Biocompatible carbon quantum dots as versatile imaging nanotrackers of fungal pathogen –<i> Candida albicans</i>

<b>Aim: </b>The development of carbon quantum dots (C-QDs) as nanotrackers to understand drug–pathogen interactions, virulence and multidrug resistance. <b>Methods: </b>Microwave synthesis of C-QDs was performed using citric acid and polyethylene glycol. Further, <i>in vitro </i>toxicity was evaluated and imaging applications were demonstrated in <i>Candida albicans </i>isolates. <b>Results: </b>Well-dispersed, ultra small C-QDs exhibited no cyto<b>/</b>microbial<b>/</b>reactive oxygen species-mediated toxicity and internalized effectively in <i>Candida </i>yeast and hyphal cells. C-QDs were employed for confocal imaging of drug-sensitive and -resistant cells, and a study of the yeast-to-hyphal transition using atomic force microscopy in <i>Candida </i>was conducted for the first time. <b>Conclusion: </b>These biocompatible C-QDs have promising potential as next-generation nanotrackers for <i>in vitro </i>and <i>in vivo </i>targeted cellular and live imaging, after functionalization with biomolecules and drugs.<b>Plain language summary: </b>Scientists have used radiolabeled drugs and radioactive tracking agents for the imaging and study of drug resistance in microbial pathogens. But, these radiolabeled drugs or radiotrackers pose health hazards and environmental risks. However, such limitations can be overcome by designing nontoxic, environment-friendly, nanotechnology-based fluorescent imaging agents. This study demonstrates the development and application of cost-effective, nontoxic carbon-based quantum dots for imaging of drug-sensitive and -resistant microbial strains and transition to different morphological forms (yeast-to-hyphae transition) in fungal pathogens. The results demonstrated the suitability of carbon quantum dots as next-generation nano-based bioimaging<b>/</b>tracking agents for cellular imaging. The availability of such nontoxic fluorescent tracking agents is likely to offer promising solutions in therapeutics and diagnostics by providing insight into various mechanisms and functional links related to drug resistance, virulence and pathogenicity.