N-doped red emissive carbon nanodots for emission shift mediated sensing and biomedical applications

Fluorescence, one of the most intriguing properties of carbon nanodots (CNDs), has garnered significant interest in sensing and biomedical applications. Particularly, emission in the red region is a desirable feature of these particles in biomedical applications. Here, sensing and biomedical applications of red emissive N-doped carbon nanodots (PD-CNDs) are discussed. A pronounced colour change in the visible light, associated with a shift in the emission colour from intense orange-red to cyan enables facile detection of sulphide ions using the system. The Limit of Detection (LOD) was noted to be 0.709 μM, well below the permissible limit of the analyte in drinking water, as set by the WHO. Naked-eye detection as well as solid state sensing of sulphide ions are achieved with LOD values 14.08 μM, and 39 nmol respectively. The solvatochromic nature of the system is extended to trace the moisture level in acetone, a key organic solvent in diverse sectors including pharmaceuticals, cosmetics, chemical synthesis, and industrial manufacturing. Increasing water content in acetone induces fluorescence red shift (yellow to orange-red) and concomitant intensity quenching of system. A linear emission peak shift enables accurate quantification of water content in acetone with less than 1% error. Additionally, PD-CNDs enable clear multicolor fluorescence imaging of cheek cells with strong signals localized within the cell boundaries, demonstrating their effectiveness as a reliable imaging probe. Cytotoxicity studies conducted towards MDCK cells showed high cell viability (85-95%) even at 100 μg/mL concentrations, confirming excellent biocompatibility of the system. It is noteworthy that the solvent-dependent emission feature also allows the use of organic fixatives, ensuring consistent imaging performance.