Highly Stable Graphene-Based Nanocomposite (GO–PEI–Ag) with Broad-Spectrum, Long-Term Antimicrobial Activity and Antibiofilm Effects

Various silver nanoparticle (AgNP)-decorated graphene oxide (GO) nanocomposites (GO–Ag) have received increasing attention owing to their antimicrobial activity and biocompatibility; however, their aggregation in physiological solutions and the generally complex synthesis methods warrant improvement. This study aimed to synthesize a polyethyleneimine (PEI)-modified and AgNP-decorated GO nanocomposite (GO–PEI–Ag) through a facile approach through microwave irradiation without any extra reductants and surfactants; its antimicrobial activity was investigated on Gram-negative/-positive bacteria (including drug-resistant bacteria) and fungi. Compared with GO–Ag, GO–PEI–Ag acquired excellent stability in physiological solutions and electropositivity, showing substantially higher antimicrobial efficacy. Moreover, GO–PEI–Ag exhibited particularly excellent long-term effects, presenting no obvious decline in antimicrobial activity after 1 week storage in physiological saline and repeated use for three times and the lasting inhibition of bacterial growth in nutrient-rich culture medium. In contrast, GO–Ag exhibited a >60% decline in antimicrobial activity after storage. Importantly, GO–PEI–Ag effectively eliminated adhered bacteria, thereby preventing biofilm formation. The primary antimicrobial mechanisms of GO–PEI–Ag were evidenced as physical damage to the pathogen structure, causing cytoplasmic leakage. Hence, stable GO–PEI–Ag with robust, long-term antimicrobial activity holds promise in combating public-health threats posed by drug-resistant bacteria and biofilms

Stable Nanocomposite Based on PEGylated and Silver Nanoparticles Loaded Graphene Oxide for Long-Term Antibacterial Activity

The increasing occurrence of antibiotic-resistant pathogens, especially superbugs, is compromising the efficacy of traditional antibiotics. Silver nanoparticles (AgNPs) loaded graphene oxide (GO) nanocomposite (GO-Ag) has drawn great interest as a promising alternative antibacterial material. However, GO-Ag nanocomposite often irreversibly aggregates in physiological solutions, severely influencing its antibacterial capacity and practical application. Herein, a PEGylated and AgNPs loaded GO nanocomposite (GO-PEG-Ag) is synthesized through a facile approach utilizing microwave irradiation, while avoiding extra reducing agents. Through PEGylation, the synthesized GO-PEG-Ag nanocomposite dispersed stably over one month in a series of media and resisted centrifugation at 10 000×<i>g</i> for 5 min, which would benefit effective contact between the nanocomposite and the bacteria. In contrast, GO-Ag aggregated within 1 h of dispersion in physiological solutions. In comparison with GO-Ag, GO-PEG-Ag showed stronger bactericidal capability toward not only normal Gram-negative/positive bacteria such as <i>E. coli</i> and <i>S. aureus</i> (∼100% of <i>E. coli</i> and ∼95.3% of <i>S. aureus</i> reduction by 10 μg/mL nanocomposite for 2.5 h), but also superbugs. Moreover, GO-PEG-Ag showed lower cytotoxicity toward HeLa cells. Importantly, GO-PEG-Ag presented long-term antibacterial effectiveness, remaining ∼95% antibacterial activity after one-week storage in saline solution versus <35% for GO-Ag. The antibacterial mechanisms of GO-PEG-Ag were evidenced as damage to the bacterial structure and production of reactive oxygen species, causing cytoplasm leakage and metabolism decrease. The stable GO-PEG-Ag nanocomposite with powerful and long-term antibacterial capability provides a more practical and effective strategy for fighting superbugs-including pathogen threats in biomedicine and public health

Dendrogram displaying the PFGE profiles of the 43 isolates.

<p>The strain number, origin, source, sequence type (ST), and H₂S phenotype are shown for each strain. +, H₂S-producing isolate; −, non-H₂S-producing isolate.</p

Effect of various viruses on (A, B) IIP_max and (C, D) IIP_atoxic toward (A, C) HIV_NL4-3 and (B, D) mutant viruses.

<p>IIP was calculated using equation (1), with the concentrations used being peak plasma concentrations for IIP_max and the maximum nontoxic concentration for IIP_atoxic. Fractional changes in IIP were calculated using equation (3). The drugs tested are grouped by class: NRTIs, NNRTI, and PIs. Within each class, different shapes indicate the various mutants.</p

Epitope Binning Assay Using an Electron Transfer-Modulated Aptamer Sensor

Surface plasmon resonance and quartz crystal microbalance are workhorses of protein–DNA interaction research for over 20 years, providing ways to quantitatively determine the protein–DNA binding. However, the cost, necessary technical expertise, and severe nonspecific adsorption poses barriers to their use. Convenient and effective techniques for the measurement of protein–DNA binding affinity and the epitope binning between DNA and proteins for developing highly sensitive detection platform remain challenging. Here, we develop a binding-induced alteration in electron transfer kinetics of the redox reporter labeled (methylene blue) on DNA aptamer to measure the binding affinity between prostate-specific antigen (PSA) and aptamer. We demonstrate that the binding of PSA to aptamer decreases the electron transfer rate of methylene blue for ∼45%. Further, we identify the best pairwise selection of aptamers for developing sandwich assay by sorting from 10 pairwise modes with the PSA detection limit of 500 ng/mL. Our study provides promising ways to analyze the binding affinity between ligand and receptor and to sort pairwise between aptamers or antibodies for the development of highly sensitive sandwich immunoassays

Sequence alignment of the <i>phs</i> gene and the protein.

<p>A nonsense mutation at position 208 of the <i>phsA</i> gene results in the replacement of a sense codon (CAG) with a termination codon (UAG) leading to the premature termination of <i>phsA</i>. The first sequence, <i>phsA</i>, is based on <i>S</i>. enterica serotype Typhimurium strain LT2 (GenBank AE006468). *, termination codon; +, H₂S-producing isolate; −, non-H₂S-producing isolate.</p

Curves of the dose-response of selected drugs.

<p>x axes indicate log of drug concentration (nM), y axes indicate the inhibitor rate of virus (%). (A) is the curve of the dose-response of 3 viruses (V179E\H221Y\T215Y, V179E\Y181C\T215Y and WT _NL4.3) in d4T. (B) is the curve of the dose-response of 2 viruses (K103N\H221Y\Y181C\T215Y and WT _NL4.3) in EFV. (C) is the curve of the dose-response of 3 viruses (G48V\I54V\V82A, M46I\N88S and WT _NL4.3) in IDV. (D) is the curve of the dose-response of 3 viruses (G48V\I54V, V82A and WT _NL4.3) in SQV.</p

The methodology of <i>Salmonella</i> detection procedure.

<p>The methodology of <i>Salmonella</i> detection procedure.</p

Effects of various resistance mutations on (A) IC50 and (B) slope, as calculated from dose-response curves.

<p>Fold changes in IC50 for mutants were relative to those for the wild-type virus, and fractional changes in slope were computed using equation (2). The drugs tested are grouped by class: NRTIs, NNRTI, and PIs. Within each class, different shapes indicate the various mutants.</p

Primers for PCR amplification of the <i>phsABC</i> genes.

<p>Primers for PCR amplification of the <i>phsABC</i> genes.</p