Fast Scan Rates Research Articles

(Keynote) Single Gold Nanowire Electrodes for Electrochemical Based Biosensing Applications

Compared to traditional macroelectrodes, nanoscale electrodes have tremendous potential as electrochemical sensors exhibiting enhanced performance. As critical dimensions of the electrodes enter the nano regime, 3D analyte diffusion profiles to the electrode dominate with a corresponding increase in mass transport, higher current densities giving rise to an increase in the ratio of faradaic to charging current, higher signal to noise ratios, steady-state sigmoidal voltammograms, low depletion of target molecules, low supporting electrolyte concentration requirements and shorter RC time constant 1-3. We and others have previously reported fabrication and in-depth electrochemical analysis of discrete gold nanowire electrodes for use in electrochemical applications. The single nanowire electrodes and nanowire electrode arrays were fabricated using a hybrid E-beam / photolithography approach, providing electrodes with well-defined and reproducible dimensions. Finite element diffusion domain simulation studies were employed to explore mass transport to nanowire electrodes. Simulation results suggested that radial diffusion to nanowires should be present at fast scan rates 4,5. This behavior was confirmed experimentally where CVs obtained in FcCOOH, were observed to be steady-state, with high currents (nA) and sigmoidal up to 50,000 mV s-1. The electrochemical responses of single and diffusionally independent arrays of nanowires, in model redox mediators, were excellently described by Butler-Volmer kinetics. To date we have employed these nanowire devices for highly sensitive detection of biochemical and chemical species including glucose and explosives 6-8. Herein we extend this work and explore the application of single on-chip gold nanowires for use as electrochemical biosensors with specificity provided by modifying the nanowire surface with polymer overlayers both with and without encapsulated biomolecules (application specific). We show highly sensitive dopamine with a measured limit of detection of 10 pM. We show real-time detection of glucose using an enzyme encapsulated within a polymer host without the need for a mediator. Finally we show label-free detection using electrochemical impedance spectroscopy of antibody-antigen binding events at a single nanowire electrode; see figure 1. Figure 1: Schematic showing the label-free detection of antibody-antigen binding at a single nanowire electrode References [1] Compton, R. G.; Wildgoose, G. G.; Rees, N. V.; Streeter, I.; et. Al., Chem. Phys. Lett. 2008, 458, 1. [2] Murray, R. W., Chem. Rev. 2008, 108, 2688. [3] Dawson, K.; Baudequin, M.; Sassiat, N.; Quinn, A.J.; O’Riordan, A. Electrochimica Acta 2013, 101, 169- [4] Dawson, K.; Wahl, A.; Murphy, R.; O’Riordan, A.,. The Journal of Physical Chemistry C 2012, 116 (27), 14665-14673. [5] Dawson, K.; Wahl, A.; Pescaglini, A.; Iacopino, D.; O'Riordan. A Journal of The Electrochemical Society 2014, 161 (2), B3049-B3054 [6] Dawson, K.; Strutwolf, J.; Rodgers, K. P.; Herzog, G.; Arrigan, D. W. M.; Quinn, A. J.; O’Riordan, A., Anal Chem 2011, 83, (14), 5535-5540. [7] Dawson, K.; Baudequin, M.; O'Riordan, A., Analyst 2011, 136, (21), 4507-4513 [8] Barry, S.; Dawson, K.; Correa, E.; Goodacre, R.; O'Riordan. A Faraday discussions 2013 164, 283-293 Acknowledgements This work was supported by Science Foundation Ireland under the US-Ireland programme (SFI12/US/I2476), by the Department of Agriculture Food and the Marine (13S405) and the Irish Higher Education Authority PRTLI programs (Cycle 3 “Nanoscience” and Cycle 4 “INSPIRE”). Figure 1

Conditions Favoring the Formation of Monomeric PtIII Derivatives in the Electrochemical Oxidation of trans‐[PtII{(p‐BrC6F4)NCH2CH2NEt2}Cl(py)

AbstractCharacterization of the anticancer active compound trans‐[PtII{(p‐BrC6F4)NCH2CH2NEt2}Cl(py)] is described along with identification of electrochemical conditions that favor formation of a monomeric one‐electron‐oxidized PtIII derivative. The square‐planar organoamidoplatinum(II) compound was synthesized through a carbon dioxide elimination reaction. Structural characterization by using single‐crystal X‐Ray diffraction reveals a trans configuration with respect to donor atoms of like charges. As PtIII intermediates have been implicated in the reactions of platinum anticancer agents, electrochemical conditions favoring the formation of one‐electron‐oxidized species were sought. Transient cyclic voltammetry at fast scan rates or steady‐state rotating disc and microelectrode techniques in a range of molecular solvents and an ionic liquid confirm the existence of a well‐defined, chemically and electrochemically reversible one‐electron oxidation process that, under suitable conditions, generates a PtIII complex, which is proposed to be monomeric [PtIII{(p‐BrC6F4)NCH2CH2NEt2}Cl(py)]+. Electron paramagnetic resonance spectra obtained from highly non‐coordinating dichloromethane/([Bu4N][B(C6F5)4]) solutions, frozen to liquid nitrogen temperature immediately after bulk electrolysis in a glove box, support the PtIII assignment rather than formation of a PtII cation radical. However, the voltammetric behavior is highly dependent on the timescale of the experiments, temperature, concentration of trans‐[PtII{(p‐BrC6F4)NCH2CH2NEt2}‐ Cl(py)], and the solvent/electrolyte. In the low‐polarity solvent CH2Cl2 containing the very weakly coordinating electrolyte [Bu4N][B(C6F5)4], a well‐defined reversible one‐electron oxidation process is observed on relatively long timescales, which is consistent with the stabilization of the cationic platinum(III) complex in non‐coordinating media. Bulk electrolysis of low concentrations of [Pt{(p‐BrC6F4)NCH2CH2NEt2}Cl(py)] favors the formation of monomeric [PtIII{(p‐BrC6F4)NCH2CH2NEt2}Cl(py)]+. Simulations allow the reversible potential of the PtII/PtIII process and the diffusion coefficient of [PtIII{(p‐BrC6F4)‐ NCH2CH2NEt2}Cl(py)]+ to be calculated. Reversible electrochemical behavior, giving rise to monomeric platinum(III) derivatives, is rare in the field of platinum chemistry.

The electrode responses of a tungsten bronze electrode differ in potentiometry and voltammetry and give access to the individual contributions of electron and proton transfer

Abstract A tungsten wire covered with Na 0.75 WO 3 acts in potentiometry as a reversible pH electrode having a pH dependent open-circuit potential E ocp with nernstian slope. The mid-peak potential E mp of cyclic voltammograms also depends on pH. At low pH (e.g., pH 2) and slow scan rates (e.g., 2 mV s –1 ) the voltammetric response is almost completely reversible. At higher pH and faster scan rates, the voltammetric systems exhibit features of increasing irreversibility. Under the conditions of reversibility, the E ocp and E mp differ significantly. E ocp is determined by the proton transfer at the electrode surface; whereas E mp is determined by the electron transfer equilibrium tungsten(VI)/tungsten(V) and the proton transfer at the electrode surface. The difference between E ocp and E mp provides the individual thermodynamic contributions of electron and proton transfer to the overall pH dependent redox electrode. This is the first time that both contributions can be separated for an insertion electrochemical system (thin surface layer). It is also shown for the first time that the mechanism of an ion-sensitive electrode can differ in potentiometry and voltammetry.

Pseudocapacitive Charge Storage at Nanoscale Silicon Electrodes

Pseudocapacitive behaviour can be accessed when Si nanowire (NW) electrodes are scanned at relatively fast potential scan rates in Li-ion battery electrolytes. Measurements using cyclic voltammetry supported by electron microscopy confirm that Si NWs formed on silicon substrates, as opposed to metallic current collectors, do not solely undergo alloying reactions. The influence of doping type, carrier concentration and bias condition during voltammetric polarization significantly alters the mechanism of electrochemical energy storage. The formation of a carrier depleted (electrically dead) layer of n-type NWs on silicon current collector electrodes limits insertion or alloying processes and rates that ordinarily form Li-Si phases, and charge is also stored within the electric double layer via pseudocapacitive processes. P-type NWs with solid crystalline cores also exhibit pseudocapacitive charge storage without structural modification of the NWs.

Heating rate dependence of melting peak temperature examined by DSC of heat flux type

Crystal melting behavior of indium and isotactic polypropylene has been examined by differential scanning calorimetry of heat flux type in terms of the heating rate, $$\beta $$ , dependence. The melting shows the dependence characterized by a power, $$z$$ , of the shift in peak temperature in proportion to $$\beta ^{\text{z}}$$ . The power, $$z$$ , differentiates the melting with and without superheating. For polymer crystal melting, intrinsic nature of the broad melting region with a fractional power, $$z\,\le\,1/2$$ , due to superheating of melting kinetics has been reconfirmed experimentally. On the other hand, the crystal melting of indium, which is supposed to proceed with negligible superheating, showed the shift in peak temperature with the power in the range of $$1/2\,\le\,z \le\,1$$ , depending on sample mass, which is due to instrumental thermal lag predicted by the Mraw’s model consisting of lumped elements. The $$\beta $$ dependence is influenced by the thermal lag determined by the thermal contact resistance between the sample pan and the stage, the effect of which has been examined in terms of the dependence on sample mass and the application of silicone grease between the sample pan and the stage. The influence of two different types of the definition of heat flow has also been examined; the simplified one without the time derivative of temperature difference showed an apparent shift in peak temperature at faster scan rates in a similar way as that of thermal lag.

A scoring model for phosphopeptide site localization and its impact on the question of whether to use MSA

The production of structurally significant product ions during the dissociation of phosphopeptides is a key to the successful determination of phosphorylation sites. These diagnostic ions can be generated using the widely adopted MS/MS approach, MS3 (Data Dependent Neutral Loss — DDNL), or by multistage activation (MSA). The main purpose of this work is to introduce a false-localization rate (FLR) probabilistic model to enable unbiased phosphoproteomics studies. Briefly, our algorithm infers a probabilistic function from the distribution of the identified phosphopeptides' XCorr Delta scores (XD-Scores) in the current experiment. Our module infers p-values by relying on Gaussian mixture models and a logistic function. We demonstrate the usefulness of our probabilistic model by revisiting the “to MSA, or not to MSA” dilemma. For this, we use human leukemia-derived cells (K562) as a study model and enriched for phosphopeptides using the hydroxyapatite (HAP) chromatography. The aliquots were analyzed with and without MSA on an Orbitrap-XL. Our XD-Scoring analysis revealed that the MS/MS approach provides more identifications because of its faster scan rate, but that for the same given scan rate higher-confidence spectra can be achieved with MSA. Our software is integrated into the PatternLab for proteomics freely available for academic community at http://www.patternlabforproteomics.org.Biological significanceAssigning statistical confidence to phosphorylation sites is necessary for proper phosphoproteomic assessment. Here we present a rigorous statistical model, based on Gaussian mixture models and a logistic function, which overcomes shortcomings of previous tools. The algorithm described herein is made readily available to the scientific community by integrating it into the widely adopted PatternLab for proteomics. This article is part of a Special Issue entitled: Computational Proteomics.

Microelectrode Voltammetry of Dioxygen Reduction in a Phosphonium Cation-Based Room-Temperature Ionic Liquid: Quantitative Studies

Microelectrode voltammetry is used to study the electrochemical reduction of dioxygen, O2, in the room-temperature ionic liquid trihexyl(tetradecyl)phosphonium trifluorotris(pentafluoroethyl)phosphate [P6,6,6,14][FAP]. The nature of the unusual voltammetric waves is quantitatively modeled via digital simulation with the aim of clarifying apparent inconsistencies in the literature. The reduction is shown to proceed via a two-electron reaction and involve the likely capture of a proton from the solvent system. The oxidative voltammetric signals seen at fast scan rates are interpreted as resulting from the reoxidation of HO2•–. In the presence of large amounts of dissolved carbon dioxide the reductive currents decrease by a factor of ca. two, consistent with the trapping of the superoxide radical, O2•–, intermediate in the two-electron reduction process.

Performance of Flexible and Binderless Polypyrrole/Graphene Oxide/Zinc Oxide Supercapacitor Electrode in a Symmetrical Two-Electrode Configuration

A fast and facile approach based on potentiostatic electrochemical polymerization was used to prepare a polypyrrole/graphene oxide/zinc oxide (PPy/GO/ZnO) nanocomposite deposited on a flexible nickel foam. Fourier transform infrared spectroscopy and energy dispersive X-ray spectroscopy revealed the presence of zinc oxide on the PPy/GO/ZnO nanocomposite. A supercapacitor was fabricated by sandwiching a filter paper immersed in a sodium sulfate solution between two nickel foam electrodes coated with the PPy/GO/ZnO nanocomposite. The electrochemical performance of the supercapacitor was characterized using a two-electrode configuration, and the cyclic voltammetry curve recorded at a fast scan rate of 100mV/s was pseudo-rectangular. A specific capacitance of 94.6F/g at a current density of 1A/g was obtained from constant current charge/discharge measurements. The utilization of the pseudo-capacitive behavior of the polypyrrole and zinc oxide, and the electrical double layer capacitance of the graphene oxide, gave rise to a high energy and power density of 10.65Wh/kg and 258.26W/kg at 1A/g, respectively. The capacitance of the supercapacitor after 1000 galvanostatic charge/discharge cycles was 74% of its original value. The potential application of the as-fabricated supercapacitor in realistic energy delivery systems was demonstrated by its ability to light up a light emitting diode for about 2minutes after being charged for approximately 30seconds.

Cerium oxide as a promoter for the electro-oxidation reaction of ethanol: in situ XAFS characterization of the Pt nanoparticles supported on CeO2 nanoparticles and nanorods.

In this study we probe the electrocatalytic activity of Pt nanoparticles supported on ceria nanoparticles (NPs) and nanorods (NRs) in the ethanol oxidation reaction (EOR) in alkaline media. The goal of this study was to relate morphology, support structure and composition to the EOR catalytic activity by using in situ X-ray absorption fine structure (XAFS) studies. Cyclic voltammetry experiments showed that both ceria supported catalysts (NP vs. NR) had similar peak current densities at fast scan rates, however at slow scan rates, the ceria NR catalyst showed superior catalytic activity. In situ XAFS studies in KOH showed that both ceria supported catalysts had more electron density in their d-band (with the ceria NR having more electron density overall) than ceria - free Pt/Vulcan standard. However, in an ethanol solution the ceria NR catalyst had the least electron density. We propose that this change is due to the increased charge transfer efficiency between the ceria nanorod support and platinum. In the KOH solution, the increased electron density makes the platinum less electrophilic and hinders Pt-OH bond formation. In the EtOH solution, platinum's increased nucleophilicity facilitates the bond formation between Pt and the electron deficient carbon in ethanol which in turn withdraws the electron density from platinum and increases the white line intensity as observed in the XAS measurements.

Concurrent Driving Method with Fast Scan Rate for Large Mutual Capacitance Touch Screens

A novel touch screen control technique is introduced, which scans each frame in two steps of concurrent multichannel driving and differential sensing. The proposed technique substantially increases the scan rate and reduces the ambient noise effectively. It is also extended to a multichip architecture to support excessively large touch screens with great scan rate improvement. The proposed method has been implemented using 0.18 μm CMOS TowerJazz process and tested with FPGA and AFE board connecting a 23-inch touch screen. Experimental results show a scan rate improvement of up to 23.8 times and an SNR improvement of 24.6 dB over the conventional method.

Selective electrochemical detection of thiol biomarkers in saliva using multiwalled carbon nanotube screen-printed electrodes

The selective electrochemical determination of homocysteine and glutathione was realized in spiked synthetic saliva using a two-part voltammetric method at a multiwalled carbon nanotube screen-printed electrode. This method involves first the use of the reaction of electro-oxidized catechol with a thiol via 1,4-Michael addition reaction; this results in an analytically useful adduct peak signal. Secondly, the procedure exploits the different rates of reaction of the targeted thiols with the ortho-quinone, coupled with variable voltage scan rates. At fast scan rate, homocysteine is only detected while at slower voltage scan rate, both homocysteine and glutathione detection is reflected in the adduct signal. Thus, the quantification of both homocysteine and glutathione can be achieved with a combination of both sets of data. Calibration curves were determined for both homocysteine and glutathione in synthetic saliva with sensitivities of ca. 13.2nAμM−1 and ca. 2.1nAμM−1 for homocysteine and glutathione respectively with limits of detection at ca. 0.9μM for homocysteine and ca. 2μM for glutathione within their corresponding linear ranges. Lastly, the use of commercially available multiwalled carbon nanotube screen-printed electrode was applied to the system for selective homocysteine and glutathione detection in different spiked synthetic saliva samples. Hitherto the method has been applied in vitro and to diluted blood plasma; the extension to saliva is attractive for diagnostic use because of the non-invasive nature of the sampling.

Kinetics of nucleation and crystallization in poly(butylene succinate) nanocomposites

Differential fast scanning calorimetry (DFSC) was employed on poly(butylene succinate) nanocomposites containing silver nanoparticles and multi-walled carbon nanotubes (MWCNT), in order to identify the temperature range of heterogeneous nucleation caused by both nanofillers. The fast scanning rates also allow investigating self-nucleation by recrystallization experiments approaching the crystallization temperature from low temperatures. The recrystallization behavior of PBSu and its nanocomposites is distinct from all other polymers studied so far as only the previously crystallized part of the material is able to recrystallize, independently on the available large number of nuclei. Since full melting of small crystals at low temperatures is observed this highlights the importance of ordered structures remaining in the polymer melt. On cooling from the melt the neat polymer did not crystallize at rates higher than 70 K/s, while the nanocomposites needed rates of 500 K/s and 300 K/s for silver and MWCNT, respectively. Below 280 K the crystallization kinetics of the matrix was almost the same with the nanocomposite samples. The nucleation mechanism changes at 280 K from heterogeneous to homogeneous. The study further confirms that below the glass transition nucleation and crystallization appears only after approaching the enthalpy value of the extrapolated supercooled liquid by enthalpy relaxation.

Enhancing the supercapacitor behaviour of novel Fe3O4/FeOOH nanowire hybrid electrodes in aqueous electrolytes

A meso-porous composite electrode in which 1-dimensional FeOx nanowires and carbon nanotubes were intertwined has been fabricated using spray deposition. The electrodes showed the highest capacitance and best rate performance in an aqueous Na2SO3 electrolyte at 2 mV s−1 where electrochemically active SO32− ions contributed to a pseudocapacitance of over 300 F g−1, amongst the highest reported for iron oxide, which was maintained at >100 F g−1 up to fast scan rates of 250 mV s−1. Electrochemical testing and impedance spectroscopy in several aqueous electrolytes (Na2SO4, Li2SO4, KCl) was also used to elucidate by comparison the underlying mechanism of charge storage and to provide guidance for further optimisation.

The use of screen-printed electrodes in a proof of concept electrochemical estimation of homocysteine and glutathione in the presence of cysteine using catechol.

Screen printed electrodes were employed in a proof of concept determination of homocysteine and glutathione using electrochemically oxidized catechol via a 1,4-Michael addition reaction in the absence and presence of cysteine, and each other. Using cyclic voltammetry, the Michael reaction introduces a new adduct peak which is analytically useful in detecting thiols. The proposed procedure relies on the different rates of reaction of glutathione and homocysteine with oxidized catechol so that at fast voltage scan rates only homocysteine is detected in cyclic voltammetry. At slower scan rates, both glutathione and homocysteine are detected. The combination of the two sets of data provides quantification for homocysteine and glutathione. The presence of cysteine is shown not to interfere provided sufficient high concentrations of catechol are used. Calibration curves were determined for each homocysteine and glutathione detection; where the sensitivities are 0.019 μA·μM−1 and 0.0019 μA·μM−1 and limit of detections are ca. 1.2 μM and 0.11 μM for homocysteine and glutathione, respectively, within the linear range. This work presents results with potential and beneficial use in re-useable and/or disposable point-of-use sensors for biological and medical applications.

Redox-Driven Ion Exchange of Poly(3,4,-ethylenedioxythiophene) Films in Deep Eutectic Solvents

Poly(3,4-ethylenedioxythiophene) (PEDOT) is one of a range of conducting polymers based on aromatic heterocyclic monomers, typified by thiophene, pyrrole and their derivatives. The substitution pattern in PEDOT has the dual advantages of shifting the potentials for polymerization and redox switching into a more convenient range (as compared to the parent thiophene) and of blocking attack at the 3- and 4- positions of the aromatic ring. Both of these attributes enhance its practical application for energy storage applications, such as batteries and supercapacitors.Quite generally, the rates of doping and undoping (charging and discharging, in the context of energy storage) of conducting polymers are limited not by the rate of electron transport along the polymer backbone, but by the transport rate(s) of the charge balancing ion(s), i.e. dopant(s). The dynamics of these processes have been widely studied during redox switching of PEDOT films immersed in diverse electrolyte media based on molecular solvent systems. Although the quantitative details vary with the electrolyte selected, the qualitative outcome is that anion transfer is commonly the dominant process accompanying PEDOT oxidation (p-doping), but that cation transfer (in the opposite direction) can be appreciable, and in any case solvent transfer is significant; in the context of nanogravimetric measurements (using the EQCM), the ion and neutral molecule transfers can be distinguished according to their correlation with transferred charge. Measurements of the absolute solvent population (cf. changes measured in an EQCM experiment) in many conducting polymer films reveal that this may represent ca. 50% by volume of the film: this facilitates both ion transfers and polymer spinal motions. While such studies have revealed many interesting phenomena, notably solvation-controlled viscoelastic phenomena, a number of limitations make conventional solvent media unsuitable for practical applications; these may include available potential window, safety, toxicity or flammability. This motivates research on the redox chemistry of electroactive polymers in novel media, such as room temperature ionic liquids. Amongst these, we have been exploring the properties of deep eutectic solvent (DES) media based on various formulations of quaternary ammonium salts (QAS), hydrogen bond donors (HBD) and metal salts, in which complexation chemistry amongst the components generates fully ionic media. From a practical perspective, this provides an essentially unlimited source of ions (dopant). From a fundamental perspective, the dramatic difference is that these fully ionic media contain no solvent to plasticise the polymer; the more subtle difference is that the question of permselectivity that prevails (or fails) at low (or high) electrolyte concentration in a conventional solvent-based medium now becomes redundant.Here we describe nanogravimetric acoustic wave (EQCM) studies of redox driven ion transfers for PEDOT films exposed to three DES formulations variously involving choline chloride (Ch+Cl-) as the QAS, ethylene glycol (EG) as the HBD and ZnCl2 as the metal salt. Viscosity effects associated with the DES are significant but, via acoustic admittance measurements, one can obtain film ion population change data. These are presented as a function of timescale (potential scan rate in a voltammetric experiment) for potentiostatically- and potentiodynamically-grown PEDOT films subsequently exposed to ZnCl2/EG, ZnCl2/acetamide and ZnCl2/Ethaline (where Ethaline is a 1:2 stoichiometric mixture of Ch+Cl- and EG). Significantly, for thicker films (consistent with practical applications), there is incomplete charge recovery at faster scan rates, with accompanying failure to restore the initial film ion composition. In multi-cycling experiments this leads to evolution of response; we discuss re-equilibration when the film is subsequently held in a resting state. Cycling over prolonged time intervals also results in evolution of film responses. The fundamental interpretation and practical consequences of these observations will be discussed.We thank EU FP7 for financial support (NMP3-SL-2008-226655)

Poster #M17 THE MECHANISM OF ACTION OF ANTIPSYCHOTICS AND INTRACORTICAL MYELINATION IN SCHIZOPHRENIA

The advent of optical coherence tomography (OCT) revolutionized both clinical assessment and research of vitreoretinal conditions. Since then, extraordinary advances have been made in this imaging technology, including the relatively recent development of swept-source OCT (SS-OCT). SS-OCT enables a fast scan rate and utilizes a tunable swept laser, thus enabling the incorporation of longer wavelengths than conventional spectral-domain devices. These features enable imaging of larger areas with reduced motion artifact, and a better visualization of the choroidal vasculature, respectively. Building on the principles of OCT, swept-source OCT has also been applied to OCT angiography (SS-OCTA), thus enabling a non-invasive in depth-resolved imaging of the retinal and choroidal microvasculature. Despite their advantages, the widespread use of SS-OCT and SS-OCTA remains relatively limited.In this review, we summarize the technical details, advantages and limitations of SS-OCT and SS-OCTA, with a particular emphasis on their relevance for the study of retinal conditions. Additionally, we comprehensively review relevant studies performed to date to the study of retinal health and disease, and highlight current gaps in knowledge and opportunities to take advantage of swept source technology to improve our current understanding of many medical and surgical chorioretinal conditions. We anticipate that SS-OCT and SS-OCTA will continue to evolve rapidly, contributing to a paradigm shift to more widespread adoption of new imaging technology to clinical practice.

Dynamic speed control in atomic force microscopy to improve imaging time and quality

Quantitative, three-dimensional surface imaging is one of the most significant advantages of atomic force microscopy (AFM). The imaging speed, however, is its major issue, due to the limited response time of the feedback loop. We present a dynamically adjusted scanning speed feature implemented on a commercial AFM instrument. The signals available in the system are utilized for that purpose. The auxiliary module controls the scanning speed in order to provide the necessary time to restore the tip–sample distance, which may deviate due to insufficient settling time. The solution allows the measurement to be performed with a relatively fast scanning rate and the desired imaging quality. Quantitative analysis of the results shows the relation between the imaging error and the settings of the system. It is shown that the image is acquired faster and with better imaging quality than using the constant speed method. Also, the data are presented showing a reduction of the topographical crosstalk in the phase imaging feature, as an example of the utilization of this feature in advanced AFM modes.

Investigation of the reduction process of dopamine using paired pulse voltammetry

The oxidation of dopamine (DA) around +0.6V potential in anodic sweep and its reduction around −0.1V in cathodic sweep at a relatively fast scanning rate (300V/s or greater) have been used for identification of DA oxidation in fast-scan cyclic voltammetry (FSCV). However, compared to the oxidation peak of DA, the reduction peak has not been fully examined in analytical studies, although it has been used as one of the representative features to identify DA. In this study, the reduction process of DA was investigated using paired pulse voltammetry (PPV), which consists of two identical triangle-shaped waveforms, separated by a short interval at the holding potential. Especially, the discrepancies between the magnitude of the oxidation and reduction peaks of DA were investigated based on three factors: (1) the instant desorption of the DA oxidation product (dopamine-o-quinone: DOQ) after production, (2) the effect of the holding potential on the reduction process, and (3) the rate-limited reduction process of DA. For the first test, the triangle waveform FSCV experiment was performed on DA with various scan-rates (from 400 to 1000V/s) and durations of switching potentials of the triangle waveform (from 0.0 to 6.0ms) in order to vary the duration between the applied oxidation potential at +0.6V and the reduction potential at −0.2V. As a result, the ratio of reduction over oxidation peak current response decreased as the duration became longer. To evaluate the effect of holding potentials during the reduction process, FSCV experiments were conducted with holding potential from 0.0V to −0.8V. We found that more negative holding potentials lead to larger amount of reduction process. For evaluation of the rate-limited reduction process of DA, PPV with a 1Hz repetition rate and various delays (2, 8, 20, 40 and 80ms) between the paired scans were utilized to determine how much reduction process occurred during the holding potential (−0.4V). These tests showed that relatively large amounts of DOQ are reduced to DA during the holding potential. The rate-limited reduction process was also confirmed with the increase of reduction in a lower pH environment. In addition to the mechanism of the reduction process of DA, we found that the differences between the responses of primary and secondary pulses in PPV were mainly dependent on the rate-limited reduction process during the holding potential. In conclusion, the reduction process may be one of the important factors to be considered in the kinetic analysis of DA and other electroactive species in brain tissue and in the design of new types of waveform in FSCV.

Investigations of Ferrous Thiamine Complex by Cyclic Voltammetry

Study of thiamine ferrous complex is carried out by intensive use of cyclic voltammetry. The different mole ratio of ferrous thiamine complexes is assessed. Acidified KCl (1M) solution is used as supporting electrolyte. Mole ratio of complex is established 1:2 (thamine: Ferrous ion) 100 mV/s scan rate is chosen as optimum. By applying the Randles Sevcik equation, their reaction is found reversible and occurred under diffusion control system. Their equilibrium constants values are also determined by using the Ipc values of this complex obtained at different scan rates (100 to 500mV/s). The mechanism of the reaction is tried to discover by these results. Thiamine in AFe2 complex is oxidized into AFe2 and then reduces again at a fast scan rate.

Speckle reduction in optical coherence tomography by image registration and matrix completion.

Speckle noise is problematic in optical coherence tomography (OCT). With the fast scan rate, swept source OCT scans the same position in the retina for multiple times rapidly and computes an average image from the multiple scans for speckle reduction. However, the eye movement poses some challenges. In this paper, we propose a new method for speckle reduction from multiply-scanned OCT slices. The proposed method applies a preliminary speckle reduction on the OCT slices and then registers them using a global alignment followed by a local alignment based on fast iterative diamond search. After that, low rank matrix completion using bilateral random projection is utilized to iteratively estimate the noise and recover the underlying clean image. Experimental results show that the proposed method achieves average contrast to noise ratio 15.65, better than 13.78 by the baseline method used currently in swept source OCT devices. The technology can be embedded into current OCT machines to enhance the image quality for subsequent analysis.