Microfluidic chip for droplet-based AuNPs synthesis with dielectric barrier discharge plasma and on-chip mercury ion detection

This paper presents a novel microfluidic chip that can achieve gas-liquid segment flow, plasma discharge, gas-liquid separation, liquid collect and mercury ion detection. Instead of using conventional chemical reaction method, this chip uses helium plasma as the reducing agent to reduce gold ion and synthesize gold nanoparticle (AuNP), such that there is no residual reducing agent in the solution after removing the electric field for plasma generation. The synthesized gold nanoparticles are further functionalized by 3-Mercaptopropionic acid (3-MPA) for mercury ion detection. The 3-MPA caped gold nanoparticles aggregate and result in the color change of the solution due to the existence of Hg
²⁺
. The absorption spectrum of the solution may shift form red to blue due to the cluster aggregation. The concentration of Hg
²⁺
can be quantitatively determined by UV-vis spectrometry and the limit of detection is found to be 10
^-6
M (0.2 ppm). The developed integrated microfluidic device provided a simple and on-demand method for synthesis AuNPs and Hg
²⁺
detection in a single chip.