Colloidal Solution Of Nanoparticles Research Articles

Antimicrobial activity of silver nanoparticle colloids of different sizes and shapes against Streptococcus mutans

Silver nanoparticles stabilized with chitosan biopolymer are a new antibacterial agent for treatment of caries. To determine whether the size and morphology of silver nanoparticles in colloidal solution altered their antimicrobial activity, four colored colloids were characterized by ultraviolet–visible (UV–Vis) spectroscopy and transmission electron microscopy (TEM), and their antimicrobial activity [minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC)] against reference stocks of Streptococcus mutans ATCC 25175 compared with chlorhexidine and silver diamine fluoride as controls. TEM revealed that the seed solution (SS) contained only spherical nanoparticles with size of 8.7 ± 3.1 nm whereas the other colloids had predominantly spherical nanoparticle shape, although colloid 1 (S1) contained 2.5% triangular nanoparticles. Colloid 2 (S2) had 15.9% triangular and 6.8% cylindrical nanoparticles, while 23.3% of the silver nanoparticles in colloid 3 (S3) were triangular and 1.5% were cylindrical. All the silver nanoparticle colloids showed antimicrobial activity with no statistically significant differences (p > 0.05) in MIC or MBC. The colloids showed antimicrobial activity higher than silver diamine fluoride (p 0.05). The size and shape of the nanoparticles did not affect the antimicrobial properties of the colored colloids. Thus, the antimicrobial activity of the colloids containing silver nanoparticles against Streptococcus mutans was considered equivalent to that of chlorhexidine, the gold-standard antibiotic in dentistry.

LSPR based Ultra-sensitive low cost U-bent optical fiber for volatile liquid sensing

In the present paper a fiber-optic volatile liquid sensor based on localized surface plasmon resonance (LSPR) has been demonstrated. The sensing probe element has been realized through deposition of colloidal nanoparticle layer on the unclad U-bent portion of a multimode fiber. Evanescent field at the sensing region excites the localized surface plasmons (LSPs) of noble metal nanoparticles (Ag and Au) of average diameter 20nm. The electric field of the plasmons interacts with the vapors of volatile liquids (such as acetone, methanol, ethanol and propanol) at different concentration causing a progressive change in resonance conditions of the localized plasmons which eventually modulate the output light signal of the fiber. The modulated light signal at the output end of the fiber falls on a photo-detector and consequently the detector registers a change in voltage response. The consistency of the designed optical sensor has been investigated using both Ag and Au nanoparticle coating on the unclad portion of the fiber. The response sensitivity for Ag nanoparticle coated probe is found to be more uniform than that of Au nanoparticles coated probe. The sensor shows quick response towards vapors of volatile liquids and requires very small amount of nanoparticle colloidal solution (∼20μL). As a proof of concept, limit of detection (LOD), sensitivity, working domain and repeatability test has been evaluated for the volatile liquids. The novelty of the proposed sensor lies in its simple and inexpensive optics design, miniaturized optical set-up and quick response towards analyte concentration.

Quantitative 3D evolution of colloidal nanoparticle oxidation in solution.

Real-time tracking of the three-dimensional (3D) evolution of colloidal nanoparticles in solution is essential for understanding complex mechanisms involved in nanoparticle growth and transformation. We used time-resolved small-angle and wide-angle x-ray scattering simultaneously to monitor oxidation of highly uniform colloidal iron nanoparticles, enabling the reconstruction of intermediate 3D morphologies of the nanoparticles with a spatial resolution of ~5 angstroms. The in situ observations, combined with large-scale reactive molecular dynamics simulations, reveal the details of the transformation from solid metal nanoparticles to hollow metal oxide nanoshells via a nanoscale Kirkendall process-for example, coalescence of voids as they grow and reversal of mass diffusion direction depending on crystallinity. Our results highlight the complex interplay between defect chemistry and defect dynamics in determining nanoparticle transformation and formation.

Structure and Properties of Nanocrystalline Iron Oxide Powder Prepared by the Method of Pulsed Laser Ablation

Colloidal solution of iron oxide nanoparticles is synthesized by nanosecond pulsed laser ablation (Nd:YAG laser, 1064 nm, 7 ns, and 180 mJ) of a metallic iron target in water, and nanocrystalline powder is prepared from this solution by vacuum drying. A composition and structure of the material obtained are investigated by methods of electron microscopy, x-ray diffraction, and optical spectroscopy. It is established that oxide particles with average size of about 5 nm and Fe3O4 magnetite structure are mainly formed during ablation. Preliminary investigation of magnetic properties of the prepared nanoparticle powders shows that they can be in ferromagnetic and/or superparamagnetic states.

A comparative study of RGO-SnO2 and MWCNT-SnO2 nanocomposites based SO2 gas sensors

An attempt has been made in the present work to develop a hybrid nanocomposite sensor by exploiting the novel properties of Tin oxide (SnO2), MWCNTs (Carbon nanotubes) and reduced graphene oxide (RGO) for the efficient detection of SO2 gas. MWCNT-SnO2 and RGO-SnO2 hybrid nanocomposite sensors have been prepared by incorporating MWCNTs and RGO into SnO2 nanoparticle colloidal solution respectively by chemical route. Low sensing response of 1.2 is obtained for bare SnO2 sensor at 220°C towards 500ppm SO2 gas. However, enhanced sensing response of ∼22 has been observed for the RGO-SnO2 sensor compared to ∼5 obtained for MWCNT-SnO2 sensor at a lower operating temperature of 60°C towards the same concentration of SO2 gas. Modulation of space charge region at the interface of n-SnO2 and p-RGO on interaction with the target SO2 gas is responsible for the enhanced response.

Fluorescence Development of Latent Fingerprint with Conjugated Polymer Nanoparticles in Aqueous Colloidal Solution.

Poly(p-phenylenevinylene) (PPV) nanoparticles in aqueous colloidal solution have been prepared via a modified Wessling method, with the addition of surfactant. The fluorescent colloidal solution was used as the developing solution to develop the fingerprints on different substrates. The developing process was accomplished simply by immersing the substrates into developing solution and then taking out, followed by rinsing with deionized water. The initial study about the fingerprints on the adhesive tapes showed that the developing solution is very effective in fluorescence development on both fresh and aged visible fingerprints; and such an effect was negligibly affected by treating the fingerprints with water or other organic solvents, whether before developing or after. Further study on latent fingerprints (LFPs) demonstrated that PPV nanoparticles in colloidal solution have high sensitivity in developing fingerprints to give very clearly fluorescent patterns. At least 6 months of storage of the colloidal solution did not reduce the developing effect; and each developing solution (3.6 mg/mL, 5.0 mL) can be used to develop at least 30 fingerprints without sacrificing the legibility of the pattern. The preliminary mechanism investigation suggested that selectivity achieved toward the ridge of the fingerprint is very likely due to the affinity between PPV molecules and oily secretions of the fingerprints. Digital magnification of the developed fingerprints provided more details about the fingerprint.

Liquid Cell Electron Microscopy of Nanoparticle Self-Assembly Driven by Solvent Drying.

Drying a colloidal solution of nanoparticles is a versatile method to construct self-assembled structures of nanoparticles. However, mechanistic understanding has mostly relied on empirical knowledge obtained from the final structures of self-assembly as relevant processes during solvent drying are likely kinetic and far from equilibrium. Here, we present in situ TEM studies of nanoparticle self-assembly under various conditions, including the concentrations of the initial solution and the types of nanoparticles and substrates. The capability of tracking trajectories of individual nanoparticles enables us to understand the mechanisms of drying-mediated self-assembly at the single-nanoparticle level. Our results consistently show that a solvent boundary primarily affects nanoparticle motions and the resulting self-assembly processes regardless of different conditions. The solvent boundary drives nanoparticles to form two-dimensional assembly mainly through two pathways, transporting scattered nanoparticles by lateral dragging and flattening aggregated nanoparticles by vertical pressing.

Radio frequency hyperthermia of cancerous cells with gold nanoclusters: an in vitro investigation

Heating response of gold nanoclusters of two different sizes (2 and 3 nm) under radio frequency electric field has been reported here for the first time. Experiments were performed on colloidal solution of nanoparticles and their in vitro hyperthermia effect was investigated on pancreatic cancer cells (MIA Paca-2). Gold nanoclusters at concentrations up to 200 ppm were found non-toxic, based on the results of cytotoxicity assay using tetrazolium dye MTT and at concentrations up to 50 ppm exhibited very low hemolytic activity. Gold nanoclusters of two sizes resulted in up to 50 °C temperature rise when in radio frequency electric field of 100 W power. Smaller clusters were found more efficient for heat generation and thus were applied in cell studies. Gold nanoclusters (at 5–200 ppm concentrations) under radio frequency electric field (100 W, 2 and 4 min of exposure duration) exhibited successful eradication of pancreatic cancerous cells.

Novel Nanoparticle-based Colorimetric Probes and Sensors for Determining Phenolic Antioxidants, Biothiols, Nitrite and Hydrogen Peroxide

This study examines the principles and milestones of nanoparticle (NP)-based colorimetric sensors and probes developed by our research group. A novel method for antioxidant capacity estimation was developed on the polyphenol-mediated growth of Ag-NPs and optical monitoring of the corresponding plasmon absorption bands. A new optical sensor using Ellman's reagent-adsorbed gold nanoparticles in colloidal solution was devised to selectively determine biothiols. Nitrite was determined by means of 4-aminothiophenol-modified Au-NPs and naphthylethylene diamine as coupling agent. Hydrogen peroxide was detected with the use of Fe3O4 magnetite NPs as peroxidase-like catalyst using a N,N-dimethyl-p-phenylenediamine (DMPD) probe.

Plant mediated greener approach for synthesis of silver nanoparticles from <i>Digitalis purpurea</i> plant and its antibacterial activity

In this paper, silver nanoparticles were biosynthesised using aqueous Digitalis purpurea leaf extract. The biosynthesised silver nanoparticles were characterised by UV-visible (UV-vis) spectrophotometer, Fourier transform infrared spectroscopy (FTIR), x-ray diffractometer (XRD), field emission scanning electron microscopy (FESEM), energy dispersive x-ray (EDX) analysis and high-resolution transmission electron microscopy (HRTEM). In the colloidal solution, the formation and stability of the silver nanoparticles were identified by UV-visible and it showed the maximum absorption at 452 nm. XRD and HRTEM analysis showed that the silver nanoparticles were cubic structured, face centred with a particle size of 25 nm and EDX evidenced the presence of silver element. The FTIR analysis revealed the existence of various functional groups. Antibacterial activity of the synthesised silver nanoparticles was evaluated against the gram-negative Escherichia coli (MTCC 1652) and gram-positive Staphylococcus aureus (MTCC 316) bacteria, showed the efficient activity against both the gram-negative and gram-positive microorganisms.

Antimicrobial Activity of Differently Concentrated Nanoparticle Dispersions

Preparation of nontoxic antimicrobial solutions is a priority in the development of new antibiotics. The in vitro effect of the chemical composition of the dispersed phase and dissolved solids in the dispersion medium on the antimicrobial properties of aqueous colloidal solutions of nanoparticles of a number of metals and metal oxides against microorganisms of different species - bacterial dental plaque, Bacillus cereus, and spores of vaccine strain Bacillus anthracis STI - 1 were studied in this work.

The Review of Small Size Silver Nanoparticle Neurotoxicity: A Repeat Study

Repeated oral gavages silver nanoparticle colloidal solution ingestion procedures for AgNps neural toxicity have been investigated in Swiss albino mouse fetuses’ brain at the ultra-structural (TEM) level by transmission electron microscopy and Nikon bright field microscopy. Transmission electron microscopy probe identified neural toxicity in the brain of mice fetuses in the form of mitochondrial autophagy, dysmorphology & dysfunction of cellular organelles vacuolization of neuronal cell, blood brain barrier inflammation, astrocytic swelling, Gliosis and a well visualized differentiation to the reaction products. Multiple reaction product localization was visible in the form of smaller size silver nano particles (1 to 20 nm range) percolation and perimembranous multiple patchy condensations focuses appeared from inside and outside of neuronal cell membrane. Histologically cell and tissue dysmorphology was observed in the form of unipolar brush cell and lugaro cells degeneration with dysmorphology of corticomedullary layers of cerebrum, cerebellum and hippocampus. In twice, lower dose (0.5 and 1 mg/kg b.w./ day) and higher dose (10 and 15 mg/kg b.w./day) small size silver nano particles were found adhered both side of cell membrane, mitochondria and endocytotic vesicle. Neural histochemistry of fetal cortex by Golgi staining procedure showed reduction number of dendrite arborisation and unipolar neuron with basket cells degeneration and dysmorphology. But the intensity of such was found almost low or equal to control in lower dose and high in higher dose and concentration. Small size silver nano particles exhibits more neurotoxic effect comparatively to other metal nanoparticles because of easy penetration and disintegrity to BBB.

Impact of Silver Nanoparticle Suspensions on Mixtures of Fungal and Bacterial Microorganisms of Food Production

Providing of food safety is a fundamental problem of food production. Silver nanoparticles demonstrate antimicrobial action against multiple bacterial species while not affecting fungal species. Nanosilver colloidal solutions stabilized with Gum Arabic and glycine with the size of nanoparticles from 7 to 12 nm were tested. The experiments were conducted upon cultivating some common fungal microorganisms implemented in food production, such as Aspergillus oryzae and Saccharomyces cerevisiae on different media contaminated with bacteria Escherichia coli, Erwinia herbicola, Pseudomonas fluorescens, Bacillus cereus, and Pediococcus claussenii. Samples were treated with silver nanoparticles colloidal solutions of various concentrations. The results show that nanoparticles inhibit the growth of bacteria within the concentration of 0.03-0.05 g/dm3 in solid media and 0.001-0.005 g/dm3 in liquid media. The specified inhibitory concentrations did not affect the growth of fungi.

Plasmonics-Based Detection of Virus Using Sialic Acid Functionalized Gold Nanoparticles.

Biosensor for the detection of virus was developed by utilizing plasmonic peak shift phenomenon of the gold nanoparticles and viral infection mechanism of hemagglutinin on virus and sialic acid on animal cells. The plasmonic peak of the colloidal gold nanoparticles changes with the aggregation of the particles due to the plasmonic interaction between nearby particles and the color of the colloidal nanoparticle solution changes from wine red to purple. Sialic acid reduced and stabilized colloidal gold nanoparticle aggregation is induced by the addition of viral particles in the solution due to the hemagglutinin-sialic acid interaction. In this work, sialic acid reduced and stabilized gold nanoparticles (d = 20.1 ± 1.8 nm) were synthesized by a simple one-pot, green method without chemically modifying sialic acid. The gold nanoparticles showed target-specific aggregation with viral particles via hemagglutinin-sialic acid binding. A linear correlation was observed between the change in optical density and dilution of chemically inactivated influenza B virus species. The detection limit of the virus dilution (hemagglutinination assay titer, 512) was shown to be 0.156 vol% and the upper limit of the linearity can be extended with the use of more sialic acid-gold nanoparticles.

Formation of platinum nanoparticle colloidal solution by gamma-ray irradiation

ABSTRACTPlatinum nanoparticle colloidal solution with a small amount of impurities was formed from a suspension of hexahydroxy platinic acid (SHHPA) by gamma-ray irradiation to suppress changes in water chemistry such as electrical conductivity and concentration of impurities in the reactor water during noble metal chemical addition in plant operation. The SHHPA was prepared from sodium hexahydroxyplatinate solution by using an H-type cation exchange resin. Optimum conditions for formation of the platinum nanoparticle colloidal solution were the following: absorbed dose of gamma-ray irradiation, >6 kGy; pH of solution, >8.2; air saturation; no methanol addition. Characteristics of the formed platinum nanoparticles were as follows: mean particle size, 2.3 ± 0.5 nm; particle charge, negative; isoelectric point at a pH of 3.5 ± 0.1; the chemical compound consisted mainly of platinum dioxide without platinum metal. No precipitation of platinum nanoparticles was observed after storage time of 1 year without any stirring in a room where the temperature varied from about 10 to about 35 °C.

Removal of mixture of ZnO and CuO nanoparticles (NPs) from water using activated carbon in batch kinetic studies.

The aim of this study was to understand the effects of pH (5, 6, 7, 8, 9) and activated carbon (AC) concentration (0.01, 0.1, 1, 10, 100 g/L) on the removal of a colloidal solution of nanoparticles (NPs) (ZnO + CuO) using AC in batch kinetic studies. Results revealed that adsorption capacities of AC for Zn and Cu (individually) were 0.9 ± 0.028 mg/g (91.3% removal) and 0.95 ± 0.036 mg/g (95.6% removal) in deionized water and 0.6 ± 0.038 mg/g (78% removal) and 0.75 ± 0.078 mg/g (83% removal) in wastewater at pH 8 (Zn) and pH 6 (Cu) respectively. In a colloidal solution mixture of zinc oxide nanoparticles (ZnONPs) and copper oxide nanoparticles (CuONPs), adsorption capacity of AC for Zn in deionized water was 0.71 ± 0.051 mg/g (74.7% removal) and in wastewater was 0.576 ± 0.019 mg/g (69% removal) and for Cu in deionized water was 0.82 ± 0.017 mg/g (81.2% removal) and in wastewater was 0.6 ± 0.032 mg/g (71.5% removal). Overall, this study provided a detailed analysis of the removal capacity of AC and indicated that AC can be used as an efficient adsorbent filter for removing engineered NPs like ZnONPs and CuONPs (single and mixture) from water. As there is a need for removing NPs from wastewater, removal of NPs using an AC-based adsorptive-filter might become a promising method.

Palladium/γ-Fe2O3 nanoparticle mixtures for acetone and NO2 gas sensors

The functionalization of Fe3O4/γ-Fe2O3 nanoparticles (NPs) gas sensors with Pd NPs was studied. NPs films were deposited from the mixtures of Fe3O4/γ-Fe2O3 and Pd NPs colloidal solutions by modified Langmuir-Schaefer technique onto Al2O3 substrates, the NP size being 6–7nm. Samples were composed from 4 Fe3O4/γ-Fe2O3 NP monolayers (MLs), either pure or doped by Pd at the different NPs Pd: Fe3O4/γ-Fe2O3 proportions. NPs and films were studied by DLS, GI XRD, SEM and EDS. Sensors were tested toward acetone vapors and NO2 at concentration range of 5–200ppm and 0.5–12ppm respectively in dry air and under working temperatures range 200–500°C. Before testing 1nm, surfactant capping was removed by UV irradiation. Pd-doped Fe3O4/γ-Fe2O3 sensors showed p-type gas response, higher conductance and higher conduction activation energies compared to pure Fe3O4/γ-Fe2O3 sensor that gives n-type gas response. Results are explained in terms of surface interactions with oxidizing and reducing species, and electrical conduction mechanisms.

Controlled preparation and visible light photocatalytic activities of corn cob-like Au–ZnO nanorods

A facile method to prepare well-shaped nanohybrids of Au–ZnO nanorods (NRs) has been demonstrated, which is through polyvinylpyrrolidone-assisted in situ nucleation and growth of ZnONRs in the colloidal solution of Au nanoparticles (NPs). The obtained Au–ZnONRs shows uniform corn cob-like morphology with AuNPs evenly deposited on the surface of hexagonal ZnONRs and can be dispersed in aqueous solution to achieve photodegradation of organics. Moreover, the loading amount of AuNPs can be tuned to optimize the photocatalytic performance. The nanohybrid of Au–ZnONRs with optimized AuNP loading exhibits superior photocatalytic activity than ZnONRs alone, demonstrating ~90% Rhodamine B degradation within 18 h under the visible light of 420–780 nm, a wavelength range that does not overlap with ZnO absorption. The observed performance improvement is likely due to the coupling effect between ZnONRs and AuNPs, which functionalizes ZnONRs with visible light utilization and enhances charge separation. The strategy presented here not only provides a new approach for the controlled modification of 1D semiconductor nanostructures, but also holds good potential for applications such as degradation of organic pollutants.

Facile synthesis of water‐dispersible magnetite nanorings from surfactant‐free hematite nanorings

Surfactant-free α-Fe2O3 nanorings (NRs) were directly converted into water-dispersible Fe3O4 NRs through a simple and straightforward approach. In this process, uniform α-Fe2O3 NRs obtained through hydrothermal synthesis method are firstly thermally reduced to hydrophobic Fe3O4 NRs in the presence of hydrophobic oleic acid surfactant and non-polar trioctylamine solvent (under a flow of 5% H2/95% Ar). Subsequently, oxidative cleavage of oleic acid capping agent using sodium periodate oxidising agent is imparted to yield water-dispersible Fe3O4 NRs. As compared with the traditional solid-state reduction in tube furnace, the obtained Fe3O4 NRs using solution-based reduction process can retain its original uniform ring shape with good crystallinity and well-defined magnetic vortex domain. Moreover, with the presence of azelaic acid on the surface of hydrophilic Fe3O4 NRs, antibody or drugs can be easily conjugated, which further boost its potential theranostics application. This work provides a convenient approach to convert surfactant-free nanoparticle (NP) powders into water-dispersible NPs colloidal solutions for various biomedical applications.

Removal of Metal Nanoparticles Colloidal Solutions by Water Plants.

The ability of seven species of aquatic plants (Elodea canadensis, Najas guadelupensis, Vallisneria spiralis L., Riccia fluitans L., Limnobium laevigatum, Pistia stratiotes L., and Salvinia natans L.) to absorb metal nanoparticles from colloidal solutions was studied. It was established that investigated aquatic plants have a high capacity for removal of metal nanoparticles from aqueous solution (30–100%) which indicates their high phytoremediation potential. Analysis of the water samples content for elements including the mixture of colloidal solutions of metal nanoparticles (Mn, Cu, Zn, Ag + Ag2O) before and after exposure to plants showed no significant differences when using submerged or free-floating hydrophytes so-called pleuston. However, it was found that the presence of submerged hydrophytes in aqueous medium (E. canadensis, N. guadelupensis, V. spiralis L., and R. fluitans L.) and significant changes in the content of photosynthetic pigments, unlike free-floating hydrophytes (L. laevigatum, P. stratiotes L., S. natans L.), had occur. Pleuston possesses higher potential for phytoremediation of contaminated water basins polluted by metal nanoparticles. In terms of removal of nanoparticles among studied free-floating hydrophytes, P. stratiotes L. and S. natans L. deserve on special attention.