Synthesis and characterization of nitrogen-doped carbon dots as fluorescent nanoprobes with antimicrobial properties and skin permeability

Nitrogen doped carbon dots (N-doped C-dots) were prepared using polyethyleneimine (PEI) and citric acid (CA) as precursors via the hydrothermal method. Various weight ratios of PEI and CA, 1:0.5, 1:1, and 1:2, were used in the synthesis of N-doped C-dots. The N-doping of prepared C-dots was confirmed with an FT-IR peak that was observed at 1652 cm−1 assigned to N–H bending. The hydrodynamic diameters of prepared N-doped C-dots were 70.2 ± 6.9, 32.2 ± 4.7, and 11.5 ± 3.1 nm by DLS measurements, and surface charges values were 1.32 ± 0.8, 0.14 ± 0.2, and −1.57 ± 0.7 mV, for 1:0.5, 1:1, and 1:2 wt ratio based on PEI of CA, respectively. A high quantum yield 53 ± 4.8% according to quinine sulfate standard was determined for 1:1 C-dot prepared from 1:1 wt ratio of PEI:CA. The C-dots were found to inhibit growth of both Gram-negative and Gram-positive bacteria with no noted toxicity to mammalian cells in vitro. Skin permeation studies indicate that the particles permeate into and through the dermis within hours, indicating their potential use for topical administration.