Mn-Engineered Carbon Dots for Dual-Responsive Fluorescence Detection of Polarity and Cysteine with Intracellular...

Simultaneous monitoring of environmental polarity and cysteine (Cys) is of considerable importance for understanding cellular microenvironments and disease-associated physiological processes. However, fluorescent probes capable of dual-responsive sensing toward both polarity and Cys remain rarely reported. Herein, Mn-engineered tryptophan-derived carbon dots (Mn-TrpCDs) were successfully synthesized using MnCl₂ and D-tryptophan as precursors. Structural characterization demonstrated that Mn atoms were atomically dispersed and stabilized within the carbon framework through N/O coordination, resulting in carbon dots with uniform particle size, moderate graphitization, and abundant surface functional groups. Under excitation at 373 nm, Mn-TrpCDs exhibited strong blue fluorescence centered at 452 nm and displayed distinct dual fluorescence responses toward both environmental polarity and Cys. The fluorescence intensity increased progressively with increasing solvent polarity and showed an excellent linear response toward Cys over the concentration range of 0-80 µM, with a limit of detection (LOD) of 0.31 µM. In addition, the probe reached a stable fluorescence response within 10 min and exhibited excellent salt tolerance, broad pH adaptability, outstanding photostability, and high selectivity toward Cys over various potential interferents. Furthermore, owing to its low cytotoxicity and favorable biocompatibility, Mn-TrpCDs enabled fluorescence imaging of intracellular Cys in HK-2 cells. To the best of our knowledge, this is the first report of Mn-engineered carbon dots as a dual-responsive fluorescent probe for the simultaneous sensing of environmental polarity and Cys. This work provides a simple strategy for constructing multifunctional Mn-Engineered carbon-dot fluorescent probes and expands their potential applications in fluorescence sensing and bioimaging.