Publications

Electrolyte-gated organic transistors (EGOTs) leveraging organic semiconductors' electronic and ionic transport characteristics are the key enablers for many biosensing and bioelectronic applications that can selectively sense, record, and monitor different biological and biochemical processes at the nanoscale and translate them into macroscopic electrical signals. Understanding such transduction mechanisms requires multiscale characterization tools to comprehensively probe local electrical properties and link them with device behavior across various bias points. Here, an automated scanning dielectric microscopy toolbox is demonstrated that performs operando in-liquid scanning dielectric microscopy measurements on functional EGOTs and carries out extensive data analysis to unravel the evolution of local electrical properties in minute detail. This paper emphasizes critical experimental considerations permitting standardized, accurate, and reproducible data acquisition. The developed approach is validated with EGOTs based on blends of organic small molecule semiconductor and insulating polymer that work as accumulation-mode field-effect transistors. Furthermore, the degradation of local electrical characteristics at high gate voltages is probed, which is apparently driven by the destruction of local crystalline order due to undesirable electrochemical swelling of the organic semiconducting material near the source electrode edge. The developed approach paves the way for systematic probing of EGOT-based technologies for targeted optimization and fundamental understanding. This study presents automated scanning dielectric microscopy toolbox for comprehensive nanoscale electrical measurements of operating electrolyte-gated organic transistors (EGOTs). It highlights critical experimental practices for accurate data acquisition and easily reproducible analysis. The approach is validated using EGOTs based on blends of organic semiconductor and insulating polymer, revealing degradation at high gate voltages due to electrochemical swelling in minute details. image

JTD Keywords: Automation, Electrolyte-gated organic transistors, Nanoscale, Operando scanning dielectric microscopy, Transistor degradatio

Multiplexed assays of variant effect (MAVEs) have emerged as a powerful approach for interrogating thousands of genetic variants in a single experiment. The flexibility and widespread adoption of these techniques across diverse disciplines have led to a heterogeneous mix of data formats and descriptions, which complicates the downstream use of the resulting datasets. To address these issues and promote reproducibility and reuse of MAVE data, we define a set of minimum information standards for MAVE data and metadata and outline a controlled vocabulary aligned with established biomedical ontologies for describing these experimental designs.

JTD Keywords: Deep mutational scanning, Dms, Genetic variants, Genomics, Mave, Multiplexed assays of variant effect, Standards

Charge transport in electrolyte-gated organic field-effect transistors (EGOFETs) is governed by the microstructural property of the semiconducting thin film that is in direct contact with the electrolyte. Therefore, a comprehensive nanoscale operando characterization of the active channel is crucial to pinpoint various charge transport bottlenecks for rational and targeted optimization of the devices. Here, the local electrical properties of EGOFETs are systematically probed by in-liquid scanning dielectric microscopy (in-liquid SDM) and a direct picture of their functional mechanism at the nanoscale is provided across all operational regimes, starting from subthreshold, linear to saturation, until the onset of pinch-off. To this end, a robust interpretation framework of in-liquid SDM is introduced that enables quantitative local electric potential mapping directly from raw experimental data without requiring calibration or numerical simulations. Based on this development, a straightforward nanoscale assessment of various charge transport bottlenecks is performed, like contact access resistances, inter- and intradomain charge transport, microstructural inhomogeneities, and conduction anisotropy, which have been inaccessible earlier. Present results contribute to the fundamental understanding of charge transport in electrolyte-gated transistors and promote the development of direct structure-property-function relationships to guide future design rules. This study delves into the charge transport properties of electrolyte-gated organic field-effect transistors by employing in-liquid scanning dielectric microscopy. By introducing a novel interpretation framework, the research achieves quantitative mapping of the local electric potential, facilitating a detailed assessment of charge transport bottlenecks across all operational regimes. The findings can fosterthe formulation ofstructure-property-function relationships for device optimization.image

JTD Keywords: Conduction anisotropy, Conductivity maps, Electrolyte-gated organic field-effect transistors, Nanoscale, Operando, Operation regimes, Potential maps, Scanning dielectric microscopy

Laser surface micropatterning of dental-grade zirconia (3Y-TZP) was explored with the objective of providing defined linear patterns capable of guiding bone-cell response.A nanosecond (ns-) laser was employed to fabricate microgrooves on the surface of 3Y-TZP discs, yielding three different groove periodicities (i.e., 30, 50 and 100 µm). The resulting topography and surface damage were characterized by confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). X-Ray diffraction (XRD) and Raman spectroscopy techniques were employed to assess the hydrothermal degradation resistance of the modified topographies. Preliminary biological studies were conducted to evaluate adhesion (6 h) of human mesenchymal stem cells (hMSC) to the patterns in terms of cell number and morphology. Finally, Staphylococcus aureus adhesion (4 h) to the microgrooves was investigated.The surface analysis showed grooves of approximately 1.8 µm height that exhibited surface damage in the form of pile-up at the edge of the microgrooves, microcracks and cavities. Accelerated aging tests revealed a slight decrease of the hydrothermal degradation resistance after laser patterning, and the Raman mapping showed the presence of monoclinic phase heterogeneously distributed along the patterned surfaces. An increase of the hMSC area was identified on all the microgrooved surfaces, although only the 50 µm periodicity, which is closer to the cell size, significantly favored cell elongation and alignment along the grooves. A decrease in Staphylococcus aureus adhesion was observed on the investigated micropatterns.The study suggests that linear microgrooves of 50 µm periodicity may help in promoting hMSC adhesion and alignment, while reducing bacterial cell attachment.Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.

JTD Keywords: abutment material, alumina toughened zirconia, antibacterial, bacterial adhesion, biofilm growth, cell adhesion, dental implants, hydrothermal degradation, implant surfaces, in-vitro, laser patterning, osseointegration, osteogenic differentiation, part 1, surface topography, y-tzp ceramics, Antibacterial, Antibacterials, Bacteria, Bone, Cell adhesion, Cell culture, Cells adhesion, Ceramics, Chemistry, Degradation resistance, Dental implants, Dental material, Dental materials, Dental prostheses, Human, Human mesenchymal stem cells, Humans, Hydrothermal degradation, Laser patterning, Laser surface, Lasers, Low-temperature degradation, Materials testing, Microscopy, electron, scanning, Nanosecond lasers, Osseointegration, Piles, Scanning electron microscopy, Staphylococcus aureus, Stem cells, Surface analysis, Surface damages, Surface properties, Surface property, Surface topography, Topography, Yttrium, Zirconia, Zirconium

The transduction of odorant binding into cellular signaling by olfactory receptors (ORs) is not understood and knowing its mechanism would enable developing new pharmacology and biohybrid electronic detectors of volatile organic compounds bearing high sensitivity and selectivity. The electrical characterization of ORs in bulk experiments is subject to microscopic models and assumptions. We have directly determined the nanoscale electrical properties of ORs immobilized in a fixed orientation, and their change upon odorant binding, using electrochemical scanning tunneling microscopy (EC-STM) in near-physiological conditions. Recordings of current versus time, distance, and electrochemical potential allows determining the OR impedance parameters and their dependence with odorant binding. Our results allow validating OR structural-electrostatic models and their functional activation processes, and anticipating a novel macroscopic biosensor based on ORs.Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.

JTD Keywords: electrochemical scanning tunneling, electrochemical scanning tunneling microscopy (ec-stm), microscopy (ec-stm), neurons, odorant binding, olfactory receptors (ors), open-circuit voltage(voc), Olfactory receptors (ors), Open-circuit voltage (v(oc)), Transport

Van der Waals layered ferroelectrics, such as CuInP2S6 (CIPS), offer a versatile platform for miniaturization of ferroelectric device technologies. Control of the targeted composition and kinetics of CIPS synthesis enables the formation of stable self-assembled heterostructures of ferroelectric CIPS and nonferroelectric In4/3P2S6 (IPS). Here, we use quantitative scanning probe microscopy methods combined with density functional theory (DFT) to explore in detail the nanoscale variability in dynamic functional properties of the CIPS-IPS heterostructure. We report evidence of fast ionic transport which mediates an appreciable out-of-plane electromechanical response of the CIPS surface in the paraelectric phase. Further, we map the nanoscale dielectric and ionic conductivity properties as we thermally stimulate the ferroelectric-paraelectric phase transition, recovering the local dielectric behavior during this phase transition. Finally, aided by DFT, we reveal a substantial and tunable conductivity enhancement at the CIPS/IPS interface, indicating the possibility of engineering its interfacial properties for next generation device applications.

JTD Keywords: copper indium thiophosphate, diffusion, elastic band method, ferroelectrics, ionic conductor, migration, nanoscale, phase transition, piezoresponse force microscopy, scanning dielectric microscopy, transition, Copper indium thiophosphate, Initio molecular-dynamics, Scanning dielectric microscopy

Tuning of the crosslink density (CLD) in the rubber compounds is very crucial for optimizing the physical and mechanical properties of the ultimate rubber products. Conventionally, CLD can be measured via rheological methods such as moving die rheometer (MDR), via mechanical tests such as temperature scanning stress relaxation analysis (TSSR), or via direct swelling experiments using Flory–Rehner approach. In the current study, two novel techniques, focused ion beam - scanning electron microscopy (FIB-SEM) processing, with simultaneous energy dispersive X-ray spectrometry (EDS) mapping analysis and scanning acoustic microscopy (SAM) were combined and correlated to conventional methods on a model recipe of ethylene propylene diene monomer (EPDM) compound having different sulphur contents. Depending on the applied technique, the increase in the crosslink density with sulphur content was found to be 1.7 fold for the Flory–Rehner approach and 1.2 fold for both TSSR and MDR. It is directly monitored from the FIB-SEM-EDS analysis that the sulphur distribution and agglomeration behavior increased in line with ZnO content, which is an indirect indication of the rise in crosslink density. The impedance maps of the crosslinked samples obtained through SAM analysis revealed that the impedance of the samples increased with the increasing sulphur content, which can be attributed to higher level of crosslink density. A quantified correlation was obtained between SAM images and the crosslink density of the samples. It was shown that SAM is a promising tool for practical and non-destructive analysis for determining the formation of crosslink density of the rubbers. © The Author(s) 2022.

JTD Keywords: blends, compressibility, crosslink density, cure characteristics, ethylene propylene diene monomer, focused ion beam, mechanical-properties, morphology, natural-rubber, particles, scanning acoustic microscopy, scanning electron microscopy, sulfur, thermal-stability, vulcanization, Composite soft materials, Cross-link densities, Crosslink density, Crosslinking, Density (specific gravity), Ethylene, Ethylene propylene diene monomer, Flory-rehner, Focused ion beam - scanning electron microscopy, Focused ion beam-scanning electron microscopies, Ii-vi semiconductors, Monomers, Moving die rheometers, Physical and mechanical properties, Propylene, Relaxation analysis, Rubber, Scanning acoustic microscopy, Scanning electron microscopy, Stress relaxation, Sulfur contents, Temperature scanning stress relaxations, Zinc oxide

The design of catalysts with controlled selectivity at will, also known as catalytic plasticity, is a very attractive approach for the recycling of carbon dioxide (CO2). In this work, we study how catalytically active hydroxyapatite (HAp) and brushite (Bru) interact synergistically, allowing the production of formic acid or acetic acid depending on the HAp/Bru ratio in the catalyst. Raman, wide angle X-ray scattering, X-ray photoelectron spectroscopy, scanning electron microscopy and electrochemical impedance spectroscopy studies, combined with an exhaustive revision of the crystalline structure of the catalyst at the atomic level, allowed to discern how the Bru phase can be generated and stabilized at high temperatures. Results clearly indicate that the presence of OH– groups to maintain the crystalline structural integrity in conjunction with Ca2+ ions less bonded to the lattice fixate carbon into C1, C2 and C3 molecules from CO2 and allow the evolution from formic to acetic acid and acetone. In this way, the plasticity of the HAp-Bru system is demonstrated, representing a promising green alternative to the conventional metal-based electrocatalysts used for CO2 fixation. Thus, the fact that no electric voltage is necessary for the CO2 reduction has a very favorable impact in the final energetic net balance of the carbon fixation reaction. © 2021

JTD Keywords:

ethanol production & nbsp, brushite, co2 reduction, conversion, electrocatalytic reduction, electrode, formate, heterogeneous catalysis & nbsp, hydrogen evolution, insights, monetite, polarized hydroxyapatite,

Charge separation and transport through the reaction center of photosystem I (PSI) is an essential part of the photosynthetic electron transport chain. A strategy is developed to immobilize and orient PSI complexes on gold electrodes allowing to probe the complex's electron acceptor side, the chlorophyll special pair P700. Electrochemical scanning tunneling microscopy (ECSTM) imaging and current-distance spectroscopy of single protein complex shows lateral size in agreement with its known dimensions, and a PSI apparent height that depends on the probe potential revealing a gating effect in protein conductance. In current-distance spectroscopy, it is observed that the distance-decay constant of the current between PSI and the ECSTM probe depends on the sample and probe electrode potentials. The longest charge exchange distance (lowest distance-decay constant ?) is observed at sample potential 0 mV/SSC (SSC: reference electrode silver/silver chloride) and probe potential 400 mV/SSC. These potentials correspond to hole injection into an electronic state that is available in the absence of illumination. It is proposed that a pair of tryptophan residues located at the interface between P700 and the solution and known to support the hydrophobic recognition of the PSI redox partner plastocyanin, may have an additional role as hole exchange mediator in charge transport through PSI.© 2021 Wiley-VCH GmbH.

JTD Keywords: azurin, current distance decay spectroscopy, cytochrome c(6), electrochemical scanning tunneling microscopy (ecstm), electrochemistry, photosystem i, photosystem-i, plastocyanin, protein electron transfer, recognition, single metalloprotein, single molecules, structural basis, tunneling spectroscopy, 'current, Amino acids, Charge transfer, Chlorine compounds, Current distance decay spectroscopy, Decay spectroscopies, Distance decay, Electrochemical scanning tunneling microscopy, Electrochemical scanning tunneling microscopy (ecstm), Electrodes, Electron transfer, Electron transport properties, Gold compounds, Photosystem i, Photosystems, Protein electron transfer, Protein electron-transfer, Proteins, Scanning tunneling microscopy, Silver halides, Single molecule, Single molecules

Microphysiological systems (MPS) or organs-on-chips (OoC) can emulate the physiological functions of organs in vitro and are effective tools for determining human drug responses in preclinical studies. However, the analysis of MPS has relied heavily on optical tools, resulting in difficulties in real-time and high spatial resolution imaging of the target cell functions. In this study, the role of scanning probe microscopy (SPM) as an analytical tool for MPS is evaluated. An access hole is made in a typical MPS system with stacked microchannels to insert SPM probes into the system. For the first study, a simple vascular model composed of only endothelial cells is prepared for SPM analysis. Changes in permeability and local chemical flux are quantitatively evaluated during the construction of the vascular system. The morphological changes in the endothelial cells after flow stimulation are imaged at the single-cell level for topographical analysis. Finally, the possibility of adapting the permeability and topographical analysis using SPM for the intestinal vascular system is further evaluated. It is believed that this study will pave the way for an in situ permeability assay and structural analysis of MPS using SPM.

JTD Keywords: cell, electrochemical microscopy, membrane-permeability, microphysiological systems, organs-chips, platform, scanning electrochemical microscopy, scanning ion conductance microscopy, scanning probe microscopy, shear-stress, surface-topography, Ion conductance microscopy, Microphysiological systems, Organs-chips, Scanning electrochemical microscopy, Scanning ion conductance microscopy, Scanning probe microscopy

Mapping the biochemical composition of eukaryotic cells without the use of exogenous labels is a long-sought objective in cell biology. Recently, it has been shown that composition maps on dry single bacterial cells with nanoscale spatial resolution can be inferred from quantitative nanoscale dielectric constant maps obtained with the scanning dielectric microscope. Here, it is shown that this approach can also be applied to the much more challenging case of fixed and dry eukaryotic cells, which are highly heterogeneous and show micrometric topographic variations. More importantly, it is demonstrated that the main bottleneck of the technique (the long computation times required to extract the nanoscale dielectric constant maps) can be shortcut by using supervised neural networks, decreasing them from weeks to seconds in a wokstation computer. This easy-to-use data-driven approach opens the door for in situ and on-the-fly label free nanoscale composition mapping of eukaryotic cells with scanning dielectric microscopy. © 2021 The Authors. Small Methods published by Wiley-VCH GmbH

JTD Keywords: eukaryotic cells, label-free mapping, machine learning, nanoscale, scanning dielectric microscopy, Biochemical composition, Cells, Constant, Cytology, Data-driven approach, Dielectric forces, Dielectric materials, Eukaryotic cells, Label-free mapping, Machine learning, Mapping, Microscopy, atomic force, Nanoscale, Nanoscale composition, Nanoscale spatial resolution, Nanotechnology, Scanning, Scanning dielectric microscopy, Supervised neural networks

Polymer nanocomposite materials based on metallic nanowires are widely investigated as transparent and flexible electrodes or as stretchable conductors and dielectrics for biosensing. Here we show that Scanning Dielectric Microscopy (SDM) can map the depth distribution of metallic nanowires within the nanocomposites in a non-destructive way. This is achieved by a quantitative analysis of sub-surface electrostatic force microscopy measurements with finite-element numerical calculations. As an application we determined the three-dimensional spatial distribution of ?50 nm diameter silver nanowires in ?100 nm-250 nm thick gelatin films. The characterization is done both under dry ambient conditions, where gelatin shows a relatively low dielectric constant, ?r ? 5, and under humid ambient conditions, where its dielectric constant increases up to ?r ? 14. The present results show that SDM can be a valuable non-destructive subsurface characterization technique for nanowire-based nanocomposite materials, which can contribute to the optimization of these materials for applications in fields such as wearable electronics, solar cell technologies or printable electronics. © The Royal Society of Chemistry.

JTD Keywords: composite, constant, electrodes, mode, nanostructures, objects, progress, subsurface, tomography, Composite materials, Dielectric materials, Electric force microscopy, Electrostatic force, Force microscopy, Low dielectric constants, Nanocomposites, Numerical calculation, Polymer nanocomposite, Printable electronics, Scanning dielectric microscopy, Silver nanowires, Solar cell technology, Stretchable conductors, Subsurface characterizations, Transparent electrodes, Wearable technology

Liposomes are widely used as drug delivery carriers and as cell model systems. Here, we measure the dielectric properties of individual liposomes adsorbed on a metal electrode by in-liquid scanning dielectric microscopy in force detection mode. From the measurements the lamellarity of the liposomes, the separation between the lamellae and the specific capacitance of the lipid bilayer can be obtained. As application we considered the case of non-extruded DOPC liposomes with radii in the range ~ 100–800 nm. Uni-, bi- and tri-lamellar liposomes have been identified, with the largest population corresponding to bi-lamellar liposomes. The interlamellar separation in the bi-lamellar liposomes is found to be below ~ 10 nm in most instances. The specific capacitance of the DOPC lipid bilayer is found to be ~ 0.75 µF/cm2 in excellent agreement with the value determined on solid supported planar lipid bilayers. The lamellarity of the DOPC liposomes shows the usual correlation with the liposome's size. No correlation is found, instead, with the shape of the adsorbed liposomes. The proposed approach offers a powerful label-free and non-invasive method to determine the lamellarity and dielectric properties of single liposomes. [Figure not available: see fulltext.].

JTD Keywords: constant, force, lamellarity, liposomes, membrane capacitance, model, nanoscale, scanning dielectric microscopy, Lamellarity, Liposomes, Membrane capacitance, Nanoscale, Polarization properties, Scanning dielectric microscopy

Mapping the dielectric properties of cells with nanoscale spatial resolution can be an im-portant tool in nanomedicine and nanotoxicity analysis, which can complement structural and mechanical nanoscale measurements. Recently we have shown that dielectric constant maps can be obtained on dried fixed cells in air environment by means of scanning dielectric force volume mi-croscopy. Here, we demonstrate that such measurements can also be performed in the much more challenging case of fixed cells in liquid environment. Performing the measurements in liquid media contributes to preserve better the structure of the fixed cells, while also enabling accessing the local dielectric properties under fully hydrated conditions. The results shown in this work pave the way to address the nanoscale dielectric imaging of living cells, for which still further developments are required, as discussed here.

JTD Keywords: atomic force microscopy (afm), capacitance, constant, dielectric properties, electrostatic force microscopy (efm), functional microscopy, nanoscale, scanning dielectric microscopy (sdm), Atomic force microscopy (afm), Dielectric properties, Dielectrophoretic separation, Electrostatic force microscopy (efm), Functional micros-copy, Functional microscopy, Scanning dielectric microscopy (sdm), Scanning probe microscopy (spm)

© 2020 Wiley-VCH GmbH Probing nanoscale electrical properties of organic semiconducting materials at the interface with an electrolyte solution under externally applied voltages is key in the field of organic bioelectronics. It is demonstrated that the conductivity and interfacial capacitance of the active channel of an electrolyte-gated organic field-effect transistor (EGOFET) under operation can be probed at the nanoscale using scanning dielectric microscopy in force detection mode in liquid environment. Local electrostatic force versus gate voltage transfer characteristics are obtained on the device and correlated with the global current–voltage transfer characteristics of the EGOFET. Nanoscale maps of the conductivity of the semiconducting channel show the dependence of the channel conductivity on the gate voltage and its variation along the channel due to the space charge limited conduction. The maps reveal very small electrical heterogeneities, which correspond to local interfacial capacitance variations due to an ultrathin non-uniform insulating layer resulting from a phase separation in the organic semiconducting blend. Present results offer insights into the transduction mechanism at the organic semiconductor/electrolyte interfaces at scales down to ≈100 nm, which can bring substantial optimization of organic electronic devices for bioelectronic applications such as electrical recording on excitable cells or label-free biosensing.

JTD Keywords: Atomic force microscopy, Bioelectronic devices, Electrolyte gated organic field effect transistors, In-liquid scanning dielectric microscopy, Organic semiconducting blend

Concentrations down to 3 nM of the rhS100A4 protein, associated with human tumor development, have been detected in undiluted urine using an integrated sensor based on microring resonators in the emerging Al2O3 photonic platform. The fabricated microrings were designed for operation in the C-band (λ = 1565 nm) and exhibited a high-quality factor in air of 3.2 × 105. The bulk refractive index sensitivity of the devices was ~100 nm/RIU (for TM polarization) with a limit of detection of ~10−6 RIU. A surface functionalization protocol was developed to allow for the selective binding of the monoclonal antibodies designed to capture the target biomarker to the surface of the Al2O3 microrings. The detection of rhS100A4 proteins at clinically relevant concentrations in urine is a big milestone towards the use of biosensors for the screening and early diagnosis of different cancers. Biosensors based on this microring technology can lead to portable, multiplexed and easy-to-use point of care devices.

JTD Keywords: Distributed feedback lasers, Effective refractive index, Laser coupling, Polarization maintaining fibers, Refractive index, Scanning electron microscopy

This article presents the application of dual focused ion beam/scanning electron microscopy (FIB-SEM) imaging for preclinical testing of calcium phosphates with osteoclast precursor cells and how this high-resolution imaging technique is able to reveal microstructural changes at a level of detail previously not possible. Calcium phosphate substrates, having similar compositions but different microstructures, were produced using low-and high-Temperature processes (biomimetic calcium-deficient hydroxyapatite [CDHA] and stoichiometric sintered hydroxyapatite, respectively). Human osteoclast precursor cells were cultured for 21 days before evaluating their resorptive potential on varying microstructural features. Alternative to classical morphological evaluation of osteoclasts (OC), FIB-SEM was used to observe the subjacent microstructure by transversally sectioning cells and observing both the cells and the substrates. Resorption pits, indicating OC activity, were visible on the smoother surface of high-Temperature sintered hydroxyapatite. FIB-SEM analysis revealed signs of acidic degradation on the grain surface under the cells, as well as intergranular dissolution. No resorption pits were evident on the surface of the rough CDHA substrates. However, whereas no degradation was detected by FIB sections in the material underlying some of the cells, early stages of OC-mediated acidic degradation were observed under cells with more spread morphology. Collectively, these results highlight the potential of FIB to evaluate the resorptive activity of OC, even in rough, irregular, or coarse surfaces where degradation pits are otherwise difficult to visualize.

JTD Keywords: Bone Regeneration, Calcium Phosphate, Focus Ion Beam, Osteoclast, Resorption, Scanning Electron Microscopy

It is often thought that the ability to control reaction rates with an applied electrical potential gradient is unique to redox systems. However, recent theoretical studies suggest that oriented electric fields could affect the outcomes of a range of chemical reactions, regardless of whether a redox system is involved1, 2, 3, 4. This possibility arises because many formally covalent species can be stabilized via minor charge-separated resonance contributors. When an applied electric field is aligned in such a way as to electrostatically stabilize one of these minor forms, the degree of resonance increases, resulting in the overall stabilization of the molecule or transition state. This means that it should be possible to manipulate the kinetics and thermodynamics of non-redox processes using an external electric field, as long as the orientation of the approaching reactants with respect to the field stimulus can be controlled. Here, we provide experimental evidence that the formation of carbon–carbon bonds is accelerated by an electric field. We have designed a surface model system to probe the Diels–Alder reaction, and coupled it with a scanning tunnelling microscopy break-junction approach5, 6, 7. This technique, performed at the single-molecule level, is perfectly suited to deliver an electric-field stimulus across approaching reactants. We find a fivefold increase in the frequency of formation of single-molecule junctions, resulting from the reaction that occurs when the electric field is present and aligned so as to favour electron flow from the dienophile to the diene. Our results are qualitatively consistent with those predicted by quantum-chemical calculations in a theoretical model of this system, and herald a new approach to chemical catalysis.

JTD Keywords: Electrocatalysis, Scanning probe microscopy

The electric polarizability of DNA, represented by the dielectric constant, is a key intrinsic property that modulates DNA interaction with effector proteins. Surprisingly, it has so far remained unknown owing to the lack of experimental tools able to access it. Here, we experimentally resolved it by detecting the ultraweak polarization forces of DNA inside single T7 bacteriophages particles using electrostatic force microscopy. In contrast to the common assumption of low-polarizable behavior like proteins (εr ~ 2–4), we found that the DNA dielectric constant is ~ 8, considerably higher than the value of ~ 3 found for capsid proteins. State-of-the-art molecular dynamic simulations confirm the experimental findings, which result in sensibly decreased DNA interaction free energy than normally predicted by Poisson–Boltzmann methods. Our findings reveal a property at the basis of DNA structure and functions that is needed for realistic theoretical descriptions, and illustrate the synergetic power of scanning probe microscopy and theoretical computation techniques.

JTD Keywords: Atomic force microscopy, Atomistic simulations, DNA packaging, DNA-ligand binding, Poisson-Boltzmann equation, capsid protein, DNA, double stranded DNA, amino acid composition, article, atomic force microscopy, bacteriophage, bacteriophage T7, dielectric constant, dipole, DNA binding, DNA packaging, DNA structure, electron microscopy, ligand binding, nonhuman, polarization, priority journal, protein analysis, protein DNA interaction, scanning probe microscopy, static electricity, virion, virus capsid, virus particle, atomic force microscopy, atomistic simulations, DNA packaging, DNA-ligand binding, Poisson-Boltzmann equation, Bacteriophage T7, Capsid, Cations, Dielectric Spectroscopy, DNA, DNA, Viral, DNA-Binding Proteins, Electrochemical Techniques, Ligands, Microscopy, Atomic Force, Models, Chemical, Nuclear Proteins

Cell adhesion processes are governed by the nanoscale arrangement of the extracellular matrix (ECM), being more affected by local rather than global concentrations of cell adhesive ligands. In many cell-based studies, grafting of dendrimers on surfaces has shown the benefits of the local increase in concentration provided by the dendritic configuration, although the lack of any reported surface characterization has limited any direct correlation between dendrimer disposition and cell response. In order to establish a proper correlation, some control over dendrimer surface deposition is desirable. Here, dendrimer nanopatterning has been employed to address arginine-glycine-aspartic acid (RGD) density effects on cell adhesion. Nanopatterned surfaces were fully characterized by atomic force microscopy (AFM), scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS), showing that tunable distributions of cell adhesive ligands on the surface are obtained as a function of the initial dendrimer bulk concentration. Cell experiments showed a clear correlation with dendrimer surface layout: Substrates presenting regions of high local ligand density resulted in a higher percentage of adhered cells and a higher degree of maturation of focal adhesions (FAs). Therefore, dendrimer nanopatterning is presented as a suitable and controlled approach to address the effect of local ligand density on cell response. Moreover, due to the easy modification of dendrimer peripheral groups, dendrimer nanopatterning can be further extended to other ECM ligands having density effects on cells.

JTD Keywords: Arginine-glycine-aspartic acid, Atomic force microscopy, Cell adhesion, Dendrimer, Focal adhesions, Scanning tunneling microscopy

We present a procedure for calibrated complex impedance measurements and dielectric quantification with scanning microwave microscopy. The calibration procedure works in situ directly on the substrate with the specimen of interest and does not require any specific calibration sample. In the workflow tip-sample approach curves are used to extract calibrated complex impedance values and to convert measured S11 reflection signals into sample capacitance and resistance images. The dielectric constant of thin dielectric SiO2 films were determined from the capacitance images and approach curves using appropriate electrical tip-sample models and the εr value extracted at f = 19.81 GHz is in good agreement with the nominal value of εr ∼ 4. The capacitive and resistive material properties of a doped Si semiconductor sample were studied at different doping densities and tip-sample bias voltages. Following a simple serial model the capacitance-voltage spectroscopy curves are clearly related to the semiconductor depletion zone while the resistivity is rising with falling dopant density from 20 Ω to 20 kΩ. The proposed procedure of calibrated complex impedance measurements is simple and fast and the accuracy of the results is not affected by varying stray capacitances. It works for nanoscale samples on either fully dielectric or highly conductive substrates at frequencies between 1 and 20 GHz.

JTD Keywords: Complex impedance, Dielectric constant, Nanotechnology: calibration, Resistivity, Scanning microwave microscopy

Lung bioengineering using decellularized organ scaffolds is a potential alternative for lung transplantation. Clinical application will require donor scaffold sterilization. As gamma-irradiation is a conventional method for sterilizing tissue preparations for clinical application, the aim of this study was to evaluate the effects of lung scaffold sterilization by gamma irradiation on the mechanical properties of the acellular lung when subjected to the artificial ventilation maneuvers typical within bioreactors. Twenty-six mouse lungs were decellularized by a sodium dodecyl sulfate detergent protocol. Eight lungs were used as controls and 18 of them were submitted to a 31kGy gamma irradiation sterilization process (9 kept frozen in dry ice and 9 at room temperature). Mechanical properties of acellular lungs were measured before and after irradiation. Lung resistance (RL) and elastance (EL) were computed by linear regression fitting of recorded signals during mechanical ventilation (tracheal pressure, flow and volume). Static (Est) and dynamic (Edyn) elastances were obtained by the end-inspiratory occlusion method. After irradiation lungs presented higher values of resistance and elastance than before irradiation: RL increased by 41.1% (room temperature irradiation) and 32.8% (frozen irradiation) and EL increased by 41.8% (room temperature irradiation) and 31.8% (frozen irradiation). Similar increases were induced by irradiation in Est and Edyn. Scanning electron microscopy showed slight structural changes after irradiation, particularly those kept frozen. Sterilization by gamma irradiation at a conventional dose to ensure sterilization modifies acellular lung mechanics, with potential implications for lung bioengineering.

JTD Keywords: Gamma irradiation, Lung bioengineering, Lung decellularization, Organ scaffold, Pulmonary mechanics, Decellularization, Gamma irradiation, Mouse lung, Pulmonary mechanics, dodecyl sulfate sodium, animal tissue, Article, artificial ventilation, bioengineering, bioreactor, compliance (physical), controlled study, freezing, gamma irradiation, lung, lung mechanics, lung resistance, male, mouse, nonhuman, room temperature, scanning electron microscopy, tissue scaffold, trachea pressure

In this study gelatin (Gel) modified with calcium phosphate nanoparticles (SG5) and polycaprolactone (PCL) were used to prepare a 3D bi-layer scaffold by collecting electrospun PCL and gelatin/SG5 fibers separately in the same collector. The objective of this study was to combine the desired properties of PCL and Gel/SG5 in the same scaffold in order to enhance mineralization, thus improving the ability of the scaffold to bond to the bone tissue. The scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and the wide angle X-ray diffraction (WAXD) measurements confirmed that SG5 nanoparticles were successfully incorporated into the fibrous gelatin matrix. The composite Gel/SG5/PCL scaffold exhibited more enhanced mechanical properties than individual Gel and Gel/SG5 scaffolds. The presence of SG5 nanoparticles accelerated the nucleation and growth of apatite crystals on the surface of the composite Gel/SG5/PCL scaffold in simulated body fluid (SBF). The osteoblast response in vitro to developed electrospun scaffolds (PCL and Gel/SG5/PCL) was investigated by using normal human primary NHOst cell lines. NHOst cell culture studies showed that higher alkaline phosphatase (ALP) activity and better mineralization were obtained in the case of composite materials than in pure PCL scaffolds. The mechanically strong PCL scaffold served as a skeleton, while the Gel/SG5 fibers facilitated cell spreading and mineralization of the scaffold.

JTD Keywords: Bilayer fibrous scaffold, Ceramic nanoparticles, Electrospinning, Gelatin, Polycaprolactone, Biomechanics, Bone, Calcium phosphate, Cell culture, Electrospinning, Fourier transform infrared spectroscopy, Mechanical properties, Mineralogy, Nanoparticles, Phosphatases, Polycaprolactone, Scanning electron microscopy, X ray diffraction, Polycaprolactone, Alkaline phosphatase activity, Bone tissue engineering, Calcium phosphate nanoparticles, Ceramic nanoparticles, Fibrous scaffolds, Gelatin, Simulated body fluids, Wide-angle x-ray diffraction, Electrospuns, Scaffolds (biology), Electrospinning

Here we have developed a simple method for the fabrication of disposable implantable all-solid-state ion-selective electrodes (ISE) in an array format without using complex fabrication equipment or clean room facilities. The electrodes were designed in a needle shape instead of planar electrodes for a full contact with the tissue. The needle-shape platform comprises 12 metallic pins which were functionalized with conductive inks and ISE membranes. The modified microelectrodes were characterized with cyclic voltammetry, scanning electron microscope (SEM), and optical interferometry. The surface area and roughness factor of each microelectrode were determined and reproducible values were obtained for all the microelectrodes on the array. In this work, the microelectrodes were modified with membranes for the detection of pH and nitrate ions to prove the reliability of the fabricated sensor array platform adapted to an endoscope.

JTD Keywords: Chemical sensors, Cyclic voltammetry, Electrochemistry, Endoscopy, Fabrication, Implants (surgical), Microelectrodes, Needles, Nitrates, Scanning electron microscopy, Biomedicine, Fabricated sensors, Fabrication equipment, Implantable devices, Implantable sensors, Optical interferometry, Planar electrode, Roughness factor, Ion selective electrodes

We report a novel fabrication process for the batch fabrication of insulated conductive scanning probe microscopy (SPM) probes for electrical and topographic characterization of soft samples in liquid media at the nanoscale. The whole SPM probe structure is insulated with a dielectric material except at the very tip end and at the contact pad area to minimize the leakage current in liquid. Additionally, the geometry of the conducting layer in the probe cantilever and substrate is engineered to reduce the parasitic capacitance coupling with the sample. The electrical characterization of the probes has shown that parasitic capacitances are significantly reduced as compared to fully metallized cantilevers.

JTD Keywords: Conductive scanning probe microscopy (C-SPM), EFM, SECM, SECM-AFM, SIM

Biogenic magnetite (Fe3O4) has been identified in human brain tissue. However, abnormal concentration of magnetite nanoparticles in the brain has been observed in different neurodegenerative pathologies. In the case of Alzheimer's disease (AD), these magnetic nanoparticles have been identified attached to the characteristic brain plaques, which are mainly formed by fibrils of amyloid β peptide (Aβ). However, few clues about the formation of the magnetite-Aβ complex have been reported. We have investigated the interaction between these important players in the AD with superconducting quantum interference, scanning electron microscope, surface plasmon resonance, and magnetic force microscopy. The results support the notion that the magnetite-Aβ complex is created before the synthesis of the magnetic nanoparticles, bringing a highly stable interaction of this couple.

JTD Keywords: Alzheimer's disease, Biogenic magnetite, Amyloid β peptide (Aβ), Superconducting quantum interference, Scanning electron microscope, Surface plasmon resonance, Magnetic force microscopy

In this study, polylactic acid (PLA) and polyethylene glycol (PEG) were combined with soluble CaP glass particles and processed by rapid prototyping to obtain fully biodegradable structures for Tissue Engineering applications. The obtained 3D biodegradable structures were characterized in terms of their architecture and mechanical properties. The scaffold morphology, internal micro-architecture and mechanical properties were evaluated using Scanning Electron Microscopy (SEM), micro-computed tomography (micro-CT) and mechanical testing, respectively. Well defined structures with pore size of 350-400μm (in the axial view), struts width of approximately 70-80μm, and a porosity ranging between 60-65% were obtained. The combination RP and PLA/PEG/CaP glass turned into promising fully degradable, mechanically stable, bioactive and biocompatible composite scaffolds for TE.

JTD Keywords: Axial view, Biodegradable composites, Composite scaffolds, Glass particles, Mechanically stable, Micro architectures, Micro computed tomography (micro-CT), Poly lactic acid, Scaffold morphology, Tissue engineering applications, Well-defined structures, Bioactive glass, Mechanical properties, Mechanical testing, Polyethylene glycols, Polymer blends, Rapid prototyping, Scaffolds (biology), Scanning electron microscopy, Computerized tomography

Near-field optical microscopy is a technique not limited by the laws of diffraction that enables simultaneous high-resolution fluorescence and topographic measurements at the nanometer scale. This chapter highlights the intrinsic advantages of near-field optics in the study of cellular structures. The first part of the chapter lays the foundations of the near-field concept and technical implementation of near-field scanning optical microscopy (NSOM), whereas the second part of the chapter focuses on applications of NSOM to the study of model membranes and cellular structures on the plasma membrane. The last part of the chapter discusses further directions of near-field optics, including optical antennas and fluorescence correlation spectroscopy approaches in the near-field regime.

JTD Keywords: Biological membranes, Cell membrane nanoscale compartmentalization, Cellular nanodomains, Fluorescence correlation spectroscopy in reduced volumes, Immunoreceptor imaging, Lipid rafts, Near-field scanning optical microscopy, Optical nano-antennas, Shear force imaging, Single molecule detection, Super-resolution microscopy

We present a method to measure directly and at the single-molecule level the distance decay constant that characterizes the rate of electron transfer (ET) in redox proteins. Using an electrochemical tunneling microscope under bipotentiostatic control, we obtained current-distance spectroscopic recordings of individual redox proteins confined within a nanometric tunneling gap at a well-defined molecular orientation. The tunneling current decays exponentially, and the corresponding decay constant (β) strongly supports a two-step tunneling ET mechanism. Statistical analysis of decay constant measurements reveals differences between the reduced and oxidized states that may be relevant to the control of ET rates in enzymes and biological electron transport chains.

JTD Keywords: Long-range electron transfer (LRET), Distance decay constant, Single-molecule electrochemistry, Redox enzyme, Metalloprotein, Blue copper protein, Azurin, Electrochemical scanning tunneling microscopy and spectroscopy, Nanoelectrodes, Debye length, Electrochemical charge screening

Lateral segregation of cell membranes is accepted as a primary mechanism for cells to regulate a diversity of cellular functions. In this context, lipid rafts have been conceptualized as organizing principle of biological membranes where underlying cholesterol-mediated selective connectivity must exist even at the resting state. However, such a level of nanoscale compositional connectivity has been challenging to prove. Here we used single-molecule near-field scanning optical microscopy to visualize the nanolandscape of raft ganglioside GM1 after tightening by its ligand cholera toxin (CTxB) on intact cell membranes. We show that CTxB tightening of GM1 is sufficient to initiate a minimal raft coalescence unit, resulting in the formation of cholesterol-dependent GM1 nanodomains <120 nm in size. This particular arrangement appeared independent of cell type and GM1 expression level on the membrane. Simultaneous dual color high-resolution images revealed that GPI anchored and certain transmembrane proteins were recruited to regions proximal (<150 nm) to CTxB-GM1 nanodomains without physical intermixing. Together with in silico experiments, our high-resolution data conclusively demonstrate the existence of raft-based interconnectivity at the nanoscale. Such a linked state on resting cell membranes constitutes thus an obligatory step toward the hierarchical evolution of large-scale raft coalescence upon cell activation.

JTD Keywords: Cholera toxin, Membrane heterogeneity, Near-field scanning optical microscopy, Raft ganglioside GM1, Single-molecule detection

For many years, it was believed that the laws of diffraction set a fundamental limit to the spatial resolution of conventional light microscopy. Major developments, especially in the past few years, have demonstrated that the diffraction barrier can be overcome both in the near- and far-field regime. Together with dynamic measurements, a wealth of new information is now emerging regarding the compartmentalization of cell membranes. In this review we focus on optical methods designed to explore the nanoscale architecture of the cell membrane, with a focal point on near-field optical microscopy (NSOM) as the first developed technique to provide truly optical super-resolution beyond the diffraction limit of light. Several examples illustrate the unique capabilities offered by NSOM and highlight its usefulness on cell membrane studies, complementing the palette of biophysical techniques available nowadays.

JTD Keywords: Membrane nanodomain, Lipid raft, Single molecule detection, Near-field scanning optical microscopy, Super-resolution optical microscopy

Quantitative measurement of the low-frequency dielectric constants of thick insulators at the nanoscale is demonstrated utilizing ac electrostatic force microscopy combined with finite-element calculations based on a truncated cone with hemispherical apex probe geometry. The method is validated on muscovite mica, borosilicate glass, poly(ethylene naphthalate), and poly(methyl methacrylate). The dielectric constants obtained are essentially given by a nanometric volume located at the dielectric-air interface below the tip, independently of the substrate thickness, provided this is on the hundred micrometer-length scale, or larger.

JTD Keywords: Borosilicate glasses, Finite element analysis, Insulating thin films, Mica, Nanostructured materials, Permittivity, Polymers, Scanning probe microscopy

We present the experimental demonstration of low-frequency dielectric constant imaging of single-layer supported biomembranes at the nanoscale. The dielectric constant image has been quantitatively reconstructed by combining the thickness and local capacitance obtained using a scanning force microscope equipped with a sub-attofarad low-frequency capacitance detector. This work opens new possibilities for studying bioelectric phenomena and the dielectric properties of biological membranes at the nanoscale.

JTD Keywords: Atomic-force microscopy, Nnear-field microscopy, Purple membrane, Scanning capacitance, Biological-systems, Fluid, Spectroscopy, Resolution, Proteins, Dynamics

Recruitment of receptor proteins to lipid rafts has been proposed as an important mechanism to regulate their cellular function. In particular, rafts have been implicated in regulation of integrin-mediated cell adhesion, although the underlying mechanism remains elusive. We used single-molecule near-field optical microscopy (NSOM) with localization accuracy of approximately 3 nm, to capture the spatio-functional relationship between the integrin LFA-1 and raft components (GPI-APs) on immune cells. Dual color nanoscale imaging revealed the existence of a nanodomain GPI-AP subpopulation that further concentrated in regions smaller than 250 nm, suggesting a hierarchical prearrangement of GPI-APs on resting monocytes. We previously demonstrated that in quiescent monocytes, LFA-1 preorganizes in nanoclusters. We now show that integrin nanoclusters are spatially different but reside proximal to GPI-AP nanodomains, forming hotspots on the cell surface. Ligand-mediated integrin activation resulted in an interconversion from monomers to nanodomains of GPI-APs and the generation of nascent adhesion sites where integrin and GPI-APs colocalized at the nanoscale. Cholesterol depletion significantly affected the reciprocal distribution pattern of LFA-1 and GPI-APs in the resting state, and LFA-1 adhesion to its ligand. As such, our data demonstrate the existence of nanoplatforms as essential intermediates in nascent cell adhesion. Since raft association with a variety of membrane proteins other than LFA-1 has been documented, we propose that hotspots regions enriched with raft components and functional receptors may constitute a prototype of nanoscale inter-receptor assembly and correspond to a generic mechanism to offer cells with privileged areas for rapid cellular function and responses to the outside world.

JTD Keywords: Integrin LFA-1, Membrane nanocompartments, Near-field scanning optical microscopy (NSOM), Single molecule detection

Interleukin 2 and interleukin 15 (IL2 and IL15, respectively) provide quite distinct contributions to T-cell-mediated immunity, despite having similar receptor composition and signaling machinery. As most of the proposed mechanisms underlying this apparent paradox attribute key significance to the individual {alpha}-chains of IL2 and IL15 receptors, we investigated the spatial organization of the receptors IL2R{alpha} and IL15R{alpha} at the nanometer scale expressed on a human CD4+ leukemia T cell line using single-molecule-sensitive near-field scanning optical microscopy (NSOM). In agreement with previous findings, we here confirm clustering of IL2R{alpha} and IL15R{alpha} at the submicron scale. In addition to clustering, our single-molecule data reveal that a non-negligible percentage of the receptors are organized as monomers. Only a minor fraction of IL2R{alpha} molecules reside outside the clustered domains, whereas [~]30% of IL15R{alpha} molecules organize as monomers or small clusters, excluded from the main domain regions. Interestingly, we also found that the packing densities per unit area of both IL2R{alpha} and IL15R{alpha} domains remained constant, suggesting a `building block' type of assembly involving repeated structures and composition. Finally, dual-color NSOM demonstrated co-clustering of the two {alpha}-chains. Our results should aid understanding the action of the IL2R-IL15R system in T cell function and also might contribute to the more rationale design of IL2R- or IL15R-targeted immunotherapy agents for treating human leukemia.

JTD Keywords: Near-field scanning optical microscopy (NSOM), Interleukin receptors IL2R, IL15R, Single-molecule detection, Nanometer-scale membrane organization

A biomimetic bone-like composite, made of self-assembled collagen fibrils and carbonate hydroxyapatite nanocrystals, has been performed by an electrochemically-assisted deposition on titanium plate. The electrolytic processes have been carried out using a single type I collagen molecules suspension in a diluted Ca(NO3)(2) and NH4H2PO4 solution at room temperature and applying a constant current for different periods of time. Using the same electrochemical conditions, carbonate hydroxyapatite nanocrystals or reconstituted collagen. brils coatings were obtained. The reconstituted collagen. brils, hydroxyapatite nanocrystals and collagen fibrils/apatite nanocrystals coatings have been characterized chemically, structurally and morphologically, as well as for their ability to bind fibronectin (FN). Fourier Transform Infrared microscopy has been used to map the topographic distribution of the coating components at different times of electrochemical deposition, allowing to single out the individual deposition steps. Moreover, roughness of Ti plate has been found to affect appreciably the nucleation region of the inorganic nanocrystals. Laser scanning confocal microscopy has been used to characterize the FN adsorption pattern on a synthetic biomimetic apatitic phase, which exhibits a higher affinity when it is inter-grown with the collagen fibrils. The results offer auspicious applications in the preparation of medical devices such as biomimetic bone-like composite-coated metallic implants.

JTD Keywords: Hydroxyapatite-collagen coating, Electrochemically-assisted deposition, Micro-imaging FTIR spectroscopy, Laser scanning confocal microscopy, Biomimetic crystal growth, Fibronectin binding

Biodegradable polymers reinforced with an inorganic phase such as calcium phosphate glasses may be a promising approach to fulfil the challenging requirements presented by 3D porous scaffolds for tissue engineering. Scaffolds' success depends mainly on their biological behaviour. This work is aimed to the in vitro study of polylactic acid (PLA)/CaP glass 3D porous constructs for bone regeneration. The scaffolds were elaborated using two different techniques, namely solvent-casting and phase-separation. The effect of scaffolds' micro and macrostructure on the biological response of these scaffolds was assayed. Cell proliferation, differentiation and morphology within the scaffolds were studied. Furthermore, polymer/glass scaffolds were seeded under dynamic conditions in a custom-made perfusion bioreactor. Results indicate that the final architecture of the solvent-cast or phase separated scaffolds have a significant effect on cells' behaviour. Solvent-cast scaffolds seem to be the best candidates for bone tissue engineering. Besides, dynamic seeding yielded a higher seeding efficiency in comparison with the static method.

JTD Keywords: Biocompatible Materials/ chemistry, Bone and Bones/ metabolism, Calcium Phosphates/ chemistry, Cell Differentiation, Cell Proliferation, Humans, Lactic Acid/ chemistry, Microscopy, Confocal, Microscopy, Electron, Scanning, Osteoblasts/metabolism, Permeability, Polymers/ chemistry, Porosity, Solvents/chemistry, Tissue Engineering/ methods