Yellow-emissive Nd-doped carbon quantum dots for ratiometric detection of anthrax biomarker with applications in food analysis and cellular imaging.

Bacillus anthracis is a pathogenic bacterium that causes an infectious disease of anthrax. Dipicolinic acid (DPA) is the main component of anthracis spores and acts as a biomarker for anthrax. Therefore, the detection of DPA has attracted considerable attention in recent years. Herein, a new yellow-emissive photoluminescent (PL) probe of neodymium-doped carbon quantum dots (Nd-CQDs) was synthesized using a one-pot hydrothermal method. The doping of Nd3+ ions effectively enhanced the PL intensity and stability of CQDs and contributed to the formation of surface-defect emission centers. The Nd-CQDs exhibited excellent PL stability at various pH levels and ionic strengths during long-term storage studies. The synthesized Nd-CQDs were characterized using FT-IR, XRD, TEM, Raman, and XPS analyses, which confirmed their functional groups, crystallinity, surface morphology, and elemental compositions. The optical response of the Nd-CQDs was yellow emission upon the addition of DPA, which resulted in a decrease in this emission. Meanwhile, a new red emissive band appeared at 660 nm, with a 610 nm isobestic point, which confirmed the radiometric detection of DPA with low LOD values of 155.4 nM and 21.0 nM at 565 nm and 660 nm, respectively. In addition, the analysis of real food samples, including milk, orange juice, and soda water, exhibited excellent performance for the determination of DPA quantity, Moreover, bioimaging studies using HCT-116 cell lines confirmed the bright fluorescence and low cytotoxicity of Nd-CQDs. Overall, the results indicate that the synthesized Nd-CQDs are potential candidates for anthrax biosensing and cellular imaging.