In-field detection method for imidacloprid by surface enhanced Raman spectroscopy

Neonicotinoids such as imidacloprid are used in agriculture worldwide. Due to their hazardous potential, their occurrence is monitored. For pesticide identification in environmental samples, the major tool, high performance liquid chromatography coupled with mass spectrometry, is not fit for field monitoring due to instrument size and technical requirements. To overcome this disadvantage, a method for fast on-site identification of imidacloprid was developed using a handheld Raman spectrometer and surface enhanced Raman spectroscopy. As enhancing agents, gold nanoparticles in solution and on textile support were compared for easy, fast and sensitive monitoring. Agglomeration of nanoparticles led to further signal enhancement. Several agglomeration reagents, filter paper and non-woven polylactide as substrates were tested for optimum enhancement. Addition of hydrochloric acid provided best amplification of imidacloprid signals in solution, while PLA as solid support yielded best sensitivity. Both the solution and solid support methods were estimated to be sufficiently sensitive for fieldable pesticide identification, which may precede standard laboratory analysis. Based on spectral analysis, a proposal for the imidacloprid-gold surface geometry was derived.