Highly fluorescent nitrogen and phosphorus-doped carbon quantum dots (N,P-CQDs) were synthesized via a one-step hydrothermal method and fully characterized via various techniques such as TEM, DLS, FT-IR, P-XRD and XPS analysis. The as-synthesized N,P-CQDs showed excellent optical properties and exhibited bright blue colour under UV-light with CIE coordinate (0.20, 0.22) along with a high quantum yield of 73%, due to which they could act as on–off fluorescent nanoprobes for the selective and sensitive detection of highly toxic Cr(VI) below its permissible limit via the inner filter effect (IFE) and static quenching mechanism. In addition, Cr(VI) could be reduced to lower valent chromium species. Therefore, the N,P-CQDs + Cr(VI) system further acted as a selective off–on sensor for reductant ascorbic acid (AA) because it reduced Cr(VI) to Cr(III) species, resulting in the elimination of IFE and recovery of fluorescence of N,P-CQDs. Notably, this system possesses excellent biocompatibility and negligible cytotoxicity; therefore, it can be potentially applied for fluorescence imaging of intracellular Cr(VI) and ascorbic acid (AA) in living cells and complex biological systems.

中文翻译：

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亮蓝色发射氮和磷掺杂的碳量子点是一种有前途的纳米探针，可用于检测纯水溶液和活细胞中的Cr（vi）和抗坏血酸†

通过一步水热法合成了高度荧光的氮和磷掺杂的碳量子点（N，P-CQDs），并通过TEM，DLS，FT-IR，P-XRD和XPS分析等各种技术对其进行了全面表征。合成后的N，P-CQDs表现出优异的光学性能，并在紫外线下以CIE坐标（0.20，0.22）呈现亮蓝色，并具有73％的高量子产率，因此它们可以作为开-关荧光纳米探针，用于通过内部过滤效应（IFE）和静态猝灭机制，选择性和灵敏地检测低于允许极限的剧毒Cr（VI）。另外，Cr（VI）可以还原为较低价的铬物种。因此，N，P-CQDs + Cr（VI）系统进一步充当了还原剂抗坏血酸（AA）的选择性开关传感器，因为它将Cr（VI）还原为Cr（III）物种，从而消除了IFE和N，P-CQDs的荧光回收 值得注意的是，该系统具有出色的生物相容性和可忽略的细胞毒性。因此，可以潜在地适用于细胞内的Cr（荧光成像VI在活细胞和复杂的生物系统）和抗坏血酸（AA）。