Coreactant-free Electrochemiluminescence: ROS Generation via Upconversion Nanoparticles-Sensitized Inverse Opal TiO₂ Photocatalysis under NIR Irradiation

Conventional electrochemiluminescence (ECL) systems typically rely on coreactants, such as hydrogen peroxide or dissolved oxygen, to generate reactive oxygen species (ROS), which are essential for effective light emission. However, these coreactants are inherently limited by self-decomposition and solubility constraints, which can hinder the detection accuracy and light emission efficiency of ECL systems. In this work, we propose an innovative method that eliminates the need for coreactants by utilizing inverse opal TiO₂ (IO-TiO₂) coupled with upconversion nanoparticles (UCNPs) as a coreaction accelerator. By harnessing near-infrared (NIR) irradiation, UCNPs efficiently convert this light into ultraviolet (UV) light, stimulating IO-TiO₂ to generate ROS through water oxidation. The generated ROS subsequently reacts with luminol anion radicals, producing robust ECL emission while eliminating interference from luminescence caused by coreactants. Electron paramagnetic resonance (EPR) results confirm the generation of hydroxyl (•OH), singlet oxygen (¹O₂), and superoxide anion radicals (O₂^•-) during the electrochemical water oxidation process, which ensured the feasibility of the experimental approach. To demonstrate the practical application of this method, human chorionic gonadotropin (HCG) was selected as a model analyte. This proposed ECL immunoassay exhibited high sensitivity and stability in detecting HCG, with a linear range of 4 pg/mL to 1 μg/mL and a low limit of detection (LoD) of 1.33 pg/mL (<i>S</i>/<i>N</i> = 3). This breakthrough offers a promising avenue for developing ECL systems that are more sensitive, efficient, and highly versatile, expanding the range of applications in bioanalysis and environmental monitoring.