Colloidal Suspensions Of Silver Nanoparticles Research Articles

Chitosan/carboxymethyl cellulose wound dressings supplemented with biologically synthesized silver nanoparticles from the ligninolytic fungus Anamorphous Bjerkandera sp. R1

Chitosan (CHI) and carboxymethyl cellulose (CMC) are naturally sourced materials with excellent physical, chemical, and biological properties, which make them a promising tool for the development of different medical devices. In this research, CHI-CMC wound dressings were manufactured, by using different colloidal suspensions of silver nanoparticles (AgNPs) synthesized from the ligninolytic fungus Anamorphous Bjerkandera sp. R1, called CS and SN. Transmission electron microscopy (TEM), UV-Vis spectroscopy, and dynamic light scattering (DLS) analysis were used to characterize AgNPs. The wound dressings were characterized, by scanning electron microscopy (SEM), optical microscopy and their mechanical, antimicrobial, and biological properties were evaluated. The results of the different characterizations revealed the formation of spherical AgNPs with a mean size between 10 and 70 nm for the different mixtures worked. The mechanical properties of CHI-CMS-AgNPs doped with CS and SN suspensions showed superior mechanical properties with respect to CHI-CMC wound dressings. Compared to the latter, CHI-CMC-AgNPs wound dressings yielded better antibacterial activity against the pathogen Escherichia coli. In biological assays, it was observed that manufactured CHI-CMC-AgNPs wound dressings were not toxic when in contact with human skin fibroblasts (Detroit). This study, then, suggests that this type of wound dressings with a chitosan matrix and carboxymethyl cellulose doped with biologically synthesized nanoparticles from the fungus Bjerkandera sp., may be an ideal alternative for the manufacture of new wound dressings.

Surface enhanced Raman scattering of brilliant green: Packing density and stabilizing effect of the cationic surfactant CTAB on the “hotspot” spacing

Surface-enhanced Raman scattering (SERS) has been applied utilizing colloidal suspensions of silver nanoparticles (AgNPs), for the detection of brilliant green (BG) at very low concentrations. Proper stimulated surface-enhanced resonance Raman scattering (SERRS) spectra collected from BG aqueous solutions at different low concentration ranges revealed a variation of the relative intensity ratio of certain BG bands attributed to a respective alteration of the molecular orientation of the analyte with respect to the AgNPs. This behavior is closely related to a different packing of the BG molecules on the nanoparticle surface when the concentration increases and the available space decreases. Additionally, the addition of suitable amounts of cetyl thrimethyl ammonium bromide (CTAB) to the BG aqueous solutions enhanced the detection limit of the analyte. This enlightens the role of the cationic surfactant in tuning the interparticle distances of AgNPs in the colloidal suspension; this presumably allows an optimization of the SERS enhancement factor. The concentration of CTAB that maximizes the SERS of BG is the same with the critical micelle concentration (CMC) of the surfactant. Most probably, CTAB at the CMC acts as a spacer keeping the AgNPs at a certain distance suitable for the generation of SE(R)RS hotspots.

Citrate-silver nanoparticles and their impact on some environmental beneficial fungi.

Colloidal suspensions of silver nanoparticles (AgNPs) with surface modified by capping with citrate ions were synthesized by chemical reduction method. Transmission and Scanning Electron Microscopy as well as darkfield Optical Microscopy provided information on the nanoparticle morphology, with fine symmetrical grains and log-normal fitted size distribution. Small Angle X-ray Scattering method allowed theoretical confirmation of colloidal silver nanoparticle fine granularity, based on measurements in the native fluid sample. UV–Vis spectrophotometry allowed studying the Localized Surface Plasmon Resonance band versus the stability of the citrate-AgNP sample after storage and after UV-C exposure. The colloidal AgNP impact on Phanerochaete chrysosporium environmental microorganisms was studied by specific biochemical investigations. Silver released from the colloidal suspension of AgNPs was supposed to induce changes in some antioxidant enzymes and in some enzymes of Krebs’ cycle. Catalase activity was moderately changed (an increase with over 50%) as well as superoxide dismutase activity, while the diminution of the activities of four dehydrogenases synthesized in the fungus mycelium was emphasized also: a decrease with about 60% for malate dehydrogenase, with over 50% for isocitrate dehydrogenase and succinate dehydrogenase and with about 40% for alpha-ketoglutarate dehydrogenase. These findings suggested the nano-toxicological issues of citrate-AgNPs impact on the environmental beneficial microorganisms.

TL/OSL signal of CaSO4:Eu,Ag samples produced by variations of the slow evaporation route

The aim of this work was to produce crystals of CaSO4 doped with europium (Eu) and silver (Ag) nanoparticles, by means of three different preparation routes, and to study their applicability in radiation dosimetry by the TL and OSL techniques. The crystals were produced by variations of the slow evaporation route. Samples of CaSO4:Eu,Ag(a) were obtained using europium oxide and silver particles as dopants. For the growth of the crystals of CaSO4:Eu,Ag(b), silver was incorporated in nitrate form. CaSO4:Eu,Ag(c) phosphorus were synthetized mixing europium oxide in a colloidal suspension of silver nanoparticles. Optical characterization confirmed the presence of Eu3+/Eu2+ in the crystal matrix. Dosimetric characteristics were evaluated after the exposure of the samples to a90Sr/90Y source. The CaSO4:Eu,Ag(a) and CaSO4:Eu,Ag(b) composites presented the most intense signals, the lowest detectable doses, and showed a linear and reproducible dose response, but the CaSO4:Eu,Ag(a) samples showed the best potential for application in TL/OSL dosimetry.

In My Element: Silver

The In My Element series celebrates the personal accounts from Chemistry – A European Journal Editorial Board members for the 2019 International Year of the Periodic Table. In this contribution, Younan Xia gives his story on silver. Silver (Ag) is my favorite chemical element due to its broad spectrum of unique properties and applications. Although a silver medal may not be as valuable as a gold medal, silver easily beats gold in an array of applications. Silver has the highest electrical and thermal conductivities among all metals. Since ancient times, the antimicrobial capability of silver was utilized to purify water, preserve fresh milk, and treat wounds. Before digital cameras came of age, silver-based photographic films were everyday commodities. Silver is also an effective catalyst for oxidation reactions as molecular oxygen can adsorb and dissociate into atomic oxygen on its surface under ambient conditions. In fact, silver is the only catalyst capable of converting ethylene to ethylene oxide (on a scale of 20 million tons in 2009!). Oh, did I mention that silver is probably the best material for the production of shiny mirrors? The last but not least, the abundance of silver in Earth's crust is much higher than that of gold (79 vs. 3.1 ppb) so the price of silver is always a small fraction of that of gold ($17 vs. $1299 per oz.). Silver is also my lucky metal. Since 2001, my group has worked on the development of methods for the colloidal synthesis of silver nanocrystals with controlled shapes in an effort to tailor their surface plasmon resonance properties. We began with the silver mirror reaction, in which a silver ammonia complex is mixed with an aldehyde compound for immediate reduction and thus formation of a shiny mirror on the surface of the container (see the photo, left panel). With the addition of a polymer stabilizer, we could use the same reaction to produce a stable suspension of silver nanoparticles. The suspension displayed a yellow color (see the photo, right panel) because of the surface plasmon resonance peaked at 400 nm. In an effort to better control the reduction kinetics, we later switched to polyol reduction, in which a polyol such as ethylene glycol is thermally oxidized to glycoaldehyde. Since the reductant can be generated in situ and then consumed to maintain a relatively stable concentration in the reaction solution, we were able to synthesize silver nanocrystals with controlled shapes and facets, including cubes, octahedrons, cuboctahedrons, bipyramids, bars, rods, and wires. These novel nanocrystals have opened up a world of opportunities for applications in areas ranging from catalysis to plasmonics, photonics, and surface-enhanced Raman scattering, as well as fabrication of touchscreens, solar cells, flexible electronic devices, and metamaterials. In addition, our technology on silver nanowires has been commercialized by various companies for the production of flexible, transparent, and conductive electrodes. Photographs of (left) a silver mirror and (right) a colloidal suspension of silver nanoparticles. Position Brock Family Chair Professor and GRA Eminent Scholar E-mail [email protected] Homepage http://nanocages.com Education B.S (University of Science and Technology of China, 9/1982 to 7/1987, Hefei, Anhui, P. R. China) M.S. (9/1991 to 5/1993, Alan G. MacDiarmid, University of Pennsylvania, Philadelphia, PA, USA) Ph.D. (9/1993 to 8/1996, George M. Whitesides, Micro- and Nanofabrication Based on Microcontact Printing and Replica Molding, Harvard University, Cambridge, MA, USA) Postdoctoral Fellow (8/1996 to 7/1997, George M. Whitesides, Harvard University, Cambridge, MA, USA) Awards MRS Medal (Materials Research Society, 2017); ACS National Award in the Chemistry of Materials (American Chemical Society, 2013); NIH Director's Pioneer Award (National Institutes of Health, 2006); Camille Dreyfus Teacher Scholar (2002); David and Lucile Packard Fellow in Science and Engineering (2000); Sloan Research Fellow (2000); CAREER Award (National Science Foundation, 1999); Victor K. LaMer Award (American Chemistry Society, 1999); New Faculty Award (Camille and Henry Dreyfus Foundation, 1997) Research interests Nanocrystals, electrospinning, self-assembly, colloid science, catalysis, plasmonics, nanomedicine, regenerative medicine Hobbies Reading, cooking, table tennis

Size is an essential parameter in governing the UVB-protective efficacy of silver nanoparticles in human keratinocytes.

BackgroundUltraviolet (UV) radiation from sun, particularly its UVB component (290–320 nm), is considered the major etiological cause of skin cancer that impacts over 2 million lives in the United States alone. Recently, we reported that polydisperse colloidal suspension of silver nanoparticles (AgNPs) protected the human keratinocytes (HaCaT) against UVB-induced damage, thus indicating their potential for prevention of skin carcinogenesis. Here we sought out to investigate if size controlled the chemopreventive efficacy of AgNPs against UVB-induced DNA damage and apoptosis.MethodsPercent cell viability was examined by WST-1 assay after treating the cells with various doses (1–10 μg/mL) of AgNPs of different sizes (10, 20, 40, 60 and 100 nm) for 12 and 24 h. For protection studies, cells were treated with AgNPs of different sizes at a uniform concentration of 1 μg/mL. After 3 h, cells were irradiated with UVB (40 mJ/cm2) and dot-blot analysis was performed to detect cyclobutane pyrimidine dimers (CPDs) as an indication of DNA damage. Apoptosis was analyzed by flow cytometry after staining the cells with 7-Amino-Actinomycin (7-AAD) and PE Annexin V. Immunoblot analysis was accomplished by processing the cells for protein extraction and Western blotting using specific antibodies against various proteins.ResultsThe data show that the pretreatment of HaCaT cells with AgNPs in the size range of 10–40 nm were effective in protecting the skin cells from UVB radiation-induced DNA damage as validated by reduced amounts of CPDs, whereas no protection was observed with AgNPs of larger sizes (60 and 100 nm). Similarly, only smaller size AgNPs (10–40 nm) were effective in protecting the skin cells from UV radiation-induced apoptosis. At the molecular level, UVB –irradiation of HaCaT cells led to marked increase in expression of pro-apoptotic protein (Bax) and decrease in anti-apoptotic proteins (Bcl-2 and Bcl-xL), while it remained largely unaffected in skin cells pretreated with smaller size AgNPs (10–40 nm).ConclusionsAltogether, these findings suggest that size is a critical determinant of the UVB-protective efficacy of AgNPs in human keratinocytes.

Laser Raman Spectroscopy with Different Excitation Sources and Extension to Surface Enhanced Raman Spectroscopy

A dispersive Raman spectrometer was used with three different excitation sources (Argon-ion, He-Ne, and Diode lasers operating at 514.5 nm, 633 nm, and 782 nm, resp.). The system was employed to a variety of Raman active compounds. Many of the compounds exhibit very strong fluorescence while being excited with a laser emitting at UV-VIS region, hereby imposing severe limitation to the detection efficiency of the particular Raman system. The Raman system with variable excitation laser sources provided us with a desired flexibility toward the suppression of unwanted fluorescence signal. With this Raman system, we could detect and specify the different vibrational modes of various hazardous organic compounds and some typical dyes (both fluorescent and nonfluorescent). We then compared those results with the ones reported in literature and found the deviation within the range of ±2 cm−1, which indicates reasonable accuracy and usability of the Raman system. Then, the surface enhancement technique of Raman spectrum was employed to the present system. To this end, we used chemically prepared colloidal suspension of silver nanoparticles as substrate and Rhodamine 6G as probe. We could observe significant enhancement of Raman signal from Rhodamine 6G using the colloidal solution of silver nanoparticles the average magnitude of which is estimated to be 103.

Synthesis of Silver Nanoparticles by the Action of Heavy Ozonized C60 Fullerene on Silver Nitrate Solutions

Heavy ozonated C60 fullerene, known also as “fullerene ozopolymer” is able to reduce silver ions to silver nanoparticles. The silver ions reduction was followed spectrophotometrically through the development of the surface plasmon resonance absorption band at 420 nm which is typical of the colloidal suspension of silver nanoparticles. The kinetic rate constant of silver ions reduction was determined. Fullerene ozopolymer acts as a reducing agent and as silver colloid protecting agent as demonstrated by the value of Z-potential which suggests the formation of a thermodynamically stable colloidal suspension.

Extracellular polysaccharide production by a novel osmotolerant marine strain of Alteromonas macleodii and its application towards biomineralization of silver.

The present study demonstrates exopolysaccharide production by an osmotolerant marine isolate and also describes further application of the purified polysaccharide for production of colloidal suspension of silver nanoparticles with narrow size distribution. Phylogenetic analysis based on 16S r RNA gene sequencing revealed close affinity of the isolate to Alteromonas macleodii. Unlike earlier reports, where glucose was used as the carbon source, lactose was found to be the most suitable substrate for polysaccharide production. The strain was capable of producing 23.4 gl−1 exopolysaccharide with a productivity of 7.8 gl−1 day−1 when 15% (w/v) lactose was used as carbon source. Furthermore, the purified polysaccharide was able to produce spherical shaped silver nanoparticles of around 70 nm size as characterized by Uv-vis spectroscopy, Dynamic light scattering and Transmission electron microscopy. These observations suggested possible commercial potential of the isolated strain for production of a polysaccharide which has the capability of synthesizing biocompatible metal nanoparticle.

Free-surface microfluidic control of surface-enhanced Raman spectroscopy for the optimized detection of airborne molecules

We present a microfluidic technique for sensitive, real-time, optimized detection of airborne water-soluble molecules by surface-enhanced Raman spectroscopy (SERS). The method is based on a free-surface fluidic device in which a pressure-driven liquid microchannel flow is constrained by surface tension. A colloidal suspension of silver nanoparticles flowing through the microchannel that is open to the atmosphere absorbs gas-phase 4-aminobenzenethiol (4-ABT) from the surrounding environment. As surface ions adsorbed on the colloid nanoparticles are substituted by 4-ABT, the colloid aggregates, forming SERS "hot spots" whose concentrations vary predictably along the microchannel flow. 4-ABT confined in these hot spots produces SERS spectra of very great intensity. An aggregation model is used to account quantitatively for the extent of colloid aggregation as determined from the variation of the SERS intensity measured as a function of the streamwise position along the microchannel, which also corresponds to nanoparticle exposure time. This allows us to monitor simultaneously the nanoparticle aggregation process and to determine the location at which the SERS signal is optimized.

Extracellular biosynthesis of silver nanoparticles using the fungus Fusarium semitectum

Development of environmental friendly procedures for the synthesis of metal nanoparticles through biological processes is evolving into an important branch of nanobiotechnology. In this paper, we report on the use of fungus “ Fusarium semitectum” for the extracellular synthesis of silver nanoparticles from silver nitrate solution (i.e. through the reduction of Ag + to Ag 0). Highly stable and crystalline silver nanoparticles are produced in solution by treating the filtrate of the fungus F. semitectum with the aqueous silver nitrate solution. The formations of nanoparticles are understood from the UV–vis and X-ray diffraction studies. Transmission electron microscopy of the silver particles indicated that they ranged in size from 10 to 60 nm and are mostly spherical in shape. Interestingly the colloidal suspensions of silver nanoparticles are stable for many weeks. Possible medicinal applications of these silver nanoparticles are envisaged.

Holographic grating formation in a colloidal suspension of silver nanoparticles

Holographic gratings are recorded in colloidal suspensions of silver nanoparticles by utilizing interfering nanosecond pulses. The diffraction efficiency is measured with continuous-wave light. An instantaneous response together with a transient grating are observed: the nanoparticles absorb the pump light and heat up. Heat is transferred to the solvent, and a delayed thermal grating appears. The final decay time constant of this grating depends quadratically on the period length and has a typical value of 1 micros for grating spacings of several micrometers.

Optical Absorbance of Colloidal Suspensions of Silver Polyhedral Nanoparticles

The optical absorption of colloidal suspensions made of silver nanoparticles with polyhedral shapes is studied experimentally and theoretically. The influence of the shape on the optical response is investigated by comparing the measured absorbance with theoretical results for icosahedral, decahedral, and cuboctahedral silver nanoparticles. The theoretical spectra are obtained within the discrete dipole approximation. We find that colloidal suspensions of silver nanoparticles with a small dispersion of size distribution show very few structural shapes.

Bioaerosol characterization by surface-enhanced Raman spectroscopy (SERS)

It is demonstrated that bioaerosols can be characterized by their surface-enhanced Raman spectra. Preliminary studies showed that Raman spectra of aqueous suspensions of Escherichia coli, Pseudomonas aeruginosa, and Salmonella typhimurium can be obtained by mixing them with a nanocolloidal suspension of silver. Adsorption of the microorganisms on the silver quenches fluorescence and yields greatly enhanced spectra. To assist in the interpretation of the spectra we also obtained SERS spectra of N -acetyl glucosamine and the amino acids L-lysine, D-alanine and D-glutamic acid. After baseline studies identified the spectral region of interest and the concentrations of microorganisms and colloid particles needed to maximize the Raman signal, aerosolized microorganisms were impacted and transferred to a colloidal suspension of silver nanoparticles to obtain reproducible Raman spectra.

Comparison of surface-enhanced resonance Raman scattering from unaggregated and aggregated nanoparticles.

The effect of excitation frequency and state of aggregation on the sensitivity obtained in ultratrace analysis using colloidal suspensions of silver nanoparticles and surface-enhanced resonance Raman scattering (SERRS) detection is explored to define suitable conditions for quantitative analysis. Two structurally similar dyes, only one of which causes aggregation, were used as analytes without the use of external aggregating agents, thus simplifying the surface chemistry and removing a major source of error. Addition of the nonaggregating dye caused no change in particle charge or size and no time-dependent aggregation as measured by zeta potential and particle size analysis. The most intense single-particle scattering was obtained using excitation at the wavelength of the plasmon resonance. Molecular resonance added approximately 2 orders of magnitude in sensitivity. Addition of the aggregating dye caused a reduction in surface charge of the particles and initiated a time-dependent aggregation process. However, constant SERRS with time is obtained at some excitation wavelengths probably because a constant number of clusters active at these wavelengths is maintained in the dynamic aggregation process. The additional enhancement caused by aggregation and molecular resonance is spread over a range of excitation frequencies. However, electronic spectra suggested that plasmon resonance enhancement would be effective at the longest wavelength of excitation used (785 nm), but there was a significant drop in intensity this far away from the absorbance maximum of the dye (429 nm). Thus, sensitive analysis using suspensions of single nanoparticles is feasible provided the excitation frequency used is close to that of the plasmon resonance frequency. Aggregation adds only an enhancement of approximately 6 in the experiments performed since only some particles in aggregates will have an active plasmon at any one wavelength, but the range of excitation wavelengths at which good enhancement is obtained is wider giving more flexibility if more complexity.