Enhanced Antimicrobial and Biofilm-Disrupting Properties of Gallium-Doped Carbon Dots

Antibiotic resistance continues to be a global health threat caused by microbial biofilms, yet carbon dots (CDs) offer a promising countermeasure. Doping CDs with metals or nonmetals further enhances their properties while maintaining biocompatibility. This work reports the sonochemical synthesis of gallium-boronic acid carbon dots (Ga-BACDs) under conditions (20 kHz, 2000 W, 60% amplitude, 60 °C, and 60 min), achieving significant gallium incorporation. Ultraviolet-visible and fluorescence analyses reveal characteristic CD absorbance peaks at 286 and 355 nm and strong emission at 397-400 nm. Fourier transform infrared spectral changes on Ga-BACDs suggest successful incorporation of gallium and confirm Ga-H/Ga-O-C (2000-2600 cm^{- 1}) and Ga-O/Ga-O-Ga (400-700 cm^{- 1}) vibrations. X-ray diffraction and Raman spectroscopy data indicate the retention of the amorphous carbon framework with enhanced local ordering. High-resolution scanning electron microscopy (HR-SEM) and high-resolution transmission electron microscopy images demonstrate morphological alterations compared to BACDs with a particle mean diameter of 8.6 ± 4.1 nm. The gallium doping in Ga-BACDs was quantified as 3.66 ppm by using inductively coupled plasma-atomic emission spectroscopy. X-ray photoelectron spectroscopy results indicated that Ga is chemically integrated inside the carbon dot framework. The zeta potential shifts from -32.5 mV (BACDs) to -23.3 mV (Ga-BACDs), evidencing surface charge modulation. The antimicrobial activity of Ga-BACDs was tested against Gram-positive (Staphylococcus epidermidis) and Gram-negative (Escherichia coli) bacterial strains; the presence of gallium contributed to improved bioactivity at 37 °C. HR-SEM images of Ga-BACD-treated bacteria presented significant structural damage, membrane rupture, and surface irregularities. Ga-BACDs inhibited biofilm formation at concentrations as low as 2.5 mg/mL and efficiently eradicated preformed biofilms, highlighting their promise for preventing biofilm-associated infections. MTT assays on normal human brain cells confirm the biocompatibility of Ga-BACD-coated cellulose discs and CD solution (0.1 mg/mL), supporting the safe use of Ga-BACD-modified fibers. Overall, our findings highlight Ga-BACDs as metal-doped carbon nanoparticles, with strong potential for novel antibacterial treatments.