Dual-channel biosensor for Hg2+ sensing in food using Au@Ag/graphene-upconversion nanohybrids as metal-enhanced fluorescence and SERS indicators

Here, we proposed a novel dual-channel biosensor for rapid and sensitive detection of Hg2+. Compared with the previous biosensors, the Au@Ag/graphene-upconversion (Au@Ag-GU) was prepared via a facile method and acted as a versatile signal indicator that can simultaneously readout surface-enhanced Raman spectroscopy (SERS) and fluorescence signals for Hg2+ detection. In this strategy, the core shell magnetite colloid nanocrystal clusters-polymethacrylic acid magnetic beads (MCNCs/PMAA MBs) were synthesized and conjugated with aptamer to specific capture the Hg2+. The dual-channel biosensor was thus fabricated by immobilizing the Au@Ag-GU onto the surface of MBs through the complementary pairing of aptamer and complementary DNA (cDNA). Upon Hg2+ incubation, Hg2+ preferably bound to the MBs-aptamer, resulting in the subsequent release of preloaded cDNA-Au@Ag-GU into supernatants. Under magnetic attraction, the MBs-aptamer was accumulated immediately, resulting in the concentration of Hg2+ become homodromous proportional to the dual channel intensity of the supernatants. Under the optimized conditions, the dual channel biosensor achieved excellent performances for Hg2+ with limits of detection (LOD) of 0.33 and 1 ppb, respectively. Furthermore, the feasibility of the biosensor to qualify Hg2+ was also established in spiked tap water and milk samples. This strategy may provide a bridge between a highly sensitive fluorescence assay and a rapid SERS assay, it can broaden the applicability of Hg2+ detection, which can be easy to detect Hg2+ in real samples by coupling with SERS or fluorescence assay.