Carbon dots (CDs)minute
carbon nanoparticles with remarkable
luminescent properties, photostability, and low toxicityshow
potential for various applications. CDs synthesized using citric acid
and urea are the least toxic to biological environments. Here, we
aimed to explore the effect of CDs synthesized using citric acid and
urea at 50, 33, and 25% (CDs 1/1, 1/2, and 1/3, respectively) weight
ratios in a microwave on bacterial cell fluorescence sensing and labeling.
The nanoscale properties of CDs were investigated via transmission
electron microscopy and dynamic light scattering particle size analysis.
X-ray powder diffraction confirmed the graphitic structures of CDs.
X-ray photoelectron spectroscopy revealed that the nitrogen content
increased gradually with increasing urea ratios, indicating functional
group changes. Transient photoluminescence decay periods demonstrated
superior fluorescence intensity of CDs 1/3 under blue, green, and
red lights. The use of CDs was notably more efficient than traditional
methods in staining bacterial cells. Fluorescence microscopy of 10
g-positive and 10 g-negative bacteria revealed enhanced staining of
Gram-positive strains, with CDs 1/3 presenting the best results. The
CDs exhibited excellent photostability, maintaining poststaining fluorescence
for 100 min, surpassing the performance of conventional dyes. CDs
could serve as potential fluorescent dyes for the rapid discrimination
of Gram-positive and Gram-negative bacteria.