Electrochemical Atomic Force Microscopy Research Articles

Electrochemical DNA Sensors with Layered Polyaniline-DNA Coating for Detection of Specific DNA Interactions.

A DNA sensor has been proposed on the platform of glassy carbon electrode modified with native DNA implemented between two electropolymerized layers of polyaniline. The surface layer was assembled by consecutive stages of potentiodynamic electrolysis, DNA drop casting, and second electrolysis, which was required for capsulation of the DNA molecules and prevented their leaching into the solution. Surface layer assembling was controlled by cyclic voltammetry, electrochemical impedance spectroscopy, atomic force, and scanning electron microscopy. For doxorubicin measurement, the DNA sensor was first incubated in the Methylene blue solution that amplified signal due to DNA intercalation and competition with the doxorubicin molecules for the DNA binding sites. The charge transfer resistance of the inner layer interface decreased with the doxorubicin concentration in the range from 1.0 pM to 0.1 μM (LOD 0.6 pM). The DNA sensor was tested for the analysis of spiked artificial urine samples and showed satisfactory recovery in concentration range of 0.05–10 μM. The DNA sensor developed can find application in testing of antitumor drugs and some other DNA damaging factors.

Atomic Force Microscopy Meets Biophysics, Bioengineering, Chemistry, and Materials Science.

Briefly, herein the use of atomic force microscopy (AFM) in the characterization of molecules and (bioengineered) materials related to chemistry, materials science, chemical engineering, and environmental science and biotechnology is reviewed. First, the basic operations of standard AFM, Kelvin probe force microscopy, electrochemical AFM, and tip‐enhanced Raman microscopy are described. Second, several applications of these techniques to the characterization of single molecules, polymers, biological membranes, films, cells, hydrogels, catalytic processes, and semiconductors are provided and discussed.

The Origin of Electrochemical Actuation of MnO2/Ni Bilayer Film Derived by Redox Pseudocapacitive Process

AbstractPseudocapacitance‐induced electrochemical actuators (EC‐actuators) have attracted great attention in robots and artificial intelligence technologies. Despite major efforts to design such EC‐actuators, a molecular‐level understanding of the deformation mechanism is still lacking. Here, a reversible deformation of a freestanding MnO2/Ni bilayer film is demonstrated and in situ electrochemical atomic force microscopy, in situ Raman spectroscopy, and density functional theory simulation are used to study the origin of the deformation. The results show that the electrochemical actuation of the MnO2/Ni film is highly related with the redox pseudocapacitive behavior of MnO2 layer. Valence state variation of Mn element, shortening and lengthening of MnO bond, and insertion and extraction of Na+ ions, which all result from the redox pseudocapacitance of MnO2 during charging and discharging, eventually lead to the reversible contraction and expansion of MnO2 morphology. Such action counters with the nonactive Ni layer, finally inducing the reversible deformation of the MnO2/Ni bilayer film. It is believed that the study can provide useful guidance to design better EC‐actuators in the future.

Cu2S nanocrystals incorporated highly efficient non-fullerene ternary organic solar cells

Here, we report Cu2S nanocrystals based non-fullerene ternary polymer solar cells by incorporating Cu2S in conjugated polymer (PBDB-T: poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b′]dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl) benzo[1′,2′-c:4′,5′-c′]dithiophene-4,8-dione))]) and small molecule non-fullerene compound (ITIC:3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene). The devices were fabricated in inverted configuration i.e. ITO/ZnO/PBDB-T: Cu2S NCs: ITIC/MoO3/Ag. Effect of concentration of Cu2S nanocrystals on the performance parameters of PBDB-T: ITIC based organic solar cells is studied. An enhancement in the power conversion efficiency from 8.24% to 9.53% is achieved for the optimum concentration of Cu2S nanocrystals in the organic photoactive blend. The cause of improvement in the performance parameters of the device is investigated by means of the light intensity dependent electrochemical impedance spectroscopy and atomic force microscopy. It is found that the devices with Cu2S nanocrystals have less trap-assisted recombination.

High electrochemical stability of meso-Ni-salen based conducting polymer manifested by potential-driven reversible changes in viscoelastic and nanomechanical properties

The potential-driven counter ion ingress and egress effect on viscoelasticity and nanomechanics of the poly(meso-Ni-SaldMe) film was examined. This effect was characterized by a new approach using two complementary operando techniques, vis., electrochemical piezoelectric microgravimetry (EC-PM) at the electrochemical quartz crystal microbalance (EQCM) and atomic force microscopy in the PeakForce Quantitative Nanomechanical Mapping mode run under electrochemical conditions (EC-PFQNM AFM). The EC-PM and EC-PFQNM AFM experiments showed that changes in viscoelastic and nanomechanical behavior of the poly(meso-Ni-SaldMe) film, caused by counter ions doping and dedoping in the course of polymer charging and discharging, were repeatable. In that way, we demonstrated that the film high stability under these electrochemical conditions resulted from reversibility of processes occurring in both bulk and surface of the poly(meso-Ni-SaldMe) film. This is why the polymer is very much suitable for application as an electrode material for electrochemical devices.

Electrochemical Scanning Probe Microscopies in Electrocatalysis

AbstractImprovements toward highly efficient electrochemical energy conversion require a detailed understanding of the underlying electrochemical processes at electrified solid–liquid interfaces. In situ and in operando studies by means of electrochemical scanning probe microscopy (EC‐SPM) have become indispensable experimental tools due to their capability of resolving surface topography down to the atomic level even within the harsh environment of electrolytes. EC‐SPM methodologies have thus contributed tremendously to the current understanding of electrocatalysis. In this review article, recent achievements in complementary EC‐SPM techniques, namely electrochemical scanning tunneling microscopy (EC‐STM), electrochemical atomic force microscopy (EC‐AFM), scanning electrochemical potential microscopy (SECPM), and scanning electrochemical microscopy (SECM), are discussed with particular focus on electrochemical phenomena important for the field of electrocatalysis. The currently available options for obtaining insight on local chemical composition and local reactivity as well as important electrocatalytic model systems are considered. In addition, the application of EC‐SPM methods to metal ion batteries is addressed.

3D Nanostructured Multielectrode Arrays: Fabrication, Electrochemical Characterization, and Evaluation of Cell–Electrode Adhesion

Abstract3D nanostructures on top of planar multielectrode array (MEA) electrodes increase the surface area and can offer a tight and stable cell–electrode interface, thus leading to a crucial increase of the signal‐to‐noise ratio during measurement. However, each individual cell type might need specific dimensions and an arrangement of nanostructures that fits ideally to a specific cell type. Therefore, a fabrication method of 3D nanostructured MEA chips based on nanoimprint lithography, gold electroplating, and microstructuring techniques is presented which allows the fabrication of a whole set of MEA chips with different nanostructure layouts in one single approach. The chips are characterized using electrochemical methods, atomic force, and scanning electron microscopy. Furthermore, an impedance measurement method is presented to quantify cell–electrode adhesion of nanostructured and unstructured electrodes using the human embryonic kidney cell line (HEK 293). Double‐layer capacitance, transferred charge, and impedance values of different nanostructure layouts revealed a significant improvement compared to unstructured electrodes. The improvement strongly correlates with the increase of the electrochemical active surface area. Impedance measurement with impedance‐stable HEK 293 cells allows discriminating differences of cell adhesion between the individual nanostructure layouts. A significant increase or decrease of cell–electrode coupling depending on the nanostructure layout is demonstrated.

Study on the effect of mischmetal (La,Ce) on the micro-galvanic corrosion of AZ91 alloy using multiscale methods

The relative potential difference can be treated as an index of local corrosion of alloys. Since local corrosion is driven by the micro-galvanic coupling, which is consist of the micro-constituent phases and the matrix. They present distinct potential difference normally. In the present work, the relationship between the Volta potential and the corrosion effect of the dominated intermetallic phase in the AZ91 Mg alloy with (La, Ce) MM addition was investigated. A multiscale approach coupling global and local measurements was used to study the corrosion behavior of the alloy and its intermetallic phase. Results showed that the microstructure of AZ91 Mg alloy with (La, Ce) MM addition was complex, with the presence of Al4(La, Ce) phases in acicular or rod shape, a small number of Al8Mn4Ce, β-Mg17Al12 and α-Mg solid solution. In this case, the improved corrosion resistance of the alloy was achieved. Scanning Kelvin probe force microscopy (SKPFM) analysis revealed that all the intermetallics were noble comparing with the α-Mg solid solution. In-situ electrochemical atomic force microscopy (EC-AFM) observation for the initial stages of corrosion showed the α-Mg matrix surrounded by β-Mg17Al12 or Al8Mn4Ce was susceptible to pitting corrosion. No noticeable corrosion occurred at the α-Mg adjacent to Al4(La,Ce) phase, in spite of the relatively higher difference of Volta potential between Al4(La,Ce) phase and the matrix. Volta potential is insufficient to determine whether the phase is an effective cathode or anode.

Revealing How Alkali Cations Affect the Surface Reactivity of Stainless Steel in Alkaline Aqueous Environments

Stainless steel is a ubiquitous structural material and one that finds extensive use in core-internal components in nuclear power plants. Stainless steel features superior corrosion resistance (e.g., as compared to ordinary steel) due to the formation of passivating iron and/or chromium oxides on its surfaces. However, the breakdown of such passivating oxide films, e.g., due to localized deformation and slip line formation following exposure to radiation, or aggressive ions renders stainless steel susceptible to corrosion-related degradation. Herein, the effects of alkali cations (i.e., K+, Li+) and the interactions between the passivated steel surface and the solution are examined using 304L stainless steel. Scanning electrochemical microscopy and atomic force microscopy are used to examine the inert-to-reactive transition of the steel surface both in the native state and in the presence of applied potentials. Careful analysis of interaction forces, in solution, within ≤10 nm of the steel surface, reveals that the interaction between the hydrated alkali cations and the substrate affects the structure of the electrical double layer (EDL). As a result, a higher surface reactivity is indicated in the presence of Li+ relative to K+ due to the effects of the former species in disrupting the EDL. These findings provide new insights into the role of the water chemistry not only on affecting metallic corrosion but also in other applications, such as batteries and electrochemical devices.

Interfacial Reactions Between Graphite and Diethyl Carbonate Solutions Containing Different Concentrations of Li.

The electrochemical reactions occurring at graphite electrodes in lithium-ion batteries using diethyl carbonate (DEC) electrolytes containing different concentrations of LiClO4 (0.85 and 2.82 mol kg-1) were examined. The poor charge-discharge performance of the electrode in the 0.85 mol kg-1 LiClO4 in DEC was improved considerably when employing 2.82 mol kg-1 LiClO4 in DEC as the electrolyte. In situ electrochemical atomic force microscopy analysis revealed that an effective film had formed on the graphite surface after the first potential cycle when using the more concentrated solution. Charge-discharge analysis revealed that the nature of the film was significantly different from that formed in ethylene carbonate-based solutions.

In Situ Electrochemical AFM Imaging of a Pt Electrode in Sulfuric Acid under Potential Cycling Conditions.

Understanding the electrochemical behavior of Pt at the solid/liquid interface is of significant importance for the development of efficient electrochemical devices, such as fuel cells and water electrolyzers. In this work, the evolution of the surface morphology of a polycrystalline platinum under potential cycling conditions was investigated by in situ electrochemical atomic force microscopy (EC-AFM). After 50 cycles between 0.05 and 1.8 V in 0.1 M H2SO4, the Pt surface is coarsened and nanoparticles of several nanometers appear on the surface. The critical upper and lower potentials for the formation of nanoparticles are found to be 1.8 and 0.8 V, respectively. The in situ AFM observation coupled with Cyclic Voltammerty reveals the periodic disappearance and reappearance of the nanoparticles, based on which the formation of nanoparticles is attributed to the deposition of dissolved Pt from solution, and a model for the nanoparticle formation is proposed. While the formation of a thick oxide layer is a prerequisite, the reduction process is found to have a strong influence on Pt nanoparticle formation as well. This investigation provides a visualization of the Pt electrode surface under electrochemical control in a large potential window, enabling a broader understanding of the Pt electrode roughening mechanisms.

Impedance evaluation of coatings from biobased material

The authors propose a modification of sodium caseinate edible coating for foodstuff protection. The aim was to improve the film’s barrier properties. It was achieved by the addition of propolis, which is a natural, environmentally friendly product known from its intrinsic sealing action. In the next step, propolis-admixed sodium caseinate films were exposed to elevated temperature for 10 min. This approach was meant to improve the barrier effect of propolis. Electrochemical impedance spectroscopy was used to evaluate the performance of the control and modified samples upon immersion in water. Atomic force microscopy-based measurements visualised the sealing effect of propolis by means of topographical images, local direct-current maps and local impedance spectra of the control and modified films. From the obtained results the authors drew the conclusion that the proposed modifications improved the barrier properties of the sodium caseinate films. Applied combination of the investigation methods, electrochemical impedance spectroscopy and atomic force microscopy, allowed successful characterisation of protective properties of sodium caseinate coatings. The proposed atomic force microscopy measurement modes can be employed for evaluation of modifications implemented into biobased coatings, particularly when there is a need for electrolyteless tests.

Nanoscale Morphological and Structural Transformations of PtCu Alloy Electrocatalysts during Potentiodynamic Cycling

PtCu bimetallic alloys are known to provide better activity than pure platinum in proton exchange membrane fuel cells. However, such catalysts undergo complex degradation processes during fuel cell operation, resulting in deterioration of their activity. By using in situ electrochemical (EC) atomic force microscopy combined with in situ EC infrared reflection absorption spectroscopy, we provide a comprehensive investigation of morphological and structural transformations of PtCu model thin film catalysts during accelerated degradation tests (ADTs). The ADTs consist of potentiodynamic cycling to three different upper potentials relevant for different modes of fuel cell operation. The results show that, depending on the upper potential limit, PtCu alloy electrocatalysts are subject to drastic changes in the surface composition, morphology, and structure.

Electrochemical Atomic Force Microscopy and First-Principles Calculations of Ferriprotoporphyrin Adsorption and Polymerization.

The adsorption and subsequent electrooxidative polymerization of ferriprotoporphyrin IX chloride (hemin; FePPCl) was investigated on highly ordered pyrolytic graphite, glassy carbon, and polycrystalline Pt electrodes using electrochemical atomic force microscopy, first-principles calculations, and cyclic voltammetry. Hemin was shown to readily adsorb to all three surfaces; however, it was more continuous over the carbon surfaces compared to the Pt surface. This disparity in adsorption appears to be a major contributing factor to differences observed between the electrodes following hemin electropolymerization. Despite differences in roughness and morphology, hemin polymerized as a continuous layer over each electrode surface. Periodic density functional theory calculations were used to model FePP (without Cl) on both the Pt(111) and graphite surfaces using the vdW-DF-optPBE functional to account for the dispersion interactions. Our calculations suggest that the FePP molecule chemisorbs to the Pt surface while at the same time exhibiting intramolecular hydrogen bonding between the carboxylic acid groups, which are extended away from the surface. In contrast to FePP-Pt chemisorption, FePP was found to physisorb to graphite. The preferred spin state upon adsorption was found to be S = 2 on Pt(111), whereas on graphite, the high and intermediate spin states were nearly isoenergetic. Additionally, gas-phase calculations suggest that much of the surface roughness observed microscopically for the polymerized porphyrin layer may originate from the nonparallel stacking of porphyrin molecules, which interact with each other by forming four intermolecular hydrogen bonds and through dispersion interactions between the stacked porphyrin rings. Regardless of polymer thickness, the underlying electrode appears to be able to participate in at least some redox processes. This was observed for the hemin-polymerized Pt electrode using the 2H+/H2 redox couple and was suspected to be due to some Pt surface atoms not being specifically coordinated to the hemin molecules and therefore available to react with H+ that was small enough to diffuse through the polymer layer.

Nanostructured electrochemical immunosensor for detection of serological alkaline phosphatase

Alkaline phosphatase (ALP) is an enzyme that plays an important role in bone mineralization and skeletal growth. Variations in physiological levels of ALP have been correlated to diseases such as osteomalacia, Paget's disease and arterial calcifications. In this context, the integration of carbon nanotubes (CNT) within osteointegration implants has shown to increase ALP's mineralization activity in virtue of their surface chemistry and their morphological resemblance to collagen nanofibers. In this study we present the development and analytical application of an impedimetric immunosensor based in gold nanoparticle-decorated CNT, which characteristics are desirable in implantable biosensors. The device effectively detects ALP within blood serum, a complex biological fluid where most expressed proteins can be found. Robustness and high sensitivity were attained by immobilizing covalently anti-ALP antibody as a specific probe towards ALP. Cyclic voltammetry, electrochemical impedance spectroscopy and atomic force microscopy were used to characterize the sensor system throughout mounting steps and real sample testing. Impedimetric responses were adjusted to a theoretical electrical circuit and charge transfer resistance showed to be an adequate parameter to evaluate the biorecognition process of the analyte. Additionally, amperometrical current variation and changes in topography found over the surface after positive samples evidenced biorecognition. The final biosensor showed excellent performance with two linear ranges from 0.5 to 50 IU.L-1 and from 100 to 600 IU.L-1; limits of detection were calculated as 0.25 and 84.6 IU.L-1 respectively with a relative standard deviation lower than 5%. The device was found to be selective, avoiding protein c, a potential interferer occurring during inflammatory processes. The proposed strategy is promising for osteogenic applications where it can improve osteointegration implants by monitoring ALP activity.

Activity and Selectivity Control in CO2 eectroreduction through Catalyst and Electrolyte Design

The electrochemical conversion of CO2 (CO2RR) into chemicals and fuels is of industrial significance since it might lead to a more efficient storage of renewable energy while closing the carbon cycle. This talk will focus on model nanostructured plasma-activated dendrites and nanoparticle (NP) electrocatalysts (Cu, Ag, Zn, Cu-M with M = Co, Zn and Ag-Sn) for the electrocatalytic reduction of CO2. We will show how to tune catalytic selectivity based on rational catalyst and electrolyte design involving controlling the NP size, shape, support interaction, as well as the electrolyte properties by adding cations and anions (Cs+, Li+, Na+, K+, I-, Br-, Cl-). 1-5 In situ and operando spectroscopic and microscopic methods have been used to gain insight into the correlation between the structure, chemical state, and reactivity of ligand-free size- and shape-controlled spherical and cubic NPs as well as plasma-activated dendritic structures and Cu single crystals during CO2RR. Dynamic changes in the morphology and composition were monitored under potential control via electrochemical atomic force microscopy, X-ray absorption fine-structure spectroscopy and quasi in situ X-ray photoelectron spectroscopy. Additionally, density functional theory calculations were used to provide new insights on the active sites and reaction mechanism of the former electrocatalysts, including the role of different electrolytes. Our results are expected to open up new routes for the reutilization of CO2 through its direct selective conversion into higher value products. 1. P. Grosse, D. Gao, F. Scholten, I. Sinev, H. Mistry, B. Roldan Cuenya, Angewandte Chemie (2018) in press. 2. H. S. Jeon, S. Kunze, F. Scholten, B. Roldan Cuenya, ACS Catal. 8 (2018) 531 3. H. Mistry, Y. Choi, A. Bagger, F. Scholten, C. Bonifacio, I. Sinev, N. J. Divins, I. Zegkinoglou, H. Jeon, K. Kisslinger, E. A. Stach, J. C. Yang, J. Rossmeisl, B. Roldan Cuenya, Angew. Chem. 56, 11394 (2017) 4. D. Gao, F. Scholten, B. Roldan Cuenya, ACS Catal. 7, 5112 (2017) 5. D. Gao, I. Zegkinoglou, N. J. Divins, F. Scholten, I. Sinev, P. Grosse, and B. Roldan Cuenya, ACS Nano 11, 4825 (2017)

Experimental and Theoretical Investigation of Thiazolyl Blue as a Corrosion Inhibitor for Copper in Neutral Sodium Chloride Solution

The anticorrosion effect of thiazolyl blue (MTT) for copper in 3% NaCl at 298 K was researched by electrochemical methods, scanning electron-microscopy (SEM), and atomic force microscopy (AFM). The results reveal that MTT can protect copper efficiently, with a maximum efficiency of 95.7%. The corrosion inhibition mechanism was investigated by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectral (FT-IR), and theoretical calculation. The results suggest that the MTT molecules are adsorbed on metal surface forming a hydrophobic protective film to prevent copper corrosion. It also indicates that the MTT and copper form covalent bonds. The molecular dynamic simulation further gives the evidence for adsorption. The adsorption isotherm studies demonstrate that a spontaneous, mixed physical and chemical adsorption occurs, which obeys Langmuir adsorption isotherm. The present research can help us better understand the corrosion inhibition process and improve it.

In-situ study of surface structure evolution of silicon anodes by electrochemical atomic force microscopy

Silicon is one of the most promising anode materials for lithium ion batteries because of its extremely high theoretical capacity. However, silicon suffers from mechanical degradation caused by huge volume change and unstable solid electrolyte interphase (SEI) layers. Herein, we report an in situ electrochemical atomic force microscopy (EC-AFM) method to directly visualize the surface topography and analyze Young’s modulus of micron-sized (Micron-Si) and nano-sized (Nano-Si) silicon electrodes. Our results show Micron-Si electrodes experienced volume expansion and contraction process which resulted in continuous growth of a thick but soft SEI layer on the surface. In contrast, Nano-Si electrodes demonstrate a thin SEI layer due to absence of volume expansion and contraction process. Young’s modulus value shows that the SEI film of Nano-Si electrodes is harder than that of the Micron-Si electrodes. Ex situ XPS analysis reveals that Nano-Si electrodes are composed of mainly inorganic components particularly LiF and carbonate-like species which might contribute to the increased hardness. Results from present study may be helpful to build better SEI layer with good Young’s modulus to buffer volume expansion of Si.

Blister evolution time invariance at very low electrolyte pH: H2SO4/graphite system investigated by electrochemical atomic force microscopy

When graphite is immersed in diluted sulfuric acid (H2SO4) electrolyte and positive potentials are applied to the sample, the surface undergoes an incipient oxidation process that develops gases (typically CO, CO2 and O2) both on the surface and in the underneath layers. These gases swell the surface and produce blisters, which damage and degrade the crystal. Some of these mechanisms are still under debate, such as the time interval Δt for blister evolution. Very recently, we studied the required Δt in 1 M H2SO4 electrolyte, finding a critical time for their formation of few seconds. Here, we give evidence that this time interval is almost unchanged if the electrolyte is further diluted until 1 mM, by combining electrochemical-atomic force microscopy, cyclic-voltammetry and normal pulse voltammetry.

Development of Local Analysis Technique of Electric Double Layer at Electrode Interfaces and Its Application to Ionic Liquid Interfaces

Abstract Local analyses of electrolyte/solid electrode interfaces at controlled electrode potentials are of fundamental importance to understanding the origin and properties of the electric double layer (EDL) at the interfaces, which is necessary for their application to electrochemical devices. This award account summarizes our recent achievements of such analyses by using the novel analytical tools of electrochemical frequency modulation AFM (EC-FM-AFM), which enables acquisition of information from the liquid molecules’ structuring as well as the atomic scale resolution of the solid side, both are often affected by the electrode potential. Potential and electrolyte dependent EDL structures at aqueous solution/graphite interfaces and strong substrate dependency on the structuring of interfacial ionic liquid are mainly discussed.