Charge Manipulation Research Articles

Surface charge manipulation and electrostatic immobilization of synaptosomes for super-resolution imaging: a study on tau compartmentalization

Synaptosomes are subcellular fractions prepared from brain tissues that are enriched in synaptic terminals, widely used for the study of neural transmission and synaptic dysfunction. Immunofluorescence imaging is increasingly applied to synaptosomes to investigate protein localization. However, conventional methods for imaging synaptosomes over glass coverslips suffer from formaldehyde-induced aggregation. Here, we developed a facile strategy to capture and image synaptosomes without aggregation artefacts. First, ethylene glycol bis(succinimidyl succinate) (EGS) is chosen as the chemical fixative to replace formaldehyde. EGS/glycine treatment makes the zeta potential of synaptosomes more negative. Second, we modified glass coverslips with 3-aminopropyltriethoxysilane (APTES) to impart positive charges. EGS-fixed synaptosomes spontaneously attach to modified glasses via electrostatic attraction while maintaining good dispersion. Individual synaptic terminals are imaged by conventional fluorescence microscopy or by super-resolution techniques such as direct stochastic optical reconstruction microscopy (dSTORM). We examined tau protein by two-color and three-color dSTORM to understand its spatial distribution within mouse cortical synapses, observing tau colocalization with synaptic vesicles as well postsynaptic densities.

Charge Manipulation in Metal–Organic Frameworks: Toward Designer Functional Molecular Materials

Abstract Multi-dimensional coordination frameworks whose charge states are controllable by the sophisticated chemical modification of the components or by the application of stimuli are fascinating targets for the design of electronic/magnetic functional materials. A simple way to design such frameworks is to assemble electron donor (D) and electron acceptor (A) units in a DmAn ratio with electronically conjugated linkages; we call this type of framework a D/A metal–organic framework (D/A-MOF). In this account article, our previous studies on D/A-MOFs composed of carboxylate-bridged paddlewheel-type diruthenium units ([Ru2]) and polycyano organic molecules such as N,N′-dicyanoquinodiimine (DCNQI) and 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) as the D and A subunits, respectively, are summarized. In this family of D/A-MOFs, the charge distribution between the internal D and A subunits can be precisely tuned by varying their electronic structure, i.e., depending on what kind of D and A we choose. Crucially, the diverse charge states, as well as anisotropic framework and often porous nature, of D/A-MOFs are well correlated with their bulk electronic and magnetic properties.

Synthesis of murunskite single crystals: A bridge between cuprates and pnictides

Numerous contemporary investigations in condensed matter physics are devoted to high temperature (high-Tc) cuprate superconductors. Despite its unique effulgence among research subjects, the enigma of the high-Tc mechanism still persists. One way to advance its understanding is to discover and study new analogous systems. Here we begin a novel exploration of the natural mineral murunskite, K2FeCu3S4, as an interpolation compound between cuprates and ferropnictides, the only known high-Tc superconductors at ambient pressure. Because in-depth studies can be carried out only on single crystals, we have mastered the synthesis and growth of high quality specimens. Similar to the cuprate parent compounds, these show semiconducting behavior in resistivity and optical transmittance, and an antiferromagnetic ordering at 100 K. Spectroscopy (XPS) and calculations (DFT) concur that the sulfur 3p orbitals are partially open, making them accessible for charge manipulation, which is a prerequisite for superconductivity in analogous layered structures. DFT indicates that the valence band is more cuprate-like, while the conduction band is more pnictide-like. With appropriate doping strategies, this parent compound promises exciting future developments.

Constructing Layered Nanostructures from Non‐Layered Sulfide Crystals via Surface Charge Manipulation Strategy

Abstract2D non‐layered metal sulfides possess intriguing properties, rendering them bright application prospects in energy storage and conversion, however, the synthesis of non‐layered metal sulfide nanosheets is still significantly challenging. Herein, a surface‐charge‐regulating strategy is developed to fabricate microsized 2D non‐layered metal sulfides via manipulation of the isoelectric point, which can easily modulate the manner of surface charge arrangement during the growth of crystal nuclei. The result of this strategy are materials that are completely assembled with a preferred orientation but comprise a large lateral size with maintaining atomic thickness. A series of modified sulfides are successfully synthesized, demonstrating that their microarchitectures are shifted in an expected manner. Then, one of these materials, In4SnS8, approaches a promising candidate for sodium storage by means of its structural integrity, boosted transfer kinetics, and abundant active sites. The proposed synthetic protocol can open up a new opportunity to explore 2D non‐layered materials for energy‐related applications.

Alkali-deficiency driven charged out-of-phase boundaries for giant electromechanical response

Traditional strategies for improving piezoelectric properties have focused on phase boundary engineering through complex chemical alloying and phase control. Although they have been successfully employed in bulk materials, they have not been effective in thin films due to the severe deterioration in epitaxy, which is critical to film properties. Contending with the opposing effects of alloying and epitaxy in thin films has been a long-standing issue. Herein we demonstrate a new strategy in alkali niobate epitaxial films, utilizing alkali vacancies without alloying to form nanopillars enclosed with out-of-phase boundaries that can give rise to a giant electromechanical response. Both atomically resolved polarization mapping and phase field simulations show that the boundaries are strained and charged, manifesting as head-head and tail-tail polarization bound charges. Such charged boundaries produce a giant local depolarization field, which facilitates a steady polarization rotation between the matrix and nanopillars. The local elastic strain and charge manipulation at out-of-phase boundaries, demonstrated here, can be used as an effective pathway to obtain large electromechanical response with good temperature stability in similar perovskite oxides.

Modulating surface charge of dexamethasone non-spherical microcrystals for improved inner ear delivery

It is important to achieve precise surface charge manipulation of non-spherical drug microcrystals using facile and time-efficient methods for local drug delivery. In this study, silk-coated dexamethasone (DEX) non-spherical microcrystals were synthesized by precipitation technique followed by alternate deposition of poly(allylamine hydrochloride) (PAH) (or PAH-coated Fe3O4) and silk fibroin (SF) via layer-by-layer assembly. EDC and glutaraldehyde were employed to manipulate positive or negative charge of particles by simple chemical cross-linking reactions, respectively. In vivo assessment was carried out by intratympanic (IT) injection of DEX non-spherical microcrystals in guinea pigs. In vivo pharmacokinetic results demonstrate that negatively charged DEX microcrystals appeared to improve outcomes of inner ear delivery in comparison to positively-charged counterparts. This is partly because of the adhesive features of the SF. The present study may provide new ideas to construct surface charge-tunable drug delivery vehicles that are capable of crossing biological barriers, especially for inner ear delivery due to the simple and practical strategy.

Charge Manipulation Using Solution and Gas-Phase Chemistry to Facilitate Analysis of Highly Heterogeneous Protein Complexes in Native Mass Spectrometry.

Structural heterogeneity is a significant challenge complicating (and in some cases making impossible) electrospray ionization mass spectrometry (ESI MS) analysis of noncovalent complexes comprising structurally heterogeneous biopolymers. The broad mass distribution exhibited by such species inevitably gives rise to overlapping ionic signals representing different charge states, resulting in a continuum spectrum with no discernible features that can be used to assign ionic charges and calculate their masses. This problem can be circumvented by using limited charge reduction, which utilizes gas-phase chemistry to induce charge-transfer reactions within ionic populations selected within narrow m/z windows, thereby producing well-defined and readily interpretable charge ladders. However, the ionic signal in native MS typically populates high m/z regions of mass spectra, which frequently extend beyond the precursor ion isolation limits of most commercial mass spectrometers. While the ionic signal of single-chain proteins can be shifted to lower m/z regions simply by switching to a denaturing solvent, this approach cannot be applied to noncovalent assemblies due to their inherent instability under denaturing conditions. An alternative approach explored in this work relies on adding supercharging reagents to protein solutions as a means of increasing the extent of multiple charging of noncovalent complexes in ESI MS without compromising their integrity. This shifts the ionic signal down the m/z scale to the region where ion selection and isolation can be readily accomplished with a front-end quadrupole, followed by limited charge reduction of the isolated ionic population. The feasibility of the new approach is demonstrated using noncovalent complexes formed by hemoglobin with structurally heterogeneous haptoglobin.

Tip-induced domain protrusion in ferroelectric films with in-plane polarization

Charge manipulation and fabrication of stable domain patterns in ferroelectric materials by scanning probe microscopy open up broad avenues for the development of tunable electronics. Harnessing the polarization energy and electrostatic forces with specific geometry of the system enables producing the nanoscale domains by-design. Along with that, domain engineering requires mastery of underlying physical mechanisms that govern the domain formation. Here, we present a theoretical description of the domain formation by a scanning probe microscopy tip in a ferroelectric film with strong in-plane anisotropy of polarization. We demonstrate that local charge injection produces wedge-shaped domains that propagate along the anisotropy axis, whereas the tip-written lines of charge generate a comb-like domain structure. The results of our calculations agree with earlier experimental observations and allow for the optimization of the targeted domain structures.

Atomic, molecular, charge manipulation and application of atomic force microscopy

In this review paper, we introduce representative research work on single atomic/molecular manipulations by atomic force microscopy (AFM), which possesses extraordinary ability to resolve atomic and chemical bonds, and charge density distributions of samples. We first introduce the working principle of AFM, then focus on recent advances in atom manipulation at room temperature, force characterization in the process of atom/molecule manipulation, and charge manipulation on insulating substrates. This review covers the following four aspects: 1) the imaging principle of AFM and the atomic characterization of typical molecules such as pentacene and C<sub>60</sub>; 2) the mechanical manipulation and atomic recognition capability of AFM at room temperature; 3) the characterization of forces in the process of surface isomerization and adsorption configuration changes of the molecules; 4) the manipulation of charge states and the characterization of single and multiple molecules on insulating substrates. The capability of manipulation by AFM in these fields widens the range in atomic/molecular manipulation, which can provide new and well-established schemes for the analysis and precise control of the manipulation process, and can further contribute to the construction of nanoscale devices, such as “molecular switches” and storage components.

Mass Analysis of Macro-molecular Analytes via Multiply-Charged Ion Attachment.

A novel gas-phase charge and mass manipulation approach is demonstrated to facilitate the mass measurement of high mass complexes within the context of native mass spectrometry. Electrospray ionization applied to solutions generated under native or near-native conditions has been demonstrated to be capable of preserving biologically relevant complexes into the gas phase as multiply charged ions suitable for mass spectrometric analysis. However, charge state distributions tend to be narrow and extensive salt adduction, heterogeneity, and so on tend to lead to significantly broadened peaks. These issues can compromise mass measurement of high mass bio-complexes, particularly when charge states are not clearly resolved. In this work, we show that the attachment of high mass ions of known mass and charge to populations of ions of interest can lead to well-separated signals that can yield confident charge state and mass assignments from otherwise poorly resolved signals.

Enhancing detection and characterization of lipids using charge manipulation in electrospray ionization-tandem mass spectrometry

Heightened awareness regarding the implication of disturbances in lipid metabolism with respect to prevalent human-related pathologies demands analytical techniques that provide unambiguous structural characterization and accurate quantitation of lipids in complex biological samples. The diversity in molecular structures of lipids along with their wide range of concentrations in biological matrices present formidable analytical challenges. Modern mass spectrometry (MS) offers an unprecedented level of analytical power in lipid analysis, as many advancements in the field of lipidomics have been facilitated through novel applications of and developments in electrospray ionization tandem mass spectrometry (ESI-MS/MS). ESI allows for the formation of intact lipid ions with little to no fragmentation and has become widely used in contemporary lipidomics experiments due to its sensitivity, reproducibility, and compatibility with condensed-phase modes of separation, such as liquid chromatography (LC). Owing to variations in lipid functional groups, ESI enables partial chemical separation of the lipidome, yet the preferred ion-type is not always formed, impacting lipid detection, characterization, and quantitation. Moreover, conventional ESI-MS/MS approaches often fail to expose diverse subtle structural features like the sites of unsaturation in fatty acyl constituents or acyl chain regiochemistry along the glycerol backbone, representing a significant challenge for ESI-MS/MS. To overcome these shortcomings, various charge manipulation strategies, including charge-switching, have been developed to transform ion-type and charge state, with aims of increasing sensitivity and selectivity of ESI-MS/MS approaches. Importantly, charge manipulation approaches afford enhanced ionization efficiency, improved mixture analysis performance, and access to informative fragmentation channels. Herein, we present a critical review of the current suite of solution-based and gas-phase strategies for the manipulation of lipid ion charge and type relevant to ESI-MS/MS.

Independent phase modulation for quadruplex polarization channels enabled by chirality-assisted geometric-phase metasurfaces

Geometric-phase metasurfaces, recently utilized for controlling wavefronts of circular polarized (CP) electromagnetic waves, are drastically limited to the cross-polarization modality. Combining geometric with propagation phase allows to further control the co-polarized output channel, nevertheless addressing only similar functionality on both co-polarized outputs for the two different CP incident beams. Here we introduce the concept of chirality-assisted phase as a degree of freedom, which could decouple the two co-polarized outputs, and thus be an alternative solution for designing arbitrary modulated-phase metasurfaces with distinct wavefront manipulation in all four CP output channels. Two metasurfaces are demonstrated with four arbitrary refraction wavefronts, and orbital angular momentum modes with four independent topological charge, showcasing complete and independent manipulation of all possible CP channels in transmission. This additional phase addressing mechanism will lead to new components, ranging from broadband achromatic devices to the multiplexing of wavefronts for application in reconfigurable-beam antenna and wireless communication systems.

Measuring Membrane Protein-Lipid Interactions in Nanodiscs with Native Mass Spectrometry

Native mass spectrometry (MS), which uses nondenaturing ionization to preserve noncovalent complexes for mass analysis, has proven to be powerful for characterizing membrane protein complex stoichiometry and interactions. Membrane proteins are traditionally solubilized using detergent micelles prior to native MS. Collisional activation is employed in the mass spectrometer to remove bound detergent and yield the membrane protein, potentially in complex with bound lipids. However, this method of solubilization can be problematic as detergents may distort the native-like structure and function of membrane proteins. Furthermore, the collisional activation required for detergent removal can lead to the loss of noncovalent interactions within fragile complexes. Lipoprotein nanodiscs provide a more natural lipid bilayer environment for delivering membrane proteins for native MS, but previous measurements have been limited by the moderate stability of nanodiscs in the gas phase. It is difficult to preserve the intact membrane protein-nanodisc complex for native MS but also difficult to efficiently eject membrane proteins from nanodiscs. To tune the stability of nanodiscs, we used chemical additives known to modulate the charge acquired during electrospray ionization (ESI). Two membrane proteins, the trimeric ammonium transporter AmtB and tetrameric aquaporin ApqZ, were reconstituted into nanodiscs for native MS. Employing charge manipulation reagents and different ionization polarities allowed us to either capture the intact membrane protein-nanodisc complex or eject the membrane protein with few bound lipids. We are currently investigating the selectivity of lipid binding to membrane proteins ejected from nanodiscs of mixed lipid compositions. Preliminary results show that distinct lipid shells corresponding to different types of protein-lipid interactions are preferentially enriched in either zwitterionic or anionic lipids. Ultimately, we expect our novel methods combining native MS and nanodiscs will provide unique insights into membrane protein-lipid interactions in model lipid bilayers.

Introducing our Inaugural Early Career Advisory Board

Introducing our Inaugural Early Career Advisory Board

Electric field control of the photoinduced resistance increase in La0.7Sr0.3MnO3/LaTiO3/SrTiO3 heterostructure

In this work we have studied the effect of light and electric field on the electrical properties of La0.7Sr0.3MnO3 (LSMO) film at 300 K. Taking advantage of it's charge, spin, orbital and lattice degrees of freedom, we have successfully shown that light and electric field together can be used to tune the resistance states of the manganite system. Using applied gate voltage (Vg) and light we were able to obtain a change in resistance of about +/-7.5%. Furthermore, incorporating an ultra thin interfacial LaTiO3 (LTO) layer provides valuable insight on the origin of the photoinduced effect. The observed photoinduced effect is attributed to photoexcited down spin eg electrons, interfacial charge injection and manipulation of orbital occupancy depending on the gate voltage and wavelength of light.

Spectral phase control of interfering chirped pulses for high-energy narrowband terahertz generation

Highly-efficient optical generation of narrowband terahertz radiation enables unexplored technologies and sciences from compact electron acceleration to charge manipulation in solids. State-of-the-art conversion efficiencies are currently achieved using difference-frequency generation driven by temporal beating of chirped pulses but remain, however, far lower than desired or predicted. Here we show that high-order spectral phase fundamentally limits the efficiency of narrowband difference-frequency generation using chirped-pulse beating and resolve this limitation by introducing a novel technique based on tuning the relative spectral phase of the pulses. For optical terahertz generation, we demonstrate a 13-fold enhancement in conversion efficiency for 1%-bandwidth, 0.361 THz pulses, yielding a record energy of 0.6 mJ and exceeding previous optically-generated energies by over an order of magnitude. Our results prove the feasibility of millijoule-scale applications like terahertz-based electron accelerators and light sources and solve the long-standing problem of temporal irregularities in the pulse trains generated by interfering chirped pulses.

Tip-Induced Control of Charge and Molecular Bonding of Oxygen Atoms on the Rutile TiO2 (110) Surface with Atomic Force Microscopy.

We study a low-temperature on-surface reversible chemical reaction of oxygen atoms to molecules in ultrahigh vacuum on the semiconducting rutile TiO2(110)-(1 × 1) surface. The reaction is activated by charge transfer from two sources, natural surface/subsurface polarons and experimental Kelvin probe force spectroscopy as a tool for electronic charge manipulation with single electron precision. We demonstrate a complete control over the oxygen species not attainable previously, allowing us to deliberately discriminate in favor of charge or bond manipulation, using either direct charge injection/removal through the tip-oxygen adatom junction or indirectly via polarons. Comparing our ab initio calculations with experiment, we speculate that we may have also manipulated the spin on the oxygens, allowing us to deal with the singlet/triplet complexities associated with the oxygen molecule formation. We show that the manipulation outcome is fully governed by three experimental parameters, vertical and lateral tip positions and the bias voltage.

Two-Dimensional Energy Band Engineering in GaAs/AlGaAs Core–Shell Nanowires by Crystal-Phase Switching for Charge Manipulation

Two-dimensional (2D) band engineering within nanowires is realized by axial switching of crystal-phase from wurtzite to zinc blende and a lateral GaAs/AlGaAs core–shell structure. Band alignment between different phases/materials is investigated through off-axis electron holography and interpolation calculations, which is further utilized for controlling the migration of carriers. Besides, the arrangement of the heterophase layers is found to affect the charge distribution severely. Above all, carrier reservoirs and a charged surface/interface could be achieved within a single nanowire by 2D band engineering. Our work offers a new idea on the construction of nanostructures for applications in photoelectric and electronic domains.

Effective steering of charge flow through synergistic inducing oxygen vacancy defects and p-n heterojunctions in 2D/2D surface-engineered Bi2WO6/BiOI cascade: Towards superior photocatalytic CO2 reduction activity

Semiconductor-based photocatalytic CO2 conversion is a promising and sustainable avenue in response to the anthropogenic climate change and imminent energy crisis, which however is unavoidably impeded by the limited photo-absorption, undesirable recombination of photogenerated charge carriers and insufficient surface active sites on semiconductors. In this study, all these challenges were overcome by selectively and chemically assembly of oxygen-deficient Bi2WO6 nanosheets onto BiOI nanosheets, forming a novel surface defect-engineered 2D/2D motif with built-in nanoscale p-n heterojunctions. This rational cascade configuration with internal electric field renders ultrafast directional migration and spatial separation of photogenerated charge carriers. Meanwhile, the oxygen vacant sites with abundant trapped electrons serve as the active sites for CO2 reduction and extend the light absorption of the photocatalytic system to NIR region. Combining these propitious properties, our delineated nanoscale p-n heterojunction on the basis of 2D/2D assembly of surface defect-engineered nanosheets presents a new and unprecedented concept for effective generation of charge carriers, directional steering of charge flow and manipulation of surface active sites, which cooperatively lead to superior photocatalytic performance. Notably, our developed oxygen-deficient Bi2WO6/BiOI binanosheets exhibit a remarkably high production yield of CH4, which represents the state-of-the-art visible light-driven CH4 production activity among all the existing 2D BiOI-based and Bi2WO6-based composites.

Size Fractionation of Graphene Oxide via Solvent‐Mediated Consecutive Charge Manipulation and Investigation of the Size Effect as Hole Transporting Layer in Perovskite Solar Cells

AbstractAlthough intensive research for graphene oxide (GO) has been conducted, the broad size distribution of as‐synthesized GO flakes still remains a challenging issue since flake size has a direct impact on the material properties and related applications. Herein, we propose a facile and scalable approach for the size fractionation of GO flakes by manipulating the surface charge of GO with an organic solvent‐mediated aqueous solution. Both the experimental and simulation results confirm that the dispersion of GO flakes is notably influenced by the bond strength with solvent, which is attributed by the charge amount of oxygen in solvent molecule. From the understanding of the dispersion mechanism, an optimal solvent for the size fractionation of GO flakes was determined and GO flakes were successfully sorted into various size groups with a narrow distribution. The effect of size fractionation on the material property and related application was confirmed through various analyses. Our results could bring significant advances in producing two‐dimensional materials with reliable and reproducible material properties toward practical applications.