Highly sensitive SERS platform using sub-10-nm Ag nanoparticles on GaN distributed Bragg reflector for detecting organic pollutants

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Surface-enhanced Raman scattering (SERS) is crucial for the development of advanced detection technology and achieving high-sensitivity optical signals. Sub-10 nm noble metal nanostructures with high specific surface area and good catalytic activity are suitable for in-situ SERS analysis, while their SERS performance is inferior compared to larger noble metal nanoparticles with sizes of tens of nm. In this study, the weak SERS signals from sub-10 nm Ag nanoparticles (NPs) are greatly enhanced by developing a highly reflective multi-component system, in which monodisperse sub-10 nm Ag NPs are deposited onto a GaN-based distributed Bragg reflector (DBR). This Ag-NP/GaN DBR system exhibits remarkable SERS enhancement, approximately two orders of magnitude. This enhancement effect is further confirmed by SERS mapping over an area of 50 × 50 µm2. Moreover, the Ag-NP/GaN DBR system enables the in-situ monitoring of catalytic reaction processes of R6G and 4-NBT molecules, indicating high analytical sensitivity. To demonstrate practical applications, this Ag-NP/GaN DBR system is exploited to detect the toxic malachite green molecules and polyethylene microplastics, which show strong fingerprint signals. This work provides an effective solution to boost the weak SERS signals of sub-10 nm Ag NPs and paves the way towards practical applications.