A gas-diffusion microfluidic paper-based analytical device (μPAD) coupled with portable surface-enhanced Raman scattering (SERS): facile determination of sulphite in wines.

A novel facile method for on-site determination of sulphite in wine using a gas-diffusion microfluidic paper-based analytical device (μPAD) combined with surface-enhanced Raman spectroscopy (SERS) was explored. The inexpensive and disposable μPAD was realized by sandwiching the ZnO-paper disc and integrating gas-diffusion separation and gas preconcentration on a paper-based platform. Through extensive condition optimization, the SERS signal at a shift of 620 cm(-1) and the concentration of SO2 showed good linearity in the range of 5-300 μg mL(-1). The linear correlation coefficient was 0.995 and the detection limit for sulphite was found to be 2 μg mL(-1). Ultimately, this proposed method was applied to the determination of sulphite in wine, which can be essentially paralleled with the official method. Endowed with portability, minimal reagent consumption, and operational simplicity, this developed device would find broad utilization for on-site monitoring of sulphite.