Enhanced Antibacterial Activity against <i>Escherichia coli</i> Based on Cationic Carbon Dots Assembling with 5-Aminolevulinic Acid
Jingfang Shangguan, Zhenjing Wu, Chengjie Qiao, Yuyang Zhang, Lin Li, Qilu Li, Yiqiao Gao, Huijuan Yan, Wei Liu
Abstract
High Resolution Image Download MS PowerPoint Slide Carbon dots (CDs) with positive surface charges are considered one of the encouraging nanomedications for antibacterial applications. However, due to the distinctive membrane structure of Gram-negative bacteria, cationic CDs with relatively high concentrations are usually required for effective treatment, which might bring out serious safety issues at high doses. Therefore, it is of substantial significance to improve the killing efficiency of cationic CDs on Gram-negative bacteria at appropriately low concentrations. In this work, optimized cationic CDs (bPEI 25 000 -CDs) were prepared via a hydrothermal method with citric acid and branched PEI 25000, which offered a positive surface potential, elimination abilities against Escherichia coli, and relatively high biosafety. The optimized bPEI 25 000 -CDs can further assemble with the clinical photodynamic therapy (PDT) drug 5-aminolevulinic acid (5-ALA) through electrostatic interaction. Moreover, compared with bPEI 25 000 -CDs and 5-ALA, the bacterial survival rate was significantly reduced by the ALA-bPEI 25 000 -CD-induced PDT effect. Even when the dose of bPEI 25 000 -CD carrier was halved, the bacterial survival could be reduced by 44.4% after light exposure compared to those incubated in the dark. The investigation of the bacterial morphology, membrane potential, and intracellular ROS production suggested that the enhanced antibacterial activity may be due to the membrane dysfunction and cell damage resulting from the high interaction between positively charged ALA-bPEI 25 000 -CDs and the bacterial cell membrane. Meanwhile, the cationic ALA-bPEI 25 000 -CDs may facilitate the cellular uptake of 5-ALA, resulting in a more efficient PDT effect. In summary, the antibacterial strategy proposed in this study will provide a novel approach for expanding the application of CD-based nanomedications.