Function Of Particle Charge Research Articles

Nanoscale CuO charge and morphology control Fusarium suppression and nutrient biofortification in field-grown tomato and watermelon

Limited data exist on how surface charge and morphology impact the effectiveness of nanoscale copper oxide (CuO) as an agricultural amendment under field conditions. This study investigated the impact of these factors on tomatoes and watermelons following foliar treatment with CuO nanosheets (NS-) or nanospikes (NP+ and NP-) exhibiting positive or negative surface charge. Results showed plant species-dependent benefits. Notably, tomatoes infected with Fusarium oxysporum had significantly reduced disease progression when treated with NS-. Watermelons benefited similarly from NP+. Although disease suppression was significant and trends indicated increased yield, the yield effects weren't statistically significant. However, several nanoscale treatments significantly enhanced the fruit's nutritional value, and this nano-enabled biofortification was a function of particle charge and morphology. Negatively charged nanospikes significantly increased the Fe content of healthy watermelon and tomato (20–28 %) and Ca in healthy tomato (66 %), compared to their positively charged counterpart. Negatively charged nanospikes also outperformed negatively charged nanosheets, leading to significant increases in the content of S and Mg in infected watermelon (37–38 %), Fe in healthy watermelon (58 %), and Ca (42 %) in healthy tomato. These findings highlight the potential of tuning nanoscale CuO chemistry for disease suppression and enhanced food quality under field conditions.

The Heterogeneous Diffusion of Polystyrene Nanoparticles and the Effect on the Expression of Quorum-Sensing Genes and EPS Production as a Function of Particle Charge and Biofilm Age.

Biofilms are abundantly present in both natural and engineered environmental systems and will likely influence broader particle fate and transport phenomena. While some developed models describe the interactions between nanoparticles and biofilms, studies are only beginning to uncover the complexity of nanoparticle diffusion patterns. With the knowledge of the nanoparticle potential to influence bacterial processes, more systematic studies are needed to uncover the dynamics of bacteria-nanoparticle interactions. This study explored specific microbial responses to nanoparticles and the heterogeneity of nanoparticle diffusion. Pseudomonas aeruginosa biofilms (cultivated for 48 and 96 hours, representing early and late stages of development) were exposed to charged (aminated and carboxylated) polystyrene nanoparticles. With a combination of advanced fluorescence microscopy and real time quantitative PCR, we characterized the diffusion of polystyrene nanoparticles in P. aeruginosa biofilms and evaluated how biofilms respond to the presence of nanoparticles in terms of the expression of key EPS production-associated genes (pelA and rpsL) and quorum-sensing associated (lasR) genes. Our findings show that nanoparticle diffusion coefficients are independent of the particle surface charge only in mature biofilms and that the presence of nanoparticles influences bacterial gene expression. Independent of the particle's charge polystyrene nanoparticles down-regulated pelA in mature biofilms. By contrast, charge-specific responses were identified in lasR and rpsL gene expression. The targeted genes expression analysis and heterogeneous diffusion models demonstrate that particle charge influences nanoparticle mobility and provides significant insight into the intrinsic structural heterogeneity of P. aeruginosa biofilms. These findings suggest that biofilm maturity and particle charge are essential factors to consider when evaluating the transport of nanoparticles within a biofilm matrix.

Charge Melting of Liposome Colloidal Crystals

Recently we measured the charge dependence of electrostatic interparticle repulsions in liposome colloidal crystals (Cohen, Wei & Ou-Yang, ms. in preparation). The liposomes were made from binary mixtures of charged and neutral phospholipids at various ratios. The shear modulus (rigidity) of each liposome suspension in deionized water was measured by laser-tweezer methods. As a function of increasing liposome charge, suspension rigidity first increased, peaked at ∼20% charged-lipid content, then decreased, becoming watery near 100% charged lipids. By analogy to colloidal-crystal “shear melting,” we call this phenomenon “charge melting.” The effect was calculated quantitatively by use of the Wigner-Seitz (WS) model, which requires solving the electrostatics problem of a radially symmetric charged sphere and its counterions in an electroneutral spherical WS shell whose radius R is determined by the liposome concentration. Electroneutrality means the entire H+ screening cloud surrounding each liposome is compressed into its WS cell. The compression creates an osmotic pressure related to the electrostatic potential ψ(R) at the WS-cell surface. The osmotic pressure is a measure of the interparticle interaction strength, which is what stiffens the sample. “Melting” as a function of particle charge Z arises because electroneutrality requires (a) as Z increases, so does the number of counterions, which increases osmotic pressure and ψ(R). This effect is linear in Z. (b) More counterions also cause more screening of Z, which decreases ψ(R) and osmotic pressure. This effect is exponential in Z, so it ultimately dominates. We solve the WS electrostatics problem analytically in the Debye-Hückel approximation and numerically with the full Poisson-Boltzmann equation. The problem must be solved self-consistently for a closed system with no reservoir, a counterion-only electrolyte, surface H+ binding with charge regulation, and zero electric fields at the WS-cell surface and liposome center.

Interaction of functionalized nanoparticles with serum proteins and its impact on colloidal stability and cargo leaching.

The majority of effort in the area of polymeric nanocarriers is aimed at providing controlled drug delivery in vivo. Therefore, it is essential to understand the delicate interplay of polymeric NPs with serum proteins in order to forecast their performance in a biological system. In this study, the interaction of serum proteins with functionalized polymeric colloids as a function of particle charge and hydrophobicity was investigated. Moreover, impact on NP stability and cargo leaching was assessed. The hard protein corona of polymeric NPs with either uncharged methoxy groups (methoxy-NPs), positively charged amine groups (amine-NPs), negatively charged carboxylic acid groups (carboxyl-NPs) or zwitterionic NPs decorated with amine and carboxylic acid groups (zwitterion-NPs) was quantitatively and qualitatively analyzed and correlated with the respective colloidal stability using fluorescence resonance energy transfer. Positively charged amine-NPs displayed an enhanced interaction with serum proteins via electrostatic interactions resulting in a hard corona consisting of diverse protein components. As revealed by FRET and agarose gel electrophoresis, the enhanced adsorption of proteins onto the colloidal surface significantly altered the NP identity and severely impaired the colloidal integrity as the lipophilic cargo was continuously leached out of the hydrophobic NP core. These results highlight the importance of generating a profound knowledge of the bio-nano interface as adherence of biomolecules can severely compromise the performance of a colloidal drug delivery system by changing its identity and integrity.

Penetration of charged particles through metallic tubes

Several theoretical studies have shown that charged particles increased the particle deposition efficiency in cylindrical tubes by image force. Some experimental investigations have also found that the deposition loss increased with increasing aerosol charge. However, the amount of charges on the aerosols or the electrical mobility was relatively low in these previous experimental studies. In order to extend to higher aerosol charge, a TSI vibrating orifice monodisperse aerosol generator was modified to generate 1-μm DEHS aerosols with charge up to 24,000 elementary units. Metallic tubes were employed to exclude the effect of Coulombic force. Tube diameter, tube length, and average velocity in tubes were among the major operating parameters. Aerosol charge was monitored using a TSI electrometer, while a TSI aerodynamic particle sizer was utilized to measure both aerosol concentrations and size distributions upstream and downstream of the tubes. Aerosol deposition loss in the sampling train of the TSI electrometer was measured to back-calculate the average aerosol charge. A closed-form theoretical model, showing the deposition efficiency as a function of particle charge, was validated by the experimental data produced.The aerosol deposition efficiency increased with increasing aerosol charge and tube length, due to stronger image force and longer retention time, respectively. The deposition efficiency decreased with increasing average velocity because of shorter retention time. Under the same average velocity, the deposition loss decreased with increasing tube diameter because the fraction of aerosols near the inner wall was higher for small-diameter tube than for large-diameter tube. The model developed from parabolic flow showed good agreement with most of the experimental data, except for data of highly charged particles. The discrepancy was probably due to the space charge effect.

Ion size effects on the electric double layer of a spherical particle in a realistic salt-free concentrated suspension

A new modified Poisson-Boltzmann equation accounting for the finite size of the ions valid for realistic salt-free concentrated suspensions has been derived, extending the formalism developed for pure salt-free suspensions [Roa et al., Phys. Chem. Chem. Phys., 2011, 13, 3960-3968] to real experimental conditions. These realistic suspensions include water dissociation ions and those generated by atmospheric carbon dioxide contamination, in addition to the added counterions released by the particles to the solution. The electric potential at the particle surface will be calculated for different ion sizes and compared with classical Poisson-Boltzmann predictions for point-like ions, as a function of particle charge and volume fraction. The realistic predictions turn out to be essential to achieve a closer picture of real salt-free suspensions, and even more important when ionic size effects are incorporated to the electric double layer description. We think that both corrections have to be taken into account when developing new realistic electrokinetic models, and surely will help in the comparison with experiments for low-salt or realistic salt-free systems.

Electrophoretic mobility and molecular distribution studies of poly(amidoamine) dendrimers of defined charges

Generation 5 ethylenediamine (EDA)-cored poly(amidoamine) (PAMAM) dendrimers (E5, E denotes the EDA core and 5 the generation number) with different degrees of acetylation and carboxylation were synthesized and used as a model system to investigate the effect of charge and the influence of dendrimer surface modifications on electrophoretic mobility (EM) and molecular distribution. The surface-modified dendrimers were characterized by size-exclusion chromatography, 1H NMR, MALDI-TOF-MS, PAGE, and CE. The focus of our study was to determine how EM changes as a function of particle charge and molecular mass, and how the molecular distribution changes due to surface modifications. We demonstrate that partially modified dendrimers have much broader migration peaks than those of fully surface functionalized or unmodified E5 dendrimers due to variations in the substitution of individual dendrimer surfaces. EM decreased nonlinearly with increases in surface acetylation for both PAMAM acetamides and PAMAM succinamic acids, indicating a complex migration activity in CE separations that is not solely due to charge/mass ratio changes. These studies provide new insights into dendrimer properties under an electric field, as well as into the characterization of dendrimer-based materials being developed for medical applications.

Calibration of plastic track detectors for use in cosmic ray experiments

Plastic track detectors calibration for heavy charged particles in cosmic ray experiments, considering track etching rates as function of particle charge and velocity