SERS Tags Derived from Silver Nanoparticles and Aryl Diazonium Salts for Cell Raman Imaging

The surface functionalization of silver nanoparticles (NPs) by Raman reporters has stimulated a wide interest in recent years for the design of Surface-Enhanced Raman Spectroscopy (SERS) labels. However, silver NPs...

Combining antibiotics with silver nanoparticles: A potential treatment strategy against antimicrobial resistance

Growing resistance to currently approved antibiotics is posing serious concern worldwide. The multidrug-resistant organisms are a major cause of mortality and morbidity around the globe. The limited options to treat infections caused by resistant organism requires alternative strategies to increase the effectiveness of antibiotic for better clinical outcomes. Recent advances in nanotechnology have enabled the drugs to be used in nanoscale to increase the effectiveness of antibiotics. The use of nanoparticles to treat infectious diseases has a long history in the pharmaceutical market, and the versatility of these particles to incorporate various materials as carriers make it an attractive option to combat the current crisis of emerging antibacterial resistance. Silver, a metal with many medical applications, has inherent antimicrobial properties. Therefore, silver NPs are appearing as one of the best options to be used in combination with antibiotics to increase effectiveness against resistant bacteria. Here, we discuss the applications and mechanisms of silver NPs to treat microbial resistance in light of recent research.

Peculiarities of synthesis and bactericidal properties of nanosilver in colloidal solutions, SiO2 films and in the textile structure: a review

The aim of this work is a comparative analysis of the biocidal efficiency of Ag nanoparticles (NPs) in the colloidal state, in the structure of films and dispersions of SiO2 and in the composition of textile fabrics, dependent on the method of synthesis, based on literature data and on own researches. Chemical reduction of silver (with borohydrides, hydrogen, hydrazine, etc.) allows one to adjust and control the size and shape of NPs. The shape of the NPs is mostly spherical, what is confirmed by the presence of a band of surface plasmon resonance in absorption spectra and by electron microscopy measurements. To prevent aggregation of NPs obtained by the method of chemical reduction in solution, the optimal ratio of two stabilizers based on surfactants and polymer at their minimum concentration was found, namely NaBH4 as a reductant and polyvinylpyrrolidone + sodium dodecyl sulfate as binary stabilizer of Ag NPs, with bactericidal activity of 99 % and stability for more than 3 years. Chemical reduction of silver ions was carried out also by the amino acid tryptophan (Trp) which has a dual function – a biocompatible reducing agent and stabilizer of silver NPs while maintaining their shape, size and stability for long-term use. Effective methods of photochemical synthesis of Ag NPs have been developed in different ways: by UV irradiation of Ag+ ions in solution in the presence of solid-state photosensitizer SiO2 with adsorbed benzophenone (SiO2/BPh); by UV irradiation of Ag+ ions in solution in the presence of the amino acid tryptophan (Trp); on silica surface when Ag/SiO2 sol-gel films production via irradiation of adsorbed Ag+ ions on SiO2 film (Ag+/SiO2) in the BPh solution. It is shown that when Ag NPs are adsorbed on the surface of highly dispersed SiO2, the logarithm of the reduction of microorganisms reduces and the time of their deactivation increases. A cheap and convenient way to modify of cotton textiles with Ag NPs by soft heat treatment of Ag+/cotton samples with high (90–95 %) efficiency of destruction of bacteria E. coli, K. pneumoniae, E. aerogenes, P. vulgaris, S. aureus, C. albicans, etc., with saving of biocidal activity after 5 cycles of washing has been developed. The dynamics of silver ions release from the surface of NPs in the structure of textile upon their contact with water for 72 hours and the number of irreversibly bound particles have been studied. The electrical resistance of the tissue is proportional to the quantity of NPs. That is NPs in the structure are in different degrees of binding, a certain part of them is retained (adsorbed) irreversibly, saving bactericidal properties after repeated contacts with water. On the basis of literature analysis it is shown that ecologically safe “green synthesis” is a promising way to silver NPs produce with pronounced bactericidal efficiency, which is becoming more common due to the large resource of cheap plant raw materials.

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.

Investigation of laser and thermal sintering processes of silver nanoparticles agglomerates synthesized by spark discharge

Changes in the shape and size of silver nanoparticles (NPs) during their laser and thermal sintering have been studied experimentally and theoretically. Aerosol silver NPs forming dendrid-like agglomerates 180 nm in size were synthesized by spark discharge and exposed to laser radiation and high temperature of 750 °C. The shape and size of the NPs were investigated depending on the power of the laser radiation and the temperature of the gas. It is estimated that, at a power density of laser radiation of the order of 103-104 W/cm2, the formation of spherical NPs with an average size of 140 nm is expected. Such particles turn out to be similar to NPs thermally heated in a gas flow at 750 °C for 6 seconds.

Nanoengineering of eco-friendly silver nanoparticles using five different plant extracts and development of cost-effective phenol nanosensor

The production of environmentally friendly silver nanoparticles (AgNPs) has aroused the interest of the scientific community due to their wide applications mainly in the field of environmental pollution detection and water quality monitoring. Here, for the first time, five plant leaf extracts were used for the synthesis of AgNPs such as Basil, Geranium, Eucalyptus, Melia, and Ruta by a simple and eco-friendly method. Stable AgNPs were obtained by adding a silver nitrate (AgNO3) solution with the leaves extract as reducers, stabilizers and cappers. Only, within ten minutes of reaction, the yellow mixture changed to brown due to the reduction of Ag+ ions to Ag atoms. The optical, structural, and morphology characteristics of synthesized AgNPs were determined using a full technique like UV–visible spectroscopy, FTIR spectrum, XRD, EDX spectroscopy, and the SEM. Thus, Melia azedarach was found to exhibit smaller nanoparticles (AgNPs-M), which would be interesting for electrochemical application. So, a highly sensitive electrochemical sensor based on AgNPs-M modified GCE for phenol determination in water samples was developed, indicating that the AgNPs-M displayed good electrocatalytic activity. The developed sensor showed good sensing performances: a high sensitivity, a low LOD of 0.42 µM and good stability with a lifetime of about one month, as well as a good selectivity towards BPA and CC (with a deviation less than 10%) especially for nanoplastics analysis in the water contained in plastics bottles. The obtained results are repeatable and reproducible with RSDs of 5.49% and 3.18% respectively. Besides, our developed sensor was successfully applied for the determination of phenol in tap and mineral water samples. The proposed new approach is highly recommended to develop a simple, cost effective, ecofriendly, and highly sensitive sensor for the electrochemical detection of phenol which can further broaden the applications of green silver NPs.

Photophysical Approach of Biological Active Benzofuran Derivatized Pyrrole with Green Synthesized Silver NPs Using C. Roseus Leaves: Computational and Spectroscopic Study

The electronic absorption and fluorescence emission spectra of N-(2,5-dimethyl-pyrrol-1-yl)-2-(5-methoxybenzofuran-3-yl)acetamide (DPMA) molecule were recorded in various solvents at room temperature with the aim of estimation of ground state (\({\mu }_{g}\)) and excited states (\({\mu }_{e}\)) dipole moments using Lippert’s, Bakshiev’s and Kawski-Chamma-Viallete’s equations. The results were signified that, the excited state dipole moment is greater than the ground state dipole moment, which indicates the excited state dipole moment is more polar than the ground state dipole moment. Ecofriendly green synthesis of silver nanoparticles (Ag NPs) were synthesized using catharanthus roseus (C.R) leaf extract was done. These synthesized Ag NPs were used as fluorescence quenchers. Fluorescence lifetime measurement is carried out using time correlated single photon counting technique of DPMA molecule with various concentrations of Ag NPs. A linear Stern-Volmer (S-V) plot was obtained in steady state and transient state method. Furthermore we have estimated computational calculations such as ground state optimized geometry, molecular electrostatic potential (MEP), highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), experimental and theoretical energy band gap, solvent polarity and normalized solvent polarity values. Morphology and sizes of green synthesized silver NPs were characterized by transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy (EDX) and also characterized by UV-Visible absorption.

Long-Term Stable Structures Formed by Ion-Beam Modification of Silver Film for SERS Applications

Ensembles of silver nanoparticles (NPs) with size ~45 nm formed from the silver film using an ion beam modification are studied. The optical spectroscopy demonstrated that the fabricated ensembles of silver NPs keep stable their plasmonic properties in an ambient atmosphere for at least 39 days due to their monocrystalline nature. We use the scanning Raman microscope to map the SERS from Crystal Violet homogeneously adsorbed on these ensembles. It was found that the manufactured ensembles have a strong amplification factor, and this factor is preserved for these ensembles even after more than one month of storage in the surrounding atmosphere. Hereby, by ion beam modification of silver film, it is possible to fabricate the NPs with stable plasmonic properties and form nanostructured surfaces to be applied in sensor technologies and SERS.

Effect of Rate and Quantum Yield of 1-alkyl-2-(arylazo) Imidazoles on the Surface of Silver Nps

1-Alkyl-2-(arylazo)imidazole(RaaiR/) exists in trans-structure about –N=N- bond at ambient condition. Upon optical excitation in UV region the trans-RaaiR/ isomerises to cis-RaaiR/. The photochromism is very susceptible to internal substituents and external environment like solvent polarity, viscosity and presence of innocent foreign molecule. The changes from cis-to-trans occurs slowly in visible light excitation it has significantly faster rate at higher temperature. In this work we have studied the effect of silver nanoparticle on the photochromic activity of RaaiR/. The quantum yield of the photoisomerisation is dropped by 9-27% in inclusion phase AgNPs@RaaiR/ than free state and the order of rate is: free state > silver nano particle. The activation energy (Ea) of cis to trans isomerisation is also diminished compared to free state of photochrome.

Synthesis of Biogenic silver nanoparticles using plant growth-promoting bacteria: Potential use as biocontrol agent against phytopathogens

Biogenic nanoparticles (NPs) derived from microbes present an excellent opportunity to deal with various challenges in medicine, diagnosis, environment and agriculture. In the area of agriculture sciences, researchers are facing challenges related to excessive utilization of pesticides which can be answered by utilizing plant growth-promoting (PGP) microbes. Herein, we have employed the culture filtrate of two PBP bacteria strains, Serratia marcescens and Burkholderia cepacia to prepare biogenic silver NPs. The biogenic silver NPs were characterized by various techniques viz. UV-VIS spectroscopy, SEM, XRD and FTIR. The biogenic AgNPs were able to control the growth of phytopathogenic fungi Aspergillus niger, A. fumigatus, Fusarium oxysporum, Pythium sp., and Rosellinia sp. by more than 80% as examined by in vitro growth reduction on agar medium. Very significantly, the growth inhibition of seedlings by phytopathogenic fungi was efficiently rescued using biogenic AgNPs derived from PGP bacteria. These results indicate the potential use of biogenic NPs to reduce the burden of chemical-based pesticides.