Effects of functional groups on carbon dots-based AuNPs for the specific detection of mercury ions

The design of highly selective Raman substrates has always been the key to metal ion detection using surface-enhanced Raman spectroscopy (SERS). Here, a solution volatilization method (SVM) by reducing carbon dots (CDs) was proposed to prepare highly selective gold nanoparticle (AuNPs) as Raman substrates for the specific detection of Hg 2+ through SERS. Five CDs-based AuNPs were synthesized by changing the group on the precursor materials for CDs preparation and the secondary reduction with seed method. The results revealed that thiol and hydroxyl groups played a pivotal role in the detection of Hg 2+ . Interestingly, the influence of the chirality, number and type of the groups on the detection of Hg 2+ is substantial. The DTT-CDs/AuNPs-2, prepared from dithiothreitol (DTT) containing two thiol groups and hydroxyl groups, was capable of selectively facilitating the formation of gold amalgamation (Au@HgNPs) with Hg 2+ , without being affected by methylmercury. The Au@HgNPs showed obviously enhanced oxidase (OXD)-like activity, which can oxidize TMB (weakly SERS-active) to ox-TMB (strongly SERS-active) with strong Raman signal. This led to a rapid and specific SERS detection of Hg 2+ with a detection limit of 9.56 nM. This work provides guidance for designing ultra-sensitive and highly specific field analysis of heavy metal ions through the modification of CDs' functional groups.