Colloidal Suspensions Of Nanoparticles Research Articles

Light Confinement with Structured Beams in Gold Nanoparticle Suspensions

We carry out an experimental campaign to investigate the nonlinear self-defocusing propagation of singular light beams with various complex structures of phase and intensity in a colloidal suspension of gold nanoparticles with a plasmonic resonance near the laser wavelength (532nm). Studying optical vortices embedded in Gaussian beams, Bessel vortices and Bessel-cosine (necklace) beams, we gather evidence that while intense vortices turn into two-dimensional dark solitons, all structured wavepackets are able to guide a weak Gaussian probe of different wavelength (632.8 nm) along the dark core. The probe confinement also depends on the topological charge of the singular pump.

Co-Encapsulation of Methylene Blue and PARP-Inhibitor into Poly(Lactic-Co-Glycolic Acid) Nanoparticles for Enhanced PDT of Cancer.

The development of resistance against photodamage triggered by photodynamic therapy (PDT) is ascribed mainly to the cellular redox defenses and repair. If the tumor tissue is not promptly eliminated by the first few PDT sessions, PDT-resistance can be favored, challenging the efficacy of the treatment. Although the mechanism of PDT resistance is still unclear, in vitro assays have evidenced that it can be developed through the PARP damage-repair signaling pathway. Therefore, inhibition of poly(adenosine diphosphate (ADP)-ribose) polymerase (PARP) has the potential to increase PDT efficacy. This work reports on the synthesis of a controlled release system of a photosensitizer, methylene blue (MB) and a PARP-inhibitor, the veliparib. MB and veliparib were co-encapsulated in poly(lactic-co-glycolic acid) (PLGA) nanoparticles (VMB-NPs). A colloidal stable aqueous suspension of nanoparticles was obtained. The average hydrodynamic diameter was 90 nm and a narrow size distribution was obtained, with a polydispersity index (PDI) of 0.08. The release kinetics of MB and veliparib from VMB-NPs showed an initial burst of 8.7% and 58.3% release of the total amounts of MB and veliparib respectively, in the first 6 h, and a delayed release of up to 11.3% and 70%, in 19 days, for MB and veliparib, respectively. The VMB-NPs showed no cytotoxicity in the dark but the viability of B16F10-Nex2 cells decreased by 36% when the cells were irradiated (102 J/cm2, 660 nm) and treated with VMB-NPs containing 1.0 µM of MB and 8.3 µM of veliparib. Considering the increased photoactivity even at low MB and veliparib concentrations and the absence of cytotoxicity in dark, the co-encapsulation of MB and veliparib was shown to be a promising strategy to improve the PDT efficacy.

Opal-based terahertz optical elements fabricated by self-assembly of porous SiO2 nanoparticles.

In this paper, we study artificial opals as a promising material platform for terahertz (THz) optics. Materials were synthesized using self-assembly of porous SiO2 nanoparticles and annealing at different temperatures to further tune their optical properties. Two distinct approaches for the fabrication of bulk THz optics from these novel materials were considered. First, THz cylindrical lenses of identical geometry but different refractive indices and focal lengths were produced using standard mechanical processing of opals, in order to highlight their compatibility with conventional technologies of bulk optics fabrication. Second, a THz axicone was made via direct sedimentation of aqueous colloidal suspension of SiO2 nanoparticles in the mold of geometry inverse to that of a desired optical shape, followed by annealing and polishing. The second approach has an advantage of being considerably less labor intensive, while capable of obtaining optical elements of complex geometries. Thus fabricated bulk THz optical elements were studied experimentally using continuous-wave THz imaging, and the results were compared with 2D and 3D numerical predictions based on the finite-difference time-domain and finite-element frequency-domain methods. Our findings highlight technological robustness of the developed THz optical material platform and, thus, open the door for creating a variety of bulk THz optical elements of complex shapes and widely-tunable optical performance.

Multifunctional Magnetic Nanocolloids for Hybrid Solar-Thermoelectric Energy Harvesting.

Present environmental issues force the research to explore radically new concepts in sustainable and renewable energy production. In the present work, a functional fluid consisting of a stable colloidal suspension of maghemite magnetic nanoparticles in water was characterized from the points of view of thermoelectrical and optical properties, to evaluate its potential for direct electricity generation from thermoelectric effect enabled by the absorption of sunlight. These nanoparticles were found to be an excellent solar radiation absorber and simultaneously a thermoelectric power-output enhancer with only a very small volume fraction when the fluid was heated from the top. These findings demonstrate the investigated nanofluid’s high promise as a heat transfer fluid for co-generating heat and power in brand new hybrid flat-plate solar thermal collectors where top-heating geometry is imposed.

Influence of Colloidal Au on the Growth of ZnO Nanostructures.

Vapor-liquid-solid processes allow growing high-quality nanowires from a catalyst. An alternative to the conventional use of catalyst thin films, colloidal nanoparticles offer advantages not only in terms of cost, but also in terms of controlling the location, size, density, and morphology of the grown nanowires. In this work, we report on the influence of different parameters of a colloidal Au nanoparticle suspension on the catalyst-assisted growth of ZnO nanostructures by a vapor-transport method. Modifying colloid parameters such as solvent and concentration, and growth parameters such as temperature, pressure, and Ar gas flow, ZnO nanowires, nanosheets, nanotubes and branched-nanowires can be grown over silica on silicon and alumina substrates. High-resolution transmission electron microscopy reveals the high-crystal quality of the ZnO nanostructures obtained. The photoluminescence results show a predominant emission in the ultraviolet range corresponding to the exciton peak, and a very broad emission band in the visible range related to different defect recombination processes. The growth parameters and mechanisms that control the shape of the ZnO nanostructures are here analyzed and discussed. The ZnO-branched nanowires were grown spontaneously through catalyst migration. Furthermore, the substrate is shown to play a significant role in determining the diameters of the ZnO nanowires by affecting the surface mobility of the metal nanoparticles.

Facile fabrication and characterization of kraft lignin@Fe3O4 nanocomposites using pH driven precipitation: Effects on increasing lignin content

This work offers a facile fabrication method for lignin nanocomposites through the assembly of kraft lignin onto magnetic nanoparticles (Fe3O4) based on pH-driven precipitation, without needing organic solvents or lignin functionalization. Kraft lignin@Fe3O4 multicore nanocomposites fabrication proceeded using a simple, pH-driven precipitation technique. An alkaline solution for kraft lignin (pH 12) was rapidly injected into an aqueous-based Fe3O4 nanoparticle colloidal suspension (pH 7) under constant mixing conditions, allowing the fabrication of lignin magnetic nanocomposites. The effects of increasing lignin to initial Fe3O4 mass content (g/g), increasing in ratio from 1:1 to 20:1, are discussed with a complete chemical, structural, and morphological characterization. Results showed that nanocomposites fabricated above 5:1 lignin:Fe3O4 had the highest lignin coverage and content (>20%), possessed superparamagnetic properties (Ms ≈ 45,000 A·m2/kg2); had a negative surface charge (−30 mV), and formed multicore nanostructures (DH ≈ 150 nm). The multicore lignin@Fe3O4 nanocomposites allowed rapid magnetically induced separations from suspension. After 5 min exposure to a rare-earth neodymium magnet (1.27 mm × 1.27 mm × 5.08 mm), lignin@Fe3O4 nanocomposites exhibited a maximum methylene blue removal efficiency of 74.1% ± 7.1%. These nanocomposites have potential in magnetically induced separations to remove organic dyes, heavy metals, or other lignin adsorbates.

Understanding the abnormal thermal behavior of nanofluids through infrared thermography and thermo-physical characterization

Nanofluids (NFs) are colloidal suspensions of nanoparticles (NPs) within a base fluid. Unlike conventional mixtures, NFs exhibit dramatically enhanced properties, such as an abnormal increase in heat capacity at low concentration of NPs (e.g., Cp values 30% higher than the base material value). Understanding the thermo-physical behavior of NFs is essential for their application as thermal energy storage systems. In this study, we analyze a sodium nitrate ionic system containing 1 wt%, 3 wt% and 7 wt% of SiO2 NPs with different techniques like infrared thermography, infrared spectroscopy and differential scanning calorimetry (DSC) in order to shed light on the mechanism behind the increase of Cp. The themographies reveal the presence of a colder layer on top of the NF with 1 wt% of NPs whereas this layer does not appear at higher concentrations of NPs. The IR spectrum of this foamy top layer evidences the high amount of SiO2 bonds suggesting the clustering of the NPs into this layer linked by the nitrate ions. The linking is enhanced by the presence of hydroxyls in the NPs’ surface (i.e., hydroxilated NPs) that once mixed in the NF suffer ionic exchange between OH− and NO3− species, leading to O2–Si–O–NO2 species at the interface where a thermal boundary resistance or Kapitza resistance appears (RT = 2.2 m2 K kW−1). Moreover, the presence of an exothermic reactive processes in the calorimetry of the mixture with 1 wt% of NPs evidences a reactive process (ionic exchange). These factors contribute to the heat capacity increase and thus, they explain the anomalous behavior of the heat capacity in nanofluids.

Evaluation of hierarchical glucose oxidase/Co3Mn-CO3 LDH modified electrodes for glucose detection

A glucose amperometric biosensor has been prepared by a multilayer deposition on a glassy carbon electrode of Co3Mn-CO3 layered double hydroxide, glucose oxidase (GOx) and a biopolymer (carrageenan), respectively. The original transduction step consists in the electrocatalytic oxidation of H2O2, enzymatically formed, in the Co3Mn-CO3 inner-layer at 0.65 V/Ag-AgCl. The sensitivity and the detection limit, obtained with this optimized bioelectrode (Co3Mn-CO3/GOx/carrageenan, 30/20/10 µg), are 12.8 mA M−1 cm−2 and 0.02 mM, respectively. A 3D-porous bioelectrode was also prepared by impregnation of a carbon felt (CF) with a colloidal suspension of Co3Mn-CO3 nanoparticles and then with GOx. The structure and the morphology of the Co3Mn-CO3/CF composite were characterized by X-ray diffraction and electron scanning microscopy and the bioelectrode GOx/Co3Mn-CO3/CF was finally tested in cyclic voltammetry in the presence of glucose.

Guiding light with singular beams in nanoplasmonic colloids

We investigate the nonlinear propagation of light beams with complex phase and intensity structures, including a Gaussian-embedded vortex, a Bessel vortex, and a Bessel-cosine necklace. We employ a colloidal suspension of bio-synthesized plasmonic gold nanoparticles, where a self-defocusing response is mediated by absorption at the laser wavelength (532 nm). We show that, by means of nonlocal nonlinearity, these structured two-dimensional beams with on-axis singularity can counteract the diffraction of the dark core and guide therein a coaxial Gaussian probe of different wavelengths (633 nm) and lower intensities. Angular steering of the confined probe is also demonstrated by tilting the propagation direction of the pump.

Effect of Particle Concentration on Surfactant-Induced Alteration of the Contact Line Deposition in Evaporating Sessile Droplets.

Controlling and suppressing the so-called "coffee-ring effect" (CRE) is an issue of cardinal importance and intense interest in many industries and scientific fields. Here, the combined effect of the particle and surfactant concentration on the CRE is investigated by gradually adding Triton X-100 surfactant to colloidal suspensions of SiO2 nanoparticles in ethanol for various particle concentrations. First, the effect of particle concentration on the contact line dynamics during the evaporation of a sessile droplet is investigated. It is shown that increasing the particle concentration leads to an increase in pinning time and ring width, whereas the droplet's initial and dynamic contact angle remains unchanged. Afterward, the effect of different concentrations of surfactant is studied for different particle concentrations. It is concluded that the surfactant concentration at which the CRE is suppressed is dependent on the initial particle concentration of the colloid, and it increases as the particle concentration increases. Furthermore, as adding surfactant with a concentration lower than this critical concentration results in an unsuppressed CRE, it is shown that surpassing this concentration will result in a depletion of particles in the contact line. Moreover, it is demonstrated that this critical surfactant concentration has no significant effect on the droplet's geometry and the total evaporation time.

Folic acid conjugation of magnetite nanoparticles using pulsed electrohydraulic discharges

The sonochemical coprecipitation reaction with moderate ultrasound irradiation in a low vacuum environment was used to obtain aqueous colloidal suspensions of iron oxide nanoparticles (IONPs). The synthesized magnetite nanoparticles were conjugated directly by folic acid using electrohydraulic discharges as a processing technique before modification of the surface of the nanoparticles. Electrohydraulic discharges were applied in two operational modes with high and low power pulsed direct currents between the electrodes. The physical and chemical properties of the obtained samples were studied using X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS) and small angle X-ray scattering (SAXS). The investigation proved an inverse cubic spinel structure of magnetite with folic acid attachment to the magnetite surface (mean crystallite diameter in the samples, D, ranges 25?31 nm by XRD and SAXS). It was found that the processing with electrohydraulic discharges increased the colloidal stability of the folic acid-magnetite nanoparticle dispersions.

Assessing the properties of a colloidal suspension with the aid of deep learning

Convolution neural networks were applied to classify speckle images generated from nanoparticle suspensions and thus to recognise suspensions. The speckle images in the form of movies were obtained from suspensions placed in a thin cuvette. The classifier was trained, validated and tested on both single component monodispersive suspensions, as well as on two-component suspensions. It was able to properly recognise all the 73 classes – different suspensions from the training set, which is far beyond the capabilities of the human experimenter, and shows the capability of learning many more. The classes comprised different nanoparticle material and size, as well as different concentrations of the suspended phase. We also examined the capability of the system to generalise, by testing a system trained on single-component suspensions with two-component suspensions. The capability to generalise was found promising but significantly limited. A classification system using neural network was also compared with the one using support vector machine (SVM). SVM was found much more resource-consuming and thus could not be tested on full-size speckle images. Using image fragments very significantly deteriorates results for both SVM and neural networks. We showed that nanoparticle (colloidal) suspensions comprising even a large multi-parameter set of classes can be quickly identified using speckle images classified with convolution neural network.

Laser fabrication of Cu nanoparticles based nanofluid with enhanced thermal conductivity: Experimental and molecular dynamics studies

Nanofluids are engineered colloidal suspensions of solid nanoparticles in aqueous and non-aqueous base fluids with enhanced thermo-physical characteristics compared to conventional heat transfer fluids (HTFs). In this study, we report on the fabrication of copper nanoparticles-ethylene glycol (CuNPs-EG) nanofluid by using a simple one-step pulsed Nd:YAG laser ablation method to ablate the surface of a pure copper target in EG base fluid under ambient conditions. Structural and morphological analysis confirmed the fabrication of pure spherical shaped CuNPs with average diameter of ~7 nm. Thermal conductivity (k) investigations of CuNPs-EG nanofluid were conducted by using a computational approach where Equilibrium Molecular Dynamics (EMD) simulations integrated with Green-Kubo (EMD-GK) method was used. The obtained EMD-GK results for k were confirmed experimentally through a guarded hot-plate technique within the temperature ranges of 298–318 K. Interestingly, a relative enhancement (η) in the percentage of thermal conductivity of CuNPs-EG nanofluids obtained after an ablation time ta = 5 min was 15% at 318 K, while sample obtained after ta = 30 min showed an enhancement of ~24% in thermal conductivity. These obtained results confirmed the suitability of using a laser based ablation method to fabricate highly efficient nanofluids which could be used as alternatives for conventional HTFs in various heat transfer applications.

Complex colloidal structures with non-linear optical properties formed in an optical trap.

Illumination of a colloidal suspension of dielectric nanoparticles (50 nm in radius) with counter-propagating non-interfering laser beams of sufficient power leads to spatial redistribution of particles due to associated optical forces and formation of colloidal structures composed of thousands of nanoparticles along the beams. We employ a weak probe beam propagating through the colloidal structure and demonstrate that the colloidal structure acts effectively as a non-linear optical medium, similar to a gradient index lens, with optical transformation properties externally tunable by trapping laser power. With an increasing number of nanoparticles we observe the formation of a more complex colloidal structure axially and even laterally and we explain the origin of this process.

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.

Low-Frequency Shear Elasticity of a Colloid Nanosuspension

The paper presents the experimental results of an acoustic impedance study of low-frequency (105 Hz) shear elasticity of a colloidal SiO2 suspension of differently sized particles in polyethylene siloxane liquid PES-2. The agreement of the experimental results obtained by different variants of the acoustic resonance method confirms that the low-frequency shear elasticity of colloidal nanoparticle suspensions is a bulk property.

A design for detecting phosphate ions in aqueous solution by luminescent Tb-coordination polymer

Phosphate usually plays an important role not only in biological processes but also in environmental pollution, and therefore there is an urgent need for a simple, quick and efficient method to detect phosphate ions. For this design, a new terbium coordination polymer (Tb-CP) has been prepared under hydro-solvothermal conditions using 3,3′-((5-carboxy-1,3-phenylene)bis(oxy))dibenzoic acid (H3cpboda) in the existence of Tb(NO3)3‧6H2O. It was studied by infrared spectroscopy (IR), single crystal X-ray diffraction, thermogravimetric analysis (TGA), and fluorescence method. Structurally, the Tb-CP gives a 2D network based on binuclear Tb(III) units. Optically, the Tb-CP is prepared as a colloidal nanoparticle suspension for detecting phosphate in water solution. Namely, the suspensions show intense green emissions gradually disappear with the addition of PO43− ions, indicating that the Tb-CP can rapidly, sensitively and reversibly detect phosphate ions in aqueous solutions. This can be applied in pollutant monitoring with a limit of detection down to 4.53 × 10−8 M (0.0096 ppm). Furthermore, a convenient method is successfully set to observe PO43− ions in applications.

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.

Characterization and experimental investigation of rheological behavior of oxide nanolubricants

Nanolubricants are nano fluid, colloidal nanoparticle suspension, which are specially used for machine lubrication of the engine. Nanolubricants exhibit special tribological properties that have potential applications in mainly automotive industries. Performance of an engine is a function of the lubricant being used. A study of rheological behaviors of nanolubricants has been beneficial in understanding the influence of nanolubricants on shear rate and shear stress. This study is concerned with characterization and rheological behavioral studies of five nanolubricants, i.e., SnO2, TiO2, Fe3O4, CuO and ZnO mixed with engine oil at 1% volume by weight concentration. In this study, the result showed that the shear rate was independent of viscosity confirming the Newtonian behavior of these nanolubricants. Non-linear decrease in the shear viscosity, with the rise of the temperature, was observed as well from the result. This non-linear behavior observed in these nanolubricants open up the potential for high-temperature application of these nanolubricants which would greatly benefit automotive industries.

Green hybrid zeolite coatings for on-orbit molecular decontamination

FAU-type and MFI-type green hybrid zeolite coatings were developed for on-orbit molecular decontamination application by using a mixture of an organic binder (silicone resin) and an inorganic binder (suspension of colloidal silica nanoparticles). The zeolite content in the final dry coatings varies from 80 to 85 wt % whereas the total amount of binders varies from 15 to 20 wt %. This amount of binder was sufficient to give the zeolite coating interesting adhesion and cohesion properties. In fact, by using an equal amount of each binder, homogeneous films without significant cracks were obtained on an aluminum alloy substrate which is the main constituent of satellites. Nitrogen adsorption-desorption measurements revealed almost no loss of micropore volume of zeolite coatings. Adsorption experiments of an organic pollutant were carried out using n -hexane as probe molecule. The n -hexane adsorption capacities of FAU-type hybrid zeolite coatings (136–143 mg/g anhydrous zeolite ) are lower than that of pure FAU-type zeolite (180 mg/g anhydrous zeolite ) due to water co-adsorption. The n -hexane adsorption capacities of MFI-type zeolite coatings (103–106 mg/g anhydrous zeolite ) are similar to that of pure MFI-type zeolite (110 mg/g anhydrous zeolite ). • Hybrid zeolite coatings were developed with high zeolite contents (80 and 85 wt %). • A combination between an organic binder an inorganic binder was studied. • Good adhesion properties of zeolite coatings on an aluminum alloy substrate. • Interesting adsorption capacities of n -hexane by zeolite coatings. • Potential applications for VOCs adsorption.