A FRET assembly of fluorescent gold nanoclusters for ratiometric monitoring peroxynitrite in living cells and zebrafish

Developing reliable probes for accurate monitoring peroxynitrite (ONOO–) in living systems with high sensitivity and selectivity is imperative for both elucidating its functions in many life-threatening diseases and improving therapeutic interventions. Herein, a novel nano-assembly structure (d-AuGP) was developed by electrostatic interaction-induced assembly between dichromatic gold nanoclusters (Au NCs). The assembly further induced fluorescence resonance energy transfer (FRET) and endowed d-AuGP with a well single-excitation, dual-emission fluorescence characteristic. The prepared nanostructure showed a quantitative ratiometric fluorescence response toward ONOO– with a remarkable decrease of emission peak at 685 nm and a stable peak at 470 nm. A good linear relationship between the ratio of emission intensities at 685 and 470 nm (I685/I470) with ONOO– concentration in the range of 0–100 μM was achieved and the limit of detection (LOD) was 0.39 μM. The possible fluorescence response mechanism was ascribed to the combined effects of dissociation-disturbed FRET and surface structure reconstruction. The Au NCs-based probe was demonstrated to possess high stability, low cytotoxicity, good cell and tissue permeability and high biocompatibility. It was effectively employed for biological imaging and monitoring exogenous and endogenous ONOO– levels in living cells and zebrafish with high contrast.