Search

Electrochemical DNA biosensors composed of a redox marker modified nucleic acid probe tethered to a solid electrode is a common experimental construct for detecting DNA and RNA targets, proteins, inorganic ions, and even small molecules. This class of biosensors generally relies on the binding-induced conformational changes in the distance of the redox marker relative to the electrode surface such that the charge transfer is altered. The conventional design is to attach the redox species to the distal end of a surface-bound nucleic acid strand. Here we show the impact of the position of the redox marker, whether on the distal or proximal end of the DNA monolayer, on the DNA interface electrochemistry. Somewhat unexpectedly, greater currents were obtained when the redox molecules were located on the distal end of the surface-bound DNA monolayer, notionally furthest away from the electrode, compared with currents when the redox species were located on the proximal end, close to the electrode. Our results suggest that a limitation in ion accessibility is the reason why smaller currents were obtained for the redox markers located at the bottom of the DNA monolayer. This understanding shows that to allow the quantification of the amount of redox labeled target DNA strand that hybridizes to probe DNA immobilized on the electrode surface, the redox species must be on the distal end of the surface-bound duplex.

This work reports a simple and scalable method to convert stainless steel (SS) felt into an effective anode for bioelectrochemical systems (BESs) by means of heat treatment. X-ray photoelectron spectroscopy and cyclic voltammetry elucidated that the heat treatment generated an iron oxide rich layer on the SS felt surface. The iron oxide layer dramatically enhanced the electroactive biofilm formation on SS felt surface in BESs. Consequently, the sustained current densities achieved on the treated electrodes (1 cm(2)) were around 1.5±0.13 mA/cm(2), which was seven times higher than the untreated electrodes (0.22±0.04 mA/cm(2)). To test the scalability of this material, the heat-treated SS felt was scaled up to 150 cm(2) and similar current density (1.5 mA/cm(2)) was achieved on the larger electrode. The low cost, straightforwardness of the treatment, high conductivity and high bioelectrocatalytic performance make heat-treated SS felt a scalable anodic material for BESs., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Multiple electrodes, combined with a chemometric strategy to calibrate the measurement response, have been used for the determination of an analyte across a broader dynamic range than is possible with a single electrode. The model system used for the detection of copper comprised electrodes modified with a self-assembled monolayer. The electrodes were modified with the copper-complexing species (3-mercaptopropionic acid, thioctic acid, and the peptides cysteine and Gly-Gly-His) and copper was determined over concentrations ranging from nanomolar to millimolar using voltammetric analysis. We have demonstrated that by combining the calibration functions from the four electrodes a better estimate (i.e. with smaller variance) of the concentration of the analyte is obtained. Measurement uncertainty is expressed for independently prepared electrodes, which allows the possibility of commercial production and factory calibration. The principles of using multiple electrodes modified with recognition elements with different affinities for the target analyte to extend the dynamic range of sensors is a general one that could be applied to other analytes.

The label-free amperometric detection of a rabbit IgG antigen by an anti-rabbit IgG antibody is achieved by observing the electrochemistry at a glassy carbon electrode modified with antibody entrapped in an electrodeposited polypyrrole membrane. In a flow injection apparatus the electrode is pulsed between -0.2 and +0.4 V versus Ag/AgCl. The pulsing of the electrode switches the polypyrrole membrane between the oxidised and reduced states. When antigen is injected into the flow stream a change in current is observed at the electrode despite the antigen or antibody being redox inactive at the potentials employed. It is proposed that this current is due to a change in the flux of ions into and out of the polypyrrole matrix during a pulse when the poly-anionic antigen is present. The immunoreaction was reversible because the 200 ms pulse at each potential was too short to allow secondary bonding forces (hydrogen bonding and hydrophobic forces) which are responsible for the strength of the antibody-antigen complex to be established. The consequence of the reversibility of the antigen-antibody binding is a low apparent affinity constant but an easily regenerated recognition interface.

Electroactive nucleoside triphosphates ("electrotides") have been incorporated into primers by DNA polymerase and detected on oligonucleotide surface-assembled monolayers. Four electrotides bearing three different electroactive moieties-ferrocene, vinylferrocene, and anthraquinone-are detected in four alternative formats.

A label free electrochemical method of detecting DNA hybridisation is presented based on the change in flexibility between a single strand of DNA and a duplex causing an ion-gating effect where hybridisation opens up the electrode to access of ions.

Nanoparticles that catalyze biochemically relevant reactions are promoted as alternative enzymes. The application of such artificial enzymes is severely restricted by poor selectivity in biological fluids; mainly because the reactions occur at active sites on the exterior surface of the nanoparticle. Enzymes in contrast typically have their active sites down a nanoconfined substrate channel where the reaction occurs in different solution conditions to bulk solution which aids in achieving selectivity for the substrate. Herein the same 3D structure of enzymes is mimicked in nanoparticles to allow selective reactions in biological fluids. This is achieved using a gold nanoparticle coated in a conducting mesoporous carbon shell where isolated nanochannels lead to the gold surface. It can detect glucose in whole blood with no interference from other species. This is achieved by electrochemically pulsing the artificial enzymes to generate the locally required alkalinity for an effective electrocatalytic reaction in the nanochannels, as well as expelling fouling agents that will otherwise passivate the electrocatalytic reaction. The artificial enzymes are shown to be capable of detecting glucose in biological fluids, without loss of signal, for several months. This study shows how nanoconfinement in nanoparticles can be exploited to potentially allow a broad range of species to be selectively detected in biological fluids with stability that can exceed that of enzymes. [ABSTRACT FROM AUTHOR]

Impact experiments enable single particle analysis for many applications. However, the effect of the trajectory of a particle to an electrode on impact signals still requires further exploration. Here, we investigate the particle impact measurements versus motion using micromotors with controllable vertical motion. With biocatalytic cascade reactions, the micromotor system utilizes buoyancy as the driving force, thus enabling more regulated interactions with the electrode. With the aid of numerical simulations, the dynamic interactions between the electrode and micromotors are categorized into four representative patterns: approaching, departing, approaching‐and‐departing, and departing‐and‐reapproaching, which correspond well with the experimentally observed impact signals. This study offers a possibility of exploring the dynamic interactions between the electrode and particles, shedding light on the design of new electrochemical sensors. [ABSTRACT FROM AUTHOR]

The use of nanoparticles and nanostructured electrodes are abundant in electrocatalysis. These nanometric systems contain elements of nanoconfinement in different degrees, depending on the geometry, which can have a much greater effect on the activity and selectivity than often considered. In this Review, we firstly identify the systems containing different degrees of nanoconfinement and how they can affect the activity and selectivity of electrocatalytic reactions. Then we follow with a fundamental understanding of how electrochemistry and electrocatalysis are affected by nanoconfinement, which is beginning to be uncovered, thanks to the development of new, atomically precise manufacturing and fabrication techniques as well as advances in theoretical modeling. The aim of this Review is to help us look beyond using nanostructuring as just a way to increase surface area, but also as a way to break the scaling relations imposed on electrocatalysis by thermodynamics. [ABSTRACT FROM AUTHOR]

Here we report a light‐assisted variant of click chemistry suitable for chemical patterning of semiconducting surfaces. Using a visible light beam to illuminate desired locations of an electrode surface, localized electrogeneration of the Cu(I) click catalyst was achieved. It was demonstrated that surface click reactions were correlated with a user‐defined 2D light pattern projected on a silicon photoelectrode. This new process is mask‐free and parallel, i. e. separate discrete regions of a semiconducting surface can be simultaneously reacted with a range of functional molecules. The covalent patterning of azido‐poly (ethylene glycol) molecules (PEG) over alkyne‐functionalized electrodes was employed as a proof‐of‐principle. By modulating the exposed chemical group of the clicked azido‐PEGs, the adhesion of antibodies and cells was further possible with spatial control. The use of structured light, instead of physical masks, drastically reduces patterning time to a couple of hours. [ABSTRACT FROM AUTHOR]

Light-activated electrochemistry (LAE) consists of employing a focused light beam to illuminate a semiconducting area and make it electrochemically active. Here, we show how to reduce the electrochemical spatial resolution to submicron by exploiting the short lateral diffusion of charge carriers in amorphous silicon to improve the resolution of LAE by 60 times. [ABSTRACT FROM AUTHOR]

Light can be used to address electrochemical reactions on a monolithic semiconducting electrode with spatial and temporal resolution. Herein, such principle was used for the electrodeposition of Au, Ag and Cu nanoparticles on a unique silicon-based electrode. The parallel nature of the process granted manufacturing speed and platforms were applied to discriminate molecules via multi-wavelength and multivariate Raman analysis. [ABSTRACT FROM AUTHOR]

Alexa Fluor 647 is a widely used fluorescent probe for cell bioimaging and super‐resolution microscopy. Herein, the reversible fluorescence switching of Alexa Fluor 647 conjugated to bovine serum albumin (BSA) and adsorbed onto indium tin oxide (ITO) electrodes under electrochemical potential control at the level of single protein molecules is reported. The modulation of the fluorescence as a function of potential was observed using total internal reflectance fluorescence (TIRF) microscopy. The fluorescence intensity of the Alexa Fluor 647 decreased, or reached background levels, at reducing potentials but returned to normal levels at oxidizing potentials. These electrochemically induced changes in fluorescence were sensitive to pH despite that BSA‐Alexa Fluor 647 fluorescence without applied potential is insensitive to pH between values of 4–10. The observed pH dependence indicated the involvement of electron and proton transfer in the fluorescence switching mechanism. [ABSTRACT FROM AUTHOR]

Spatial confinement of electrochemical reactions at solid/liquid interfaces is a mature area of research, and a central theme from cell biology to analytical chemistry. Monitoring or manipulating the kinetics of a charge transfer reaction in 2D is generally achieved using scanning electrochemical microscopy or multielectrode arrays, techniques that rely on moving physical probes or on a network of electrical connections. This tutorial is introducing concepts and instruments to confine faradaic electrochemical reactions in 2D without resorting to the mechanical movement of a probe, and with the simple design of one semiconducting electrode, one electrical lead and a single-channel potentiostat. We provide a theoretical background of semiconductor electrochemistry, and describe the use of localised visible light stimuli on photoconductor/liquid and semiconductor/liquid interfaces to address electrical conductivity – hence chemical reactivity – only at one specific site defined by the experimentalist. This enables shifting of the tenet of one electrode/one wire towards one wire/many electrodes. We discuss the applications of this emerging platform in the context of surface chemistry patterning, redox imaging, chemical and biological sensing, generating chemical gradients, electrocatalysis, nanotechnology and cell biology. [ABSTRACT FROM AUTHOR]

Herein is reported a new type of transparent electrode, prepared by depositing a thin layer of amorphous silicon film on indium tin oxide, which enables photoswitchable electrochemistry and optical imaging to be performed simultaneously. This offers the opportunity to visualise a spatially controlled electrochemical event on an unstructured electrode surface. [ABSTRACT FROM AUTHOR]

We report here on a light addressable potassium (K+) sensor where light illumination of a semiconducting silicon electrode substrate results in a localized activation of the faradaic electrochemistry at the illuminated spot. This allows one, by electrochemical control, to oxidize surface bound ferrocene moieties that in turn trigger K+ transfer from the overlaid K+‐selective film to the solution phase. The resulting voltammetric response is shown to be K+‐selective, where peak position is a direct function of K+ activity at the surface of electrode. This concept was used to measure extracellular K+ concentration changes by stimulating living breast cancer cells. The associated decrease of intracellular K+ level was confirmed with a fluorescent K+ indicator. In contrast to light addressable potentiometry, the approach introduced here relies on dynamic electrochemistry and may be performed in tandem with other electrochemical analysis when studying biological events on the electrode. K+ sensing: A light‐addressable electrochemical K+ sensor is introduced that consists of a thin polymer film containing an ionophore deposited on a semiconducting silicon electrode. Ferrocene is covalently attached to oxide‐free silicon and the electrode exhibits surface confined electrochemistry under light illumination. The sensor exhibits a Nernstian response to [K+] in a light‐defined spatial region. Changes in extracellular [K+] associated with living cells upon stimulation are monitored electrochemically. [ABSTRACT FROM AUTHOR]

Etching rate is a major concern for the effective mass production of high-aspect-ratio microstructures, especially in p-type silicon. In this work, controlled electrochemical growth of high-aspect-ratio (from 15 to 110) macropores in p-type silicon at ultrafast etching rate (from 16 to 30 µm min−1) has been studied. Based on current-burst-model, pore formation was systematically investigated from the nucleation phase to stable pore growth. Good macropores with depth up to 180 µm and aspect ratio beyond 110 was achieved in just 11 min. This sets a new record on state-of-the-art p-type silicon microfabrication and can promote the development of microdevices. High-aspect-ratio macropores at ultrahigh etching rate were achieved in p-type silicon, which sets a novel record among p-type silicon microfabrication and can promote the effective mass production of microdevices. [ABSTRACT FROM AUTHOR]

Predicting or manipulating charge-transfer at semiconductor interfaces, from molecular electronics to energy conversion, relies on knowledge generated from a kinetic analysis of the electrode process, as provided by cyclic voltammetry. Scientists and engineers encountering non-ideal shapes and positions in voltammograms are inclined to reject these as flaws. Here we show that non-idealities of redox probes confined at silicon electrodes, namely full width at half maximum <90.6 mV and anti-thermodynamic inverted peak positions, can be reproduced and are not flawed data. These are the manifestation of electrostatic interactions between dynamic molecular charges and the semiconductor's space-charge barrier. We highlight the interplay between dynamic charges and semiconductor by developing a model to decouple effects on barrier from changes to activities of surface-bound molecules. These findings have immediate general implications for a correct kinetic analysis of charge-transfer at semiconductors as well as aiding the study of electrostatics on chemical reactivity. [ABSTRACT FROM AUTHOR]

Gold-coated magnetic nanoparticles (Au@MNPs) have attracted significant interest in electrochemistry in recent years. This is especially the case with their application as dispersible electrodes where modified Au@MNPs are dispersed into a solution, selectively bind to the analyte of interest and are then brought to an electrode via application of a magnetic field for measurement. This paper characterizes four types of Au@MNPs with different sizes, shapes, and method of synthesis as dispersible electrodes. The Au@MNPs were characterized by transmission electron microscopy and X-ray photoelectron spectroscopy and scanning electron microscopy. In addition, the electrochemical behaviour of Au@MNPs was investigated using cyclic voltammetry. The four sorts of Au@MNPs were evaluated with regards to the three main features required in the dispersible electrodes approach, well-defined morphology, well-defined electrochemistry and fast response to a magnetic field. The Cubic-Au@MNPs, which presents the simplest synthetic route, showed the best electrochemical stability and performance, responding quickly to a magnet and had a well defined shape. [ABSTRACT FROM AUTHOR]

In this study we have modified indium tin oxide (ITO) by electrografting phenylphosphorylcholine (PPC) and evaluated its protein-resistance performance using electrochemical impedance spectroscopy. During electrografting, significant amounts of PPC gets physically adsorbed on the surface, which cannot be removed by simply rinsing with water or buffer, and as a consequence the electrochemical response of such electrode is quite unstable. We have developed a simple protocol to remove the physically adsorbed PPC such that a stable interface is produced. It was found that such a stable surface, with appropriate amount of PPC, can dramatically reduce nonspecific adsorption of protein, giving us a platform of performing both electrochemical and spectroscopic studies in biological fluids. [ABSTRACT FROM AUTHOR]

The article focuses on the use of single entity electrochemistry techniques for mammalian cell counting. Topics discussed include the use of fluorescence-activated cell sorting (FACS) for red blood cells counting, application of the nanoparticle collision in experiments as a subject and the use of hemocytometer to diagnose blood disorder by counting red blood cells.

Abstract: A label-free immunosensor based on the modulation of the electrochemistry of a surface bound redox species, to detect the presence of antibodies, is demonstrated. In this proof of concept study the model epitope was biotin and the model antibody was anti-biotin IgG. Glassy carbon (GC) electrode surfaces were first modified with 4-nitrophenyl groups by electrochemical reductive adsorption of the corresponding aryl diazonium salt. Subsequently, the nitro group was reductively converted into an amine, giving 4-aminophenyl groups. Oxidatively shortened single walled carbon nanotubes (SWNTs) were then covalently attached to the electrode via self-assembly; a procedure that has previously been shown to give SWNTs aligned normal to the surface. 1,1-Di(aminomethyl)ferrocene was attached to the carboxylic acid terminated SWNTs followed by attachment of biotin to the remaining free amine of the ferrocene derivative. Binding of anti-biotin IgG to the surface bound epitope resulted in attenuation of the ferrocene electrochemistry. This label-free immunosensor was successfully able to detect anti-biotin between 30 and 450ngmL−1. [Copyright &y& Elsevier]

Abstract: Carbon nanotubes have begun to attract enormous interest in electrochemistry because of their small size and good electrochemical properties. The vast majority of studies thus far have used ensembles of carbon nanotubes to nanostructure macroscopic electrodes either with randomly dispersed nanotubes or with aligned carbon nanotubes. The resultant nanotube modified electrodes have most frequently been used for electro-analytical purposes such as the development of biosensors. This review introduces carbon nanotubes and approaches to nanostructuring electrodes with carbon nanotubes, discusses what is known of their electrochemical properties and briefly outlines some of the exciting applications to which they are being targeted for use. [Copyright &y& Elsevier]

We report on the light-induced systematic changes to the thermodynamics and kinetics of ferrocene units attached to a n-type silicon(100) photoelectrode. Both the reaction rate and the energetics of the charge transfer are simultaneously affected by changes in the intensity of the incident light. Cyclic voltammetry shows that increases in the intensity of illumination can drive the redox process toward less positive potentials, with a downhill shift in E1/2 of ca. 160 mV by increasing the light intensity from 3 to 94 mW cm-2. However, this thermodynamic shift is paralleled by an increase in the kinetics of the charge transfer. This latter observation light-induced kinetic effects at monolayers on silicon electrodes is made possible only by the stability of the surface chemistry construct. Furthermore, electrochemical impedance measurements showed that the electrodes exhibit faster electron-transfer kinetics under illumination than previously reported for ferrocene-terminated highly doped silicon (around 1 order of magnitude faster). An explanation for the kinetic effects is proposed on the basis of the consistent increase in photogenerated charge carriers inside silicon and the enlarged potential difference between the valence band of silicon and the surface-attached ferrocene. [ABSTRACT FROM AUTHOR]

Electron transfer (ET) reactions through molecules attached to surfaces, whether they are through single molecules or ensembles, are the subject of much research in molecular electronics, bioelectronics, and electrochemistry. Therefore, understanding the factors that govern ET is of high importance. The availability of rigid hydrocarbon molecular scaffolds possessing well-defined configurations and lengths that can be systematically varied is crucial to the development of such devices. [ABSTRACT FROM AUTHOR]

Abstract: An electrochemical sensor for the detection of lead ions is described which is made by modifying a gold electrode substrate with self-assembled monolayers (SAMs) of 3-mercaptopropionic acid (MPA) or thioctic acid (TA) followed by covalent attachment of a lead binding peptide, human angiotensin I. Cyclic voltammetry of MPA–angiotensin modified gold electrodes complexed with lead displayed voltammograms with prominent lead peaks at E 0′, −0.29V. A detection limit of 1nM was achieved using Osteryoung square wave voltammetry. However, the electrodes were not stable over repeated electrochemical cycles due to partial electrochemical desorption of the SAM. The TA–angiotensin modified gold electrode showed greater stability and were able to be regenerated several times. Using Osteryoung square wave voltammetry for TA–angiotensin modified electrodes, lead concentrations down to 1.9nM were detected. Although the detection limit of the TA–angiotensin modified electrode is higher than achieved with MPA–angiotensin, it is still well below Australian drinking water guidelines. Studies of interference effects on the Pb2+ current showed Hg2+ as a significant interferent but only at levels significantly greater than those found in natural waters. [Copyright &y& Elsevier]

Abstract: An electrochemical sensor for cadmium ions is described which is made by modifying a gold electrode with 3-mercaptopropionic acid followed by covalently coupling the cadmium-selective hexapeptide His–Ser–Gln–Lys–Val–Phe. The resultant electrode had significantly superior analytical performance compared with a glutathione (GSH) modified electrode for the detection of Cd2+, having a greater sensitivity, broader detectable concentration range and a five times lower detection limit of 0.9 nM. Interference from Pb2+ was observed which is an improvement from the GSH modified electrode which had Pb2+ and Cu2+ as interfering ions. The effects of Cu2+, Ni2+, Zn2+, Cr3+ and Ba2+were insignificant. [Copyright &y& Elsevier]

Electrochemical DNA biosensors composed of a redox marker modified nucleic acid probe tethered to a solid electrode is a common experimental construct for detecting DNA and RNA targets, proteins, inorganic ions, and even small molecules. This class of biosensors generally relies on the binding-induced conformational changes in the distance of the redox marker relative to the electrode surface such that the charge transfer is altered. The conventional design is to attach the redox species to the distal end of a surface-bound nucleic acid strand. Here we show the impact of the position of the redox marker, whether on the distal or proximal end of the DNA monolayer, on the DNA interface electrochemistry. Somewhat unexpectedly, greater currents were obtained when the redox molecules were located on the distal end of the surface-bound DNA monolayer, notionally furthest away from the electrode, compared with currents when the redox species were located on the proximal end, close to the electrode. Our results suggest that a limitation in ion accessibility is the reason why smaller currents were obtained for the redox markers located at the bottom of the DNA monolayer. This understanding shows that to allow the quantification of the amount of redox labeled target DNA strand that hybridizes to probe DNA immobilized on the electrode surface, the redox species must be on the distal end of the surface-bound duplex. [ABSTRACT FROM AUTHOR]

Light-activated electrochemistry is a powerful concept, where faradaic electrochemistry at a monolayer protected monolithic silicon electrode can be ‘turned on’ at any location with micron scale resolution simply by illuminating that region with light. The three requirements for light-activated electrochemistry are that i) the silicon must be protected from oxidation with a self-assembled monolayer (SAM), ii) the semiconducting electrode must be biased into depletion at the redox potential of the species of interest and iii) the redox couple must be covalently attached to the electrode. Herein it is shown that light-activated electrochemistry can be performed with solution species if they adsorb to the surface of the SAM. It is shown that redox species such as ferrocene and ruthenium hexamine adsorb onto the 1,8-nonadiyne modified silicon surface and undergo electron transfer upon illumination while potassium ferrocyanide does not. It is proposed this adsorption causes an increase in electronic coupling between the redox species and the silicon electrode such that appreciable electron transfer through the monolayer was achieved. Furthermore, it is demonstrated that light-activated electrochemistry can be used to rapidly switch between macroelectrode- and microelectrode-type voltammetry at the same interface by simple means of modulating the light intensity. This work expands our understanding of light-activated electrochemistry and its application for interrogating discrete regions on an electrode in a highly parallel way. [ABSTRACT FROM AUTHOR]

The immobilization of gold nanoparticles (AuNPs) on functionalized electrodes has been shown to be an effective way for switching on the electrochemistry at an otherwise passivated surface. Herein, the attachment of AuNPs onto the industrially available p + - Si(100) electrodes was studied by means of cyclic voltammetry and X-ray photoelectron spectroscopy. The hydrosilylation of p + -Si(100) with 1,8-nonadiyne followed by the “click” of azido propylamine onto the alkyne end formed a self-assembled monolayer (SAM), which protected the p + -Si(100) against oxidation and prevented the electron transfer from dissolved Ru(NH 3 ) 6 3 + . Upon the attachment of AuNPs, however, electron transfer was initially restored. The performance of the p + –Si–SAM–AuNP electrode was found to decay with repeated voltammetric cycling due to the formation of SiO x underneath the SAM. These results suggest that p + –Si–SAM–AuNP electrodes can be used in electrochemical devices for single use applications but are not suitable for long-term use. [ABSTRACT FROM AUTHOR]

Herein we combined the use of self-assembled monolayer (SAM) modified electrodes and gold coated magnetic nanoparticles (Au@MNPs) to modulate faradaic electrochemistry when nanoparticles are absorbed on and removed from, a passivated electrode using an external magnetic field. Substantial faradaic electrochemistry of potassium ferricyanide in solution is first prevented by modifying gold electrodes with 11-mercaptoundecanoic acid to form a passivating SAM. Restoration of the faradaic electrochemistry is then achieved by introducing Au@MNPs which are brought to the surface using an external magnetic field. The faradaic electrochemistry can again be suppressed by removing Au@MNPs from the SAM using another external magnetic field. [ABSTRACT FROM AUTHOR]

Alterations in DNA methylation, a stable epigenetic marker, are important components in the development of cancer. It is vital to develop diagnostic systems with the ability to rapidly quantify DNA methylation with high sensitivity and selectivity. However, the analysis of DNA methylation must address two main challenges: (i) ultralow abundance and (ii) differentiating methylated cytosine from normal cytosine on target DNA sequence in the presence of an overwhelming background of circulating cell-free DNA. Here we report the development of an ultrasensitive and highly-selective electrochemical biosensor for the rapid detection of DNA methylation in blood. The sensing of DNA methylation involves the hybridization on a network of probe DNA modified gold-coated magnetic nanoparticles (DNA-Au@MNPs) complementary to target DNA, and subsequently enzymatic cleavage to differentiate methylated DNA strands from corresponding unmethylated DNA strands. The biosensor presents a dynamic range from 2 aM to 20 nM for 110 nucleotide DNA sequences containing a single-site methylation with the lowest detected concentration of 2 aM. This DNA-Au@MNPs based sensor provides a promising method to achieve 35 min response time and minimally invasive diagnosis of ovarian cancer. • We report a rapid and ultrasensitive sensor for detecting DNA methylation in blood. • The biosensor targets a 110 nucleotide DNA sequence with a single-site methylation. • The sensor has a broad dynamic range and low detection limits to the target DNA. • The sensor offers a promising method to rapidly diagnose ovarian cancer in 35 min. [ABSTRACT FROM AUTHOR]

Abstract: The gold-coated magnetic nanoparticles (Au@MNPs) have been proposed to act as “dispersible electrodes” in sensing applications with the dual advantages of reduced detection time and increased sensitivity. As a sensor the Au@MNPs would be modified with ligands to capture the analyte, with exposure of a magnetic field bringing the nanoparticles back to a macroelectrode for electrochemical detection of the amount of analyte. In this paper, the potential of Au@MNPs as dispersible electrodes is assessed via (1) characterization of how they assemble onto a macroelectrode upon application of a magnetic field, (2) their electron transfer behaviour to redox species in solution and redox species attached to the Au@MNPs and (3) how low a detection limit is possible. Visualization with atomic force (AFM), scanning electron (SEM) and light microscopy showed the particles formed a coral-like structure on the electrode. Electron transfer kinetics of the Au@MNPs-modified electrode was shown to be similar to a bare electrode by both cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The electrochemistry of the Os(bpy)2(AMP) modified Au@MNPs enabled an estimation of the smallest number of redox molecules per Au@MNP that could be detected. It was estimated that as little as 0.144±0.007 redox molecules per nanoparticle could be detected with the lowest actual detected number being 0.79±0.11 molecule per nanoparticle. [Copyright &y& Elsevier]

Abstract: Electrochemical impedance spectroscopy and in-situ IR spectroscopy were employed to investigate potential-induced structural changes, and associated ionic permeability, of alkanethiol self-assembled monolayers (SAMs) deposited on gold surfaces. SAMs terminated with hydroxyl or methyl groups were investigated. It is shown that both SAMs are highly permeable to ions once the dc potential is increased above a value of approximately +500mV vs Ag/AgCl in a 0.1M HClO4 aqueous solution. At potentials more anodic than 500mV, there exists a reversible change in the resistance and the capacitance of the SAMs. The change in the dielectric properties exhibits the same trend for both methyl and hydroxyl terminated SAMs and is accompanied with a structural change as confirmed using in-situ IR spectroscopy as a function of the applied potential. [Copyright &y& Elsevier]

Abstract: High-density, surface-mounted ferrocene has been prepared using covalent immobilisation of an alcohol substituted ferrocene derivative to a pre-assembled single-walled carbon nanotubes directly anchored to silicon(100) surface (SWCNTs-Si). The formation of these ferrocene-modified electrodes (Fc-SWCNTs-Si) has been followed using X-ray photoelectron spectroscopy and atomic force microscopy. Electrochemical results show the surface concentration of ferrocenemethanol molecules is 9.26×10−8 molcm−2, which is about 500–1000 times greater than the experimentally measured coverage of ferrocene directly attached to flat Si(100) surfaces. The reversible one-electron wave of the ferrocene/ferrocenium couple was observed at 490mV versus Ag+/Ag and the apparent rate constant of electron transfer, k app, was 21s−1. These results suggest these ferrocene-modified electrodes are excellent candidates for molecular memory devices. [Copyright &y& Elsevier]

Abstract: This paper studies the analytical performance and characterization of a peptide modified biosensor towards detection of Cu2+ ions. The peptide modified biosensor is developed by carbodiimide attachment of the Gly-Gly-His tripeptide onto a 3-mercaptopropionic acid (MPA) modified gold surface. X-ray photoelectron spectroscopy (XPS) was used to characterize the steps in the biosensor fabrication. Detection of Cu2+ ions are determined by cyclic and Osteryoung square wave voltammetry. The analytical performance of this biosensor is found to be affected by the pH, salt concentration, temperature and accumulation time of the test solution. Interference studies and investigations of the reusability of this biosensor have also been performed. [Copyright &y& Elsevier]