Engineering the hierarchical heterostructure of core-shell nanoparticles to improve SERS enhancement and cysteine detection

Cysteine (Cys), a conditionally essential amino acid in biological systems and widely utilized in the food industry. While dietary intake of cysteine-rich foods replenishes exogenous sources, aberrant levels can instigate pathological conditions. The scarcity of reliable methods for quantifying cysteine in food matrices underscores the urgent need for accurate and sensitive detection methodologies to safeguard food safety and human health. In our study, a self-assembly method is employed to construct a porous, highly cross-linked shell around Au NPs via the oxidation-polymerization reaction of Dopamine (DA) and N-aminoethyl piperazine propane sulfonate (AEPPS) at room temperature. The polymeric shell strengthens the interaction between the Au NPs and the DA-AEPPS layer via hydrogen and covalent bonds, and effectively mitigates Au NP aggregation. It can be applied to the quantification of Cys in food matrices with short detection times and high selectivity, enabling precise differentiation and measurement. The detection limit of this method reached 78.4 nmol/L, demonstrating high sensitivity and promising applications in the field of food safety. A series of Cys spiking recovery experiments is conducted using the present method and high-performance liquid chromatography (HPLC). While the Cys is commonly found in milk, apples, and flour, which selected as the analyte for testing in these food samples. The RSD of the present method with different spiking and samples is found range from 1.3-4.4%, with recoveries ranging from 95.1% to 110.1% (the HPLC method yielded a recovery rate of 86.3% to 111.7%, with an RSD ranging from 1.2% to 2.1%). The adsorption and detection capabilities for Cys can be significantly enhanced through specific chemical interactions, providing an efficient means for food safety detection.