Design of Red Emissive Carbon Dots: Robust Performance for Analytical Applications in Pesticide Monitoring.

Synthesis of red emissive carbon dots (CDs) are highly desirable for sensing application, still remaining bottlenecks in terms of precursor synthesis and product purification. Herein, we have designed a new strategy of realizing efficient red emissive CDs optimal emission at 610 nm (fluorescence quantum yield ca. 24.0 %) based on solvothermal treatment of citric acid and thiourea using dimethylformamide as solvent. Further investigations reveal that the conjugating sp2-domain controlling, the incorporation of nitrogen and surface engineering are mainly responsible for the obtained red-emission of CDs. Taking advantage of optical properties and abundant surface functional groups, CDs were considered to facilely construct ratiometric fluorescent platform for quantifying trace-level organophosphorus pesticides (OPs). Combining acetylcholinesterase-mediated the polymerization of dopamine and the inhibition of pesticide toward enzyme, the degree of polymerization of dopamine rationally depend on the concentration of OPs. By measuring the fluorescence intensity ratio, the proposed platform exhibited highly selective and robust performance toward OPs, displaying ultrasensitive recognition in pg L-1 level. The multi-excitation format could efficiently shield background interference from complex samples by introducing a self-calibrated reference signal, which afford accurate and reliable quantitative information, endowing CDs as a universal candidate for biosensing application by combining target-specific recognition elements.