Red fluorescent nanoprobe based on Ag@Au nanoparticles and graphene quantum dots for H₂O₂ 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 H₂O₂. 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 H₂O₂ and a wide linear range from 5 to 200 μM, superior to most of the reported fluorescent probes. The RSD value for 100 μM H₂O₂ was 1.4%. The nanoprobe exhibits excellent anti-interferences and shows low cytotoxicity. The recovery of 100 μM standard H₂O₂ in a cancer cell lysate was 85.8%. Most satisfactorily, it can realize monitoring and imaging H₂O₂ in living cells. This study not only presents a sensitive H₂O₂ probe but also provides a platform for detecting other types of reactive oxygen species.