Synthesis of Silver and Gold Nanoparticles: Chemical and Green Synthesis Method and Its Toxicity Evaluation against Pathogenic Bacteria Using the ToxTrak Test

In the current investigation, silver/gold nanoparticles (NPs) were synthesized using two methods: chemical and biological, and then characterized colloidal solutions of both NPs using UV-Vis, transmission electron microscopy (TEM) and zeta potential analyzers, X-ray powder diffraction (XRD), and energy dispersive X-ray (EDX) as well as the ToxTrak test for in vitro toxicity and antibacterial activity against Gram-positive bacteria (B. subtilis) and Gram-negative bacteria (E. coli). The plasmon peak of chemical synthesized silver NPs (CH-AgNPs) and gold NPs (CH-AuNPs) was observed at 414 and 530 nm, respectively, while the sharp plasmon peak of biological synthesized silver NPs (Bio-AgNPs) and gold NPs (Bio-AuNPs) was observed at 410 and 525 nm. Under transmission electron microscopy (TEM), the average sizes of CH-AgNPs and CH-AuNPs were 50.56 and 25.98 nm, respectively. Bio-AgNPs and Bio-AuNPs, on the other hand, had average sizes of 25.25 and 16.65 nm, respectively. The stability of NPs was also investigated using the zeta potential. The crystalline structure of AgNPs was confirmed through XRD, and EDX results confirm the element compositions. In the ToxTrak test, the toxic effect value/percentage inhibition (TEV/PI) was calculated. The results showed that CH-AgNPs have the highest TEV/PI value (85.45% for B. subtilis and 83.77% for E. coli) when compared to Bio-AgNPs (55.75% for B. subtilis and 54.42% for E. coli). CH-AuNPs, on the other hand, were 33.51% toxic to B. subtilis and 36.85% toxic to E. coli, compared to Bio-AuNPs, which were 23.36% toxic to B. subtilis and 24.46% toxic to E. coli. The antibacterial activity of Ag/Au NPs was tested and monitored; zone of inhibition (mm in diameter) against B. subtilis and E. coli, with the following pattern emerging: CH-AgNPs (24.80) had the highest antibacterial activity followed by Bio-AgNPs (22.80) < CH-AuNPs (10.60) < Bio-AuNPs (09.00), whereas the control sample (tetracycline antibiotic) revealed a 25.08 mm, zone of inhabitation. Overall, Bio-AgNPs and Bio-AuNPs are the most effective pathogen-killing materials with the lowest toxicity. Our suggestion is that such materials instead of chemical synthesized NPs can be used to coat antibiotic drugs and could be a game-changer for the pharmaceutical industry in terms of effectively controlling the pathogenic bacteria.

Multifunctional activity of graphene oxide-based nanoformulation against the disease vector, Aedes aegypti

Aedes aegypti management is a global concern due to the absence of medication and effective vaccines. The pesticide-mediated health hazards and rising insecticide resistance in mosquitoes have aggravated the issues. As graphene Oxide (GO)- based nanoformulations are considered a novel mosquito management strategy; the present investigation evaluated the efficacy of GO-based nanoformulations conjugated with malathion (ML) and endosulphan (EN) against Ae. aegypti. The GO was synthesised by Hummers’ method and was confirmed by UV-visible spectral analysis. The GO-ML and GO-EN binary mixtures (1:1 and 1:2) were assayed for toxic potential against mosquito larvae as per WHO protocol and the dead larvae were scrutinized for morphological deformations/abnormalities. The contact irritancy potential of GO nanoformulations was also evaluated against adult Ae. aegypti. The UV-visible spectrum of GO showed a narrow and high peak at ~300 nm corresponding to an n-π* plasmon peak. The GO-insecticide binary mixtures augmented the ML and EN toxicity by 80.43% and 6.43-fold, respectively. The GO-ML mixture-exposed larvae revealed cuticular deposition of black soot while larvae exposed to GO-EN exhibited disintegrated gut viscera. GO-insecticide combinations increased flights in Ae. aegypti denoting irritant potential. The effectual toxic, abrasive and irritant activity of GO-insecticide nanoformulations recommends developing graphene-based toxicants for mosquito management

Plasmons in the van der Waals charge-density-wave material 2H-TaSe2

Plasmons in two-dimensional (2D) materials beyond graphene have recently gained much attention. However, the experimental investigation is limited due to the lack of suitable materials. Here, we experimentally demonstrate localized plasmons in a correlated 2D charge-density-wave (CDW) material: 2H-TaSe2. The plasmon resonance can cover a broad spectral range from the terahertz (40 μm) to the telecom (1.55 μm) region, which is further tunable by changing thickness and dielectric environments. The plasmon dispersion flattens at large wave vectors, resulted from the universal screening effect of interband transitions. More interestingly, anomalous temperature dependence of plasmon resonances associated with CDW excitations is observed. In the CDW phase, the plasmon peak close to the CDW excitation frequency becomes wider and asymmetric, mimicking two coupled oscillators. Our study not only reveals the universal role of the intrinsic screening on 2D plasmons, but also opens an avenue for tunable plasmons in 2D correlated materials.

Photoelectron spectra of alkali metal–ammonia microjets: From blue electrolyte to bronze metal

Experimental studies of the electronic structure of excess electrons in liquids—archetypal quantum solutes—have been largely restricted to very dilute electron concentrations. We overcame this limitation by applying soft x-ray photoelectron spectroscopy to characterize excess electrons originating from steadily increasing amounts of alkali metals dissolved in refrigerated liquid ammonia microjets. As concentration rises, a narrow peak at ~2 electron volts, corresponding to vertical photodetachment of localized solvated electrons and dielectrons, transforms continuously into a band with a sharp Fermi edge accompanied by a plasmon peak, characteristic of delocalized metallic electrons. Through our experimental approach combined with ab initio calculations of localized electrons and dielectrons, we obtain a clear picture of the energetics and density of states of the ammoniated electrons over the gradual transition from dilute blue electrolytes to concentrated bronze metallic solutions.

Морфология и оптические свойства композитного материала на основе наночастиц золота и нестехиометрического оксида кремния

In this work, the morphology, structural and optical properties of a composite material based on gold nanoparticles and a thin film of amorphous non-stoichiometric silicon oxide (a-SiOx, x = 1.8) were studied for the first time. Based on the results obtained, it was experimentally shown that the a-SiO1.8 layer conformally covered the spherical nanoparticles. An analytical model based on the Mie theory well described the optical properties of the gold nanoparticles and the composite material in the ultraviolet region of the spectrum obtained from the experiment, as well as the change in the amplitude of the plasmon peak that occurs during the formation of the composite material.

(Gold nanorod core)/(poly(3,4-ethylene-dioxythiophene) shell) nanostructures and their monolayer arrays for plasmonic switching

(Gold nanorod core)/(poly(3,4-ethylene-dioxythiophene) shell) nanostructures are prepared. The nanostructure arrays exhibit a remarkable and reversible plasmon peak shift of about 70 nm by controlling the doping level of the polymer shell.

Усиление фотолюминесценции и комбинационного рассеяния в гибридных тонкопленочных структурах a-C:H с наночастицами серебра

n this work, we studied changes in the spectra of optical density, photoluminescence (PL) and Raman spectra of hybrid thin-film structures based on a-C: H and granular silver films before and after annealing of samples at 200 ° C. The hypsochromic shift of the main plasmon peak, the formation of double resonance spectra, and an increase in the band intensity were observed after annealing of samples with the gravimetric Ag film thickness of 10 nm. The influence of both the morphology of the nanostructure of Ag films and the features of the electronic structure of a-C: H films were observed on the plasmon enhancement of the PL and Raman spectra. For samples based on a-C:H with an optical gap Eg = 0.4 eV, a more effective PL enhancement was observed after annealing of the samples. At the same time, in the samples with Eg = 2.7 eV, the PL intensity practically did not change, remaining higher. The amplification of resonant Raman scattering was selective. It was associated with scattering by polycyclic aromatic groups predominant in the structure of the a-C: H film with a narrower optical gap.

Polyelectrolyte-Coated Gold Nanoparticles: The Effect of Salt and Polyelectrolyte Concentration on Colloidal Stability

Gold nanoparticles are widely used in biomedical applications. Their ease of surface modification, biocompatibility and the presence of surface plasmons makes them ideal tools for a variety of investigations. Polyelectrolyte-coated gold nanoparticles are employed in areas such as imaging, drug delivery and gene therapy; however, it is not well understood how different factors such as the polyelectrolyte and salt concentration affect the coating on the nanoparticles and hence their performance. Here, these parameters were systematically varied and their effect on the stability of the colloidal nanoparticle suspension was monitored. An increase in the polyelectrolyte concentration from 0 to 30 mg/mL led to a red shift of the surface plasmon peak and an increase in the zeta potential. Concentrations between 5 mg/mL and 30 mg/mL resulted in the most stable systems, with 1 mg/mL being the most unstable. Stable nanoparticle suspensions were formed in salt concentrations below 50 mM, while higher concentrations caused colloidal instability and irreversible aggregation.

Investigation on the Effect of Centrifugation Speed on the Shape Separation of Gold Nanorods

High-quality gold nanorods (AuNRs) with a uniform aspect ratio and sizes are crucial for applications in biomedical or sensor industry. AuNRs is implementing Localized Surface Plasmon Resonance (LSPR) as sensing method which is highly dependent on the size, separation of nanoparticles, aspect ratio and the shape of the nanoparticles. Thus, in this process, the shape, surface density and aspect ratio of AuNRs were investigated to be used further as LSPR sensing material. The AuNRs was prepared using Seed Mediated Growth Method (SMGM) and the growth solution of the AuNRs was centrifuged with the speed ranging from 2500 rpm to 5000 rpm to separate the particles shaper prior to deposition as thin film. The XRD result shows the peak at 2θ = 38º which shows the (111) crystal orientation of the AuNRs. There are also two distinct peaks formed at the absorption spectra graph obtained from the UV-Vis result which associated with transverse plasmon peak (t-LSPR) and longitudinal plasmon peak (l-LSPR). The t-LSPR peak is significantly smaller than the l-LSPR and located in the wavelength ranges from 500 nm to 560 nm whereas the l-LSPR of the AuNRs shows a stronger and a higher peak which is located in the wavelength ranges from 700 nm to 780 nm. The morphological analysis using FESEM shows that the higher centrifugation speed separates the AuNRs with higher aspect ratio and higher surface density.