Innovation of Ratiometric Sensing Strategies Based on Graphitic Carbon Nitride

Graphitic carbon nitride (g-C₃N₄), a π-conjugated semiconductor with visible-light absorption, has emerged as a versatile material for ratiometric sensing due to its thermal/chemical stability, biocompatibility, and tunable optoelectronic properties. This review highlights recent advances in g-C₃N₄-based ratiometric electrochemiluminescence (ECL), fluorescence (FL), and photoelectrochemical (PEC) sensors for ultrasensitive detection of diverse analytes. Ratiometric ECL platforms achieved remarkable detection limits, such as 0.2 nM for Hg²⁺ and 59 aM for SARS-CoV-2 RdRp gene, leveraging dual-potential or dual-wavelength strategies. FL sensors enabled selective quantification of analysts, such as Ce³⁺ (6.4 × 10^-8 mol/L) and tetracycline (5.0 nM) via aggregation-induced emission or inner filter effect mechanisms. In PEC sensing, spatial-resolved dual-electrode systems attained ultrahigh sensitivity for Escherichia coli (0.66 cfu/mL) and alpha-fetoprotein (0.2 pg/mL). These g-C₃N₄-based sensors demonstrated enhanced sensitivity and reliability across environmental, biomedical, and food safety applications. The synergy of g-C₃N₄'s structural advantages and ratiometric design principles demonstrates broad application prospects in fields such as food and environmental safety analysis, as well as early disease diagnosis.