Surface‐Engineered Dual‐Emission of Carbon Dots for Ratiometric Detection of Hydroxyl Radicals

ABSTRACT Carbon dots (CDs) have emerged as versatile photoluminescent nanomaterials with exceptional optical properties and biocompatibility, demonstrating considerable potential in bioimaging, energy conversion, and sensing applications. However, the development of aqueous CDs with tunable red dual‐emission remains challenging owing to limitations in electronic energy‐level alignment and ongoing debates concerning the photoluminescence mechanisms. Herein, we report a facile hydrothermal synthesis strategy employing trehalose as the carbon precursor and sulfuric acid serving as both an oxidation regulator and a polymerization agent to regulate the distribution of surface states and endow the CDs with dual emission properties. The resulting CDs exhibit well‐resolved tunable dual emission bands around 450 and 590 nm, attributed to core states and surface‐oxidized states, respectively. Time‐resolved spectroscopic investigations reveal that the engineered surface motifs effectively facilitate ultrafast electron migration from the carbon core to the oxidized states. Intriguingly, hydroxyl radicals induce selective static quenching of the surface‐oxidation‐associated red emission, endowing CDs‐based sensors with ultralow detection limits, self‐calibration capabilities, and real‐time visualization through ratiometric performance. Furthermore, the as‐prepared unique CDs have been validated for the reliable quantification of hydroxyl radical levels in plant onion cells under oxidative stress.