In situ dispersion of oil-based Ag nanocolloids by microdroplet coalescence and their applications in SERS detection

Abstract

Monodispersity and size uniformity of the nanoparticles coated on film-like nanosensors are critical for detection efficiency. However, there is limited controllability in the dispersion of these nanoparticles during their preparation and surface modification processes. Herein, we have developed a method for the in situ dispersion of surface-modified Ag nanoparticles by controlling microdroplet coalescence, and fabricated surface-enhanced Raman scattering (SERS) films by spin-coating the nano-Ag suspensions. In the dispersion process, a two-plate type microchannel was employed to promote microdroplet coalescence. Under the experimentally optimized conditions, about 88% surface-modified Ag nanoparticles with an average size of 16–19 nm could be in situ dispersed. Upon the deposition of the resulting nanosuspensions on PDMS film surfaces, the films could be used to detect a target analyte, rhodamine 6G (R6G), at a detection limit of approximately 1.0 × 10⁻⁸ mol L⁻¹. The Ag-coated films were also confirmed to be stable and highly reusable.