Nanocomposite of Ag nanoparticles and catalytic fluorescent carbon dots for synergistic bactericidal activity through enhanced reactive oxygen species generation

Abstract

Microwave mediated synthesis of catalytic fluorescent carbon dots (Cdots) has been reported using biodegradable starch as precursor. The as-synthesized Cdots were then characterized using various techniques such as fluorescence spectroscopy, fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS) analysis. Interestingly, Cdots showed high catalytic activity in the photo-reduction of Ag+ to silver nanoparticles (Ag NPs). During the photo-reduction process, no additional surface passivating agents was needed to stabilize the Ag NPs. Further, TEM results indicated the formation of Cdot–Ag NP nanocomposite i.e. Ag NPs surrounded with Cdots, and the emission intensity of Cdots was significantly decreased whereas the lifetime of Cdots remained almost unaltered in the presence of Ag NPs following static quenching. Finally, combination therapy of Cdots and Ag NPs using Cdot–Ag NP nanocomposite was performed which indicated synergistic bactericidal activity against antibiotic resistant recombinant E. coli bacteria. The treatment elevated the reactive oxygen species (ROS) level as compared to its individual components. Additionally, the flow cytometer study demonstrated that combination therapy causing bacterial cell wall perforation that was possibly leading to synergistic bactericidal activity against both Gram positive and Gram negative bacteria. The presence of Cdots on the surface of the Ag NPs due to their ground state complexation, possibly facilitated electrons towards Ag NPs which enhanced the ROS production in comparison to only Ag NPs.

MIL-101 (Fe) @Ag Rapid Synergistic Antimicrobial and Biosafety Evaluation of Nanomaterials

“…Therefore, it is meaningful to use synthetic bimetallic MOF materials to inhibit bacterial growth. The growth curves of E. coli and S. aureus under normal conditions clearly show four periods of bacterial growth: delayed, logarithmic, stable, and decaying periods [ 51 , 52 , 53 , 54 , 55 ]. The progressive decrease in the logarithmic phase for different concentrations of MIL-101(Fe)@Ag (Ag 0.0127 wt%) (60, 80, 100 and 120 μg/mL), along with the decrease in the time for the bacteria to reach the plateau phase ( Figure 12 a,b), indicated that the inhibition of E. coli and S. aureus by MIL-101(Fe)@Ag (Ag 0.0127 wt%) was concentration-dependent.…”

Facile synthesis of a carbon dots and silver nanoparticles (CDs/AgNPs) composite for antibacterial application

“…Moreover, CDs play an important role in reducing silver ions and stabilizing the nanoparticles, the addition of fluorescent CDs to silver nanoparticles can increase the negative surface charge and hydrophilicity. 30 Meanwhile, the fluorescent CDs could be quenched by silver nanoparticles due to their proximity, resulting in surface plasmon enhanced energy transfer from CDs to AgNPs. 31 Currently, a great deal of effort has been put into the synthetic process of CDs/AgNPs composite, however, a series of reducing agents, such as sodium borohydride, sodium citrate, citric acid and so on, are still used to assist in reducing silver ions.…”

State of Art Technology: Synthesis of Carbon Dots and Their Potential Applications in Biomedical, Research and Environmental Remediation

“…The use of biodegradable starch as precursor has been documented by Verma et al, using microwave-controlled synthesis of catalytic fluorescent carbon dots. The synthesized C-dots demonstrated catalytic activity in the Ag NPs' photo-reduction [185]. This treatment of Ag NPs and C-dots has been observed to be highly bactericidal, with substantially low silver concentration compared to Ag NPs.…”