L-Cysteine and N-acetyl-L-cysteine-mediated synthesis of nanosilver-based sols and hydrogels with antibacterial and antibiofilm properties.

The need of the synthesis of a new generation of medicines aimed at combating bacteria and biofilms that cause various infections is a great urgency. There has been a gradual decrease in the conventional techniques of treatment with the use of antibiotics. Consequently, much effort has focused on the search for new methods and approaches to obtain antibacterial drugs and determine their rational use such that microorganisms do not acquire resistance. Although silver nanoparticles (AgNPs) and silver nanoclusters (AgNCs) have exhibited certain levels of effectiveness against multidrug-resistant bacteria and biofilms, there are very few simple, cheap and easy-to-scale methods to obtain AgNPs and AgNCs with well-desired characteristics. In this study, we carried out the one-pot synthesis of sols and gels containing AgNPs and AgNCs using only L-cysteine (CYS) or N-acetyl-L-cysteine (NAC), as bioreducing/capping/gel-forming agents, and different silver salts - nitrate, nitrite and acetate. HRTEM, SAED, EDX mapping, AFM, SEM, EDX, ICP-MS and FTIR spectroscopy analysis confirmed the formation of spherical/elliptical CYS-AgNP and NAC-AgNC particles consisting of AgNPs or AgNCs "core" and CYS/Ag+ or NAC/Ag+ complexes "shell" with mean average diameters of 10 and 5 nm, respectively. UV-Vis spectroscopy fixed the localized surface plasmon resonance (LSPR) at 390-420 nm for the CYS-AgNPs systems and LSPR absence for the NAC-AgNCs ones. DLS and nanoparticle tracking analysis (NTA) data indicated that the mean average diameter of the particles is about 80 nm for the CYS-AgNPs systems and 20 nm for the NAC-AgNCs ones. The Zeta potential measurements showed that the particles possess positive and negative charge values for CYS-AgNPs and NAC-AgNCs systems, respectively. The prepared materials demonstrated the high antibacterial activity against the most common types of bacteria at the MIC range of 10-100 µM, wherein the effect of the NAC-AgNCs systems is 2 times stronger than that of the CYS-AgNPs ones. Both systems are non-toxic or have low-toxicity at 300 µM for normal human cells: erytrocytes, fibroblasts and macrophages. Sols and hydrogels in the concentration range of 20-40 µM showed the complete inhibition of the formation of biofilms from Acinetobacter baumannii and Pseudomonas aeruginosa, which belong to the ESKAPE pathogenes group and represent the most serious problem in practical medicine. NAC-AgNCs systems were the most active. The simple strategy of the preparation of AgNP/AgNC-based sols and gels, along with their pronounced antibacterial and antibiofilm activity, could open new perspectives for its applications in medicine.

Spark Discharge Synthesis and Characterization of Ge/Sn Janus Nanoparticles.

Germanium-tin nanoparticles are promising materials for near- and mid-infrared photonics thanks to their tunable optical properties and compatibility with silicon technology. This work proposes modifying the spark discharge method to produce Ge/Sn aerosol nanoparticles during the simultaneous erosion of germanium and tin electrodes. Since tin and germanium have a significant difference in the potential for electrical erosion, an electrical circuit damped for one period was developed to ensure the synthesis of Ge/Sn nanoparticles consisting of independent germanium and tin crystals of different sizes, with the ratio of the atomic fraction of tin to germanium varying from 0.08 ± 0.03 to 0.24 ± 0.07. We investigated the elemental and phase composition, size, morphology, and Raman and absorbance spectra of the nanoparticles synthesized under different inter-electrode gap voltages and the presence of additional thermal treatment directly in a gas flow at 750 °C. The research shows that the in-flow thermal treatment of aerosol-agglomerated nanoparticles produced special individual bicrystalline Janus Ge/Sn nanoparticles with an average size of 27 nm and a decreasing absorption function with a changing slope at 700 nm.

Plasmon-Enhanced Ultraviolet Luminescence in Colloid Solutions and Nanostructures Based on Aluminum and ZnO Nanoparticles.

Aluminum nanoparticles attract scientific interest as a promising low-cost material with strong plasmon resonance in the ultraviolet region, which can be used in various fields of photonics. In this paper, for the first time, ultraviolet luminescence of zinc oxide nanoparticles in colloid solutions and nanostructure films in the presence of plasmonic aluminum nanoparticles 60 nm in size with a metal core and an aluminum oxide shell were studied. Mixture colloids of ZnO and Al nanoparticles in isopropyl alcohol solution with concentrations from 0.022 to 0.44 g/L and 0.057 to 0.00285 g/L, correspondingly, were investigated. The enhancement of up to 300% of ZnO emission at 377 nm in colloids mixtures with metal nanoparticles due to formation of Al-ZnO complex agglomerates was achieved. Plasmon nanostructures with different configurations of layers, such as Al on the surface of ZnO, ZnO on Al, sandwich-like structure and samples prepared from a colloidal mixture of ZnO and Al nanoparticles, were fabricated by microplotter printing. We demonstrated that photoluminescence can be boosted 2.4-fold in nanostructures prepared from a colloidal mixture of ZnO and Al nanoparticles, whereas the sandwich-like structure gave only 1.1 times the amplification of luminescence. Calculated theoretical models of photoluminescence enhancement of ideal and weak emitters near aluminum nanoparticles of different sizes showed comparable results with the obtained experimental data.

Investigation of Nonlinear Optical Processes in Mercury Sulfide Quantum Dots.

The authors report the third-harmonic generation, nonlinear refraction, and nonlinear absorption in HgS quantum dot (QD) suspensions and films using the nanosecond and femtosecond pulses. High conversion efficiency (7 × 10-4) towards the third harmonic (TH) of the 900-1700 nm, 150 fs laser in the thin (70 nm) films containing HgS QDs deposited on the glass substrates is obtained. The authors analyze spectral dependencies of the TH, nonlinear refractive indices, and nonlinear absorption coefficients of QDs in the 500-1700 nm range and discuss the relation between the TH process and the low-order nonlinear optical properties of these quantum dots.

Third-order optical nonlinearities of exfoliated Bi2Te3 nanoparticle films in UV, visible and near-infrared ranges measured by tunable femtosecond pulses.

We characterize the nonlinear optical properties of synthesized Bi2Te3 nanoparticle-contained thin films using the tunable femtosecond laser in the spectral range of 400-1000 nm. These nanoparticles possess a strong saturable absorption and positive nonlinear refraction (-6.8×10-5 cm W-1 in the case of 500 nm, 150 fs probe pulses, and 3×10-10 cm2 W-1 in the case of 400 nm, 150 fs probe pulses, respectively). The spectral, intensity, and temporal variation of saturable absorption and nonlinear refraction of the thin films containing exfoliated Bi2Te3 nanoparticles are discussed.

Nonlinear Absorption and Refraction of Picosecond and Femtosecond Pulses in HgTe Quantum Dot Films.

We report measurements of the saturated intensities, saturable absorption, and nonlinear refraction in 70-nm thick films containing 4 nm HgTe quantum dots. We demonstrate strong nonlinear refraction and saturable absorption in the thin films using tunable picosecond and femtosecond pulses. Studies were carried out using tunable laser pulses in the range of 400-1100 nm. A significant variation of the nonlinear refraction along this spectral range was demonstrated. The maximal values of the nonlinear absorption coefficients and nonlinear refractive indices determined within the studied wavelength range were -2.4 × 10-5 cm2 W-1 (in the case of 28 ps, 700 nm probe pulses) and -3 × 10-9 cm2 W-1 (in the case of 28 ps, 400 nm probe pulses), respectively. Our studies show that HgTe quantum dots can be used in different fields e.g., as efficient emitters of high-order harmonics of ultrashort laser pulses or as laser mode-lockers.

Ag/α-Ag2MoO4/h-MoO3 nanoparticle based microspheres: synthesis and photosensitive properties.

We report a new and the most simple strategy for the synthesis of silver molybdate functional composite microspheres based on low molecular weight gelators -amino acids, silver salts and heptamolybdate ions. The resulting material shows a high photocatalytic activity with respect to the methylene blue dye degradation at neutral pH.

Synthesis and low-order optical nonlinearities of colloidal HgSe quantum dots in the visible and near infrared ranges.

We synthesize colloidal HgSe quantum dots and characterize their nonlinear refraction and nonlinear absorption using a Nd:YAG laser and its second harmonic. The 7.5 nm quantum dots were synthesized using the hot-injection method. The nonlinear absorption (ß = 9×10-7 cm W-1) and negative nonlinear refraction (γ = -5×10-12 cm2 W-1) coefficients of colloidal quantum dots were determined using the 10 ns, 532 nm laser radiation. The joint influence of above processes was realized at a higher intensity of probe pulses. In the case of 10 ns, 1064 nm radiation, only negative nonlinear refraction dominated during z-scans of these quantum dots. The studies of optical limiting using two laser sources demonstrated the effectiveness of this process at 532 nm. The role of nonlinear scattering is analyzed. We discuss the mechanisms responsible for the nonlinear refraction processes in colloidal HgSe quantum dots.

Microplotter printing of planar solid electrolytes in the CeO2-Y2O3 system.

The formation process for planar solid electrolytes in the CeO2-Y2O3 system has been studied using efficient, high-performance, high-resolution microplotter printing technology, using functional ink based on nanopowders (the average size of crystallites was 12-15 nm) of a similar composition obtained by programmed coprecipitation of metal hydroxides. The dependence of the microstructure of the oxide nanoparticles obtained and their crystal structure on yttrium concentration has been studied using a wide range of methods. According to X-ray diffraction (XRD), the nanopowders and coatings produced are single-phase, with a cubic crystal structure of the fluorite type, and the electronic state and content of cerium and yttrium in the printed coatings have been determined using X-ray photoelectron spectroscopy (XPS). The results of scanning electron (SEM) and atomic force microscopy (AFM) have shown that the coatings produced are homogeneous, they do not contain defects in the form of fractures and the height difference over an area of 1 µm2 is 30-45 nm. The local electrophysical characteristics of the oxide coatings produced (the work function of the coating surface, capacitance values, maps of the surface potential and capacitive contrast distribution over the surface) have been studied using Kelvin-probe force microscopy (KPFM) and scanning capacitive microscopy (SCM). Using impedance spectroscopy, the dependence of the electrophysical characteristics of printed planar solid electrolytes in the CeO2-Y2O3 system on yttrium content has been determined and the prospects of the technology developed for the manufacture of modern, intermediate-temperature, solid oxide fuel cells have been demonstrated.

Synthesis of Nanoparticles by Spark Discharge as a Facile and Versatile Technique of Preparing Highly Conductive Pt Nano-Ink for Printed Electronics.

A cost-effective, scalable and versatile method of preparing nano-ink without hazardous chemical precursors is a prerequisite for widespread adoption of printed electronics. Precursor-free synthesis by spark discharge is promising for this purpose. The synthesis of platinum nanoparticles (PtNPs) using a spark discharge under Ar, N2, and air has been investigated to prepare highly conductive nano-ink. The size, chemical composition, and mass production rate of PtNPs significantly depended on the carrier gas. Pure metallic PtNPs with sizes of 5.5 ± 1.8 and 7.1 ± 2.4 nm were formed under Ar and N2, respectively. PtNPs with sizes of 18.2 ± 9.0 nm produced using air consisted of amorphous oxide PtO and metallic Pt. The mass production rates of PtNPs were 53 ± 6, 366 ± 59, and 490 ± 36 mg/h using a spark discharge under Ar, N2, and air, respectively. It was found that the energy dissipated in the spark gap is not a significant parameter that determines the mass production rate. Stable Pt nano-ink (25 wt.%) was prepared only on the basis of PtNPs synthesized under air. Narrow (about 30 µm) and conductive Pt lines were formed by the aerosol jet printing with prepared nano-ink. The resistivity of the Pt lines sintered at 750 °C was (1.2 ± 0.1)·10-7 Ω·m, which is about 1.1 times higher than that of bulk Pt.

Hematite Nanoparticles from Unexpected Reaction of Ferrihydrite with Concentrated Acids for Biomedical Applications.

The development of synthetic ways to fabricate nanosized materials with a well-defined shape, narrow-sized distribution, and high stability is of great importance to a rapidly developing area of nanotechnology. Here, we report an unusual reaction between amorphous two-line ferrihydrite and concentrated sulfuric or other mineral and organic acids. Instead of the expected dissolution, we observed the formation of new narrow-distributed brick-red nanoparticles (NPs) of hematite. Different acids produce similar nanoparticles according to scanning (SEM) and transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray diffraction (XRD), infrared spectroscopy (FTIR), and energy-dispersive X-ray spectroscopy (EDX). The reaction demonstrates new possibilities for the synthesis of acid-resistant iron oxide nanoparticles and shows a novel pathway for the reaction of iron hydroxide with concentrated acids. The biomedical potential of the fabricated nanoparticles is demonstrated by the functionalization of the particles with polymers, fluorescent labels, and antibodies. Three different applications are demonstrated: i) specific targeting of the red blood cells, e.g., for red blood cell (RBC)-hitchhiking; ii) cancer cell targeting in vitro; iii) infrared ex vivo bioimaging. This novel synthesis route may be useful for the development of iron oxide materials for such specificity-demanding applications such as nanosensors, imaging, and therapy.