Droplet microfluidic preparation of au nanoparticles-coated chitosan microbeads for flow-through surface-enhanced Raman scattering detection

An integrated microfluidic device was fabricated to enable on-chip droplet forming, trapping, fusing, shrinking, reaction and producing functional microbeads for a flow-through single bead-based molecule detection. Dielectrophoresis (DEP) force was used to transport target polymer droplets into different predefined microwells, where the droplets were fused through electrocoalescence to form a new one with a desired diameter. In a continuous water loss process with water diffusion to oil phase, the polymer droplet was shrunken and solidified to form a polymer microbead. For a demonstration, Au nanoparticles-coated chitosan microbeads were in situ fabricated through droplet trapping, fusion and shrinking, followed by synthesis of Au nanoparticles on the microbead surface via a photoreduction process. The produced Au nanoparticle/chitosan microbead embedded in the microwell resulted in a highly sensitive, flow-through surface-enhanced Raman scattering (SERS) detection of Rhodamine 6G (R6G). This work successfully demonstrates an integrated droplet based lab-on-a chip and its application to fabricate an extremely high-throughput single bead based detection platform.