The synthesis of chitosan-based silver nanoparticles and their antibacterial activity

Chitosan-based silver nanoparticles were synthesized by reducing silver nitrate salts with nontoxic and biodegradable chitosan. The silver nanoparticles thus obtained showed highly potent antibacterial activity toward both Gram-positive and Gram-negative bacteria, comparable with the highly active precursor silver salts. Silver-impregnated chitosan films were formed from the starting materials composed of silver nitrate and chitosan via thermal treatment. Compared with pure chitosan films, chitosan films with silver showed both fast and long-lasting antibacterial effectiveness against Escherichia coli. The silver antibacterial materials prepared in our present system are promising candidates for a wide range of biomedical and general applications.     

Antimicrobial activity of highly stable silver nanoparticles embedded in agar-agar matrix as a thin film

Highly stable silver nanoparticles (Ag NPs) in agar-agar (Ag/agar) as inorganic-organic hybrid were obtained as free-standing film by in situ reduction of silver nitrate by ethanol. The antimicrobial activity of Ag/agar film on Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), and Candida albicans (C. albicans) was evaluated in a nutrient broth and also in saline solution. In particular, films were repeatedly tested for antimicrobial activity after recycling. UV-vis absorption and TEM studies were carried out on films at different stages and morphological studies on microbes were carried out by SEM. Results showed spherical Ag NPs of size 15-25 nm, having sharp surface plasmon resonance (SPR) band. The antimicrobial activity of Ag/agar film was found to be in the order, C. albicans > E. coli > S. aureus, and antimicrobial activity against C. albicans was almost maintained even after the third cycle. Whereas, in case of E. coli and S. aureus there was a sharp decline in antimicrobial activity after the second cycle. Agglomeration of Ag NPs in Ag/agar film on exposure to microbes was observed by TEM studies. Cytotoxic experiments carried out on HeLa cells showed a threshold Ag NPs concentration of 60 μg/mL, much higher than the minimum inhibition concentration of Ag NPs (25.8 μg/mL) for E. coli. The mechanical strength of the film determined by nanoindentation technique showed almost retention of the strength even after repeated cycle.     

Antibiofilm and antimicrobial activities of green synthesized silver nanoparticles using marine red algae Gelidium corneum

In our study, green synthesis of silver nanoparticles was carried out using a red algae Gelidium corneum extract as reducing agent. The obtained silver nanoparticles were characterized by UV–vis, TEM, XRD, FTIR and ICP-MS measurements. FTIR measurements indicated the possible functional groups responsible for the stabilization and reduction of nanoparticles, while XRD analysis results explained the crystalline structure of the particles with centric cubic geometry. TEM micrographs showed that the size of the nanoparticles was between 20–50 nm. According to the broth microdilution test results, AgNPs showed a high antimicrobial activity with very low MIC values (0.51 μg/ml for Candida albicans yeast and 0.26 μg/ml for Escherichia coli bacteria). The different ultrastructural effects of silver nanoparticles on yeast and bacterial cells were observed by TEM. Antibiofilm efficacy studies were also examined in two stages as prebiofilm and postbiofilm effect. In prebiofilm effect studies, AgNPs (0.51 μg/ ml) exhibited 81% reducing effect on biofilm formation. The highest reduction rate in postbiofilm studies was 73.5% and this was achieved with 2.04 μg/ml AgNPs. Our data support that the silver nanoparticles obtained by this environmentally friendly process have potential to be used for industrial and therapeutic purposes.     

Shape-Controlled Synthesis of Silver Nanoparticles for Plasmonic and Sensing Applications

The localized surface plasmon resonance of a silver nanoparticle is responsible for its ability to strongly absorb and scatter light at specific wavelengths. The absorption and scattering spectra (i.e., plots of cross sections as a function of wavelength) of a particle can be predicted using Mie theory (for a spherical particle) or the discrete dipole approximation method (for particles in arbitrary shapes). In this review, we briefly discuss the calculated spectra for silver nanoparticles with different shapes and the synthetic methods available to produce these nanoparticles. As validated in recent studies, there is good agreement between the theoretically calculated and the experimentally measured spectra. We conclude with a discussion of new plasmonic and sensing applications enabled by the shape-controlled nanoparticles.     

Preparation and antibacterial activity of chitosan nanoparticles

Chitosan nanoparticles, such as those prepared in this study, may exhibit potential antibacterial activity as their unique character. The purpose of this study was to evaluate the in vitro antibacterial activity of chitosan nanoparticles and copper-loaded nanoparticles against various microorganisms. Chitosan nanoparticles were prepared based on the ionic gelation of chitosan with tripolyphosphate anions. Copper ions were adsorbed onto the chitosan nanoparticles mainly by ion-exchange resins and surface chelation to form copper-loaded nanoparticles. The physicochemical properties of the nanoparticles were determined by size and zeta potential analysis, atomic force microscopy (AFM), FTIR analysis, and XRD pattern. The antibacterial activity of chitosan nanoparticles and copper-loaded nanoparticles against E. coli, S. choleraesuis, S. typhimurium, and S. aureus was evaluated by calculation of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). Results show that chitosan nanoparticles and copper-loaded nanoparticles could inhibit the growth of various bacteria tested. Their MIC values were less than 0.25 microg/mL, and the MBC values of nanoparticles reached 1 microg/mL. AFM revealed that the exposure of S. choleraesuis to the chitosan nanoparticles led to the disruption of cell membranes and the leakage of cytoplasm.     

Phytosynthesis of silver nanoparticles using Mangifera indica flower extract as bioreductant and their broad-spectrum antibacterial activity

The present study focused on the evaluation of antibacterial property of silver nanoparticles (AgNPs) synthesized using mango flower extract. The morphology of the synthesized AgNPs was observed under transmission electron microscopy and the particles have shown spherical shape in the range of 10–20 nm. X-ray powder diffraction analysis confirmed the crystalline nature of the AgNPs. The atomic percentage of the Ag element in the nanoparticles was about 7.58% which is greater than the other elements present in the sample. The AgNPs showed extensive lethal effect on both Gram-positive (Staphylococcus sp.) and Gram-negative (Klebsiella sp., Pantoea agglomerans, and Rahnella sp.) bacteria. The extensive lethal effect of AgNPs against clinically important pathogens demonstrated that the mango flower mediated AgNPs could be applied as potential antibacterial agent to control the bacterial population in the respective industries.     

Silver nanoparticles as a new generation of antimicrobials

Silver has been in use since time immemorial in the form of metallic silver, silver nitrate, silver sulfadiazine for the treatment of burns, wounds and several bacterial infections. But due to the emergence of several antibiotics the use of these silver compounds has been declined remarkably. Nanotechnology is gaining tremendous impetus in the present century due to its capability of modulating metals into their nanosize, which drastically changes the chemical, physical and optical properties of metals. Metallic silver in the form of silver nanoparticles has made a remarkable comeback as a potential antimicrobial agent. The use of silver nanoparticles is also important, as several pathogenic bacteria have developed resistance against various antibiotics. Hence, silver nanoparticles have emerged up with diverse medical applications ranging from silver based dressings, silver coated medicinal devices, such as nanogels, nanolotions, etc.     

Green synthesis of silver nanoparticles by Conocarpus Lancifolius plant extract and their antimicrobial and anticancer activities

Due to drug addiction and the emergence of antibiotic resistance in pathogens, the disease load and medication intake have risen worldwide. The alternative treatment for drug-resistant infections is Nano formulation-based antimicrobial agents. The plant extract of Conocarpus Lancifolius fruits was used to synthesize silver nanoparticles in the current study, and it was further employed as an antimicrobial and anticancer agent. Nanoparticles have been characterized by UV–visible spectrometer revealed the notable peak of λ_max = 410–442 nm, which confirms the reduction of silver ion to elemental silver nanoparticles, and the biological moieties in the synthesis were further confirmed by FTIR analysis. The stability and crystalline nature of materials were approved by XRD analysis and expected the size of the nanomaterials of 21 to 173 nm analyzed by a nanophox particle-size analyzer. In vitro, synthesized materials act as an antibacterial agent against Streptococcus pneumonia and Staphylococcus aureus. The inhibition zones of 18 and 24 mm have been estimated to be antibacterial activity against both bacteria. The potency of up to 100% of AgNPs for bacterial strains was incubated overnight at 60 μg/ml. Based on our results, biogenic AgNPs reveal significant activity against fungal pathogen Rhizopusus stolonifera and Aspergillus flavus that cause leading infectious diseases. Additionally, nanomaterials were biocompatible and demonstrated the potential anticancer activities against MDA MB-231 cells after 24-hour exposure.     

纳米银的抗菌机制及临床应用研究

纳米银因具备抗菌谱广、效果好、安全性高等特性,其医疗制品在临床治疗方面应用广泛。现普遍认为纳米银可通过释放银离子(Ag+)和诱导活性氧自由基的表达等方式达到杀菌目的,但其发挥抗菌作用的效果受到表面正电荷和粒子直径等因素影响。本文就纳米银的抗菌机制及临床实践应用进行综述,对现有的各种抗菌材料进行分类,重点探讨纳米银对金黄色葡萄球菌、大肠埃希菌、白假丝酵母菌和铜绿假单胞菌的杀菌和抑菌原理,以及其在抗菌过程中的影响因素,并阐述了纳米银及其复合材料在临床实践中的应用,以期为纳米银抗菌应用方面的后续研究提供一些参考。     

Effect of gemini surfactant (16-6-16) on the synthesis of silver nanoparticles: A facile approach for antibacterial application

In this report, we describe the effect of Gemini surfactants1, 6-Bis (N, N-hexadecyldimethylammonium) adipate (16-6-16) on synthesis, stability and antibacterial activity of silver nanoparticles (AgNPs). The stabilizing effect of Gemini surfactant and aggregation behavior of AgNPs was evaluated by plasmonic property and morphology of the AgNPs were characterized by UV–vis spectroscopy, Dynamic Light Scattering (DLS), X-ray diffraction (XRD), High resolution transmission electron microscopy (HRTEM) and Energy dispersive X-ray analysis (EDX) techniques. Interestingly, the formation of quite mono-dispersed spherical particles was found. Apart from the stabilizing role, the Gemini surfactant has promoted the agglomeration of individual AgNPs in small assemblies whose Plasmon band features differed from those of the individual nanoparticles. The antibacterial activity of the synthesized AgNPs on Gram-negative and Gram-positive bacterium viz., E. coli and S. aureus was carried out by plate count, growth kinetics and cell viability assay. Furthermore, the mechanism of antibacterial activity of AgNPs was tested by Zeta potential and DLS analysis, to conclude that surface charge of AgNPs disrupts the cells causing cell death.     

Antioxidant,antibacterial and cytotoxic potential of silver nanoparticles synthesized using terpenes rich extract of Lantana camara L. leaves

Several attempts have been made for green synthesis of silver nanoparticles (AgNPs) using different plant extracts. Present study revealed that, antioxidant, antibacterial and cytotoxic AgNPs were synthesized using terpenes-rich extract (TRE) of environmentally notorious Lantana camara L. leaves. AgNPs were characterized by advanced techniques like UV–Visible and Infra red spectroscopy; XRD, SEM techniques as terpenes coated sphere shaped NPs with average diameter 425 nm. Further, on evaluation, AgNPs were found to exhibit dose – dependent antioxidant potential, good to moderate antibacterial activity against Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa; and toxicity on Brine shrimp (A. salinanauplii) with LD₅₀ value 514.50 µg/ml.     

Green synthesis of silver nanoparticles using Citrus limon peels and evaluation of their antibacterial and cytotoxic properties

The present work aimed to synthesis silver nanoparticles (AgNPs) using biological waste products Citrus limon peels, its characterization, antimicrobial activities and the cytotoxic effect of the synthesized green AgNPs. Characterization of the prepared AgNPs showed the formation of spherical, and few agglomerated AgNPs forms as measured by UV–visible spectrophotometer. The average size of the prepared AgNPs was 59.74 nm as measured by DLS technique. The spectrum of the synthesized AgNPs was observed at 3 KeV using the EDX. On the other hand, FTIR analysis of the green synthesized AgNPs showed the presence of alcohols, phenolics, mono-substituted alkynes, aliphatic primary amines, sodium salt, amino acid, or SiOH alcohol groups. The antimicrobial studies of the formed AgNPs showed positive activity against most of the studied human pathogenic bacteria with varying degrees. Finally, the evaluation of the cytotoxic effect of the green synthesized AgNPs were done using two types of cell lines, human breast cancer cell line (MCF-7) and human colon carcinoma cell line (HCT-116). The results revealed the concentration has a direct correlation with cell viability. The 50% inhibitory concentration (IC₅₀) of MCF-7 cell line was in of 23.5 ± 0.97 µL/100 µL, whereas the HCT-116 cell line was in 37.48 ± 5.93 µL/100 µL.     

Three-Dimensional Analysis of Scattering Field Interactions and Surface Plasmon Resonance in Coupled Silver Nanospheres

Scattering field interactions and surface plasmon resonance (SPR) in coupled silver nanospheres are simulated by using the finite-element method, which includes the influences of near-field enhancements of electric field by the particle sizes, separation distances, propagation directions, as well as the polarizations of the incident wave. The proposed structures exhibit a red- and blue-shifted that can be tuned by varying the particle sizes and the separation distances, respectively. Implications for surface-enhance Raman scattering and nano-optics are discussed in three-dimensional models. The evolution of SPR and nano-photonic device with the structural variations can be designed in a controlled manner.     

Optical Saturable Absorption in Gold Nanoparticles

In this work, we present the experimental study of the nonlinear absorption of gold nanospheres and nanorods in aqueous suspension, using picosecond white-light supercontinuum open-aperture Z-scan. We demonstrate a saturable absorption effect in all particle suspensions at low-pulse energy. In the high-pulse energy regime, the apparent reverse-saturable absorption, observed in gold nanorods, was determined to be induced by photodegradation. Using the Lorentzian deconvolution method for the absorption spectra, we explain the variations on nonlinear optical effects and prove that saturable absorption only occurs within the plasmonic bands.     

Preparation of chitosan-nylon-6 blended membranes containing silver ions as antibacterial materials

Chitosan-nylon-6 blended membranes were prepared by combining solvent evaporation and a phase inversion technique, and then used to chelate silver ions. Gram-positive bacteria (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli) were used to study the antibacterial properties of the membranes. Fourier-transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) indicated hydrogen-bond interactions between chitosan and nylon-6. From the scanning electron microscopy (SEM) pictures, it was observed that with the increase of nylon-6 content, the blended membrane gradually became a material with porous morphology. After chelating silver ions, the tensile strength of the membranes increased. The antibacterial activity with the variation of chitosan content, the pH value and the concentration of the silver nitrate solution used to prepare Ag(+)-loaded membranes were investigated systematically. The results indicated that the chitosan-nylon-6 blended membranes with Ag(+) were antibacterial to both Gram-positive bacteria and Gram-negative bacteria. The antibacterial activity improved with the increased chitosan content due to the larger amount of silver ions loaded. The antibacterial property of the chitosan-nylon-6 blended membranes could be primarily attributed to the content of chitosan and silver ions as well as the surface morphology of the membranes.     

Biosynthesis and antibacterial activity of ZnO nanoparticles using Trifolium pratense flower extract

Zinc oxide (ZnO) has broad applications in various areas. Nanoparticle synthesis using plants is an alternative to conventional physical and chemical methods. It is known that the biological synthesis of nanoparticles is gaining importance due to its simplicity, eco-friendliness and extensive antimicrobial activity. Also, in this study we report the synthesis of ZnO nanoparticles using Trifolium pratense flower extract. The prepared ZnO nanoparticles have been characterized by UV–Vis absorption spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM) with Energy dispersive X-ray analysis (EDX). Besides, this study determines the antimicrobial efficacy of the synthesized ZnO nanoparticles against clinical and standard strains of S. aureus and P. aeruginosa and standard strain of E. coli.     

Synthesis of silver nanoparticles by endosymbiont Pseudomonas fluorescens CA 417 and their bactericidal activity

The present study emphasizes on biogenic synthesis of silver nanoparticles and their bactericidal activity against human and phytopathogens. Nanoparticle synthesis was performed using endosymbiont Pseudomonas fluorescens CA 417 inhabiting Coffea arabica L. Synthesized nanoparticles were characterized using hyphenated spectroscopic techniques such as UV–vis spectroscopy which revealed maximum absorption 425 nm. Fourier transform infrared spectroscopy (FTIR) analysis revealed the possible functional groups mediating and stabilizing silver nanoparticles with predominant peaks occurring at 3346 corresponding to hydroxyl group, 1635 corresponding carbonyl group and 680 to aromatic group. X-ray diffraction (XRD) analysis revealed the Bragg’s diffraction pattern with distinct peaks at 38° 44°, 64° and 78° revealing the face-centered cubic (fcc) metallic crystal corresponding to the (111), (200), (220) and (311) facets of the crystal planes at 2θ angle. The energy dispersive X-ray spectroscopy (EDS) analysis revealed presence of high intense absorption peak at 3 keV is a typical characteristic of nano-crystalline silver which confirmed the presence of elemental silver. TEM analysis revealed the size of the nanoparticles to be in the range 5–50 nm with polydisperse nature of synthesized nanoparticles bearing myriad shapes. The particle size determined by Dynamic light scattering (DLS) method revealed average size to be 20.66 nm. The synthesized silver nanoparticles exhibited significant antibacterial activity against panel of test pathogens. The results showed Klebsiella pneumoniae (MTCC 7407) and Xanthomonas campestris to be more sensitive among the test human pathogen and phyto-pathogen respectively. The study also reports synergistic effect of silver nanoparticles in combination with kanamycin which displayed increased fold activity up to 58.3% against Klebsiella pneumoniae (MTCC 7407). The results of the present investigation are promising enough and attribute towards growing scientific knowledge on development of new antimicrobial agents to combat drug resistant microorganisms. The study provides insight on emerging role of endophytes towards reduction of metal salts to synthesize nanoparticles.     

钩状木霉生物合成纳米银及其杀菌性能

【目的】以钩状木霉为微生物材料合成纳米银粒子,并对其杀菌性能进行测定。【方法】将钩状木霉与2 mmol/L的Ag NO3溶液混合暗培养合成纳米银,采用UV-vis、XRD和TEM等方法对纳米银进行表征;利用原子吸收光谱仪和热重分析仪测定并计算银离子的转化率和纳米银的产率;以大肠杆菌和枯草芽孢杆菌为受试菌株检测纳米银的杀菌性能。【结果】钩状木霉与硝酸银混合的培养液颜色为红褐色,UV-vis图谱显示在420 nm左右出现了强的吸收峰;XRD图谱出现了4个特征性衍射峰,分别对应纳米银的4个晶面;TEM照片可以看出纳米银多数为球形,具有单分散性;粒度分布仪显示纳米银具有很窄的粒径分布,在1-13 nm之间,平均粒径为6.69 nm;根据原子光谱吸收仪测定的结果得到银的转化率为84.41%,根据热重分析结果得到纳米银的产率为67.12%;纳米银对大肠杆菌的MBC为10 mg/L,MIC为7 mg/L;对枯草芽孢杆菌的MBC为5 mg/L,MIC为4 mg/L。【结论】钩状木霉与Ag NO3溶液混合培养可以合成纳米银。合成的纳米银大小均匀,粒径小且分布很窄,具有面心立方结构,是纯净的,产率约为67.12%;纳米银对枯草芽孢杆菌的致死效果好于对大肠杆菌的致死效果。     

Surface plasmon resonance imaging on a microchip for detection of DNA-modified gold nanoparticles deposited onto the surface in a non-cross-linking configuration

We report theoretical predictions and experimental observations of the reduced detection volume with the use of surface-plasmon-coupled emission (SPCE). The effective fluorescence volume (detection volume) in SPCE experiments depends on two near-field factors: the depth of evanescent wave excitation and a distance-dependent coupling of excited fluorophores to the surface plasmons. With direct excitation of the sample (reverse Kretschmann excitation) the detection volume is restricted only by the distance-dependent coupling of the excitation to the surface plasmons. However, with the excitation through the glass prism at surface plasmon resonance angle (Kretschmann configuration), the detection volume is a product of evanescent wave penetration depth and distance-dependent coupling. In addition, the detection volume is further reduced by a metal quenching of excited fluorophores at a close proximity (below 10nm). The height of the detected volume size is 40-70nm, depending on the orientation of the excited dipoles. We show that, by using the Kretschmann configuration in a microscope with a high-numerical-aperture objective (1.45) together with confocal detection, the detection volume can be reduced to 1-2attoL. The strong dependence of the coupling to the surface plasmons on the orientation of excited dipoles can be used to study the small conformational changes of macromolecules.     

Development and evaluation of different strategies for the clean synthesis of silver nanoparticles using Yarrowia lipolytica and their antibacterial activity

An environment-friendly, cheap method, biogenic synthesis of silver nanoparticles (AgNPs) is interesting as compared to physical and chemical synthesis methods. The aim of the present study was to utilize the inherent capability of Yarrowia lipolytica as a novel biocatalyst for green production of AgNPs using different strategies, including growing cells, resting cells, and cell-free extracts (CFE) under optimized reaction conditions. The produced AgNPs were evaluated with UV–vis spectroscopy, field emission scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction, and Fourier transform infrared spectrometry. In the growing cells strategy, Y. lipolytica produced spherical AgNPs under the optimized conditions, 2.5 mM of silver ions, 7.5 g/l of yeast biomass, a temperature of 30 °C, a pH of 6, and a shaking rate of 50 rpm after 48 h. The sizes and monodispersity of the AgNPs in the resting cells strategy were better than those in the other two. However, the AgNPs were produced faster in the CFE strategy. The antibacterial activity and minimal inhibitory concentration of the AgNPs against certain Gram-positive and Gram-negative bacteria were determined by the agar well diffusion and broth microdilution methods. The AgNPs had a considerable antibacterial effect compared to chloramphenicol as a broad-spectrum antibiotic.