Mesoporous Cu₂O coated Au/Ag plasmonic nanocomposites as SERS sensing platform for ultrasensitive detection

Surface enhanced Raman scattering (SERS) is a suited detection technique for trace and ultrasensitive detection that extends even to single molecule levels. However, SERS application is currently limited by three main factors: 1) how to create more hotspots to enhance the sensitivity of SERS; 2) how to enrich trace target molecules in SERS hotspots; and 3) how to maintain the stability and reproducibility of SERS detection under environmental interference. In this study, mesoporous Cu₂O coated Au/Ag plasmonic nanocomposites (NCs) were designed and prepared as SERS substrates. The tightly packed Au/Ag nanoaggregates (NAs) create more hotspots, oxygen vacancies in Cu₂O can also enhances Raman signal by photoinduced charge transferring. Meanwhile, mesoporous Cu₂O coating is beneficial for enriching more target molecules, so the as-prepared Au/Ag@Cu₂O NCs showed excellent SERS sensitivity. When the target molecules 4-mercaptobenzoic acid (4-MBA) was detected on the Au/Ag@Cu₂O substrate, the substrate showed high SERS activity. The enhancement factor reached as high as 3.78 × 10⁶, and the detection limit was as low as 10^-11 M. Meanwhile, the SERS spectra demonstrate excellent selectivity and reproducibility. In addition, the Au/Ag@Cu₂O NCs substrate was applied to detect volatile organic compounds (VOC) pyridine molecules in the air, and when it was naturally adsorbed in air for 20 min, it showed an obvious SERS signal of pyridine. Therefore, these Au/Ag@Cu₂O NCs with high SERS detection performance have important practical value in applications of volatile organic gas molecule.