Surface-enhanced Raman spectroscopy (SERS) substrate based on gold nanostars-silver nanostars for imidacloprid detection

Surface-enhanced Raman spectroscopy (SERS) is a powerful molecular spectroscopy technique that combines Raman spectroscopy with nanostructured metallic surfaces to amplify the Raman signals of target molecules by more than 103. The high sensitivity of SERS poses a significant opportunity for pesticide detection in complex matrices at ultralow concentrations. In this study, we improved the SERS sensitivity for imidacloprid (IMD) by employing silver nanostars (AgNs) coated with gold nanostars (AuNs) as the SERS-active substrate. The SERS response towards IMD detection increased based on the combination of AuNs and AgNs on the substrate surface. The intensity of the SERS signal of IMD using the AuNs/AgNs substrate increased compared to using individual metal nanoparticle substrates. The excellent reproducibility of SERS intensity using the AuNs/AgNs substrate was achieved with a low relative standard derivative (RSD) of 4.87% for 20 different spots on the same sample and 5.19% for 20 different samples. This detection system can be used for multiple tests, which is crucial for the advancement of handheld sensors designed for field use, where minimal or no high-level technical support is accessible. This manuscript reports the first introduction of gold nanostars on silver nanostars surface as the Surface-enhanced Raman spectroscopy (SERS) active elements to increase the SERS response towards imidacloprid pesticide. This combination of two metal nanostars showed an enhancement in imidacloprid signal at low concentrations on the AuNs/AgNs surface when compared to the signal on the surface composed of a single type of metal nanostars. The substrates were shown to be stable over a month in storage and can be reused many times. (Image credit: N. Abu Bakar.)