Low-temperature rapid synthesis of high-stable carbon dots and its application in biochemical sensing

Carbon dots (CDs) have wide applications in chemical sensor, electrocatalysis, and photocatalysis, but most preparations of carbon dots need high temperature and long reaction time. In this work, a chemical oxidation and surface passivation approach was introduced to synthesize fluorescent CDs in low-temperature condition using phosphoric acid and ammonium hydroxide as the oxidant and passivator, respectively. The as-prepared CDs exhibited two emission bands at 356 nm and 440 nm with different excited wavelengths, and high quantum yield (25.51%). More important, the fluorescent CDs display good water-solubility and high biocompatibility even under broad pH range or high ionic strengths. Moreover, this high-stable fluorescent CDs was also employed as a ratiometric fluorescence probe for ascorbic acid sensing based on the inner filter effect (IFE) between ascorbic acid and CDs. This strategy represented excellent sensitivity and selectivity for ascorbic acid analysis both in buffer and biological samples, providing a valuable platform for ascorbic acid detection in clinic diagnosis.