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A New Ratiometric Fluorescent Probe for Specific Monitoring of hROS under Physiological Conditions Using Boric Acid-Protected L-DOPA Gold Nanoclusters.

The specific monitoring of physiological highly reactive oxygen species (hROS) using fluorescent gold nanoclusters (AuNCs) remains a challenge for scientists. Herein, SLB-AuNCs was first synthesized via an eco-friendly one-pot method using starch as template, L-3,4-dihydroxyphenylalanine (L-DOPA) as reducing and capping agent, and boric acid as protecting agent for the catechol moiety of L-DOPA. The ingenious introduction of starch and boric acid enhanced the dispersibility, quantum yield and photostability of fluorescent SLB-AuNCs. The obtained SLB-AuNCs possessed good monodispersity with an average diameter of 2.9 ± 0.8 nm and exhibited highly stable fluorescence with maximum emission at 480 nm under physiological conditions. A ratiometric fluorescent probe for hROS was developed through an oxidization-regulated Förster-resonance-energy transfer process between SLB-AuNCs and 2,3-diaminophenazine (the oxidative product of hROS and o-phenylenediamine, with maximum fluorescence emission at 560 nm). With increasing amount of hROS, the outstanding fluorescence variation of probe (I560 nm/I480 nm) enhanced about 300 folds accompanying with distinguishable colour changing from cyan to yellow. The detection limits of •OH, ClO-, and ONOO- were calculated as 0.11 μM, 0.50 μM and 0.69 μM, respectively. High selectivity was achieved by using o-phenylenediamine as a specific signal response for hROS to enable no interference reaction of other ROS towards SLB-AuNCs. The practicability of proposed probe with super biocompatibility was evaluated by measuring exogenous and endogenous hROS levels in HeLa cells through fluorescence imaging. This work provides a novel strategy to design fluorescent AuNCs probe for physiological hROS with great potential for the application of bioassay and bioimaging.