Probing trace Hg2+ in a microfluidic chip coupled with in situ near-infrared fluorescence detection

A novel microfluidic chip coupled with near-infrared (NIR) fluorescence detection set-up was established for specific analysis of trace Hg2+. Based on the NIR fluorescence changes caused by Hg2+-induced dissolution and aggregation of label-free single-strand DNA (ssDNA) wrapped single-walled carbon nanotubes (SWNTs), Hg2+ in aqueous solution were detected sensitively and specifically in the microfluidic chips system. Due to the small device dimension effect as well as the high efficiency of microfluidic chips, the reagent volume reduced from 500 μL to 9 μL and the minimum reaction time reaching the plateau was shortened from 60 min to 30 min, while the detection limit for Hg2+ decreased from 10.5 nM to 1.5 nM, compared with that of measured in regular Eppendorf tube. The idea of detecting NIR fluorescence spectra in microfluidic systems opens new avenues to optical analysis and bioassays in probing trace species.