Ligand-Engineered Self-Assembly of Noble Metal Nanostructures for Flexible Patch SERS Substrates Enabling In Situ Detection of Trace Contaminants

Through a surface modification strategy involving hydrophobic ligand functionalization on noble metal nanoparticles, we demonstrate the facile and rapid fabrication of monolayer film assemblies of Au nanoparticles (Au NPs), Au nanostars (Au NSs), and Au@Ag nanostars (Au@Ag NSs). Computational analyses were performed to investigate structural and electronic descriptors of the ligand molecules, revealing the intrinsic mechanisms governing the self-assembly dynamics at the nanoscale. The resulting self-assembled nanoarrays exhibit highly uniform large-scale monolayer architectures with superior SERS homogeneity and exceptional detection limits, enabling efficient identification of trace TNT explosive residues. Notably, we designed a flexible patch-type SERS substrate with a layered architecture (T/PDMS/Au@Ag NSs array/PET/T). This “band-aid-like” device enables both real-time in situ detection and in situ paste-peel sampling, demonstrating successful application in the quantitative analysis of thiram residues on apple surfaces. The integrated design combines mechanical flexibility with robust analytical performance, showcasing promise for on-site environmental and food safety monitoring.