Long-wavelength emissive N-doped carbon dots as a fluorescent probe for sensitive detection of pyrophosphate and cellular imaging.

Nitrogen-doped carbon dots (N-CDs) exhibiting long-wavelength fluorescence were successfully synthesized via a one-step hydrothermal method using neutral red and thiosemicarbazide as precursors, specifically to address limitations in pyrophosphate (PO, PPi) detection. As an essential adenosine triphosphate (ATP) hydrolysis byproduct and disease biomarker, PPi quantification remains challenged by costly instrumentation and complex procedures in conventional methods. The synthesized N-CDs demonstrated optimal excitation/emission at 520/600 nm with a quantum yield (QY) of 4.8%, enabling rapid (1 min response time), selective PPi detection through fluorescence quenching. Quantitative analysis revealed a linear detection range of 1.38-85.60 μmol/L R = 0.9983 and low detection limit of 0.42 μmol/L. Practical validation in milk samples yielded excellent recovery rates of 95.26-105.74% with ≤1.86% relative standard deviation, confirming reliability in complex matrices. Critically, the N-CDs' deep-tissue penetration capability facilitated real-time monitoring of intracellular PPi dynamics in HeLa cells, while maintaining high biocompatibility. This work establishes multi-element doped carbon dots as both a cost-effective analytical alternative and a versatile platform for biomedical imaging applications.