Red fluorescent nanoprobe based on Ag@Au nanoparticles and graphene quantum dots for HO determination and living cell imaging.

A sensitive and turn-on fluorescence nanoprobe based on core-shell Ag@Au nanoparticles (Ag@AuNPs) as a fluorescence receptor and red emissive graphene quantum dots (GQDs) as a donor was fabricated. They were conjugated together through π-π stacking between the GQDs and single-strand DNA modified at the Ag@AuNPs surface. The absorption spectrum of the receptor significantly overlapped with the donor emission spectrum, leading to a strong Förster resonance energy transfer (FRET) and thus a dramatic quenching. The sensing mechanism relies on fluorescence recovery following DNA cleavage by •OH produced from Fenton-like reaction between the peroxidase-like Ag nanocore and HO. The red emissive feature (Ex/Em, 520 nm/560 nm) provides low background in physiological samples. The •OH production, great spectrum overlapping, and red emission together contributes to good sensitivity and living cell imaging capability. The fluorescence assay (intensity at 560 nm) achieves a low detection limit of 0.49 μM HO and a wide linear range from 5 to 200 μM, superior to most of the reported fluorescent probes. The RSD value for 100 μM HO was 1.4%. The nanoprobe exhibits excellent anti-interferences and shows low cytotoxicity. The recovery of 100 μM standard HO in a cancer cell lysate was 85.8%. Most satisfactorily, it can realize monitoring and imaging HO in living cells. This study not only presents a sensitive HO probe but also provides a platform for detecting other types of reactive oxygen species.