Quinones as Optical Signal Transducers: Emerging Roles in Spectroscopic Sensing, Carbon Dots, and Enzyme-Free Immunoassays

Abstract

Quinones have emerged as versatile optical signal transducers in spectroscopic analytical chemistry because of their unique redox activity, electron-transfer capability, reactive oxygen species generation, and tunable photophysical properties. Beyond their traditional roles as biologically active molecules and electrochemical mediators, quinones now function as derivatization reagents, fluorescence-modulating probes, recyclable chemiluminescent and colorimetric signal amplifiers, functional nanomaterial components, and stable labels for enzyme-free immunoassays. This review presents a unified analytical framework that organizes these diverse applications according to their mechanistic roles in molecular recognition, optical signal generation, redox amplification, and nanomaterial-assisted sensing. The molecular principles governing quinone redox cycling, photoinduced electron transfer, fluorescence quenching and recovery, reactive oxygen species-mediated amplification, and nanoparticle coupling are critically discussed to explain analytical performance and guide rational platform design. Recent advances in quinone-derived and quinone-functionalized carbon dots, chemiluminescent and colorimetric amplification systems, fluorogenic derivatization, and quinone-based enzyme-free immunoassays are comprehensively evaluated with emphasis on sensitivity, selectivity, stability, portability, and practical applicability. Current limitations, including matrix interference, mechanistic validation, aqueous compatibility, and reproducibility, are critically assessed, and future opportunities for biomedical diagnostics, food analysis, environmental monitoring, and point-of-care testing are highlighted. Collectively, this review establishes quinones as multifunctional analytical building blocks for next-generation optical sensing platform development.