Unaggregated Nanoparticles Research Articles

Small-angle neutron scattering study of differences in phase behavior of silica nanoparticles in the presence of lysozyme and bovine serum albumin proteins

The differences in phase behavior of anionic silica nanoparticles (88Å) in the presence of two globular proteins [cationic lysozyme (molecular weight (MW) 14.7 kD) and anionic bovine serum albumin (BSA) (MW 66.4 kD)] have been studied by small-angle neutron scattering. The measurements were carried out on a fixed concentration (1wt%) of Ludox silica nanoparticles with varying concentrations of proteins (0-5wt%) at pH=7. It is found that, despite having different natures (opposite charges), both proteins can render to the same kind of aggregation of silica nanoparticles. However, the concentration regions over which the aggregation is observed are widely different for the two proteins. Lysozyme with very small amounts (e.g., 0.01wt%) leads to the aggregation of silica nanoparticles. On the other hand, silica nanoparticles coexist with BSA as independent entities at low protein concentrations and turn to aggregates at high protein concentrations (>1wt%). In the case of lysozyme, the charge neutralization by the protein on the nanoparticles gives rise to the protein-mediated aggregation of the nanoparticles. The nanoparticle aggregates coexist with unaggregated nanoparticles at low protein concentrations, whereas, they coexist with a free protein at higher protein concentrations. For BSA, the nonadsorbing nature of the protein produces the depletion force that causes the aggregation of the nanoparticles at higher protein concentrations. The evolution of the interaction is modeled by the two Yukawa potential, taking account of both attractive and repulsive terms of the interaction in these systems. The nanoparticle aggregation is found to be governed by the short-range attraction for lysozyme and the long-range attraction for BSA. The aggregates are characterized by the diffusion limited aggregate type of mass fractal morphology.

PH-Dependent Interaction and Resultant Structures of Silica Nanoparticles and Lysozyme Protein

Small-angle neutron scattering (SANS) and UV-visible spectroscopy studies have been carried out to examine pH-dependent interactions and resultant structures of oppositely charged silica nanoparticles and lysozyme protein in aqueous solution. The measurements were carried out at fixed concentration (1 wt %) of three differently sized silica nanoparticles (8, 16, and 26 nm) over a wide concentration range of protein (0-10 wt %) at three different pH values (5, 7, and 9). The adsorption curve as obtained by UV-visible spectroscopy shows exponential behavior of protein adsorption on nanoparticles. The electrostatic interaction enhanced by the decrease in the pH between the nanoparticle and protein (isoelectric point ∼11.4) increases the adsorption coefficient on nanoparticles but decreases the overall amount protein adsorbed whereas the opposite behavior is observed with increasing nanoparticle size. The adsorption of protein leads to the protein-mediated aggregation of nanoparticles. These aggregates are found to be surface fractals at pH 5 and change to mass fractals with increasing pH and/or decreasing nanoparticle size. Two different concentration regimes of interaction of nanoparticles with protein have been observed: (i) unaggregated nanoparticles coexisting with aggregated nanoparticles at low protein concentrations and (ii) free protein coexisting with aggregated nanoparticles at higher protein concentrations. These concentration regimes are found to be strongly dependent on both the pH and nanoparticle size.

Aggregation and dissolution of silver nanoparticles in a laboratory-based freshwater microcosm under simulated environmental conditions

Silver nanoparticles (NP) are used in several applications, including their use as antimicrobial agents in textiles, personal care, and other domestic products. As such, there is a high potential for the release of silver nanoparticles (AgNP) in the aquatic environment. In aquatic ecosystems, nanomaterials are affected by abiotic factors, such as temperature, that alter their chemistry and influence their fate in the environment. Preliminary studies indicate that NP tend to form aggregates which are potentially more recalcitrant than unaggregated NP. These and other fate processes are largely dependent on both the characteristics of the NP and that of the environment. In this study, lab experiments were conducted to investigate the physicochemical properties and temperature solubility of AgNP (<100 nm) that may potentially influence the fate and behavior of AgNP in the aqueous environment. Results indicated that, under these tested conditions, AgNP may be transformed in size and thereby affect fate, bioavailability, and toxicity. In this study, a novel method was used to determine whether AgNP would form agglomerates, or behave as isolated particles, or dissolve when in aqueous media and under different environmental conditions. The new aspects evaluated in this study demonstrated that AgNP are transformed in both size and state under variable environmental conditions.

Preparation and enzymatic hydrolysis of nanoparticles made from single xyloglucan polysaccharide chain

In this work, polysaccharide nanoparticles based on tamarind seeds xyloglucan are prepared, analyzed in term of characteristic sizes and morphology, and degraded by the action of a glycoside-hydrolase. Obtained in an aqueous NaNO2 solution (0.1M), these unaggregated nanoparticles have a characteristic diameter of ca. 60nm (DLS, AFM and TEM measures). They are not compact, but highly swollen and look like hyperbranched and dendrimer-like (soft sphere model) structures. This observation is coherent with the native structure of the xyloglucan macromolecules which are themselves branched. The enzymatic hydrolysis by cellulase of Trichoderma reesei of the xyloglucan nanoparticles is investigated. In particular, the apparent mass molecular weight drastically decreases meaning that the xyloglucan nanoparticles are effectively fully hydrolyzed by the endo-β-(1,4)-glucanase. Furthermore, we observe that the enzyme has to uncoil the nanoparticles before cutting the β-(1→4) bonds and digesting the xyloglucan.

A Wet Electrostatic Precipitator (WESP) for Soft Nanoparticle Collection

Many nanoparticle collection devices have limitations related to retention of particle integrity from bounce, shattering, or aggregation. Suspensions of soft nanoparticles (e.g., proteins, lipids) are required for drug delivery and therapy. To enable direct collection of soft nanoparticles into liquid media, a wet electrostatic precipitator (WESP) was designed and evaluated in this work. Different sections were used for ion generation and particle charging, for minimal contact between the corona wire and particles, which were charged using positive nitrogen ions. WESP dimensions and operating parameters were optimized using charge distribution modeling. The prototype WESP was designed for operation with a continuous flow of liquid over the collection plate, to allow continuous particle collection from the exit stream of an aerosol reactor. The collection efficiency of the WESP, in dry and wet modes, was measured using aerosols of monodisperse polystyrene latex (PSL), polydisperse sucrose, and stearic acid (soft lipid) particles, through SMPS measurements, corrected for diffusional losses, at the entry and exit of the device. Measured collection efficiency was 70%–90% for particles of sizes 80–600 nm diameter in reasonable agreement with theoretical estimates. However, for small particles (20–80 nm diameter) measured collection efficiency ranged 40%–70%, significantly lower than theoretical estimates, possibly from incomplete neutralization of negative charges attained during air-jet atomization. Transmission electron microscopy (TEM) images and dynamic light scattering (DLS) measurements confirm that wet collection produces a suspension of free, unaggregated nanoparticles with sizes similar to their measured mean mobility diameter. Copyright 2012 American Association for Aerosol Research

Fractal analysis as a complimentary technique for characterizing nanoparticle size distributions

Fractal analysis of nanoparticles can provide extra information about primary particle size distributions as well as their associations in various media. Fractal dimension and lacunarity of nanoparticles were determined using two-dimensional images and particle size distributions, from either electron microscopy or dynamic light scattering measurements. Metal oxide nanoparticles, both commercial products and in-lab synthesized, were analyzed to determine fractal dimension and lacunarity coefficients. The box counting method appears to be the most robust of the methods evaluated. For aggregated nanoparticles synthesized in the vapor phase, the fractal dimensions appear to reflect aggregate growth mechanisms. For unaggregated nanoparticles that have agglomerated, fractal dimensions appear to reflect differences in surface chemistries. For the aggregated nanoparticle materials in this study, both fractal coefficients (fractal dimension and lacunarity) can provide information about powder morphology, which could be useful for quality control. For nanoparticles that agglomerate, lacunarity may be useful for defining the stability of these colloidal systems in toxicological, environmental or drug delivery applications.

Optical characteristics of cadmium sulfide nanoparticles synthesized in polyethylene matrix and ortho-xylene solution

The properties of CdS nanoparticles synthesized in a polyethylene matrix and an ortho-xylene solution are compared. It is shown that these nanoparticles have different shapes, structures, and degrees of imperfection. Due to these differences, unaggregated nanoparticles in solution exhibit luminescence in contrast to nanoparticles in polyethylene. The stabilization of nanoparticles in polyethylene most probably occurs via OH groups, while nanoparticles in solution are stabilized due to partial interaction with dissolved sulfur. The absorption and luminescence spectra of samples with polyethylene are strongly distorted by reabsorption and scattering, while this effect in solution is absent due to a small concentration of nanoparticles.

Formation and properties of composites based on microgels of a responsive polymer and TiO 2 nanoparticles

Organic–inorganic composites were prepared with titanium dioxide (TiO 2) nanoparticles embedded within colloidal particles of a cross-linked, thermally responsive polymer. To promote the incorporation of unaggregated nanoparticles of TiO 2, temperature responsive microspherical gels (microgels) of N-isopropylacrylamide (NIPAM) with interpenetrating (IP) linear chains of poly(acrylic acid) (PAAc) were synthesized. Dynamic light scattering (DLS) measurements revealed that these microgels reversibly shrink and swell in diameter from 300–400 nm to 600–800 nm with temperature. Two types of nanoparticles of TiO 2 were immobilized within the IP-microgels—fine TiO 2 nanoparticles synthesized by the hydrolysis of titanium(IV) isopropoxide and commercially available Degussa P25. Characterization of the composite was conducted using transmission electron microscopy (TEM) and UV–vis absorption spectroscopy from which it was determined that the extent of loading of the TiO 2 within the colloidal particles can be easily manipulated from a low value of 10% (weight) to a value as high as 75%. The TiO 2 nanoparticles were in a dispersed state within the microgels and the composites showed rapid (∼minutes) sedimentation, which is useful for gravity separations. By using turbidometry to characterize the settling behavior of the organic–inorganic composites, it was found that the settling time decreases as the content of TiO 2 increases within the particles.