Size-dependent Antibacterial Activity Research Articles

Size-dependent antibacterial of carbon dots by selective absorption and differential oxidative stress of bacteria

Carbon dots (CDs), as one kind of zero-dimensional carbon-based nanomaterials, show great potential in combating emerging infectious diseases and antimicrobial infections. CDs with outstanding optical properties and benign biocompatibility have been reported as excellent antibacterial agents. However, few reports were focused on the relationship between the CDs’ size and their antibacterial activity. Herein, the desired CDs (VCDs) were fabricated by a one-step electrochemical oxidation method using l-ascorbic acid as raw material, and four types of VCDs with different sizes were obtained by adjusting the reaction times. The effectiveness of antibacterial activity demonstrates the VCDs display size-dependent antibacterial activity, where the VCDs-2 (average size: 2.92 nm) exhibit superior antibacterial activity to others, attributing to the synergy of the absorption capacity of bacteria to VCDs and the ROS stimulated by VCDs. The VCDs-2 could more easily penetrate bacterial cells, stimulate the production of ROS, damage the cell walls of E. coli, and inhibit the growth and reproduction of bacteria. This work helps to understand the effect of CDs’ size on antibacterial properties, and provides a direction for the design of novel antimicrobials with drug resistance.

Fish mucus stabilized iron oxide nanoparticles: fabrication, DNA damage and bactericidal activity

A facile method to produce iron oxide nanoparticles (FeO NPs) has been introduced as a part of green approach. Here, we introduce a semi-green method to fabricate FeO NPs using Channa straitus (C. straitus). The formation of FeO NPs was optimized with mucus extract (1, 2, and 3 mL) to study the size and morphology. The results reveal that the FeO NPs produced using 2 mL mucus possess the minimum size. The morphology, size, and crystallinity of nanoparticles was confirmed by UV-Vis spectroscopy (UV-Vis), X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron diffraction spectroscopy (EDS). Formation and the functional groups responsible for reduction and stabilization of nanoparticles were confirmed by UV-Vis and FTIR analysis. The synthesized FeO NPs were examined for their size dependent antibacterial activity. The FeO stabilized with mucus exhibited zone of inhibition against Escherichia coli, Streptococcus faecalis, Streptococcus oralis, Bacteroides fragilis, and Proteus vulgaris. The DNA cleavage study revealed that the FeO NPs induce cell death by apoptosis. The results of the present study suggest that the iron oxide might be used for medicinal applications especially for cancer therapeutics.

Green synthesis of poly-L-lysine-coated sericin nanoparticles and their molecular size-dependent antibacterial activity

Investigating the role of molecular size and interfacial potential dependent antimicrobial propensity of nanoparticles (NPs) against bacteria is the important goal for secure usage of NPs to any living systems. In this study, crude silk sericin protein of Antheraea mylitta cocoon was fractionated into three different molecular size-ranges fractions such as fraction-1 (50−300 kDa), fraction-2 (30−50 kDa) and fraction-3 (10−30 kDa), and used to prepare crude sericin nanoparticles (CRSNPs), as well as fraction specific negative surface potential nanoparticles : n-SNP1, n-SNP2 and n-SNP3, respectively. SNPs were coated with poly-l-lysine to make the surface potential positive (p-SNPs) and confirmed through UV–vis spectroscopy, FTIR, zeta sizer and zeta potential measurement. The shape and sizes of all SNPs were determined by electron microscopy and found spherical in shape having diameter ranging from 110−165 nm (CRSNPs), 66−85 nm (SNP1), 33−49 nm (SNP2) and 14−24 nm (SNP3) for n-SNPs and p-SNPs, respectively. Evaluation of antibacterial activity using different concentrations (50, 100, 200 μg/mL) of all these SNPs showed significantly more activity of p-SNPs than n-SNPs against Staphylococcus aureus and Escherichia coli. Among these, SNP2 showed the strongest antibacterial activity followed by SNP3, SNP1 and CRSNPs. Relatively higher amounts of reactive oxygen species (ROS) generation were observed after treatment of bacteria with p-SNP2 (50 μg/mL) which is non-toxic to human cells. FE-SEM analysis showed more disruption of bacterial cell membrane after treatment with p-SNPs than n-SNPs. All these data suggested that molecular size and interfacial potential of SNPs enhance ROS generation to exert their antibacterial activity.

Nanoparticle Size-Dependent Antibacterial Activities in Natural Minerals

The size-dependent antibacterial activities of three minerals namely; alkali feldspar, calcite and stibnite are reported as examined individually against Escherichia coli and Staphylococcus aureus by evaluating minimum inhibitory concentration (MIC) with colony counting method, along with cell survivability assay (MTT). Each of these minerals were grinded into fine-size fractions-S1 (bulk), S₂ (ball milled) and S3 (nanosized) and spectroscopically characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and ultraviolet-visible (UV-Vis) spectroscopy. Antibacterial activity was found to be highest in the nanosized (S3) minerals. Interaction between bacteria and nanosized mineral samples produce intracellular reactive oxygen species (ROS), which might cause higher bacterial mortality. The penetration due to nano-dimension is another significant observation as evidenced by bacterial FESEM micrographs. The current findings thus provide a pathway for future research on antibacterial products retrievable from widely available geological materials. The size dependant antibacterial activity of naturally formed minerals is a new insight to reduce bacterial contamination in living systems.

Chitosan encapsulated water-soluble silver bionanocomposite for size-dependent antibacterial activity

Surface coating of metallic nanoparticles, designed for antibacterial effect, is a major challenge. Herein we report a one-pot, facile, green synthesis of silver bionanocomposite (AgBNC) with water-soluble chitosan (stabilizer) in the presence of citric acid (reducing agent). Three different AgBNC samples with varying sizes (average 39, 51 and 58 nm) were synthesized by varying the concentration of silver nitrate (AgNO3, precursor) alone. It was found that size of the AgBNC increased with increasing concentration of AgNO3. Particle size and its dispersion, surface morphology, and stability up to 3 months were confirmed by DLS, UV–Vis and FTIR spectroscopy, FESEM and TEM study. Furthermore, theoretical simulation using Density Functional Theory (DFT) was performed in order to investigate the mode of interaction of chitosan associated with silver nanoparticles (AgNP). Structural studies imply that though the amino and hydroxyl groups are responsible for stabilization and binding of AgNPs with chitosan, predominant interaction occurs through the amino group of the latter. Size-dependent antibacterial activity of the synthesized AgBNC against one gram-positive (Bacillus subtilis) and one gram-negative (Escherichia coli) bacteria indicated that it had antibacterial effect against both the bacteria and also its toxicity increased with decreasing size of the AgBNC. Bacterial growth curve indicated that synthesized AgBNC maintained its antibacterial activity up to 12 h where efficiency of AgBNC against gram-positive bacteria is more than against gram-negative bacteria.

Size-dependent antibacterial activity of copper nanoparticles against Xanthomonas oryzae pv. oryzae – A synthetic and mechanistic approach

Xanthomonas oryzae pv. oryzae (X. oryzae), causing devastating bacterial leaf blight (BLB) disease in rice, is fast developing resistance against many available antibiotics, warranting an urgent need to develop an alternative control strategy. In this manuscript, we report copper nanoparticles (CuNPs) as an effective antibacterial agent against X. oryzae. We synthesized four different sized CuNPs in a narrow-size range (CuNP-1 – 18 nm, CuNP-2 – 24 nm, CuNP-3 – 28 nm and CuNP-4 – 33 nm) by chemical reduction method. The physicochemical characterizations of CuNPs were done by X-ray diffraction (XRD), dynamic light scattering (DLS), UV–Visible Spectroscopy (UV–Vis Spectroscopy) and transmission electron microscopy (TEM). The antibacterial activity of the CuNPs was found to be size and concentration dependent. Among all the CuNPs, CuNP-3 exerted the best antibacterial efficiency against X. oryzae due to the increased production of reactive oxygen radicals than the others. It also displayed increased activity compared to commercial antibiotic streptomycin sulphate.

Size dependent optical and antibacterial properties of Ag3PO4 synthesized by facile precipitation and colloidal approach in aqueous solution

Present study reports the synthesis of Ag3PO4 nano/mircoparticles by facile precipitation and colloidal synthesis approach in aqueous solution. Importantly, the presented approach does not require complicated instruments, difficult processes, and harsh conditions such as high temperature and high pressure. The obtained samples were characterized using SEM with EDS, XRD, TEM with HR-TEM and SAED, and FTIR. Their optical properties were studied using UV–vis diffusive reflectance spectra. Size dependent antibacterial activity towards Gram-positive (S. aureus) and Gram-negative (E. coli, K. pneumoniae and P. aeruginosa) bacteria. Experimental results showed that the antibacterial performances of nanoparticles obtained by mixing 0.01M of each reactant (colloidal synthesis approach) were found to be much higher than that of other formulation under identical conditions.

Effect of different physicochemical conditions on the synthesis of silver nanoparticles using fungal cell filtrate of Aspergillus oryzae (MTCC No. 1846) and their antibacterial effect

Synthesis of silver nanoparticles (AgNPs) under different physicochemical conditions like concentration of silver nitrate (AgNO3), pH and temperature, using fungal cell filtrate of Aspergillus oryzae (MTCC No. 1846) and its antibacterial properties were demonstrated. When fungal cell filtrate having neutral pH was exposed to different concentrations of aqueous solution AgNO3 (1–10 mM), formation of stable AgNPs of different sizes was observed. The size of the AgNPs decreased with the increase of AgNO3 concentration from 1 mM to 8 mM, however, the particles size increased with the increase of AgNO3 concentration from 9 mM to 10 mM. When fungal cell filtrate exposed to aqueous solution of 1 mM AgNO3 at different pH (4–10), the silver ions (Ag+) were reduced leading to the formation of stable AgNPs of different sizes. The size of the AgNPs decreased with the increase of alkaline conditions. When aqueous solution of 1mM AgNO3 with fungal cell filtrate, having neutral pH, was exposed to different temperatures (10, 30, 50, 70 and 90 °С), formation of stable AgNPs having different sizes were obtained. The size of the AgNPs decreased with the increase of temperature. Synergetic effect with antibiotics and size dependent antibacterial activities were also demonstrated against Escherichia coli (MTCC 1687), Staphylococcus aureus (MTCC 737), Bacillus subtilis (MTCC 441) and Klebseilla pneumoniae (MTCC 4030). The formation AgNPs was characterized by UV–vis spectrophotometer. Transmission electron microscope (TEM) confirmed the sizes of the obtained nanoparticles. X-ray diffractometer (XRD) spectrum confirmed the formation of metallic silver. The Fourier transform infrared spectroscopy (FTIR) confirmed the presence of protein as stabilizing agent around AgNPs. Scanning electron microscope (TEM) confirmed the morphological changes in the treated bacterial organisms.

Evaluation of antibacterial, antibofilm and antioxidant activities of synthesized silver nanoparticles (AgNPs) and casein peptide fragments against Streptococcus mutans

IntroductionInappropriate antibiotic advising and consumption have been identified as the major factors in the development of antibiotic resistance in Streptococcus mutans. According to recent evidence, the microbial flora responsible for causing dental caries has developed resistance to the commercially available drugs. MethodsIn the current study, the silver nanoparticles (AgNPs) were synthesized in the presence of E. coli supernatant. Casein peptide fragments were produced by the partial proteolysis of cow milk caseins in the presence of pepsin and trypsin. Then, the antibacterial, antibiofilm and antioxidant activity of AgNPs and casein peptide fragments were assessed. The cariogenic bacterium Streptococcus mutans which is the major cause of dental caries worldwide was used as the target cells. Different spectroscopic practices and microscopic analyses were applied. ResultsThe AgNPs, with almost spherical morphology demonstrated significant antibacterial, antibiofilm and antioxidant activities. The casein hydrolysates which were obtained with the partial/precise enzymatic hydrolysis indicated a size-dependent antibacterial activity. Additionally, a significant improvement in the antibacterial activity was observed when a combined mixture of casein hydrolysates and AgNPs were applied. ConclusionA combination of casein peptide fragments and AgNPs may offer a novel practical strategy against the cariogenic bacterium S. mutans.

Antibacterial activity of biochemically capped iron oxide nanoparticles: A view towards green chemistry

A green approach to fabricate nanoparticles has been evolved as a revolutionary discipline. Eco-compatible reaction set ups, use of non-toxic materials and production of highly active biological and photocatalytic products are few benefits of this greener approach. Here, we introduce a green method to synthesize Fe oxide NPs using Punica granatum peel extract. The formation of Fe oxide NPs was optimized using different concentrations of peel extract (20mL, 40mL and 60mL) to achieve small size and better morphology. The results indicate that the FeNPs, obtained using 40mL concentration of peel extract possess the smallest size. The morphology, size and crystallinity of NPs was confirmed by implementing various techniques i.e. UV–Vis spectroscopy, X-ray diffraction, Scanning Electron Microscopy and Electron Diffraction Spectroscopy. The bio-chemicals responsible for reduction and stabilization of FeNPs were confirmed by FT-IR analysis. The biogenic FeNPs were tested for their size dependent antibacterial activity. The biogenic FeNPs prepared in 40mL extract concentrations exhibited strongest antibacterial activity against Pseudomonas aeruginosa i.e. 22 (±0.5) mm than FeNPs with 20mL and 60mL extract concentrations i.e. 18 (±0.4) mm and 14 (±0.3) mm respectively. The optimized FeNPs with 40mL peel extract are not only highly active for ROS generation but also show no hemolytic activity. Thus, FeNPs synthesized using the greener approach are found to have high antibacterial activity along with biocompatibility. This high antibacterial activity can be referred to small size and large surface area.

Size-controlled synthesis of Cu2O nanoparticles: size effect on antibacterial activity and application as a photocatalyst for highly efficient H2O2 evolution

Size-controlled synthesis and size-dependent antibacterial activity of Cu2O nanoparticles with high efficiency for H2O2 evolution.

Facile synthesis of silver nanoparticles and its antibacterial activity against Escherichia coli and unknown bacteria on mobile phone touch surfaces/computer keyboards

In recent years, there has been significant interest in the development of novel metallic nanoparticles using various top-down and bottom-up synthesis techniques. Kenaf is a huge biomass product and a potential component for industrial applications. In this work, we investigated the green synthesis of silver nanoparticles (AgNPs) by using kenaf (Hibiscus cannabinus) cellulose extract and sucrose, which act as stabilizing and reducing agents in solution. With this method, by changing the pH of the solution as a function of time, we studied the optical, morphological and antibacterial properties of the synthesized AgNPs. In addition, these nanoparticles were characterized by Ultraviolet–visible spectroscopy, transmission electron microscopy (TEM), field-emission scanning electron microscopy, Fourier transform infrared (FTIR) spectroscopy and energy-dispersive X-ray spectroscopy (EDX). As the pH of the solution varies, the surface plasmon resonance peak also varies. A fast rate of reaction at pH 10 compared with that at pH 5 was identified. TEM micrographs confirm that the shapes of the particles are spherical and polygonal. Furthermore, the average size of the nanoparticles synthesized at pH 5, pH 8 and pH 10 is 40.26, 28.57 and 24.57 nm, respectively. The structure of the synthesized AgNPs was identified as face-centered cubic (fcc) by XRD. The compositional analysis was determined by EDX. FTIR confirms that the kenaf cellulose extract and sucrose act as stabilizing and reducing agents for the silver nanoparticles. Meanwhile, these AgNPs exhibited size-dependent antibacterial activity against Escherichia coli (E. coli) and two other unknown bacteria from mobile phone screens and computer keyboard surfaces.

Particle Size-Dependent Antibacterial Activity and Murine Cell Cytotoxicity Induced by Graphene Oxide Nanomaterials

Recent studies have indicated that graphene and its derivative graphene oxide (GO) engage in a wide range of antibacterial activities with limited toxicity to human cells. Here, we systematically evaluate the dependence of GO toxicity on the size of the nanoparticles used in treatments: we compare the cytotoxic effects of graphene quantum dots (GQDs, <15 nm), small GOs (SGOs, 50–200 nm), and large GOs (LGOs, 0.5–3 μm). We synthesize the results of bacterial colony count assays and SEM-based observations of morphological changes to assess the antibacterial properties that these GOs bring into effect againstE. coli. We also use Live/Dead assays and morphological analysis to investigate changes to mammalian (Murine macrophage-like Raw 264.7) cells induced by the presence of the various GO particle types. Our results demonstrate that LGOs, SGOs, and GQDs possess antibacterial activities and cause mammalian cell cytotoxicity at descending levels of potency. Placing our observations in the context of previous simulation results, we suggest that both the lateral size and surface area of GO particles contribute to cytotoxic effects. We hope that the size dependence elucidated here provides a useful schematic for tuning GO-cell interactions in biomedical applications.

Highly stable and re-dispersible nano Cu hydrosols with sensitively size-dependent catalytic and antibacterial activities.

Highly stable monodispersed nano Cu hydrosols were facilely prepared by an aqueous chemical reduction method through selecting copper hydroxide (Cu(OH)2) as the copper precursor, poly(acrylic acid) (PAA) and ethanol amine (EA) as the complexing agents, and hydrazine hydrate as the reducing agent. The size of the obtained Cu colloidal nanoparticles was controlled from 0.96 to 26.26 nm by adjusting the dosage of the copper precursor. Moreover, the highly stable nano Cu hydrosols could be easily concentrated and re-dispersed in water meanwhile maintaining good dispersibility. A model catalytic reaction of reducing p-nitrophenol with NaBH4 in the presence of nano Cu hydrosols with different sizes was performed to set up the relationship between the apparent kinetic rate constant (kapp) and the particle size of Cu catalysts. The experimental results indicate that the corresponding kapp showed an obvious size-dependency. Calculations revealed that kapp was directly proportional to the surface area of Cu catalyst nanoparticles, and also proportional to the reciprocal of the particle size based on the same mass of Cu catalysts. This relationship might be a universal principle for predicting and assessing the catalytic efficiency of Cu nanoparticles. The activation energy (Ea) of this catalytic reaction when using 0.96 nm Cu hydrosol as a catalyst was calculated to be 9.37 kJ mol(-1), which is considered an extremely low potential barrier. In addition, the synthesized nano Cu hydrosols showed size-dependent antibacterial activities against Pseudomonas aeruginosa (P. aeruginosa) and the minimal inhibitory concentration of the optimal sample was lower than 5.82 μg L(-1).

Antibacterial activity of silver: The role of hydrodynamic particle size at nanoscale

Silver shows the highest antimicrobial activities amongst all metals. It is better than many first line antibiotics. The antimicrobial properties of silver can be tuned by altering its physical and surface properties. Researchers have demonstrated enhancement in the antibacterial properties of silver with decreasing particle size from bulk to nano. In the present article, we study the effect of particle size of silver at nanoscale on their antimicrobial properties. Two samples of silver nanoparticles (SNPs) of same physical size (≈8 nm) but different hydrodynamic size (59 and 83 nm) are prepared by chemical reduction of AgNO3 with oleylamine followed by phase transfer with triblock copolymer Pluronic F-127. Their antimicrobial properties are investigated by microdilution method against clinically important strains of gram positive (S. aureus and B. megaterium) and gram negative (P. vulgaris and S. sonnei) bacteria. Nearly 38-50% enhancement in the antibacterial action of SNPs was observed when their hydrodynamic size was reduced to 59 nm from 83 nm. It has been observed that the antibacterial action of SNPs was governed by their hydrodynamic size and not by their crystallite and physical size. The phenomenological model was also proposed which makes an attempt to explain the microscopic mechanism responsible for the size dependent antibacterial activities of silver.

Comparison of antibacterial activity of Ag nanoparticles synthesized from leaf extract of Parthenium hystrophorus L in aqueous media and Gentamicin sulphate: in-vitro

Monodisperse silver (Ag) nanoparticles were synthesized by using Parthenium hystrophorus L leaf extract in aqueous media. The synthesized nanoparticles were characterized by using UV-vis spectrophotometer, X-ray diffracto-meter (XRD), transmission electron microscope (TEM), and dynamics light scattering (DLS). Size-dependent antibacterial activities of Ag nanoparticles were tested against Gram negative Pseudomonas aeruginosa and Gram positive Staphylococcus aureus. Ag nanoparticles having 20 ± 2 nm size in diameter show maximum zone of inhibition (23 ± 2.2 mm) in comparison to 40 nm and 70 nm diameter nanoparticles for Pseudomonas aeruginosa. The zone of inhibition against Staphylococcus aureus were 19 ± 1.8 mm, 15 ± 1.5 mm and 11 ± 1 mm for 20 nm, 40 nm, and 70 nm, respectively. In addition, affect of concentration of 20 nm size Ag nanoparticles on Bacillus cereus, Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus species were also reported and results were compared with 10 µg/ml dose of Gentamicin sulphate. The Parthenium hystrophorus L leaf extract capped 20 ± 2 nm Ag nanoparticles (7.5 µg/ml) shows statistically significant antibacterial activity than Gentamicin sulphate (10 µg/ml) against Staphylococcus aureus.

Highly Selective Antibacterial Activities of Silver Nanoparticles Against <I>Bacillus subtilis</I>

Silver nanoparticles (AgNPs) with different sizes (5, 15 and 55 nm) were synthesized via simple method, and characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray microanalysis (EDX) and ultraviolet-visible absorption spectroscopy (UV-Vis). The antibacterial activities of the prepared AgNPs against Gram-negative Escherichia coli (E. coli), Gram-positive Staphylococcus aureus (S. aureus) and Bacillus subtilis (B. subtilis) were evaluated by inhibition zone, inhibition curve, and colony counting methods. The results showed that the AgNPs exhibited obvious bacterium-selective and size-dependent antibacterial activities. The Gram-positive bacteria S. aureus and B. subtilis were more sensitive to AgNPs than Gram-negative bacterium E. coli. Interestingly, AgNPs displayed remarkably antibacterial activities against B. subtilis among Gram-positive bacteria, regardless of whether in separately or cocultured bacteria. It also showed that AgNPs with 5 nm in size presented the highest antibacterial activity against both Gram-negative and Gram-positive bacteria. The effects of AgNPs on the membrane leakage of the reducing sugars from three bacteria were also measured by 3,5-dinitrosalicylic acid method. The leakage amount of reducing sugars from B. subtilis was the highest among the tested bacteria, indicating that AgNPs could damage the structure of bacteria cell membrane and resulted in the leakage of reducing sugars, leading to the death of bacteria.

Size-dependent antibacterial activities of silver nanoparticles against oral anaerobic pathogenic bacteria

Dental caries and periodontal disease are widespread diseases for which microorganism infections have been identified as the main etiology. Silver nanoparticles (Ag Nps) were considered as potential control oral bacteria infection agent due to its excellent antimicrobial activity and non acute toxic effects on human cells. In this work, stable Ag Nps with different sizes (~5, 15 and 55nm mean values) were synthesized by using a simple reduction method or hydrothermal method. The Nps were characterized by powder X-ray diffraction, transmission electron microscopy and UV-vis absorption spectroscopy. The antibacterial activities were evaluated by colony counting assay and growth inhibition curve method, and corresponding minimum inhibitory concentration (MIC) against five anaerobic oral pathogenic bacteria and aerobic bacteria E. coli were determined. The results showed that Ag Nps had apparent antibacterial effects against the anaerobic oral pathogenic bacteria and aerobic bacteria. The MIC values of 5-nm Ag against anaerobic oral pathogenic bacteria A. actinomycetemcomitans, F. nuceatum, S. mitis, S. mutans and S. sanguis were 25, 25, 25, 50 and 50μg/mL, respectively. The aerobic bacteria were more susceptible to Ag NPs than the anaerobic oral pathogenic bacteria. In the mean time, Ag NPs displayed an obvious size-dependent antibacterial activity against the anaerobic bacteria. The 5-nm Ag presents the highest antibacterial activity. The results of this work indicated a potential application of Ag Nps in the inhibition of oral microorganism infections.

Lateral Dimension-Dependent Antibacterial Activity of Graphene Oxide Sheets

Graphene oxide (GO) is a promising precursor to produce graphene-family nanomaterials for various applications. Their potential health and environmental impacts need a good understanding of their cellular interactions. Many factors may influence their biological interactions with cells, and the lateral dimension of GO sheets is one of the most relevant material properties. In this study, a model bacterium, Escherichia coli ( E. coli ), was used to evaluate the antibacterial activity of well-dispersed GO sheets, whose lateral size differs by more than 100 times. Our results show that the antibacterial activity of GO sheets toward E. coli cells is lateral size dependent. Larger GO sheets show stronger antibacterial activity than do smaller ones, and they have different time- and concentration-dependent antibacterial activities. Large GO sheets lead to most cell loss after 1 h incubation, and their concentration strongly influences antibacterial activity at relative low concentration (<10 μg/mL). In contrast, when incubating with small GO sheets up to 4 h, the inactivation rate of E. coli cells continues increasing. The increase of small GO sheet concentration also results in persistent increases in their antibacterial activity. In this study, GO sheets with different lateral sizes are all well dispersed, and their oxidation capacity toward glutathione is similar, consistent with X-ray photoelectron spectroscopy and ultraviolet-visible absorption spectroscopy results. This suggests the lateral size-dependent antibacterial activity of GO sheets is caused by neither their aggregation states, nor oxidation capacity. Atomic force microscope analysis of GO sheets and cells shows that GO sheets interact strongly with cells. Large GO sheets more easily cover cells, and cells cannot proliferate once fully covered, resulting in the cell viability loss observed in the followed colony counting test. In contrast, small GO sheets adhere to the bacterial surfaces, which cannot effectively isolate cells from environment. This study highlights the importance of tailoring the lateral dimension of GO sheets to optimize the application potential with minimal risks for environmental health and safety.

Size-dependent antimicrobial properties of CuO nanoparticles against Gram-positive and -negative bacterial strains

BackgroundCuO is one of the most important transition metal oxides due to its captivating properties. It is used in various technological applications such as high critical temperature superconductors, gas sensors, in photoconductive applications, and so on. Recently, it has been used as an antimicrobial agent against various bacterial species. Here we synthesized different sized CuO nanoparticles and explored the size-dependent antibacterial activity of each CuO nanoparticles preparation.MethodsCuO nanoparticles were synthesized using a gel combustion method. In this approach, cupric nitrate trihydrate and citric acid were dissolved in distilled water with a molar ratio of 1:1. The resulting solution was stirred at 100°C, until gel was formed. The gel was allowed to burn at 200°C to obtain amorphous powder, which was further annealed at different temperatures to obtain different size CuO nanoparticles. We then tested the antibacterial properties using well diffusion, minimum inhibitory concentration, and minimum bactericidal concentration methods.ResultsXRD spectra confirmed the formation of single phase CuO nanoparticles. Crystallite size was found to increase with an increase in annealing temperature due to atomic diffusion. A minimum crystallite size of 20 nm was observed in the case of CuO nanoparticles annealed at 400°C. Transmission electron microscopy results corroborate well with XRD results. All CuO nanoparticles exhibited inhibitory effects against both Gram-positive and -negative bacteria. The size of the particles was correlated with its antibacterial activity.ConclusionThe antibacterial activity of CuO nanoparticles was found to be size-dependent. In addition, the highly stable minimum-sized monodispersed copper oxide nanoparticles synthesized during this study demonstrated a significant increase in antibacterial activities against both Gram-positive and -negative bacterial strains.