Antibacterial Properties of Citric Acid/β-Alanine Carbon Dots against Gram-Negative Bacteria

Abstract

While multi-drug resistance in bacteria is an emerging concern in public health, using carbon dots (CDs) as a new source of antimicrobial activity is gaining popularity due to their antimicrobial and non-toxic properties. Here we prepared carbon dots from citric acid and β-alanine and demonstrated their ability to inhibit the growth of diverse groups of Gram-negative bacteria, including E. coli, Salmonella, Pseudomonas, Agrobacterium, and Pectobacterium species. Carbon dots were prepared using a one-pot, three-minute synthesis process in a commercial microwave oven (700 W). The antibacterial activity of these CDs was studied using the well-diffusion method, and their minimal inhibitory concentration was determined by exposing bacterial cells for 20 h to different concentrations of CDs ranging from 0.5 to 10 mg/mL. Our finding indicates that these CDs can be an effective alternative to commercially available antibiotics. We also demonstrated the minimum incubation time required for complete inhibition of bacterial growth, which varied depending on bacterial species. With 15-min incubation time, A. tumefaciens and P. aeruginosa were the most sensitive strains, whereas E. coli and S. enterica were the most resistant bacterial strains requiring over 20 h incubation with CDs.

Citric acid/β-alanine carbon dots as a novel tool for delivery of plasmid DNA into E. coli cells

“…The prepared CDs showed peaks at 1168 cm −1 (C–O) of carbonyls group, 1400 cm −1 (C–N) of nitrile group, 1693 cm −1 (C=O) of ketone group and 2981 cm −1 (C–H) of alkane group. The successful passivation of β-alanine is indicated by the presence of 1400 cm −1 (C–N stretching) 6 , 16 . The obtained peaks were in accordance with previous literatures, suggesting successful synthesis of CDs 6 , 16 .…”

“…The successful passivation of β-alanine is indicated by the presence of 1400 cm −1 (C–N stretching) 6 , 16 . The obtained peaks were in accordance with previous literatures, suggesting successful synthesis of CDs 6 , 16 .…”

“…Photoluminescence properties of CDs synthesized using bottom-up approach, showed two characteristic absorbance peaks at 275 nm and 350 nm. The peak at 275 nm is due to sp 2 ‐carbon network and peak at 350 nm is due to n–π* transition of surface carbonyl groups 16 , 17 . The fluorescence emission profile showed excitation dependent emission spectra of carbon dots synthesized using CA + β-alanine at pH 3.…”

“…The fluorescence emission profile showed excitation dependent emission spectra of carbon dots synthesized using CA + β-alanine at pH 3. With an increase of excitation wavelength from 335 to 440 nm, the emission peak shifts along with variation in the intensity 16 , giving longer wavelength photoluminescence 18 . Maximum emission peak for CDs is 425 nm upon excitation at 375 nm which is similar to other carbon dots and emits blue fluorescence 16 , 19 .…”

“…CDs synthesized using water at pH 3 had a zeta-potential of −5.46 ± 5.68 mV when measured using Malvern Zetasizer Nano-ZS ZEN 3600 16 . This negative charge is due to the presence of two negatively charged functional groups (C=O and C–O) at the surface of the synthesized CDs which provide sufficient colloidal stability to CDs 20 , 21 .…”