Highly sensitive trace analysis of paraquat using a surface-enhanced Raman scattering microdroplet sensor.

We report a rapid and highly sensitive trace analysis of paraquat (PQ) in water using a surface-enhanced Raman scattering (SERS)-based microdroplet sensor. Aqueous samples of PQ, silver nanoparticles, and NaCl as the aggregation agent were introduced into a microfluidic channel and were encapsulated by a continuous oil phase to form a microdroplet. PQ molecules were adsorbed onto particle surfaces in isolated droplets by passing through the winding part of the channel. Memory effects, caused by the precipitation of nanoparticle aggregates on channel walls, were removed because the aqueous droplets were completely isolated by a continuous oil phase. The limit of detection (LOD) of PQ in water, determined by the SERS-based microdroplet sensor, was estimated to be below 2×10(-9) M, and this low detection limit was enhanced by one to two orders of magnitude compared to conventional analytical methods.