Gold nanoparticle-based NSET turn-on nanosensor for sensitive hydrogen peroxide imaging in cells and tumors

Hydrogen peroxide (H₂O₂), a key reactive oxygen species (ROS) involved in redox signaling and oxidative stress, remains challenging to detect in complex biological environments because of background interference and photobleaching. Herein, we report a gold nanoparticle (AuNP)-quenched nanometal surface energy transfer (NSET)-based "turn-on" nanosensor for H₂O₂ detection. The probe, mFBS@AuNP, integrates an arylboronate (AB)-responsive fluorescein molecule (mFBS) with AuNPs, which function as fluorescence quenchers that suppress background fluorescence via NSET. mFBS incorporates carboxyfluorescein (FAM) as the reporter, an arylboronate moiety as the H₂O₂-responsive trigger, and a thiol group for stable AuS conjugation. Upon H₂O₂ exposure, oxidative cleavage of the AB releases the FAM fluorophore from the AuNP surface, resulting in fluorescence recovery and activation. The nanosensor was fully characterized and enabled sensitive detection of H₂O₂ in living MDA-MB-231 cells. The mFBS@AuNP nanoprobe exhibited a pronounced, concentration-dependent fluorescence response to H₂O₂, with a detection limit of 37.9 μM and a linear response. The mFBS@AuNP enabled fluorescence imaging of both exogenous H₂O₂ and phorbol12-myristate13-acetate (PMA)-stimulated endogenous ROS, while N-acetylcysteine (NAC) treated substantially suppressed the fluorescence response, supporting the H₂O₂-responsive behavior of the nanoprobe. Furthermore, the nanoprobe exhibited effective fluorescence activation in 4T1 tumor tissues following local administration, demonstrating H₂O₂-responsive imaging in tumor-relevant environments. Collectively, this nanoparticle-based NSET strategy establishes an activatable fluorescence platform for sensitive H₂O₂ sensing and oxidative-stress imaging in biologically relevant environments.