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.

碳点（CD）在化学传感器，电催化和光催化中具有广泛的应用，但是大多数碳点的制备都需要高温和较长的反应时间。在这项工作中，引入了一种化学氧化和表面钝化方法，以在低温条件下分别使用磷酸和氢氧化铵作为氧化剂和钝化剂来合成荧光CD。所制备的CD在356nm和440nm处显示两个发射带，具有不同的激发波长，并且具有高的量子产率（25.51％）。更重要的是，即使在宽pH范围或高离子强度下，荧光CD也显示出良好的水溶性和高生物相容性。此外，基于抗坏血酸和CD之间的内部过滤效果（IFE），该高稳定的荧光CD也用作抗坏血酸检测的比例荧光探针。该策略代表了缓冲液和生物样品中抗坏血酸分析的出色灵敏度和选择性，为临床诊断中的抗坏血酸检测提供了有价值的平台。