A fluorimetric and colorimetric dual-mode sensor based on N, S co-doped carbon dots functionalized silver nanoparticles for glucose detection.

A fluorescent-colorimetric dual-signal platform, N, S co-doped carbon dots functionalized silver nanoparticles (NS-CDs-AgNPs), was designed in situ by reducing AgNO in the presence of N, S co-doped carbon dots (NS-CDs) under the assistance of microwave irradiation for glucose determination. With the formation of silver nanoparticles (AgNPs), the intrinsic fluorescence of NS-CDs was quenched, showing the fluorescence state was off. Whereas the fluorescence of NS-CDs can be switched on when a trace amount of HO was added. Based on this novel phenomenon, the peroxidase-like activity of NS-CDs-AgNPs by using 3,3',5,5'-tetramethylbenzidine (TMB) chromogen and HO as substrates was evaluated. The K values of the prepared probe for HO and TMB were 0.84 mM and 0.01 mM with the V of 6.65 × 10 M S and 3.01 × 10 M S, respectively. The results showed that NS-CDs-AgNPs had good peroxidase-like activity and strong affinity to TMB and HO. It confirmed that there is a redox interaction between AgNPs and HO, and HO can oxidize Ag to produce Ag, which is the main reason that the fluorescence of NS-CDs-AgNPs can be activated by HO. The hydroxyl radical (·OH) was formed in the process of reaction, which can further oxidize TMB for color reaction. Meanwhile, glucose can be oxidized to produce HO in the presence of glucose oxidase (GOx). Based on the phenomenon, a fluorimetric and colorimetric dual-mode sensor for glucose detection was established. Satisfactory results were obtained with the linear range of 0.1-80 μM for fluorimetric mode and 0.5-5 μM for colorimetric mode, respectively. Additionally, the LOD was below 0.32 μM and 0.21 μM, respectively. The method was successfully applied to determine the glucose in human serum with satisfactory recovery and RSD.