Surface Charge Modulation Research Articles

Directed Assembly of Proteinaceous-Polysaccharide Nanofibrils to Fabricate Membranes for Emerging Contaminant Remediation.

Emerging contaminants, including per- and polyfluoroalkyl substances and heavy metals, are threatening the health of humans and ecosystems. Their removal from the environment remains challenging. Here, we designed silk fibroin-cellulose nanocrystal (silk-CNC) nanofibrillar and nanoporous membranes for emerging contaminant remediation. The protein-polysaccharide nanofibrils were fabricated by templating the assembly of silk fibroin using CNCs. Silk fibroin polymorphic nature combined with surface charge modulation of CNCs produced cationic silk-CNC(+) and anionic silk-CNC(-) nanofibrils that can target a broad spectrum of contaminants. Silk-CNC(+) nanofibrils and membranes exhibited antimicrobial properties and captured both short-chain heptafluorobutyric acid, perfluorobutanesulfonic acid, and long-chain perfluorooctanoic acid by virtue of hydrophobic attraction from β-sheeted silk fibroin and electrostatic interactions with CNC(+). Silk-CNC(-) provided the opportunity to target cations such as heavy metal cocontaminants. The nanofabrication of biopolymer-based membranes combines high performance with environmentally benign and cost-effective removal of emerging contaminants for water purification, wastewater treatment, and remediation.

Enzyme-Triggered Degradation of Supramolecularly Cross-Linked Polymersomes of Azobenzene-Based Polyurethane: Cell-Selective Anticancer Drug Release.

Enzyme-responsive self-assembled nanostructures for drug delivery applications have gained a lot of attention, as enzymes exhibit dysregulation in many disease-associated microenvironments. Azoreductase enzyme levels are strongly elevated in many tumor tissues; hence, here, we exploited the altered enzyme activity of the azoreductase enzyme and designed a main-chain azobenzene-based amphiphilic polyurethane, which self-assembles into a vesicular nanostructure and is programmed to disassemble in response to a specific enzyme, azoreductase, with the help of the nicotinamide adenine dinucleotide phosphate (NADPH) coenzyme in the hypoxic environment of solid tumors. The vesicular nanostructure sequesters, stabilizes the hydrophobic anticancer drug, and releases the drug in a controlled fashion in response to enzyme-triggered degradation of azo-bonds and disruption of vesicular assembly. The biological evaluation revealed tumor extracellular matrix pH-induced surface charge modulation, selective activated cellular uptake to azoreductase overexpressed lung cancer cells (A549), and the release of the anticancer drug followed by cell death. In contrast, the benign nature of the drug-loaded vesicular nanostructure toward normal cells (H9c2) suggested excellent cell specificity. We envision that the main-chain azobenzene-based polyurethane discussed in this manuscript could be considered as a possible selective chemotherapeutic cargo against the azoreductase overexpressed cancer cells while shielding the normal cells from off-target toxicity.

Modulating zero charge potential of Zn-doped N, P-containing carbon electrodes for efficient copper ion electrosorption

Nitrogen/phosphorus (N/P) doped carbon materials exhibit enhanced electro adsorption capability in capacitive deionization (CDI) applications. However, the incorporation of N/P atoms may introduce electron-withdrawing groups to the electrode surface, impacting the potential of zero charge (EPZC) and thereby influencing its electro adsorption efficiency. This research explores the modulation of electrode surface charge by varying the N/P doping composition. Specifically, it presents a Zn and N/P co-doped carbon material employed as the CDI cathode, showcasing selective adsorption of Cu2+ ions. Under a voltage of 1.2 V, the adsorption capacity achieves 250 mg/g in a 500 mg/L Cu2+ ion solution. Furthermore, it demonstrates outstanding cycling stability, maintaining an adsorption capacity of 233 mg/g even after 21 cycles. This investigation introduces an innovative approach for EPZC adjustment and offers a fresh theoretical framework for fabricating high-performance CDI electrodes.

Remotely Controlled Surface Charge Modulation of Magnetoelectric Nanogenerators for Swift and Efficient Drug Delivery.

We have developed a highly efficient technique of magnetically controlled swift loading and release of doxorubicin (DOX) drug using a magnetoelectric nanogenerator (MENG). Core-shell nanostructured MENG with a magnetostrictive core and piezoelectric shell act as field-responsive nanocarriers and possess the capability of field-triggered drug release in a cancerous environment. MENGs generate a surface electric dipole when subjected to a magnetic field due to the strain-mediated magnetoelectric effect. The capability of directional magnetic field-assisted modulation of the surface electrical dipole of MENG provides a mechanism to create/break ionic bonds with DOX molecules, which facilitates efficient drug attachment and on-demand swift detachment of the drug at a targeted site. The magnetic field-assisted drug-loading mechanism was minutely analyzed using spectrophotometry and Raman spectroscopy. The detailed time-dependent analysis of controlled drug release by the MENG under unidirectional and rotating magnetic field excitation was conducted using field-emission scanning electron microscopy, energy-dispersive X-ray, and atomic force microscopic measurements. In vitro, experiments validate the cytocompatibility and magnetically assisted on-demand and swift DOX drug delivery by the MENG near MCF-7 breast cancer cells, which results in a significant enhancement of cancer cell killing efficiency. A state-of-the-art experiment was performed to visualize the nanoscale magnetoelectric effect of MENG using off-axis electron holography under Lorentz conditions.

Ultrahigh Salt Adsorption Capacity of Carbonaceous Electrode in a Rocking-Chair Capacitive Deionization through Surface Charge Modulation

Ultrahigh Salt Adsorption Capacity of Carbonaceous Electrode in a Rocking-Chair Capacitive Deionization through Surface Charge Modulation

Super-Nernstian pH detection using out-of-equilibrium body potential in silicon on insulator ISFET sensors: Proof-of-concept and optimization paths

In this work, we demonstrate pH sensing using the out-of-equilibrium body potential (VB) monitored in silicon-on-insulator (SOI) double-gate “ISFET-like” devices with deposited metal contacts. Similar to the behavior of a dual-gate ISFET, in this study, the conductive channel induced by the back-gate voltage at the silicon/buried oxide (Si/BOX) interface is modulated by the charges to-be-sensed that are intentionally placed on the top silicon oxide layer SiO2 covering the Si film. The detection of the surface charge modulation was evidenced by monitoring in real-time the out-of-equilibrium body potential, while the classic shift in the drain current served as control experiment and for benchmarking. These first experiments demonstrate the successful implementation of this new pH detection paradigm, with super-Nernstian sensitivity. To provide optimization options for the body-potential sensing, TCAD simulations of the pH sensors were performed in a 2D structure and illustrated the possibility to further enhance the device sensitivity with an optimized architecture. Moreover, the pH-induced shift occurs at very high applied gate biases for the drain current, contrary to the body potential, which implies a sensor with lower power consumption when VB is used as reading method. Thus, body potential monitoring provides a promising reading method to reach the required low-power consumption regime of the tomorrow’s sensing devices.

Revealing the Regulation Effect of Surface Charge at Aromatic Interface to Dynamic Conformational Changes of α‐Synuclein at Early Aggregation Stage

Comprehensive SummaryThe aggregation of α‐synuclein (α‐syn) is strongly influenced by membrane interfaces, but the mechanism of transition from monomers to oligomers at early aggregation stage is not clear. Here, we investigate the adsorption and structure changes of α‐syn on oppositely charged aromatic interfaces through in‐situ surface‐enhanced infrared absorption (SEIRA) spectroscopy and nano‐IR technique. The results show that the synergy of electrostatic and hydrophobic interactions leads to a “fast‐slow” two‐step aggregation pathway on negatively charged interface. Surface adsorption induces the formation of an extended helix structure and subsequently partial helix unwinding in NAC region, which enables the hydrophobic stacking between nearby NAC regions. Stable antiparallel β‐sheet rich aggregates are gradually emerging as further interactions of monomers with the fast formed “first layer”. Monomers electrostatically adsorb on positively charged interface by C‐terminus with NAC region and N‐terminus stretched in solvent, which serve as an aggregation core and induce further adsorption and gradual formation of aggregates with C‐terminus exposure. Our results demonstrate the modulation of surface charge and synergy of electrostatic and hydrophobic interactions on the interaction modes and aggregation pathways, which provide insights into dynamic conformation changes of α‐syn at early aggregation stage and imply the important role of spatial‐temporal heterogeneity of membranes in α‐synucleinopathies.

Graphene Field-Effect Transistors with Surface-Charge Modulation for C-Reactive Protein Detection in Artificial Saliva

Graphene Field-Effect Transistors with Surface-Charge Modulation for C-Reactive Protein Detection in Artificial Saliva

Photogenerated outer electric field induced electrophoresis of organic nanocrystals for effective solid-solid photocatalysis

Rapid mass transfer in solid-solid reactions is crucial for catalysis. Although phoretic nanoparticles offer potential for increased collision efficiency between solids, their implementation is hindered by limited interaction ranges. Here, we present a self-driven long-range electrophoresis of organic nanocrystals facilitated by a rationally designed photogenerated outer electric field (OEF) on their surface. Employing perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) molecular nanocrystals as a model, we demonstrate that a directional OEF with an intensity of 13.6-0.4 kV m−1 across a range of 25–200 μm. This OEF-driven targeted electrophoresis of PTCDA nanocrystals onto the microplastic surface enhances the activity for subsequent decomposition of microplastics (196.8 mg h−1) into CO2 by solid-solid catalysis. As supported by operando characterizations and theoretical calculations, the OEF surrounds PTCDA nanocrystals initially, directing from the electron-rich (0 1 1) to the hole-rich (112¯)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(11\\bar{2})$$\\end{document} surface. Upon surface charge modulation, the direction of OEF changes toward the solid substrate. The OEF-driven electrophoretic effect in organic nanocrystals with anisotropic charge enrichment characteristics indicates potential advancements in realizing effective solid-solid photocatalysis.

Hydrophilicity and surface charge modulation of Ti3C2T x MXene based membranes for water desalination.

Lamellar membranes obtained by stacking 2D layers possess ample transport pathways due to their intricate network of interlayer gaps. This makes them suitable for molecular separation applications. However, controlling the surface chemistry of the nanochannels within the membrane to tune the desired transport properties of water and ions is challenging. Ti3C2T x has been considered for water desalination because of its hydrophilic surface and negative surface charge. Most of the studies of Ti3C2T x membranes have presented promising salt rejection values in forward osmosis mode, which is less practical for water purification. Here, we investigate two types of reverse osmosis MXene-based lamellar membranes consisting of Ti3C2T x nanosheets hybridized with (i) WS2 nanosheets and (ii) polyvinyl phosphonic acid (PVPA). When hydrophilic and flexible Ti3C2T x nanosheets are interleaved with softer and more hydrophobic WS2 nanosheets in 2 : 1 mass ratio, nano capillaries with Janus chemistry are created with comparable rejection to bare Ti3C2T x membrane and threefold higher permeance values. Further, we find that decorating Ti3C2T x nanosheets with anionic polymers improves salt rejection. Our Ti3C2T x /PVPA composite membranes reject ∼97% of divalent ions and ∼80% of monovalent ions with ∼0.2 Lm-2 h-1 bar-1 of water permeance when tested with brackish water, and exhibit significantly improved chlorine resistance and cost benefits over the commercial Toray membranes.

Surface charge modulation boosts electrocatalytic water splitting over iridium catalysts on a polyimide support.

Developing high-performance iridium (Ir)-based catalysts with minimal precious Ir metal is a significant but challenging step towards the acidic oxygen evolution reaction (OER). Here, we report a high-performance OER catalyst with Ir nanoparticles on a polyimide support, where the polyimide support can effectively modulate the electronic structures of the Ir active sites for decreased thermodynamic barriers, but also enrich the local proton concentration near the Ir active sites, enhancing the OER rates.

Modulating selective ionic enrichment and depletion zones in straight nanochannels via the interplay of surface charge modulation and electric field mediated fluid-thickening.

We report the possibilities of achieving highly controlled segregation of ion-enriched and ion-depleted regions in straight nanochannels. This is achieved via harnessing the interplay of an axial gradient of the induced transverse electric field on account of electrical double layer phenomenon and the localized thickening of the fluid because of intensified electric fields due to the large spatial gradients of the electrical potential in extreme confinements. By considering alternate surface patches of different charge densities over pre-designed axial spans, we illustrate how these effects can be exploited to realize selectively ion-enriched and ion-depleted zones. Physically, this is attributed to setting up of an axial concentration gradient that delves on the ionic advection due to the combined effect of an externally applied electric field and induced back-pressure gradient along the channel axis and electro-migration due to the combinatorial influences of the applied and the induced electrostatic fields. With an explicit handle on the pertinent parameters, our results offer insights on the possible means of imposing delicate controls on the solute-enrichment and depletion phenomena, a paradigm that remained unexplored thus far.

Biosensing with Surface-Charge-Modulated Graphene Field-Effect Transistors beyond Nonlinear Electrolytic Screening.

In field-effect transistor (FET) biosensors, charge screening in electrolyte solutions limits the sensitivity, thereby restricting the applicability of FET sensors. This is particularly pronounced in graphene FET (GFET) biosensors, where the bare graphene surface possesses a strongly negative charge, which impedes the high sensitivity of GFETs owing to nonlinear electrolytic screening at the interfaces between graphene and liquid. In this study, we counteracted the negative surface charge of graphene by decorating positively charged compounds and demonstrated the sensing of C-reactive protein (CRP) with surface-charge-modulated GFETs (SCM-GFETs). We integrated multiple SCM-GFETs with anti-CRP antibodies and nonfunctionalized GFETs into a chip and measured differentials to eliminate background changes to improve measurement reliability. The FET response corresponded to the fluorescence images, which visualized the specific adsorption of CRP. The estimated dissociation constant was consistent with previously reported values; this supports the conclusion that the results are attributed to specific adsorption. Conversely, the signal in GFETs without decoration was obscured by noise because of nonlinear electrolytic screening, further emphasizing the significance of surface-charge modulation. The limit of detection of the system was determined to be 2.9 nM. This value has the potential to be improved through further optimization of the surface charges to align with specific applications. Our devices effectively circumvent nonlinear electrolytic screening, opening the door for further advancements in GFET biosensor technology.

Graphene Oxide-Mediated Regulation of Volume Exclusion and Wettability in Biomimetic Phosphorylation-Responsive Ionic Gates.

Replicating phosphorylation-responsive ionic gates via artificial fluidic systems is essential for biomolecular detection and cellular communication research. However, current approaches to governing the gates primarily rely on volume exclusion or surface charge modulation. To overcome this limitation and enhance ion transport controllability, we introduce graphene oxide (GO) into nanochannel systems, simultaneously regulating the volume exclusion and wettability. Moreover, inspired by (cAMP)-dependent protein kinase A (PKA)-regulated L-type Ca2+ channels, we employ peptides for phosphorylation which preserves them as nanoadhesives to coat nanochannels with GO. The coating boosts steric hindrance and diminishes wettability, creating a substantial ion conduction barrier, which represents a significant advancement in achieving precise ion transport regulation in abiotic nanochannels. Leveraging the mechanism, we also fabricated a sensitive biosensor for PKA activity detection and inhibition exploration. The combined regulation of volume exclusion and wettability offers an appealing strategy for controlled nanofluidic manipulation with promising biomedical applications in diagnosis and drug discovery.

Graphene Oxide/Polyethyleneimine-Modified Cation Exchange Membrane for Efficient Selective Recovery of Ammonia Nitrogen from Wastewater.

Competition for the migration of interfering cations limits the scale-up and implementation of the Donnan dialysis process for the recovery of ammonia nitrogen (NH4+-N) from wastewater in practice. Highly efficient selective permeation of NH4+ through a cation exchange membrane (CEM) is expected to be modulated via tuning the surface charge and structure of CEM. In this work, a novel CEM was designed to form a graphene oxide (GO)-polyethyleneimine (PEI) cross-linked layer by introducing self-assembling layers of GO and PEI on the surface of a commercial CEM, which rationally regulates the surface charge and structure of the membrane. The resulting positively charged membrane surface exhibits stronger repulsion for divalent cations compared to monovalent cations according to Coulomb's law, while, simultaneously, GO forms π-metal cation conjugates between metal cations (e.g., Mg2+ and Ca2+), thus limiting metal cation transport across the membrane. During the DD process, higher NH4+ concentrations resulted in a longer time to reach Donnan equilibrium and higher NH4+ flux, while increased Mg2+ concentrations resulted in lower NH4+ flux (from 0.414 to 0.213 mol·m-2·h-1). Using the synergistic effect of electrostatic interaction and non-covalent cross-linking, the designed membrane, referred to as GO-PEI (20) and prepared by a 20 min impregnation in the GO-PEI mixture, exhibited an NH4+ transport rate of 0.429 mol·m-2·h-1 and a Mg2+ transport rate of 0.003 mol·m-2·h-1 in single-salt solution tests and an NH4+/Mg2+ selectivity of 15.46, outperforming those of the unmodified and PEI membranes (1.30 and 5.74, respectively). In mixed salt solution tests, the GO-PEI (20) membrane showed a selectivity of 15.46 (~1.36, the unmodified membrane) for NH4+/Mg2+ and a good structural stability after 72 h of continuous operation. Therefore, this facile surface charge modulation approach provides a promising avenue for achieving efficient NH4+-selective separation by modified CEMs.

Template-Based Porous Hydrogel Microparticles as Carriers for Therapeutic Proteins.

Hydrogels have been extensively researched for over 60 years for their limitless applications in biomedical research. In this study, porous hydrogel microparticles (PHMPs) made of poly(ethylene glycol) diacrylamide were investigated for their potential as a delivery platform for therapeutic proteins. These particles are made using hard calcium carbonate (CaCO3) templates, which can easily be dissolved under acidic conditions. After optimization of the synthesis processes, both CaCO3 templates and PHMPs were characterized using a wide range of techniques. Then, using an array of proteins with different physicochemical properties, the encapsulation efficiency of proteins in PHMPs was evaluated under different conditions. Strategies to enhance protein encapsulation via modulation of particle surface charge to increase electrostatic interactions and conjugation using EDC/NHS chemistry were also investigated. Conjugation of bovine serum albumin to PHMPs showed increased encapsulation and diminished release over time, highlighting the potential of PHMPs as a versatile delivery platform for therapeutic proteins such as enzymes or antibodies.

Interfacial Structure and Electrostatics Related to Solute Activity in a Model Anionic-Surfactant/Polymer Self-Assembly.

Polymer/surfactant composites are used in industry as an excipient for water-insoluble solutes. Such enhanced dissolution ability of composite media is related to the spontaneous formation of pre-micellar polymer surfactant aggregates (PS) at a magnitude of order lower than the surfactant critical micelle concentration in water. Combining electrochemical and spectroscopic studies, we investigate the microscopic interfacial structure (i.e., interface electrostatics and surface polarity) of PS formed in composite media. We establish that in a composite system, a mere change in the polymer concentration at a fixed surfactant concentration makes possible to regulate the counter-ion binding ability, surface potential, surface charge density, packing and surface polarity of the PS interface. Our study shows that the higher dissolution of water-insoluble nonionic solutes in composite media is driven by the depressing of surface charge density and polarity of the PS interface. A similar modulation of the PS interface acts as a barrier for the passive relocation of water-soluble charged solutes into the PS pseudo-phase. The time-resolved fluorescence anisotropy study allows us to underline the effect of surface charge modulation on the dynamical aspects of solutes at the PS interface.

Tumor acidity-induced surface charge modulation in covalent nanonetworks for activated cellular uptake: targeted delivery of anticancer drugs and selective cancer cell death.

A β-thioester and tertiary amine based covalently cross-linked nanoassembly coined as a nanonetwork (NN) endowed with dual pH responsive features (tumor acidity induced surface charge modulation and endosomal pH triggered controlled degradation) has been designed and synthesized for stable sequestration and sustained release of drug molecules in response to endosomal pH. An amphiphile integrated with tertiary amine and acrylate (ATA) functionalities was synthesized to fabricate the nanonetwork. This amphiphile showed entropically driven self-assembly and micellar nanostructures (nanoassemblies), which can sequester hydrophobic drug molecules at neutral pH. To further stabilize the nanoassemblies and the sequestered drug molecules even below its critical aggregation concentration (CAC), the micellar core was cross-linked via the thiol-acrylate Michael addition click reaction to generate multiple copies of acid labile β-thioester functionalities in the core, which undergo slow hydrolysis at endosomal pH (∼5.0), thus enabling sustained release of the anti-cancer drug doxorubicin at endosomal pH. The nanonetworks showed a significant decrease in drug leakage compared to the nanoassemblies (NAs), which was also justified by a low leakage coefficient calculated from the fluorescence resonance energy transfer experiment. The NN also exhibited dilution insensitivity and high serum stability, whereas the NA disassembled upon dilution and during serum treatment. The biological evaluation revealed tumor extracellular matrix pH (∼6.4-6.8) induced surface charge modulation and cancer cell (HeLa) selective activated cellular uptake of the doxorubicin loaded nanonetwork (NN-DOX). In contrast, the benign nature of NN-DOX towards normal cells (H9c2) suggests excellent cell specificity. Thus, we believe that the ease of synthesis, nanonetwork fabrication reproducibility, robust stability, smart nature of tumor microenvironment sensitive surface charge modulation, boosted tumoral-cell uptake, and triggered drug release will make this system a potential nanomedicine for chemotherapeutic treatments.

Compacting Electric Double Layer Enables Carbon Electrode with Ultrahigh Zn Ion Storage Capability.

Carbon-based cathodes for aqueous zinc ion hybrid supercapacitors (ZHSCs) typically undergo low Zn ion storage capability due to their electric double layer capacitance (EDLC) energy storage mechanism that is restricted by specific surface area and thickness of electric double layer (EDL). Here, we report a universal surface charge modulation strategy to effectively enhance the capacitance of carbon materials by decreasing the thickness of EDL. Amino groups with lone pair electrons were chosen to increase the surface charge density and enhanced the interaction between carbon electrode and Zn ions, thus effectively compacting the EDL. Consequently, amino functionalized porous carbon based ZHSCs can deliver an ultrahigh capacity of 255.2 mAh g-1 along with excellent cycling stability (95.5 % capacity retention after 50 000 cycles) in 1 M ZnCl2 electrolyte. This study demonstrates the feasibility of EDL modified carbon as Zn2+ storage cathode and great prospect for constructing high performance ZHSCs.

Compacting Electric Double Layer Enables Carbon Electrode with Ultrahigh Zn Ion Storage Capability

AbstractCarbon‐based cathodes for aqueous zinc ion hybrid supercapacitors (ZHSCs) typically undergo low Zn ion storage capability due to their electric double layer capacitance (EDLC) energy storage mechanism that is restricted by specific surface area and thickness of electric double layer (EDL). Here, we report a universal surface charge modulation strategy to effectively enhance the capacitance of carbon materials by decreasing the thickness of EDL. Amino groups with lone pair electrons were chosen to increase the surface charge density and enhanced the interaction between carbon electrode and Zn ions, thus effectively compacting the EDL. Consequently, amino functionalized porous carbon based ZHSCs can deliver an ultrahigh capacity of 255.2 mAh g−1 along with excellent cycling stability (95.5 % capacity retention after 50 000 cycles) in 1 M ZnCl2 electrolyte. This study demonstrates the feasibility of EDL modified carbon as Zn2+ storage cathode and great prospect for constructing high performance ZHSCs.