Impact Of Surface Charge Research Articles

Molecular simulation on CO2 adsorption heterogeneity in montmorillonite nanopores with different surface charges in presence of water

Understanding the CO2 adsorption mechanism in clay nanopores is crucial for enhancing carbon capture and storage in shale reservoirs. Nonetheless, the impact of surface charge on the heterogeneity of CO2 adsorption and its subsequent effects on adsorption capacity within clay nanopores are not fully understood. By employing molecular dynamics simulations and grand canonical Monte Carlo techniques, we examine the effects of surface charge, pressure, and nanopore water on the adsorption capacity, density distribution, and free energy profile of CO2 in montmorillonite (Mt) nanopore. Utilizing density entropy as an innovative metric for adsorption heterogeneity, we shed light on how isomorphous substitution, which results in a non-uniform distribution of negative charges within Mt layers, triggers heterogeneous distribution of CO2 and water in Mt nanopore. Our findings highlight a unique correlation between the density entropy of CO2 and its adsorption capacity. The maximum adsorption capacity is strongly associated with surface charge heterogeneity in dry Mt nanopores and is governed by the heterogeneity of water distribution in wet Mt nanopores. We find that a greater heterogeneity in the CO2 distribution within the Mt nanopore system aligns with an increased maximum adsorption energy for CO2, consequently resulting in an enhanced overall adsorption capacity.

Tadpole-like cationic single-chain nanoparticles display high cellular uptake.

The successful delivery of nanoparticles (NPs) to cancer cells is dependent on various factors, including particle size, shape, surface properties such as hydrophobicity/hydrophilicity, charges, and functional moieties. Tailoring these properties has been explored extensively to enhance the efficacy of NPs for drug delivery. Single-chain polymer nanoparticles (SCNPs), notable for their small size (sub-20 nm) and tunable properties, are emerging as a promising platform for drug delivery. However, the impact of surface charge on the biological performance of SCNPs in cancer cells remains underexplored. In this study, we prepared a library of SCNPs with varying charge types (neutral, anionic, cationic, and zwitterionic), charge densities, charge positions, and crosslinking densities to evaluate their effects on cellular uptake in MCF-7 breast cancer cells. Key findings include that cationic SCNPs are more likely to translocate into cells than neutral, anionic, or zwitterionic counterparts. Furthermore, cellular uptake was enhanced with increased charge density (from 10 to 15 mol%) before reaching a critical point (20 mol%) where excessive positive charge led to NP adhesion to the cell membrane, resulting in cell death. We also found that the position of the charge on the polymer chain also impacted the delivery of NPs to cancer cells, with tadpole-shaped SCNPs achieving the highest uptake. Furthermore, crosslinking density significantly influenced cellular uptake, with SCNPs at 50% crosslinking conversion showing the highest cytosolic localization, while other densities resulted in retention primarily at the cell membrane. This study offers valuable insights into how charge type, density, position, and crosslinking density affect the biological performance of SCNPs, guiding the rational design of more effective and safer drug delivery systems.

Triphenylphosphonium conjugated gold nanotriangles impact Pi3K/AKT pathway in breast cancer cells: a photodynamic therapy approach

Although gold nanoparticles based photodynamic therapy (PDT) were reported to improve efficacy and specificity, the impact of surface charge in targeting cancer is still a challenge. Herein, we report gold nanotriangles (AuNTs) tuned with anionic and cationic surface charge conjugating triphenylphosphonium (TPP) targeting breast cancer cells with 5-aminoleuvinic acid (5-ALA) based PDT, in vitro. Optimized surface charge of AuNTs with and without TPP kill breast cancer cells. By combining, 5-ALA and PDT, the surface charge augmented AuNTs deliver improved cellular toxicity as revealed by MTT, fluorescent probes and flow cytometry. Further, the 5-ALA and PDT treatment in the presence of AuNTs impairs cell survival Pi3K/AKT signaling pathway causing mitochondrial dependent apoptosis. The cumulative findings demonstrate that, cationic AuNTs with TPP excel selective targeting of breast cancer cells in the presence of 5-ALA and PDT.

Impact of surface charges on energy deposition in surface dielectric barrier discharge: a modeling investigation

Surface charges have significant impact on the evolution of surface dielectric barrier discharge (SDBD). In this work, the role of residual surface charges on repetitively nanosecond pulsed SDBD in atmospheric air is investigated using a two-dimensional fluid model, based on the assumption of preserving the distribution of surface charges at the end of the previous high voltage (HV) pulse. In the bipolar mode when the polarity of residual surface charges is opposite to that of the current HV pulse, a lower breakdown voltage and more deposited energy can be observed, showing an obvious enhancement of SDBD. In the unipolar mode, residual surface charges suppress the development of discharges and energy deposition. It is found that more residual surface charges are accumulated during the negative pulsed discharge, which have a more pronounced effect on the subsequent positive pulsed one. This is explained by the fact that the negative surface streamers directly contact the dielectric and charge it, while the positive surface streamers float above the dielectric, forming a ion-rich region near the surface. The results in this work demonstrate the mechanism of how residual surface charges affect discharge dynamics, which can be utilized to regulate energy deposition in SDBDs.

Measurements of surface charge dynamics and surface-breakdown characteristics of surface dielectric barrier discharges

The surface charge distribution in a surface dielectric barrier discharge driven by repetitive pulse bias superimposed on AC voltage is measured using the Pockels effect of an electro-optic crystal. The impact of surface charge on surface-breakdown characteristics is investigated by varying the phase of the pulse superimposition. It is demonstrated that the surface charge accumulation varies at different superimposition phases depending on the potential difference between the two electrodes. The accumulated positive/negative surface charge will facilitate the following surface discharge when the AC voltage polarity changes. In addition, different spatiotemporal characteristics of the surface charge distribution are presented when changing the polarity of superimposed pulses. Positive surface discharges are usually easier to develop than negative surface discharges due to their lower breakdown voltage caused by the accumulation of negative surface charges near the edges of exposed electrodes. The decay of positive surface charge is dominated by neutralization of negative surface charge and negatively charged particles (free electrons and negative ions) from the volume above the dielectric. There are two decay modes of positive surface charge: exponential decay and linear decay.

The impact of the distribution of surface charge on the ionic current rectification of nanochannel diodes

As ionic current rectification (ICR) in nanochannel diodes originates from non-uniformly distributed surface charge, the impact of surface charge on rectification offers many insights. However, previous research mainly focused on the symmetrical bipolar diode and the unipolar diode, and fabricated nanochannel diodes usually deviate from ideal assumptions. Here, we comprehensively discuss the impact of different kinds of surface charge distribution. The results show ICR will become stronger with the increasing algebraic difference of surface charge density, if the surface charge density at one terminal is fixed. When the algebraic difference is the same, ICR in a symmetrical bipolar diode exceeds the maximum. When the surface charge density in two terminals is the same, ICR reaches the maximum if the junction is located in the middle of the nanochannel. Finally, the magnitude of ICR decreases with increasing nanochannel radius. We believe that this work provides a reference for the fabrication of nanochannel diodes.

Protein-liposome interactions: the impact of surface charge and fluidisation effect on protein binding

At the dawn of a new nanotechnological era in the pharmaceutical field, it is very important to examine and understand all the aspects that influence in vivo behaviour of nanoparticles. In this point of view, the interactions between serum proteins and liposomes with incorporated anionic, cationic, and/or PEGylated lipids were investigated to elucidate the role of surface charge and bilayer fluidity in protein corona’s formation. 1,2-dipalmitoyl-sn-glycero-3- phosphocholine (DPPC), hydrogenated soybean phosphatidylcholine (HSPC), and 1,2-dioctadecanoyl-sn-glycero-3-phosphocholine (DSPC) liposomes with the presence or absence of 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (sodium salt) (DPPG), 1,2-di-(9Z-octadecenoyl)-3-trimethylammonium-propane (chloride salt) (DOTAP), and/or 1,2-dipalmitoylsn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-5000] (DPPE-PEG 5000) lipids were prepared by the thin-film hydration method. The evaluation of their biophysical characteristics was enabled by differential scanning calorimetry and dynamic and electrophoretic light scattering. The physicochemical characteristics of mixed liposomes were compared before and after exposure to foetal bovine serum (FBS) and were correlated to calorimetric data. Our results indicate protein binding to all liposomal formulations. However, it is highlighted the importance of surface charge and fluidisation effect to the extent of protein adsorption. Additionally, considering the extensive use of cationic lipids for innovative delivery platforms, we deem PEGylation a key parameter, because even in a small proportion can reduce protein binding, and thus fast clearance and extreme toxicity without affecting positive charge. This study is a continuation of our previous work about protein-liposome interactions and fraction of stealthiness (Fs) parameter, and hopefully a design road map for drug and gene delivery.

Template-assisted alloying of atom-precise silver nanoclusters: a new approach to generate cluster functionality.

To acquire the atomic design of new functional Ag(i) nanoclusters (NCs), a new synthetic approach of site-specific alloying has been unveiled, by which the neutral CO2 templated Ag20 core is confined through Cu containing two peripheral motif units. The impact of surface charge, size and shape of the template on the self-assembly of Ag(i) has been precisely controlled here for the first time and as a result, a similar pentagonal gyrobicupola-like Ag20 core is formed while varying the templates (S2-, CO3 2- and CO2). However, the surface charge generated on the Ag(i) core due to the presence of a neutral template opens up the possibility of this novel alloying process. The introduction of strongly interacted peripheral motif units (DMA-CuS-) on the Ag20 core enforces more rigidity in the skeleton that reduces the probability of non-radiative transition in the excited state by lowering the intramolecular vibration. In addition to this, the incorporation of electron-donating peripheral motif units modulates the frontier molecular arrangement that helps in attaining the synergy which would ultimately turn on the room-temperature emission properties. The electron-donating effect of the peripheral motif units further leads to a sharp reduction of the bandgap and the symmetric position of the heterometal in the cluster minimizes the intercluster distances which further influences the intercluster charge carrier transport. So, the precise structure-property correlation with this novel synthetic approach will pave the way for a well-functioning NC design.

Automatic Actin Filament Quantification and Cell Shape Modeling of Osteoblasts on Charged Ti Surfaces

Surface charges at the cell–biomaterial interface are known to determine cellular functions. Previous findings on cell signaling indicate that osteoblastic cells favor certain moderately positive surface charges, whereas highly positive charges are not tolerated. In this study, we aimed to gain deeper insights into the influence exerted by surface charges on the actin cytoskeleton and the cell shape. We analyzed surfaces with a negative, moderately positive, and highly positive zeta (ζ) potential: titanium (Ti), Ti with plasma polymerized allylamine (PPAAm), and Ti with a polydiallyldimethylammonium chloride (PDADMA) multilayer, respectively. We used the software FilaQuant for automatic actin filament quantification of osteoblastic MG-63s, analyzed the cell edge height with scanning ion conductance microscopy (SICM), and described the cellular shape via a mathematical vertex model. A significant enhancement of actin filament formation was achieved on moderately positive (+7 mV) compared with negative ζ-potentials (−87 mV). A hampered cell spreading was reflected in a diminished actin filament number and length on highly positively charged surfaces (+50 mV). Mathematical simulations suggested that in these cells, cortical tension forces dominate the cell–substrate adhesion forces. Our findings present new insights into the impact of surface charges on the overall cell shape and even intracellular structures.

Gut Organoid as a New Platform to Study Alginate and Chitosan Mediated PLGA Nanoparticles for Drug Delivery.

Intestinal organoids can be used as an ex vivo epithelial model to study different drug delivery effects on epithelial cells’ luminal surface. In this study, the impact of surface charge on the delivery of 5-ASA loaded PLGA nanoparticles into the lumen of organoids was investigated. Alginate and chitosan were used to coat the nanoparticles and provide negative and positive charges on the particles, respectively. The organoid growth and viability were not affected by the presence of either alginate- or chitosan-coated nanoparticles. It was shown that nanoparticles could be transported from the serosal side of the organoids to the lumen as the dye gradually accumulated in the lumen by day 2–3 after adding the nanoparticles to the Matrigel. By day 5, the dye was eliminated from the lumen of the organoids. It was concluded that the positively charged nanoparticles were more readily transported across the epithelium into the lumen. It may be attributed to the affinity of epithelial cells to the positive charge. Thus, the organoid can be utilized as an appropriate model to mimic the functions of the intestinal epithelium and can be used as a model to evaluate the benefits of nanoparticle-based drug delivery.

Impact of surface charge on the motion of light-activated Janus micromotors

Control over micromotors’ motion is of high relevance for lab-on-a-chip and biomedical engineering, wherein such particles encounter complex microenvironments. Here, we introduce an efficient way to influence Janus micromotors’ direction of motion and speed by modifying their surface properties and those of their immediate surroundings. We fabricated light-responsive Janus micromotors with positive and negative surface charge, both driven by ionic self-diffusiophoresis. These were used to observe direction-of-motion reversal in proximity to glass substrates for which we varied the surface charge. Quantitative analysis allowed us to extract the dependence of the particle velocity on the surface charge density of the substrate. This constitutes the first quantitative demonstration of the substrate’s surface charge on the motility of the light-activated diffusiophoretic motors in water. We provide qualitative understanding of these observations in terms of osmotic flow along the substrate generated through the ions released by the propulsion mechanism. Our results constitute a crucial step in moving toward practical application of self-phoretic artificial micromotors.Graphic abstract

Nanocellulose-Based Inks for 3D Bioprinting: Key Aspects in Research Development and Challenging Perspectives in Applications-A Mini Review.

Nanocelluloses have emerged as a catalogue of renewable nanomaterials for bioink formulation in service of 3D bioprinting, thanks to their structural similarity to extracellular matrices and excellent biocompatibility of supporting crucial cellular activities. From a material scientist’s viewpoint, this mini-review presents the key research aspects of the development of the nanocellulose-based bioinks in 3D (bio)printing. The nanomaterial properties of various types of nanocelluloses, including bacterial nanocellulose, cellulose nanofibers, and cellulose nanocrystals, are reviewed with respect to their origins and preparation methods. Different cross-linking strategies to integrate into multicomponent nanocellulose-based bioinks are discussed in terms of regulating ink fidelity in direct ink writing as well as tuning the mechanical stiffness as a bioactive cue in the printed hydrogel construct. Furthermore, the impact of surface charge and functional groups on nanocellulose surface on the crucial cellular activities (e.g., cell survival, attachment, and proliferation) is discussed with the cell–matrix interactions in focus. Aiming at a sustainable and cost-effective alternative for end-users in biomedical and pharmaceutical fields, challenging aspects such as biodegradability and potential nanotoxicity of nanocelluloses call for more fundamental comprehension of the cell–matrix interactions and further validation in in vivo models.

Adsorption of amino acids at clay surfaces and implication for biochemical reactions: Role and impact of surface charges

Almost all clay minerals carry an abundance of surface charges. The role and impacts of surface charges during adsorption of amino acids and biochemical reactions are of great importance while currently remain elusive, which are to be tackled in this study by first-principles density functional calculations. A wide range of surface charges (−0.42˜ + 0.42 C m−2) have been considered. Distribution of different amino acid isomers and their interaction with clay minerals rely strongly on the sign and amount of surface charges. Zwitterionic structures remain stable for all negative surface charges and become dominant when negative surface charges are abundant (σ ≤ −0.28 C m−2), whereas only very high positive surface charges (σ ≥ +0.35 C m−2) can stabilize zwitterionic glycine. Increase of surface charges pronouncedly enhances the interactions of amino acids with clay minerals, which favors their gathering at clay surfaces and condensation to protein fragments. The superior binding of amino acids by negatively rather than positively charged clay minerals is due to stronger H bonding and electrostatic interactions. The biochemical reactions are greatly accelerated at higher surface charges and zwitterion formation becomes almost barrierless; however, the reverse reactions of forming canonical isomers have so moderate activation barriers that can occur facilely and get ready for the condensation to protein fragments. Accordingly, clay minerals, even in the anhydrous state, should be the suitable birthplace for life, where surface charges play a central role.

The impact of surface charge on the ionic dissociation of common salt (NaCl)

The ionic dissociation of NaCl has long been thought to be fully understood in terms of the simultaneous removal and hydration of the constituent ions from the surface. However, there are two observations that trouble the current model of ionic dissociation. The first of these observations is that the surface is charged. This has been established by several of studies using laser doppler electrophoresis and membrane electrochemistry. This has not been accounted for in descriptions of ionic dissociation, dissolution or crystallization of salt. The second observation is that the current model, which envisages sodium and chloride ions hydrating and departing the surface, does not yield a rate law consistent with experimental data. These two observations are resolved in this work. It is proposed that the removal of ions form ionic vacancies while deposition forms excess ions on the surface. Vacancies and excess ions are the source of surface charge. The effect of this surface charge affects the rate of removal of ions from the surface, resulting in a feedback mechanism: ionic vacancies are formed by the removal of ions, which affects the rate at which ions are removed. From this model, expressions are derived for the establishment of the charge on the surface and for the kinetics of ionic dissociation, dissolution and crystallization of NaCl.

Electrical Double Layer Probed by Surface-Specific Vibrational Technique

In this issue of Chem, Paesani and co-workers present a computational analysis of sum-frequency generation (SFG) spectra of water to disentangle the interfacial χ(2) and bulk χ(3) contributions. SFG line shapes are in good agreement with experimental results. The analysis reveals the molecular response of interfacial water, which is usually masked by the bulk water spectra at the water-charged surfactant interface.

Impact of Surface Charge on Cerium Oxide Nanoparticle Uptake and Translocation by Wheat (Triticum aestivum).

Nanoparticle (NP) physiochemical properties, including surface charge, affect cellular uptake, translocation, and tissue localization. To evaluate the influence of surface charge on NP uptake by plants, wheat seedlings were hydroponically exposed to 20 mg/L of ∼4 nm CeO2 NPs functionalized with positively charged, negatively charged, and neutral dextran coatings. Fresh, hydrated roots and leaves were analyzed at various time points over 34 h using fluorescence X-ray absorption near-edge spectroscopy to provide laterally resolved spatial distribution and speciation of Ce. A 15-20% reduction from Ce(IV) to Ce(III) was observed in both roots and leaves, independent of NP surface charge. Because of its higher affinity with negatively charged cell walls, CeO2(+) NPs adhered to the plant roots the strongest. After 34 h, CeO2(-), and CeO2(0) NP exposed plants had higher Ce leaf concentrations than the plants exposed to CeO2(+) NPs. Whereas Ce was found mostly in the leaf veins of the CeO2(-) NP exposed plant, Ce was found in clusters in the nonvascular leaf tissue of the CeO2(0) NP exposed plant. These results provide important information for understanding mechanisms responsible for plant uptake, transformation, and translocation of NPs, and suggest that NP coatings can be designed to target NPs to specific parts of plants.

Tailoring surface charge and wetting property for robust oil-fouling mitigation in membrane distillation

The efforts of developing anti-oil-fouling membranes have so far been focusing on tailoring membrane surface wetting properties, whereas the impacts of surface charge are often eclipsed. In this study, we investigated the impacts of surface charge and wetting property on oil fouling kinetics in membrane distillation (MD). Two composite membranes with in-air hydrophilic and underwater oleophobic surfaces, one of positive charge and the other of negative charge, were fabricated by modifying a hydrophobic polyvinylidene fluoride (PVDF) membrane with hydrophilic polyelectrolytes with different charges. The modified composite membranes were compared with the reference PVDF membrane for their contact angles, adhesion force curves, and fouling kinetics in MD processes. It was found that the negatively charged composite membrane performed the best in mitigating fouling by the negatively charged oil emulsion, followed by the positively charged composite membrane, with the pristine PVDF membrane being the most susceptible to oil fouling in MD experiments. The results from underwater oil CA measurements and oil probe force spectroscopy corroborated the results in the fouling experiments. The impact of surface charges on oil-membrane interaction and associated mechanism were also discussed.

Size-dependent line broadening in the emission spectra of single GaAs quantum dots: Impact of surface charge on spectral diffusion

Making use of droplet epitaxy, we systematically controlled the height of self-assembled GaAs quantum dots by more than one order of magnitude. The photoluminescence spectra of single quantum dots revealed the strong dependence of the spectral linewidth on the dot height. Tall dots with a height of ~30 nm showed broad spectral peaks with an average width as large as ~5 meV, but shallow dots with a height of ~2 nm showed resolution-limited spectral lines (<120 micro eV). The measured height dependence of the linewidths is in good agreement with Stark coefficients calculated for the experimental shape variation. We attribute the microscopic source of fluctuating electric fields to the random motion of surface charges at the vacuum-semiconductor interface. Our results offer guidelines for creating frequency-locked photon sources, which will serve as key devices for long-distance quantum key distribution.

Surface charge mapping with a nanopipette.

Nanopipettes are emerging as simple but powerful tools for probing chemistry at the nanoscale. In this contribution the use of nanopipettes for simultaneous surface charge mapping and topographical imaging is demonstrated, using a scanning ion conductance microscopy (SICM) format. When a nanopipette is positioned close to a surface in electrolyte solution, the direct ion current (DC), driven by an applied bias between a quasi-reference counter electrode (QRCE) in the nanopipette and a second QRCE in the bulk solution, is sensitive to surface charge. The charge sensitivity arises because the diffuse double layers at the nanopipette and the surface interact, creating a perm-selective region which becomes increasingly significant at low ionic strengths (10 mM 1:1 aqueous electrolyte herein). This leads to a polarity-dependent ion current and surface-induced rectification as the bias is varied. Using distance-modulated SICM, which induces an alternating ion current component (AC) by periodically modulating the distance between the nanopipette and the surface, the effect of surface charge on the DC and AC is explored and rationalized. The impact of surface charge on the AC phase (with respect to the driving sinusoidal signal) is highlighted in particular; this quantity shows a shift that is highly sensitive to interfacial charge and provides the basis for visualizing charge simultaneously with topography. The studies herein highlight the use of nanopipettes for functional imaging with applications from cell biology to materials characterization where understanding surface charge is of key importance. They also provide a framework for the design of SICM experiments, which may be convoluted by topographical and surface charge effects, especially for small nanopipettes.

The Impact of Surface Charge on the Mechanical Behavior of High-Porosity Chalk

We present rock mechanical test results and analytical calculations which demonstrate that a negative surface charge, resulting from sulfate adsorption from the pore water, impacts the rock mechanical behavior of high-porosity chalk. Na2SO4 brine flooded into chalk cores at 130 °C results in significantly reduced bulk modulus and yield point compared with that of NaCl brine at the same conditions. The experimental results have been interpreted using a surface complexation model combined with the Gouy-Chapman theory to describe the double layer. The calculated sulfate adsorption agrees well with the measured data. A sulfate adsorption of about 0.3 μmol/m2 and 0.7–1 μmol/m2 was measured at 50 and 130 °C, respectively. Relative to a total sites of 5 sites/nm2 these values correspond to an occupation of 4 % and 8–13 % which sufficiently explains the negative charging of the calcite surfaces. The interaction between charged surfaces specifically in the weak overlaps of electrical double layer gives rise to the total disjoining pressure in granular contacts. The net repulsive forces act as normal forces in the grains vicinity, counteracting the cohesive forces and enhance pore collapse failure during isotropic loading, which we argue to account for the reduced yield and bulk modulus of chalk cores. The effect of disjoining pressure is also assessed at different sulfate concentrations in aqueous solution, temperatures, as well as ionic strength of solution; all together remarkably reproduce similar trends as observed in the mechanical properties.