Bifunctional fluorescent silver-based peroxidase-mimetic nanozymes: A novel ratiometric fluorescence/colorimetric...

Dopamine (DA) is a common neurotransmitter in living organisms, which is involved in a variety of physiological functions and behavioral responses, making the monitoring of its level crucial. Herein, a novel dual-signal sensing strategy based on a silver-based bifunctional nanozymes (Ag-HA) has been proposed for sensitive detection of DA concentration. The prepared Ag-HA exhibited both blue fluorescence and peroxidase-like activity. In the presence of H₂O₂, Ag-HA could catalyze the generation of reactive oxygen species radicals, effectively oxidizing the colorless chromogenic substrate o-phenylenediamine (OPD) into the yellow oxidized product 2,3-diaminophenazine (DAP), which exhibited fluorescence emission at 570 nm and had a characteristic absorption peak at 415 nm. Meanwhile, due to the inner filter effect (IFE), DAP could quench the blue fluorescence of Ag-HA. The addition of DA hindered the oxidation of OPD, thereby reducing DAP formation and consequently decreasing its fluorescence and absorption signals, while recovering the blue fluorescence of Ag-HA in the system. Thus, a dual-signal detection platform was established for the determination of DA concentration by monitoring changes in the fluorescence intensity ratio (F₄₄₂/F₅₇₀) and colorimetric signal, with detection limits (LOD) of 0.035 μM and 0.23 μM, respectively. In addition, the proposed dual-mode strategy has achieved good practicability and application prospects in agarose hydrogel-smartphone visualization for detecting DA.