Label-free identification of trace microcystin-LR with surface-enhanced Raman scattering spectra

The analysis of trace microcystin-LR (MC-LR) plays important roles in environmental fields, especially in monitoring domestic water quality and safety, since it has particularly harmful effect on wild and domestic animals as well as humans at low doses. Herein, we combine confocal Raman spectroscopy with SERS-AG substrate to characterize the "fingerprint" information of MC-LR directly. High sensitivity of SERS-AG substrates was verified by utilizing the probe molecule Rhodamine 6 G. Mapping spectra demonstrated good reproducibility of MC-LR identification with label-free surface-enhanced Raman scattering (SERS) strategy. Differences between SERS spectra of MC-LR and R6G, microcystin-RR were evaluated by calculating their scores and loading weights with an unsupervised exploratory principal component analysis method. Then, relationship between Raman intensities and concentrations was preliminary analyzed with SERS spectra of MC-LR and the lowest concentration of MC-LR identification was 10^-6 mg L^-1 while using SERS-AG substrate. Thereafter, 68.6% quantitative recovery of 10^-3 mg L^-1 MC-LR in tap water samples was obtained by the proposed label-free SERS method. These results showed that confocal Raman spectroscopy with label-free surface-enhanced Raman scattering strategy can handle the identification of trace MC-LR for monitoring water quality and safety worldwide in future.