Synthesis of red emissive carbon dots (CDs) is highly desirable for sensing applications, as they still remain as bottlenecks in terms of precursor synthesis and product purification. Herein, we have designed a new strategy for realizing efficient red emissive CD 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 sp^2-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 a ratiometric fluorescent platform for quantifying trace levels of organophosphorus pesticides (OPs). Combining the acetylcholinesterase-mediated polymerization of dopamine and the inhibition of pesticide toward the enzyme, the degree of polymerization of dopamine rationally depends 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 the pg L-1 level. The multiexcitation format could efficiently shield background interference from complex samples by introducing a self-calibrated reference signal, which affords accurate and reliable quantitative information, endowing CDs as a universal candidate for a biosensing application by combining target-specific recognition elements.