Target Recognition of ^• OH via Customized <i>o</i> -Hydroxyphenyl Pillar[5]arenes-Functionalized Gold Photochemical Sensors in Cells

The hydroxyl radical (^•OH), one of the most reactive oxygen species (ROS), exhibits unparalleled oxidative capacity, inducing direct damage to proteins, lipids, and DNA, thereby triggering cellular dysfunction and death. Herein, we develop a triple-signal-amplified biosensor based on <i>N</i>-(2-hydroxyphenyl)acetamido- and sulfhydryl-modified pillar[5]arene (HE/SH-P5)-functionalized gold nanoparticles (Au@HE/SH-P5 NPs) for the highly specific detection of ^•OH under visible light irradiation. HE/SH-P5 confers specificity and enables signal amplification through the reaction of its functional groups with ^•OH. Notably, the host molecule concentrates hydroxyl radicals within its cavity via host-guest complexation, while the localized surface plasmon resonance of gold nanoparticles synergistically enhances photoelectrochemical (PEC) signal amplification. The sensor achieves pH-dependent ultralow detection limits (0.3 μM at pH 2; 0.1 μM at pH 7.4, S/N = 3) and a broad linear range (1-250 μM at pH 2; 0.3-100 μM at pH 7.4). Significantly, the PEC platform demonstrates exceptional performance in monitoring ^•OH within HeLa cells, underscoring its considerable potential for fundamental ROS research, pathophysiological studies, and clinical diagnostics.