A sensitive and reproducible SERS sensor based on natural lotus leaf for paraquat detection

A facile and green approach of using natural lotus leaf as a superhydrophobic platform was proposed for sensitive and reproducible surface enhanced Raman scattering (SERS) detection. The surface of a lotus leave provides hydrophobic concentrating effect. After the mixture of an Ag nanoparticle (NP) dispersion and the target solution is dropped on the lotus leave chip, Ag NPs assemble into closely packed Ag arrays after solvent evaporation, producing numerous hot spots for SERS enhancement. The hydrophobic concentrating effect of the lotus leave surface greatly enhances the assembling. The final assembled Ag spot can shrink a small disc with a diameter of only about 0.5 mm. This leads to easy fabrication of a sensitive and reproducible SERS sensor based on natural lotus leaves. It was found that the state of the natural lotus leaves (growth stage, size and parts, water loss degree, storing condition) did not influence markedly the detection performance of the lotus leave-based SERS sensor. When the sensor was used to detect paraquat, the SERS signal intensity of paraquat was linearly correlated with its concentration in a very wide range from 5 μg L−1 and 50 mg L−1, with a detection limit of as low as 1.2 μg L−1. The multiple detection experiment demonstrated that this sensor method had high reproducibility with relative standard deviation (RSD) of 11.6%.