Self-Assembled Microgels Arrays for Electrostatic Concentration and Surface-Enhanced Raman Spectroscopy Detection of Charged Pesticides in Seawater

Development of flexible surface-enhanced Raman spectroscopy (SERS) substrate with controllable "hot spots" has spurred increasing interest because of its unique structure and plasmonic properties. Here, charged poly(vinyl alcohol) microgels containing silver nanoparticles are developed by using microfluidic emulsification to produce a "smart" SERS sensor with charge screening and signals amplification. Importantly, this charged microgel enables the selective concentration of counter-charged molecules and induces the formation of assembled arrays at an immiscible liquid-liquid interface because of the electrostatic interaction. The SERS-active microgels arrays possess controllable structures and facilitate on-site determination of charged pesticides with an enhancement factor of 5.0 × 10⁵. Such nanostructures present the ease of assembly, stability, and reproducibility which allow multiplex detection of analytes at aqueous and organic phases without any pretreatment of the complex matrix samples. The interfacial sensing platform for on-site SERS analysis of charged pesticides will open vast possibilities for a wide range of in-field applications.