Colloidal Solution Of Nanoparticles Research Articles

On-demand nanoparticle-on-mirror (NPoM) structure for cost-effective surface-enhanced Raman scattering substrates

We report a robust technique to fabricate a cost-efficient Raman substrate which is composed of polyvinylpyrrolidone (PVP) coated gold nanoparticles layer on commercial aluminum foil. The layer of metal nanoparticles on the aluminum foil, i.e., the nanoparticle-on-mirror (NPoM) structure was fabricated by spraying nanoparticle colloidal solution directly on the foil. The detection limit (LOD) of NPoM substrate is investigated by performing the SERS for Rhodamine 6G (R6G) with the concentration ranging from mM to nM without any post treatment of the substrate. The findings show that the LOD of 1 nM and maximum intensity enhancement factor of ~ 24 is accomplished. Field enhancement owing to reflection from the metallic mirror is the reason behind the signal enhancement and it would be beneficial for routine clinical applications, trace chemical detection, and disease diagnostics.

Photoluminescent Recognition of Strong Alcoholic Beverages with Carbon Nanoparticles.

A simple sensitive method for nonspecific recognition of armagnac, cognac, whiskey, and ethanol/water mixture was developed by using photoluminescence (PL) of carbon nanoparticles (NPs). The carbon NPs were synthesized from the mixture of urea and anhydrous citric acid, followed by few annealing processes to achieve the full effect by solvothermal carbonization. PL features of carbon NPs depend on the alcohol environments in which the NPs are dispersed. PL/PL excitation maps of the alcoholic beverages were mathematically treated, and a final principal component analysis diagram allows visualization of different clusters corresponding to each beverage. The optimal measurement conditions (concentration of NPs in colloidal solution and excitation wavelength) were defined to ensure a reliable recognition level.

Genomic Damage Induced in Nicotiana tabacum L. Plants by Colloidal Solution with Silver and Gold Nanoparticles.

Tobacco seedlings (Nicotiana tabacum L cv. Wisconsin 38) were treated for 24 h with colloidal solution of silver and gold nanoparticles (AgNPs and AuNPs) of different size or cultivated for 8 weeks on soil polluted with these NPs. DNA damage in leaf and roots nuclei was evaluated by the comet assay. AgNPs of the size 22–25 nm at concentrations higher than 50 mg·L−1 significantly increased the tail moments (TM) values in leaf nuclei compared to the negative control. Ag nanoparticles of smaller size 12–15 nm caused a slight increase in tail moment without significant difference from the negative control. The opposite effect of AgNPs was observed on roots. The increasing tail moment was registered for smaller NPs. Similar results were observed for AuNPs at a concentration of 100 mg·L−1. DNA damaging effects after growing tobacco plants for 8 weeks in soil polluted with AgNPs and AuNPs of different size and concentrations were observed. While lower concentrations of both types of particles had no effect on the integrity of DNA, concentration of 30 mg·kg−1 of AgNPs caused significant DNA damage in leaves of tobacco plants. AuNPs had no effect even at the highest concentration. The content of Ag was determined by ICP–MS in above-ground part of plants (leaves) after 8 weeks of growth in soil with 30 mg·kg−1. AgNPs and was 2.720 ± 0.408 µg·g−1. Long term effect is much less harmful probably due to the plant restoration capability.

Fabrication of gold-immobilized quantum dots/silica core–shell nanoparticles and their multimodal imaging properties

This work describes the fabrication of quantum dot (QD)/silica (SiO2) core–shell particles immobilized with Au nanoparticles and the evaluation of their abilities in fluorescence and x-ray computed tomography (CT) imaging. The QD nanoparticles were coated with silica shells by a sol-gel method using tetraethyl orthosilicate (QD/SiO2). Reduction of Au3+ in a citrate aqueous solution gave an Au nanoparticle colloidal solution. (3-Mercaptopropyl)trimethoxysilane thiolated the QD/SiO2 particle surface (QD/SiO2/SH). Immobilization of the Au nanoparticles on the QD/SiO2/SH particle surface was performed with the addition of the Au nanoparticle colloidal solution to the QD/SiO2/SH nanoparticle colloidal solution (QD/SiO2/SH/Au). Surface-PEGylated QD/SiO2/SH/Au particles were fabricated using thiol-terminated polyethylene glycol (PEG) (QD/SiO2/SH/Au/PEG). The QD/SiO2/SH/Au/PEG nanoparticle colloidal solution was imaged by fluorescence and x-ray CT imaging techniques. The CT value per unit concentration of Au (M) for the QD/SiO2/SH/Au/PEG nanoparticle colloidal solution was 1.5 × 104 HU/M. The QD/SiO2/SH/Au/PEG nanoparticle colloidal solution was injected into the tail vein of a mouse and circulated in the blood, although some QD/SiO2/SH/Au/PEG nanoparticles were trapped and remained in the liver and spleen.

Solgel synthesis of Gd2O3:Nd3+ nanopowders and the study of their luminescent properties

The paper presents the results of the sol-gel synthesis of Gd2O3:Nd3+ nanopowders by the citrate method, as well as the study of their structure and luminescent properties. A technique for using two different organic stabilizers with different thermal stability in sol-gel synthesis has been proposed and tested. The luminescent properties of the obtained Gd2O3:Nd3+ powders have been studied in the ultraviolet and near infrared spectral regions. The citrate sol-gel method was used to synthesize the materials. Aqueous solutions of metal nitrates were used as the main initial components. Citric acid and polyvinylpyrrolidone were used as organic modifying components, playing a double role in the synthesis process, i.e. acting as stabilizers of forming nanoparticles in colloidal solutions and serving as a fuel additive in the process of heat treatment of materials. Infrared spectroscopy and differential thermal and thermogravimetric analyses were used to study the evolution of the structure of materials during synthesis. Crystalline Gd2O3:Nd3+ nanopowders were obtained by a low-temperature sol-gel method using citric acid and polyvinylpyrrolidone as stabilizers. The data of infrared spectroscopy and differential thermal and thermogravimetric analyses show that the formation of Gd2O3:Nd3+ nanoparticles begins at the stage of the crude gel and the evolution process develops during the drying and heat treatment of materials. It is shown that the use of two different organic stabilizers with different thermal stability provides stabilization of the forming Gd2O3:Nd3+ nanoparticles at different stages of synthesis in a wide temperature range. The luminescence spectra are observed in the UV spectral region under excitation of the synthesized nanopowders by radiation with a wavelength of 238 nm. They are determined by electronic transitions in the Gd2O3 crystalline matrix. The synthesized Gd2O3:Nd3+ nanopowders exhibit intense photoluminescence in the UV and near-IR spectral regions. The results can be used in the development of a technology for the synthesis of various composite phosphors, as well as in the creation of luminescent nanopowders for nanothermometry in medicine.

Effect of laser beam propagation through the plasmonic nanoparticles suspension

Gold nanoparticles are excellent light absorbers at the surface plasmon resonance wavelength. This absorption process generates highly energetic electrons near the surface that enhances the local electric field on the gold nanoparticles surface, and results in modification of the refractive index. The present work focuses on interaction of the laser, both near and far from the resonance wavelength, with colloidal solution of plasmonic nanoparticles. For the laser beam interaction, we first prepared the gold nanoparticles by sol gel method and characterized the absorption spectrum in terms of particle size and morphology. The absorption peak in visible range confirmed to the formation of Au nanoparticles. Therefore, a laser at 532 nm was selected to study light matter interaction with Au nanoparticles in solution. The interaction produced diffraction rings, which changed shape over time due to convection of colloidal nanoparticles. In another experiment, a 405 nm laser with the same power produced only a laser spot on the screen. Thus, the 532 nm is closer to the surface plasmon excitation and is responsible for producing a pattern of diffraction rings in the far-field region. The produced diffraction rings provide a very simple and sensitive technique to find out induced nonlinear refractive index for the plasmonic nanoparticles. Finding plasmonic resonances holds importance for variety of applications in plasmonic sensing and these rings could be used to characterize the resonances.

Optical nonlinearities in chemically synthesized and femtosecond laser fabricated gold nanoparticle colloidal solutions

Gold nanoparticles prepared by two different methodologies, wet-chemical- citrate reduction synthesis and femtosecond laser ablation, are studied for optical nonlinearities. Femtosecond laser pulses at 800 nm wavelength are employed to study the optical nonlinear refraction and absorption through the Z-scan technique, up to 23.37 GW/cm2 laser intensities. Here we demonstrate the distinct crossovers of nonlinear absorption, from varieties of nonlinear absorption mechanisms, saturation of linear absorption, reverse saturation of absorption. The reverse saturation of absorption is primarily contributed by an initial two-photon absorption followed by three-photon absorption process. We could observe that in laser-ablated gold nanoparticles, the transition from saturable to reverse saturable absorption takes place at a lower excitation threshold compared to that in chemically produced samples. The nonlinear refraction data depicted a pronounced asymmetry for chemically synthesized samples, which could possibly be due to the dominance of absorption phenomenon. We observed that nonlinear refractive index of chemically produced samples is higher by one order of magnitude compared to those produced by laser ablation. An appealing application in optical limiting is studied, and we see that the laser-produced samples, due to their strong nonlinear absorption, serve as a suitable choice for the optical limiting application. This study provides an insight into the selection of synthesis method towards their optimized utilization in nonlinear optical domain given that we achieve particle size tunability in the two methods.

Spectroscopic characteristics of colloidal solutions of metal nanoparticles

Nanoparticles are finding more and more practical applications in various fields of human activity, including veterinary and medicine. Due to the fact that the effectiveness of activity of colloidal solutions of nanoparticles is directly related to the state of aggregation of nanosized particles, it is urgent to use fast and convenient methods for assessing the physicochemical characteristics of such preparations. Nanoparticles have unique optical properties that depend on their size and shape. They can be determined by the refractive index of the light on the surface of the nanoparticles in a phenomenon known as plasmon resonance, which makes UV-Vis spectroscopy a valuable tool for studying and evaluating the characteristics of nanomaterials. Goal of the study is to study the optical characteristics of several samples of colloids of nanoparticles of noble metals (silver) and bioelements (copper, silicon dioxide) in order to determine the possibility of further application of UV-Vis spectroscopy for evaluation of activity and stability of colloidal solutions of nanoparticles. Commercial preparations based on nanoparticles of noble metals (silver) or bioelements (copper, silicon dioxide) in working dilutions recommended by manufacturers were used to study optical characteristics of the colloidal solutions. Optical density and absorption spectra were determined at the wavelengths (nm): 300-800 nm. The f plasmon surface resonance has been found in all test preparations, while all of them exhibited obvious nonlinear optical properties. The most pronounced plasma resonance peak is found in the colloidal solution of silver nanoparticles within a wavelength of 420 nm. In the case of a colloidal solution of copper nanoparticles, the peak of plasmon resonance was less pronounced and had a red shift (peak at 560 nm). In the colloidal solution of silicon silica, the plasmon resonance was less pronounced than other test preparations, being shifted to the blue side of the spectrum (360 nm).

Experimental methods in chemical engineering: Zeta potential

AbstractZeta potential (ZP) is a parameter that expresses the electrochemical equilibrium between particles and liquids like in nanoparticle (NP) colloidal solutions with applications in medicine, pharmaceuticals, chemical production, mineral processing, and water and soil purification. Smoluchowski's theory applies to the ZP particles that are larger the interfacial layer but neglects surface conductivity. The Debye‐Hückel theory correctly approximates the concentration of ions in a double layer but fails to account for the dependence of ZP on the concentration of counterions. Determining ZP of NPs is essential to proper NP characterization. For instance, developing well‐defined therapeutic‐relevant nanoformulations needs information on NPs size, surface charge, stability and agglomeration behaviour. This approach has many practical challenges, from inadequate knowledge of operating standards to sampling, data interpretation and good laboratory practice for the experiments replicability. However, in drug delivery research, very little literature can provide a clear, succinct explanation of these techniques. Looking for specific guidelines to overcome frequently encountered problems during ZP measurements. This article explores factors influencing colloidal particle stability. Measurement criteria such as applied voltage, number of measurements, electrophoretic mobility (EPM), size distribution, surface shape, temperature, viscosity, particle concentration, zeta potential, nanoparticles, colloidal suspension, electrophoretic mobility, and pH.

ВПЛИВ НАНОЧАСТИНОК НА ЯКІСТЬ РОБОТИ ТЕПЛООБМІННИХ АПАРАТІВ МАЛОЇ ХОЛОДИЛЬНОЇ МАШИНИ

In recent years, a new direction of energy saving in small refrigeration machines has been widely studied in the world, namely the use of new classes of substances as a working fluid. Studies of the thermophysical properties of colloidal solutions of nanoparticles with oils and refrigerants show the high prospects for the use of this class of substances in refrigeration. Therefore, the task of studying heat exchangers operating as part of small refrigeration machines on nanofluids seems relevant. The article provides information on the prospects for the use of nanoparticles in heat exchangers of a re-frigeration machine running on isobutane. The influence of nano impurities is considered in the ex-ample of theoretical and experimental study of the capacitor. At the same time, modern studies of the influence of nanofluids on the heat exchange characteristics of heat exchangers of refrigeration ma-chines were taken into account. Experimental study of a small refrigeration machine running on iso-butane with nanoparticle impurities was performed on a calorimetric stand, which allows the machine to operate in a wide range of modes with support for specified cycle parameters and high-precision determination of the key performance of all elements of the refrigerator, including compressors and heat exchangers. The study showed the high prospects for the use in small refrigeration machines of condensers such as "pipe in a pipe" and the possibility of significantly improving their heat transfer characteristics through the use of nanofluids as a refrigerant. The results show an increase in the heat transfer coefficient in the condenser by 4.5-16 %.

Silicon and Silver Nanoparticles Obtained by Laser Ablation in Liquid

The obtained colloidal solutions of nanoparticles are studied during laser ablation of silicon and silver in ethanol. It is shown that silver nanoparticles are present in the form of both polycrystals and single crystals and have two polymorphic modifications with a cubic and a hexagonal structure. Silicon nanoparticles are mainly amorphous; there are also silicon nanoparticles with a single-crystal structure.

Electrospray deposition for single nanoparticle studies.

Single entity electrochemical (SEE) studies that can probe activities and heterogeneity in activities at nanoscale require samples that contain single and isolated particles. Single, isolated nanoparticles are achieved here with electrospray deposition of colloidal nanoparticle solutions, with simple instrumentation. Role of three electrospray (ES) parameters, viz. spray distance (emitter tip-to-substrate distance), ES current and emitter tip diameter, in the ES deposition of single Au nano-octahedra (Au ODs) is examined. The ES deposition of single, isolated Au ODs are analyzed in terms of percentage of single NPs and local surface density of deposition. The local surface density of ES deposition of single Au ODs was found to increase with decrease in spray distance and emitter tip diameter, and increase in ES current. While the percentage of single particle ES deposition increased with increase in spray distance and decrease in emitter tip size. No significant change in the single Au ODs ES deposition percentage was observed with change in ES current values included in this study. The most favourable conditions in the ES deposition of Au ODs in this study resulted in the local surface density of 0.26 ± 0.05 single particles per μm2 and observation of 96.3% single Au OD deposition.

Ultrastable Hydrophilic Gold Nanoclusters Protected by Sulfonic Thiolate Ligands

Increasing surface charge is a commonly used and efficient strategy to improve the stability of colloidal nanoparticles in solution, but the use of this strategy in metal nanoclusters (NCs) has not...

Water Decomposition Occurring During Laser Breakdown of Aqueous Solutions Containing Individual Gold, Zirconium, Molybdenum, Iron or Nickel Nanoparticles

Generation rates of hydrogen peroxide (H2O2), hydroxyl radicals (•OH), molecular hydrogen (H2), and molecular oxygen (O2) forming during the optical breakdown of aqueous colloidal solutions containing Au, Mo, Zr, Fe, and Ni nanoparticles have been studied. It is shown that the processes occurring during the dissociation of water molecules under the influence of laser breakdown plasma and leading to the formation of various chemical products depend on the material of the nanoparticles present in the colloid. It was found that the highest rates of generation of water decomposition products are observed in aqueous colloidal solutions of Fe and Ni nanoparticles. The use of Au nanoparticles leads to the lowest generation rate. In general, the materials from which the nanoparticles are made, depending on the efficiency of the formation of water decomposition products, are arranged as follows: Ni> Fe> Mo> Zr> Au.

Influence of Gases Dissolved in Water on the Process of Optical Breakdown of Aqueous Solutions of Cu Nanoparticles

The paper investigates the effect of gases dissolved in water on the processes occurring during the laser breakdown of colloidal solutions of nanoparticles. The dynamics of the dependences of the plasma luminosity and acoustic signals on the concentration of nanoparticles under irradiation of colloids of nanoparticles saturated with air, argon, and molecular hydrogen has been studied. It is shown that irradiation of colloids saturated with molecular hydrogen and argon leads to an increase in the integral luminosity and integral acoustic signals in comparison with the control sample saturated with atmospheric gases, which indicates the obvious presence of the influence of gases dissolved in the liquid on the optical breakdown process. The most intense acoustic signals, as well as the brightest breakdowns, were observed when the colloidal solution was saturated with molecular hydrogen.

Effect of Nano-colloidal Inks’ composition on the fabrication and properties of High-Quality Electrospray Coated Copper-Indium-diSelenide micro-films

A nano-particle solution processing route to the cost effective and easy fabrication of Copper Indium diSelenide (CIS) layers is presented in this study via the Electrospray Deposition of six different inks containing CIS nano-particle colloid solutions. Six different inks have been developed after synthesizing the CIS nanoparticles via solvo-thermal process. The inks differ from each other based on solvents and particle concentrations. Molybdenum coated glass was used as a substrate to deposit ~1 µm thick CIS layers. These deposited layers were then characterized according to their deposition parameters, surface morphology, structural analysis, transmittance behavior and electrical properties. Highly uniform chalcopyrite films were obtained with good purity and more than 90% absorbance characteristics with an average sheet resistivity of ~50 Ω.cm thereby confirming the applicability of the films to be utilized in the ultimate manufacture of solar cells.

On the measurements of magnetic nanoparticle concentration in a biological medium using a superconducting quantum magnetometer

Magnetic nano-particles are used in medicine both as medical means, and for the transport of medicines in the pathological area of an organism. Simultaneous influence on these particles of ultrasonic radiation and a constant magnetic field allows summarising a magnetic field of an nano-particles ensemble to the value, sufficient for its registration by the remote magnetic detector. The parity connecting the measured magnetic flux of the nanoparticles with parameters of the particles, ultrasound, and the measuring system using as the magnetic detector superconducting quantum magnetometer is received. Calculations have shown, that such a system can measure a concentration of the nano-particles in colloidal solution, modeling the biological medium, in the unattainable earlier dynamic range of values (from 1 vol % to 10−7 vol %).

Continuous Flow Synthesis of Iron Oxide Nanoparticles Using Water-in-Oil Microemulsion

A continuous laminar flow reactor for the synthesis of nanopowder in microemulsion is described. The reactor is suitable for separated handling with nucleation, growth, and stabilization processes. The synthesis of iron oxide nanoparticles was selected as a model case. A water−sodium dodecyl sulphate−cyclohexene system was used as the microemulsion system for dissolving reactive aqueous solution, precursor, and a particle stabilizer. The product was purified and transferred to the aqueous phase. The result was a colloid solution of iron oxide nanoparticles in water of 50–200 nm in size with a zeta potential ranging from –25 to –57 mV. The product was characterized by UV-VIS spectroscopy, powder XRD, dynamic light scattering, electron microscopy, and electron diffraction. The results showed that water-in-oil microemulsion method is useful for the synthesis of nanopowders to obtain large amounts of stable product.

Optical properties of colloidal solutions of metal nanoparticles

Nanoparticles are finding more practical applications in various fields of human activity, including veterinary and medicine. Due to the fact that the effectiveness of colloidal solutions of nanoparticles is directly related to their aggregate state, convenient methods for assessing the physicochemical characteristics of such preparations is of high priority. Nanoparticles have unique optical properties that depend on their size and shape. They can be determined by the refractive index of light on the surface of nanoparticles in a phenomenon known as plasmon resonance, which makes the UV-Vis spectroscopy a valuable tool for studying and evaluating the properties of nanomaterials. Optical characteristics of NPs colloidal solutions of noble metals (silver) or bioelements (copper, silicon dioxide) were determined at various wavelengths (nm): 300-800 nm. The surface plasmon resonance has been found in all test preparations, while all of them exhibited obvious nonlinear optical properties. The most pronounced plasmon resonance peak was found in the colloidal solution of silver NPs within a wavelength of 420 nm. In the case of a colloidal solution of copper NPs, the peak of plasmon resonance was less pronounced and had a red shift (peak at 560 nm). In the colloidal solution of silicon dioxide, the plasmon resonance was less pronounced than in other test preparations, being shifted to the blue side of the spectrum (360 nm). UV-Vis spectroscopy of metal NPs requires further studies to assess their stability and influence of various external factors on their activity

Synthesis of gold nanostar using chitosan as reductive agent by the seedless reduction method

The gold nanostars (AuNS) were prepared through seedless reductive method by using the natural biodegradable polymer chitosan acting both as the stabilizing and shape-directing agent, ascorbic acid as a reducting agent. This reaction synthesis was carried out at room temperature and facile conditions. In an effort to control the size and shape of AuNS, many experimental parameters were investigated for the thorough understanding the role of chitosan in the formation of gold nanostar. In this novel method, the pH condition and appropriate stabilizer concentration were crucial factors to prepare the well-defined AuNS. The obtained AuNS were characterized by many physical-chemistry analysis method such as transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), UV-Vis spectroscopy, dynamic light scattering (DLS), and X-Ray diffraction (XRD). The AuNS have an average size of about 55 nm and narrow size distribution when characterized by TEM images. UV-Vis spectroscopy of the gold nanoparticles colloidal solution showed the characteristic peaks at 587-700 nm, corresponding to the surface plasmon resonance of star-shaped nanostructure. The specific interactions between the functional groups of chitosan chain and the as-prepared gold nanostars are analyzed by the FT-IR spectroscopy technique. These results provided insight into the role of biopolymer as both a protecting agent and structure-directing agent. This novel method can overcome previous limitations in controlled synthesis of star-shaped gold nanoparticles such as surfactant use and complex implementation. Besides, the gold nanostars stabilized by chitosan could be a potential material in many applications in the field of biomedical medicine.