ABSTRACT Increasing prevalence of drug‐resistant tuberculosis (TB) challenges global health and current diagnostic techniques are insufficient to meet clinical demands. Imaging of microbial processes and host–pathogen interactions provide crucial insights into TB drug resistance mechanisms. Carbon dots (CDs) are promising new generation imaging agents because of their ultra‐small size (1‐10 nm), excellent photostability and low cellular non‐toxicity. This study reports an eco‐friendly microwave‐assisted synthesis of zein, a natural corn protein‐derived fluorescent, spherical carbon dots (ZCDs) of size 3‐4 nm, as revealed by transmission electron microscopy (TEM). ZCDs exhibited UV‐vis shoulder peak at 280 nm, strong emission peak at 450 nm and quantum yield of 32%. X‐ray diffraction (XRD) spectrum showed broad hump centered at 2θ≈23°, a typical characteristic of amorphous carbon and implying short‐range molecular ordering. Zeta potential of ‐11.6 mV in ZCDs indicated stable, negatively charged surface, which was attributed to surface functional groups (O–H, N–H, C≡C, C═O) as confirmed by Fourier Transform Infra‐Red (FTIR) spectroscopy. Elemental analysis revealed presence of carbon (C,) oxygen (O), nitrogen (N), sodium (Na), and sulphur (S). Further, ZCDs were demonstrated as effective fluorescent probes for imaging bacteria, Mycobacterium smegmatis (a non‐pathogenic surrogate for Mycobacterium tuberculosis ). Broth microdilution assay confirmed non‐toxicity of ZCDs towards M. smegmatis , maintaining >80% cell viability at high concentrations of 5 mg/mL. ZCDs were effectively internalized in M. smegmatis , as revealed by flow cytometry and microscopy. ZCDs displayed bright blue fluorescence within cell boundaries, confirming ZCDs as effective fluorescent nanoprobes, with promising potential for tracking cellular processes and imaging microbial cells.
Varshney et al. (2026) studied this question.