Biomimetic synthesis of 3D Au-decorated chitosan nanocomposite for sensitive and reliable SERS detection

•Biosynthesis of Au NPs was facially achieved using an alkali chitosan solution.•Dissolved chitosan with anchored Au NPs were self-assembled into a 3D architecture.•Well dispersed Au NPs with nanogaps led to excellent SERS EF and reproducibility.•Shapable, porous and pH-sensitive feature promoted good molecular selectivity. As a cost-efficient method for detecting analyses at trace level, chitosan-based surface-enhanced Raman scattering (SERS) sensor is a promising alternative. However, research on this technique is frequently hindered to complicated operations, dissatisfactory sensing and reproducible property. Herein, a biosynthesis of Au nanoparticles (NPs) was facially achieved through adding AuCl4 ions into a dissolved alkali chitosan dope without using any heating operation or extra reductant. Subsequently, through hydrogen bonds-driven self-assembly during the coagulation process, chitosan nanofibrils anchored with Au NPs grew into a three-dimensional (3D) architecture. Because of the well-dispersed Au NPs with a content of 0.91–2.78 wt% and emerged sub-10 nm nanogaps, the prepared Au-embedded chitosan (Au@CS) nanocomposite could serve as excellent SERS substrate. The enhancement factor approached 107 and spot-to-spot reproducibility could be as low as 5.66% for detecting 4-mercaptobenzoic acid (4-MBA). Besides, owing to the innate pH-sensitive characteristic, the SERS substrate demonstrated molecular-selective detection of charge dye molecules. Furthermore, thanks to its hierarchical porosity and mechanical flexibility, straightforward trace detections of melamine in milk and pesticides on the fruit surface were realized using this SERS substrate. This simple and highly efficient SERS substrate provides great opportunity in the field of environmental management and food safety.