0.9832, respectively. Moreover, the PVA/PB@Au film was successfully applied to detect the residual MG from real-life fish. This work provides an avenue to improve the reproducibility of Raman signals for flexible SERS substrates in detection of residue under varied and complex conditions.