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We studied here the influence of Li+ ions on the benzene rings of nematic mixture E7, which is electrochemically adsorbed onto gold electrode surface, to highlight the ability of this mixture for the applications in the field of the rechargeable Li+-ion batteries. Raman spectra support the changes observed in electrochemical analyses while contact angle measurements show that wetting properties of E7 layer were modified after deposition of this mixture onto gold support and the doping with Li+ ions. [ABSTRACT FROM AUTHOR]

The biosensing of bacterial pathogens is of a high priority. Electrochemical biosensors are an important future tool for rapid bacteria detection. A monolayer of bacterial-binding peptides can serve as a recognition layer in such detection devices. Here, we explore the potential of random peptide mixtures (RPMs) composed of phenylalanine and lysine in random sequences and of controlled length, to form a monolayer that can be utilized for sensing. RPMs were found to assemble in a thin and diluted layer that attracts various bacteria. Faradaic electrochemical impedance spectroscopy was used with modified gold electrodes to measure the charge-transfer resistance (RCT) caused due to the binding of bacteria to RPMs. Pseudomonas aeruginosa was found to cause the most prominent increase in RCT compared to other model bacteria. We show that the combination of highly accessible antimicrobial RPMs and electrochemical analysis can be used to generate a new promising line of bacterial biosensors. [ABSTRACT FROM AUTHOR]

[Display omitted] • First comparative report on the electrochemical behavior of NAR using unmodified electrodes. • Selective and sustainable electroanalytical method for detecting NAR. • Linear range of 1.36 to 19.1 mg L-1 (LOD 0.11 mg L-1) for GCE. • Electronic structure of NAR probed using B3LYP/Def2-TZVPPD calculations alongside Fukui and dual descriptor analyses. • Cost-effective strategy for electroanalysis of pharmaceutical formulations. Naringenin (NAR) is a versatile herbal flavonoid known for its broad pharmacological benefits, including antioxidant, anti-inflammatory, and anticancer properties. These properties underscore its potential and necessity for industrial applications within the pharmaceutical sector, making its detection and quantification crucial for ensuring the quality and efficacy of pharmaceutical products. Addressing the imperative for a sensitive and sustainable screening approach, this research leverages electrochemical analysis techniques including electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and differential pulse voltammetry (DPV). Complementary to experimental investigations, the electronic structure of NAR was probed using B3LYP/Def2-TZVPPD calculations alongside Fukui and dual descriptor analyses. Our findings delineate the dissociation kinetics of the hydroxyl groups within NAR, with particular emphasis on the phenolic group's proton as the primary dissociation site, elucidating pivotal insights into the oxidation mechanism of NAR. Noteworthy is the irreversibility of the electrochemical oxidation process observed on both non-modified glassy carbon electrode (GCE) and gold electrode (GE), indicating a one-electron-one-proton mechanism. Utilizing the external calibration method and GCE, a linear range from 1.36 to 19.1 mg L-1 in Britton-Robinson (BR) supporting electrolyte was established, exhibiting a limit of detection (LOD) of 0.11 mg L-1 (R2 = 0.9945). For GE, the standard addition calibration approach revealed one linear range, from 0.27 to 0.48 mg L-1 (LOD of 0.04 mg L-1, R2 = 0.9960). Importantly, the proposed methodologies demonstrate satisfactory selectivity against potential interferences, with intra- and inter-day precision exhibiting low relative standard deviation (RSD) values. This study introduces a simple, sensitive, stable, selective, and sustainable electroanalytical method for the detection of NAR in pharmaceutical formulations, harnessing the advantages of unmodified electrodes and rigorous experimental validation. [ABSTRACT FROM AUTHOR]

In contrast to reported enzyme-based immunoassays, an enzyme-free immunoassay (optical and electrochemical) is presented here for the first time that can be used as point-of-need detection bioplatforms of bovine IgG as goat milk adulterant. In the first format, Prussian blue nanoparticles (PBNPs) were used as antibody catalytic labels in a competitive colorimetric microplate immunoassay. Absorbance measurement was performed photometrically at 450 nm. After in-depth optimization, excellent sensitivity was achieved (0.01% cow/goat volume ratio), which is 100 times lower than the limit allowed by the European legislation (EL) (1% v/v), thanks to the high catalytic activity of PBNPs compared with natural peroxidase. Moreover, the antibody-PBNPs bioconjugates showed excellent stability over 4 weeks (> 94% of the initial response) confirming the successful anchoring of the antibodies to the surface of the PBNPs. On the other hand, a label-free voltammetric immunoassay for the detection of bovine IgG was developed. The sensing principle was based on the hindrance of charge transfer between ferri-ferrocyanide redox couple and the screen-printed gold electrodes modified with bovine IgG antibody. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to characterize the step-by-step modification of the electrode surface. Under optimal conditions, this single-step electrochemical analysis achieved a high sensitivity of 0.1% (cow/goat) when monitoring the ferrocyanide oxidation at + 0.092 V (vs. Ag/AgCl) using differential pulse voltammetry (DPV). The selectivity of the developed immunoassays was evaluated for different species of milk of similar composition, and both immunoassays exhibited a selective response only to bovine IgG. Unlike conventional immunoassays, the developed enzyme-free immunoassays have many attractive features for the detection of milk adulteration, whether they are used in quality control laboratories for routine milk analysis (optical immunoassay) or at on-site checkpoints (electrochemical immunoassay) using wireless electrochemical detectors. The sensors provide high sensitivity (≤ 0.1%), excellent precision (RSD < 6%), low cost (no enzyme is required) and ease of operation, including handling of milk samples. [ABSTRACT FROM AUTHOR]

To further explore the possibility of the electrochemical reduction of NaBO2 into NaBH4, the electrochemical reduction of NaBO2 into NaBH4 was fulfilled with pulse voltage using the Eu-Co-Ni-B coating electrode. A simple electroless plating technique was used to prepare the Eu-Co-Ni-B coating electrode. It has been proved that NaBO2 was converted into NaBH4 by electrochemical analysis method. The results showed that the method of detection and quantitative analysis of NaBH4 with gold electrode was feasible (R2=0.98). When the reverse pulse voltage was + 0.5 V, the forward pulse voltage was −1.5 V, the reverse pulse duration was 2 s and the forward pulse duration was 2 s, the concentration of NaBH4 reaches a maximum of 1.25 × 10−4 mol/L. With the continuous increase of electrolytic time, the concentration of NaBH4 shows a trend of increasing first and then decreasing. When the electrolytic time was 2 h, the maximum concentration of NaBH4 reaches 1.61 × 10−4 mol/L. [ABSTRACT FROM AUTHOR]

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An SU-8 probe with an array of nine, individually addressable gold microband electrodes (100 μm long, 4 μm wide, separated by 4-μm gaps) was photolithographically fabricated and characterized for detection of low concentrations of chemicals in confined spaces and in vivo studies of biological tissues. The probe's shank (6 mm long, 100 μm wide, 100 μm thick) is flexible, but exhibits sufficient sharpness and rigidity to be inserted into soft tissue. Laser micromachining was used to define probe geometry by spatially revealing the underlying sacrificial aluminum layer, which was then etched to free the probes from a silicon wafer. Perfusion with fluorescent nanobeads showed that, like a carbon fiber electrode, the probe produced no noticeable damage when inserted into rat brain, in contrast to damage from an inserted microdialysis probe. The individual addressability of the electrodes allows single and multiple electrode activation. Redox cycling is possible, where adjacent electrodes serve as generators (that oxidize or reduce molecules) and collectors (that do the opposite) to amplify signals of small concentrations without background subtraction. Information about electrochemical mechanisms and kinetics may also be obtained. Detection limits for potassium ferricyanide in potassium chloride electrolyte of 2.19, 1.25, and 2.08 μM and for dopamine in artificial cerebral spinal fluid of 1.94, 1.08, and 5.66 μM for generators alone and for generators and collectors during redox cycling, respectively, were obtained. [ABSTRACT FROM AUTHOR]

Heavy metals are one of the major pollutants found in drinking water and their abnormal level may pose a threat to human's health and life. Manganese also belongs to heavy metals group, and it is generally used in production of batteries, fertilizers, and ceramics. Even though, Mn is necessary for proper development of central nervous system, its elevated concentration might lead to certain diseases such as epilepsies, cell death in focal cerebral ischemia as well as neurodegenerative diseases such as Huntington and Alzheimer. Hence, it is crucial to elaborate novel methods for manganese ions detection that could be applied for in situ analysis of water samples. Herein, we present the studies on the electrochemical detection of manganese ions using aptamer-modified electrodes. This is the first attempt of application of aptamer strands as receptor layers for electrochemical analysis of manganese ions and for that purpose gold disk electrodes served as transducers, which were further modified with disulfide - based aptamers and 6-mercapto-1-hexanol blocking agent. The electrochemical measurements concerned the choice of the conditions for formation of aptamer receptor layer as well as the type of redox indicator that served as the source of current signal. The studies referred to the definition of aptasensor working parameters including the verification of the possibility of manganese ion detection in cell culture media. It was shown that it was possible to detect Mn2+ ions within 25 nM–1 μM concentration and the proposed aptasensor exhibited high selectivity towards target analyte for which at least 2 – times higher response was recorded than for interfering ions. Moreover, the possibility of Mn2+ detection in real samples was depicted followed by stability and regeneration studies. [Display omitted] • A novel 32 nucleotide DNA aptamer specific to manganase ions was selected through SELEX process. • DNA aptamer was applied for development of receptor layer for manganese ions using voltammetric techniques. • Elaborated aptasensor allowed for Mn2+ ions detection in the range from 25 nM to 1 μM. • Aptasensor showed high selectivity towards Mn2+ ions allowing for their detection in water samples and cell culture medium. [ABSTRACT FROM AUTHOR]

• The electroreduction of Cr(VI) to Cr(III) was performed using gold electrode in acidic sodium alginate solution as the electrolytic medium. • The conditions for electroreduction processes were optimized, being pH 2.0 and 10 mmol L−1 of sodium alginate the best conditions. • Under optimized conditions, the complete electroreduction of Cr(VI) to Cr(III) was reached. • The electrolyzed solution of Cr(VI) was successfully removed from water by means polymer-enhanced ultrafiltration. Chromium (Cr) is used in many manufacturing processes, and its release into natural waters is a major environmental problem today. Low concentrations of Cr(VI) are toxic to human health and living organisms due to the carcinogenic and mutagenic nature of this mineral. This work examined the conversion of Cr(VI) to Cr(III) via electrochemical reduction using gold electrode in an acidic sodium alginate (SA) solution and subsequent removal of the produced Cr(III)-SA by the polymer-enhanced ultrafiltration (PEUF) technique. A solution of SA in nitric acid was used both as an electrolytic medium during the voltammetric measurements and bulk electrolysis and as an extracting agent during the PEUF technique. The electroanalysis of Cr(VI) was performed by linear sweep voltammetry in the presence of acidic SA solution to study its voltammetric behavior as a function of the Cr(VI) concentration, pH, presence of Cr(III), SA concentration and scan rate. In addition, the quantitative reduction of Cr(VI) to Cr(III) was studied through the bulk electrolysis technique. The results showed efficient reduction with well-defined peaks at approximately 0.3 V vs. Ag/AgCl, using a gold working electrode. As the pH increased, the reduction signal strongly decreased until its disappearance. The optimum SA concentration was 10 mmol/L, and it was observed that the presence of Cr(III) did not interfere in the Cr(VI) electroanalysis. Through the quantitative reduction by bulk electrolysis in the presence of acidic SA solution, it was possible to reduce all Cr(VI) to Cr(III) followed by its removal via PEUF. Image, graphical abstract [ABSTRACT FROM AUTHOR]

We present electrochemical biosensors for the analysis of a target miR‐155 that work through the formation of miRNA‐DNA hybrid duplexes by hybridization of miR‐155 with its complementary DNA and through the subsequent intercalation of appropriate intercalating agents on gold electrodes. In the first method, the electrochemical behavior of methylene blue intercalated to the miRNA‐DNA hybrid duplex, formed between miR‐155 and its complementary DNA, on the gold electrode was measured. In the second method, the miRNA‐DNA hybrid duplex formed between ferrocene‐labeled DNA and miR‐155 in solution is intercalated to the pyrenes immobilized on the electrode surface. This lead to an electrochemical signal being generated from the oxidized ferrocene accumulated on the electrode surface. For each method, the limit of detections for the detection of miR‐155 were determined to be 0.96 and 2.22 pM, respectively. In addition, the developed electrochemical biosensors were effective in the quantitation of miR‐155 in serum sample. [ABSTRACT FROM AUTHOR]

Dopamine (DA) is a significant neurotransmitter in the central nervous system, coexisting with uric acid (UA) and ascorbic acid (AA). UA and AA are easily oxidizable compounds having potentials close to that of DA for electrochemical analysis, resulting in overlapping voltammetric response. In this work, a novel molecularly imprinted (MI) electrochemical sensor was proposed for selective determination of DA (in the presence of up to 80‐fold excess of UA and AA), relying on gold nanoparticles (Aunano)‐decorated glassy carbon (GC) electrode coated with poly(carbazole (Cz)‐co‐aniline (ANI)) copolymer film incorporating DA as template (DA imprinted‐GC/P(Cz‐co‐ANI)‐Aunano electrode, DA‐MIP‐Aunano electrode). The DA recognizing sensor electrode showed great electroactivity for analyte oxidation in 0.2 mol L−1 pH 7 phosphate buffer. Square wave voltammetry (SWV) was performed within 10−4–10−5 mol L−1 of DA, of which the oxidation peak potential was observed at 0.16 V. The limit of detection (LOD) and limit of quantification (LOQ) were 2.0×10−6 and 6.7×10−6 mol L−1, respectively. Binary and ternary synthetic mixtures of DA‐UA, DA‐AA and DA‐UA‐AA yielded excellent recoveries for DA. Additionally, DA was quantitatively recovered from a real sample of bovine serum spiked with DA, and determined in concentrated dopamine injection solution. The developed SWV method was statistically validated against a literature potentiodynamic method using a caffeic acid modified‐GC electrode. [ABSTRACT FROM AUTHOR]

In this article, an electrochemical sensor based on a gold nanocage (AuNC)‐modified carbon ionic liquid electrode (CILE) was fabricated and applied to the sensitive rutin determination. The presence of AuNCs on the electrode surface greatly improved the electrochemical performance of the working electrode due to its specific microstructure and high metal conductivity. Electrochemical behavior of rutin on AuNCs/CILE was studied using cyclic voltammetry and differential pulse voltammetry with the related electrochemical parameters calculated. Under the optimal experimental conditions, the oxidation peak current of rutin and its concentration had good linear relationship in the range from 4.0 × 10−9 to 7.0 × 10−4 mol/L with a low detection limit of 1.33 × 10−9 mol/L (3σ). This fabricated AuNCs/CILE was applied to direct detection of the rutin concentration in drug samples with satisfactory results, showing the real application of AuNCs in the field of chemically modified electrodes. [ABSTRACT FROM AUTHOR]

Nanostructured gold electrodes have been widely used for electrochemical trace analysis of Hg2+ because Hg2+ has superior specificity for the formation of gold amalgam. However, it is still very challenging to achieve both high sensitivity and reproducibility, especially for real environmental water samples due to surface poisoning by organic residues. In this work, we developed two strategies for addressing these challenges. First, we added NaBr (with a final concentration of 0.01 M) to the analytes; this enhanced the sensitivity by two orders of magnitude and improved the reproducibility to be better than RSD <15% because of the synergetic interaction of Br− with Hg2+ and gold at the interface. Second, we developed a pre-oxidation method using a glassy carbon electrode to remove organic residue from the analyte before Hg2+ analysis. The combination of these two approaches results in an efficient, reliable, and fast electrochemical detection technique for on-site trace analysis of Hg2+ that is in concentrations lower than that required by WHO for drinking water. Image 1 • The batch preparation of a novel gold micro-nanostructured electrode. • The significantly improved sensitivity and reproducibility with the addition of small amount of Br−. • The effective removal of organic residues in ambient water by simple electrochemical oxidation pretreatment. [ABSTRACT FROM AUTHOR]

Flexible, three‐dimensional nanoporous gold (NPG) electrodes were fabricated on polydimethylsiloxane (PDMS) surfaces without any functionalization, and their electrochemical properties examined in the absence and presence of common biofouling agents using cyclic voltammetry and redox potentiometry. In this work, potassium ferricyanide and fibrinogen were used as a model redox probe and denaturing agent, respectively, to demonstrate that flexible NPG electrodes behave ideally and can make electrochemical measurements in biofouling solutions. Using cyclic voltammetry, the non‐faradaic capacitive current was shown to be directly proportional to the scan rate, while the redox chemistry of potassium ferricyanide in the presence and absence of fibrinogen demonstrated reversible voltammetry. Using redox potentiometry, Nernst plots for the potassium ferri‐/ferrocyanide redox system gave rise to an expected Nernstian slope of 60 mV. These flexible electrodes could be particularly beneficial in electrochemical sensing in complex environments. Proof of concept was demonstrated through the measurement of uric acid in red blood cell packets using cyclic voltammetry. [ABSTRACT FROM AUTHOR]

Specific monitoring of cystatin C (CysC) levels in biological fluids is critical for diagnosis, treatment and mechanistic understanding of a spectrum of diseases, particularly chronic kidney disease (CKD). Despite evidences that CysC correlates with the high risk and/or progression of CKD, its use in clinical practice is still scarce. In this context, we report the development of a simple and sensitive immunosensor for the detection of CysC. The biosensor combines the technology of cost-effective screen-printed electrodes with the high specificity of a sandwich immunoassay. Optimized conditions showed that the sensor operates in a linear range between 10 and 100 ng mL−1, with a detection limit and a sensitivity of 6.0 ng mL−1 and 6.4 ± 0.3 μA ng mL−1 cm−2, respectively. Moreover, the sensor provided precise results (RSD ≤ 6.2%) and the quantification of CysC in CKD serum samples revealed to be in agreement with the values obtained by a particle-enhanced nephelometric immunoassay. In this light, the proposed immunosensor qualifies for clinical application, constituting a step forward in the development of fast, sensitive and cost-effective diagnostic tools that can improve the current medical care settings of CKD patients. Image 1 • An immunosensor for CysC, a chronic kidney disease biomarker, was developed. • Screen-printed carbon electrodes nanostructured with gold nanoparticles were used. • The sensor showed a linear concentration range with clinical utility. • The sensor was applied to CysC quantification in serum samples from CKD patients. [ABSTRACT FROM AUTHOR]

This report describes the preparation and evaluation of an immunosensor based on chemical modification of gold surface with hantavirus (strain Araucaria) antigen/protein and the antibody detection by electrochemical analysis. The viral nucleoprotein was immobilized onto gold by SAM formation with 3-mercaptopropionic acid (MPA) followed by activation of the surface using N -(3-Dimethylaminopropyl)- N ′-ethylcarbodiimide hydrochloride and N -Hydroxysuccinimide (EDC/NHS). Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and quartz crystal microbalance (QCM) measurements were used for evaluation of each step involved in the construction of the proposed immunosensor. Several experimental conditions were studied and after optimization of immobilization parameters, the device showed good stability within 21 days and selectivity for a qualitative detection of specific antibody (IgG) directed against hantavirus Araucaria. The proposed sensor had shown a linear response for concentration varying between 0.400 and 300 μg mL−1 allowing its application in spiked serum samples for detection of specific antibody of hantavirus Araucaria based on a cutoff value. The immunosensor showed a sensitive response to the spiked samples and can be employed as an alternative for the qualitative diagnosis of hantavirus infections. • Selective device to diagnosis of infections using hantavirus (strain Araucaria) antigen/protein • Simple route to prepare a label-free electrochemical immunosensor using gold electrodes • Different techniques applied in the characterization of immunosensor construction • Linear sweep voltammetry as a fast, alternative and low-cost tool for detection of specific antibody • Quick detection of specific antibody in spiked serum human samples [ABSTRACT FROM AUTHOR]

The effect of instabilities on the nonlinear electrochemical impedance spectroscopic (NLEIS) response of a simple electron transfer reaction in a kinetic and diffusion-controlled regime was studied using classical Fe2+/Fe3+ redox couple on a gold electrode. Numerical simulations were employed to calculate the NLEIS response, and the predictions were compared with experimentally acquired NLEIS data. Instabilities were introduced by continuously changing the dc potential or the active species concentrations. At high frequencies, the effect of potential instabilities manifested more clearly in higher harmonic signals than at the fundamental frequency. In case of changes in species concentrations which did not break the symmetry, the higher harmonics were not particularly more sensitive than the fundamental. An analysis of the results shows that multiple factors contribute to the higher harmonics. The sensitivity of second harmonics to the instabilities arises from the nonlinear component of the rate constant as well as the interaction between the rate constant oscillations and concentration oscillations at the applied frequency. The results show that NLEIS can be used to quickly identify instabilities which alter the symmetry. [ABSTRACT FROM AUTHOR]

Abstract Studies have well documented that mutations in the adenomatous polyposis coli gene (APC) are involved in the development of different types of cancer. Therefore, the objective of the present report was to design and construct a sensitive nanostructured genosensor able to detect specific sequences of the APC gene in order to be applied in early carcinogenesis diagnosis. We used screen-printed gold electrodes (SPGE) modified with DNA probes and mercaptoundecanoic acid chemically immobilized on a gold sensor surface. APC complementary DNA sequences were hybridized on the previously immobilized DNA probes. Besides, we tested effects of different intercalating agents, and various temperatures on the hybridization reaction to increase the sensitivity and selectivity of our device. The evaluation of these processes was carried out by means of the cyclic voltammetry technique (CV) to monitor the redox reaction of [Fe(CN) 6 ]3−/4− on the SPGE-s. The constructed genosensor exhibited an excellent response to identify the APC gene in a concentration range from 100 pM to 100 μM, with 43.92 pM as the limit of detection in the presence of doxorubicin as DNA intercalating agent. The selectivity of the device was tested by using a DNA sequence different from the APC gene, which shows negative response. Considering the importance of APC mutations in the development of tumors in the digestive, urogenital, and mammary tissues, here developed electrochemical genosensor, due to its easy management, short time of response, and high performance, may be useful for early cancer detection. Graphical abstract Unlabelled Image Highlights • It was developed a genosensor to identify a mutation in the APC gene. • The genosensor detected pM concentration of the APC mutation. • Such capacity was due to the presence of doxorubicin. • Our genosensor may be of help in the diagnosis of cancers with the APC mutation. [ABSTRACT FROM AUTHOR]

Abstract An electrochemical impedimetric immunosensor was developed for the detection of the neuropeptide Corticotropin Releasing Hormone (CRH) based on the immobilization of half-antibody fragments on gold nanoparticles (AuNp). Then, the optimal conditions for the obtainment of AuNp through electroplating on a bare gold electrode were studied. The results showed that the obtainment of AuNp at a fixed potential of −0.2 V for 330 s, at 80 °C and 2·10-3 mol·L-1 of HAuCl 4 generates an adequate nanostructured surface and is a highly reproducible method. Also, the optimal conditions for immobilizing the half-antibody on AuNp were studied. The interaction of the CRH with the recognition layer of the immobilized half-antibody on the nanostructured surface was carried out by incubation at 4 °C for 2 h. A dissolution of [Fe(CN) 6 ]4-/[Fe(CN) 6 ]3− as a redox probe was used to study the electrochemical responses of the nanostructured surface and the immobilization processes of the half-antibody and detection of CRH, using cyclic voltammetry and electrochemical impedance spectroscopy. An immunosensor was obtained for the specific detection of CRH, within a range of 10.0–80.0 μg mL-1, with a limit of detection of 2.7 μg mL-1 and a limit of quantification of 9.2 μg mL-1. Additionally, the association constant between the CRH and the immobilized half-antibody was calculated at 1.96·105 M−1. Highlights • First electrochemical immunosensor developed for Corticotropin Releasing Hormone. • The adequate electrochemical surface was obtained under optimal condition experimentals. • Electrochemical impedance spectroscopy was used for the electrochemical determination. • The modified electrode possesses good specificity and stability. [ABSTRACT FROM AUTHOR]

Electrical properties of self‐assembling DNA nanostructures underlie the paradigm of nanoscale bioelectronics, and as such require clear understanding. DNA‐mediated electron transfer (ET) from a gold electrode to DNA‐bound Methylene Blue (MB) shows directional preference, and it is sequence‐specific. During the electrocatalytic reduction of [Fe(CN)6]3− catalyzed by DNA‐bound MB, the ET rate constant for DNA‐mediated reduction of MB reaches (1.32±0.2)103 and (7.09±0.4)103 s−1 for (dGdC)20 and (dAdT)25 duplexes. The backward oxidation process is less efficient, making the DNA duplex a molecular rectifier. Lower rates of ET via (dGdC)20 agree well with its disturbed π‐stacked sub‐molecular structure. Such direction‐ and sequence‐specific ET may be implicated in DNA oxidative damage and repair, and be relevant to other polarized surfaces, such as cell membranes and biomolecular interfaces. Current events: DNA‐mediated long‐range ET in gold‐tethered DNA duplexes shows directional preference for reduction, thereby making DNA a molecular rectifier. [ABSTRACT FROM AUTHOR]

Highlights • Raman spectra obtained at 532, 633, and 785 nm excitations show different dependencies on electrochemical variables. • Intensities of selected Raman bands correlate with absorption spectra of different redox forms of polyaniline. • The shift of the onset potential for Raman bands intensity growth to less positive values proceeds by increasing of solution pH. Abstract Polyaniline has been electrodeposited at a gold electrode, and subjected to Raman spectroelectrochemical study at a red (633 nm) and NIR (785 nm) laser line excitations at electrode potentials varying from −0.5 V to 0.8 V, and different solution pH values ranging from 1 to 9. The results obtained are compared with 532 nm excitation spectra. Some new phenomena have been observed and discussed. The 1620 cm−1 Raman band diminishes in its intensity with a positive potential shift at a green excitation, whereas a maximum of intensity for this band around 0.6 V was observed for the red excitation. Adversely, a positive potential shift causes an increase of intensity for 1585 cm−1 band for both these excitation wavelengths. For NIR excitation, both these bands grow in intensity by positive potential shift. This behavior, as well as increase of spectral intensity with a progressive oxidation of polyaniline layer, were interpreted based on the differences of optical absorption and its changes with changing electrode potential. For the most Raman bands, the shift of the onset potential for their intensity growth to less positive values has been observed by increasing of solution pH. [ABSTRACT FROM AUTHOR]

The mutual interference in the sensing detection of heavy metal ions (HMIs) is considerably serious and complex. Besides, the co-existed ions may change the stripping peak intensity, shape and position of the target ion, which partly makes peak current analysis inaccurate. Herein, a promising approach of partial peak area analysis was proposed firstly to research the mutual interference. The interference between two species on their electrodeposition processes was investigated by simulating different kinetics parameters, including surface coverage, electro-adsorption, -desorption rate constant, etc. It was proved that the partial peak area is sensitive and regular to these interference kinetics parameters, which is favorable for distinctly identifying different interferences. Moreover, the applicability of the partial peak area analysis was verified on the experiments of Cu2+, As(III) interference at four sensing interfaces: glassy carbon electrode, gold electrode, Co 3 O 4 , and Fe 2 O 3 nanoparticles modified electrodes. The interference behaviors between Cu2+ and As(III) relying on solid-solution interfaces were revealed and confirmed by physicochemical characterizations and kinetics simulations. This work proposes a new descriptor (partial peak area) to recognize the interference mechanism and provides a meaningful guidance for accurate detection of HMIs in actual water environment. [Display omitted] • Peak area was proved more accurate to estimate interference than peak current. • The feasibility of peak area analysis was verified on four solid-solution interfaces. • The interference behavior was found to be dependent on the sensing interface. • Three typical Cu2+ and As(III) interference behaviors were classified by peak area. [ABSTRACT FROM AUTHOR]

Abstract Sensitive and specific detection of DNA methylation in genomic DNA is imperative for rapid epigenetic evaluations. Here, a novel sensitive electrochemical strategy was developed for ultrasensitive detection of DNA methylation in genomic DNA via padlock probe primer generating rolling circle amplification (RCA). Typically, after bisulfite treatment of methylated DNA, the methylation-specific linear padlock is only circularized in the presence of methylated DNA and subsequently serves as a template containing a DNA tetrahedron for RCA. The DNA tetrahedron is utilized as a nanocarrier that can be immobilized on a gold electrode to generate RCA product to load hemin, an iron-containing porphyrin with chlorine, forming the G-quadruplex as a horseradish peroxidase like DNAzyme, which reduces methylene blue (MB) in the presence of H 2 O 2 to yield a distinct current signal. Using the developed DNAzyme with the RCA signal amplification strategy, the DNA biosensor can achieve a detection limit as low as 0.1 fM for the ultrasensitive electrochemical detection of methylated DNA sequence with a detection range from 10–15 M to 10−9 M. At the same time, the satisfactory specificity, reproducibility, stability and recovery performances indicated its satisfied potentials for clinical diagnosis. Most importantly, this method can be further applied to analyse other genomic DNA also. Highlights • An sensitive electrochemical strategy was developed for DNA methylation detection. • DNA tetrahedron probes was served as signal primers to initiate RCA reactions. • The hemin/G-quadruplex acting as DNAzyme could improve the sensitivity of methylated DNA. [ABSTRACT FROM AUTHOR]

Abstract The present study aimed to develop a highly sensitive label-free electrochemical aptasensor for the detection of Diazinon (DZN), as one of the most widespread organophosphorus compounds. The aptasensor was assembled using screen-printed gold electrode modified by thiolated aptamers which were immobilized on gold nanoparticles (Au NPs). Optimum deposition time, in which the highest electrochemical response occurred, was found in 150 s. Electrochemical impedance spectroscopy and cyclic voltammetry were used to characterize electrochemical properties of the novel aptasensor. Electrochemical detection was carried out through differential pulse voltammetry in [Fe(CN) 6 ]3-/4- solution. Fluctuation of the current was examined in the DZN concentration range of 0.1–1000 nM. According to the results, the designed aptasensor provided an extremely lower limit of detection (0.0169 nM) compared with HPLC and other colorimetric techniques for DZN detection. The present highly specific designed aptasensor doesn’t interact with other analytes in the real sample. Consequently, the present aptasensor is easy to use and relatively inexpensive with a good sensitivity, stability, and reproducibility for this application. We are now evaluating all approaches to make a portable device for fast and sensitive quantification of DZN and related OPs. Highlights • Electrochemical aptasensor for determination of Diazinon. • Gold nanoparticles-modified screen-printed gold electrode. • To make a portable and fast sensitive device. [ABSTRACT FROM AUTHOR]

The development of rapid, sensitive and convenient methods for the monitoring of rare circulating tumor cells (CTCs) is of great significance in cancer diagnostics and therapy. Herein a label-free and competitive electrochemical aptasensor was proposed for the efficient capture, ultrasensitive detection and controlled release of CTCs. Firstly, the DNA nanotetrahedron (NTH)-based TLS11a aptamer probe was immobilized on a disposable screen-printed gold electrode (SPGE) surface via the Au−S bonds for the highly enhanced capture of liver cancer HepG2 cells. Then, hybrid nanoprobes of Pd-Pt nanocages labeled with complementary DNA (cDNA), hemin/G-quadruplex DNAzyme and horseradish peroxidase (HRP) were attached on the SPGE substrate by the DNA hybridization, resulting in the formation of dendritic structure (DS) nanoprobes with self-assembly methods for the greatly enhanced sensitivity. When the target HepG2 cells existed, they can compete with DS nanoprobes to bind with NTH-based aptamer probe, resulting in the release of the DS nanoprobes from the SPGE. This method exhibits ultrahigh selectivity and sensitivity toward HepG2 with detection limits of 5 cells per ml. Furthermore, our strategy allows for easy detachment of the captured cells from the SPGE without compromising cell viability by an electrochemical cleavage of the Au–S bonds. The present study provides a label-free technique for highly selective and efficient quantification of tumor cells, which is essential in the early cancer diagnosis and treatment of cancer. [ABSTRACT FROM AUTHOR]

Deep eutectic solvents are a class of green and sustainable solvents in chemical processes. An electrochemical method was developed to fabricate nanoporous gold electrodes by alloying and dealloying Au–Zn alloy in ZnCl2–urea deep eutectic solvent. The as-prepared active nanoporous gold electrodes facilitate the electrochemical detections of water pollutants with superior sensitivities. [ABSTRACT FROM AUTHOR]

The challenge of the early diagnosis of pancreatic cancer in routine clinical practice requires low-cost means of detection, and this may be achieved with immunosensors based on electrical or electrochemical principles. In this paper, we report a potentially low-cost immunosensor built with interdigitated gold electrodes coated with a self-assembled monolayer and a layer of anti-CA19-9 antibodies, which is capable of detecting the pancreatic cancer biomarker CA19-9 using electrical impedance spectroscopy. Due to specific, irreversible adsorption of CA19-9 onto its corresponding antibody, according to data from polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS), the immunosensor is highly sensitive and selective. It could detect CA19-9 in commercial samples with a limit of detection of 0.68 U mL−1, in addition to distinguishing between blood serum samples from patients with different concentrations of CA19-9. Furthermore, by treating the capacitance data with information visualization methods, we were able to verify the selectivity and robustness of the immunosensor with regard to false positives, as the samples containing higher CA19-9 concentrations, including those from tumor cells, could be distinguished from those with possible interferents. [ABSTRACT FROM AUTHOR]

Abstract: SERS‐active screen‐printed electrodes (SPEs) are extensively applied for electrochemical SERS biosensors with the advantages of portable, inexpensive cost, fast measurement, and sensitive detection. In our work, a useful fabrication method of sputtering deposition for SERS‐active SPEs was proposed. Two kinds of working electrodes of SPE which were carbon electrode and gold electrode were successfully deposited by silver nanoparticles. Besides, the sputtering experiments of different substrates (paper, glass epoxy and polyethylene terephthalate) of the SPE were also conducted. The comparison of SERS enhancement of rhodamine 6G (R6G) on different kinds of SERS‐active SPEs was introduced. In addition, the relationship between the surface roughness and SERS enhancement has been investigated. The enhancement factor (EF) of Ag/carbon and Ag/gold electrode were estimated as 2.8×105 and 2.2×107, respectively. From the SERS experiments, the lower background noise of SERS signals could be observed through sputtering deposition method compared with the citrate reduction method. Furthermore, spectro‐electrochemical analysis of uric acid was studied. The SERS signals were strongly increased upon the modulation of the applied voltage. These results demonstrated the applicability of this mass producible fabrication method for producing SERS‐active SPEs, as well as, highlighting the future potential of commercial bio‐applications. [ABSTRACT FROM AUTHOR]

The potential dependent adsorption of urea and its self-condensation product, biuret, have been studied on polycrystalline gold electrodes using electrochemical and in situ infrared spectroscopy. Voltammetry reveals that biuret displays a wider double-layer region compared to its parent compound and can only be oxidized at potentials that overlap with Au oxidation. Chronocoulometric measurements indicate that the adsorption of biuret is stronger than that of urea and the surface coverage is potential dependent. Surface enhanced infrared absorption spectroscopy (SEIRAS) experiments have been performed on both urea and biuret adsorption from neutral solutions made from heavy water. Urea provides low intensity IR signals consistent with relatively weak adsorption over a very restricted potential domain whereas biuret is spectroscopically much more pronounced. Analysis of the SEIRAS results support at least two distinct configurations of adsorbed biuret involving oxygen coordination to the metal surface. At the limit of the positive potentials studied spectroscopic evidence of the adsorption of partially oxidized biuret (ureayl-type species) is provided. [ABSTRACT FROM AUTHOR]

Herein we study the electrochemical potential-dependent and time-dependent stability of thiols and disulfides as self-assembled monolayers on gold electrodes. The stability of four representative sulfur-containing compounds: 3-mercaptopropionic acid, 2-mercaptoethanol, 1,4-dithiothreitol and dl -thioctic acid, was assessed in simulated physiological conditions (i.e. phosphate buffer saline). The stability of these molecules was evaluated using cyclic voltammetry and step-potential chronoamperometry. Coordination of the thiols and disulfides significantly affects the stability of the self-assembled monolayer. In addition, studies performed using gold single crystal (100) and (111) electrodes show the superior binding strength of the SAM on the Au(100) surface structure. [ABSTRACT FROM AUTHOR]

A comparative in situ time-resolved Raman spectroelectrochemical study on aniline polymerization at platinum, smooth gold, and roughened gold electrodes was performed with 785 nm laser excitation. Under the constant anodic current density electrolysis performed at the platinum electrode, the intensity of Raman bands grows continuously reaching a steady state within 8-10 min. At the smooth gold electrode, the maximum intensity is observed in a few or few tens of seconds, and appears to be ca. 1.5 orders of magnitude higher than for the platinum one. At the roughened gold electrode, again, a fast growth of intensity is observed, being ca. 3 orders higher than for the platinum one. After a prolonged electrolysis of ca. 150-200 mC/cm2, the intensities for all three electrodes appear to be of a similar intensity. The results obtained show a strong surface enhancement of Raman spectra at the gold electrode, a very strong at the roughened gold one, and no enhancement at the platinum electrode at the beginning of electrooxidation, turning into a regular Raman scattering at a prolonged electrolysis, sufficient for the formation of a stable layer of polyaniline at the electrode surface. [ABSTRACT FROM AUTHOR]

This paper reports the use of multiple square wave voltammetry (MSWV) in the development of a simple, sensitive, fast and low-cost electroanalytical procedure for the diquat herbicide detection in different samples employing a custom-made gold microelectrode (Au-ME). The experimental and voltammetric parameters were optimized, and the use of eight pulses superimposed in each step in the MSWV yielded the detection limits two orders of magnitude greater than those obtained by SWV or previously published chromatographic procedures. Also, the Au-ME allied to MSWV was used to determine diquat in beetroot, onion, peach, environmental water and river sediments. All samples were spiked, and the obtained recovery percentage values were satisfactory for the analytical procedure, showing that Au-ME and MSWV is a suitable tool for diquat residues detection in complex samples. [ABSTRACT FROM AUTHOR]

The cationic lipid didodecyldimethylammonium bromide (DDAB) is one of the agent that is included in formulations for liposomes with anchored gold nanoparticles as drugs carriers because its positive charge facilitates the anchoring of the negatively charged stabilized gold nanoparticles to the lipid components of the liposomes. In this paper a thermodynamic analysis of Langmuir isotherms was performed, as a first step in the preparation of liposomes including DDAB, the phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), and cholesterol(Ch),to decide about the most stable combination. Monolayers of DMPC:Ch:DDAB with the most energetically favourable composition, were transferred to Au(111) electrodes by the Langmuir-Schaefer technique in the electrochemical cell and characterized by impedance spectroscopy. The results were compared with those obtained with electrodes coated with DMPC:Ch films that did not contain DDAB. In both cases the frequency dispersion of impedance data indicates high homogeneity of the films in a wide potential range around the capacitance minimum. The inclusion of the anticancer drug doxorubicin (DOX) into the mixed lipid monolayers and its electrochemical reduction at pH 4.5 were studied by voltammetry and by impedance spectroscopy. At potentials out of the faradaic region the inclusion of DOX does not affect significantly the frequency dispersion of the impedance but decreases the capacitance. However, at negative potentials the analysis of the high frequency dispersion of the impedance and the influence of the scan rate on the voltammograms indicate a reduction process with contribution of adsorption and diffusion of DOX. Diffusion was avoided by transferring the electrodes coated in the Langmuir trough to the electrochemical cells that do not contain the drug. Under these conditions the reduction of the adsorbed DOX was found to obey the model of a surface confined electrode and the charge transfer resistance, R a , and adsorption capacitance, C a , were obtained at potentials of the faradaic region. The combination of both parameters provides the rate constant for the reduction in a wide potential range that allows us to propose a sequential mechanism with two determining steps. [ABSTRACT FROM AUTHOR]

Herein, novel and versatile electrochemical aptasensors were constructed on a self-supported nanoporous gold (np-Au) microelectrode, integrating with an exonuclease III (Exo III) induced signal amplification strategy. Self-supported np-Au microelectrode with 3D bicontinuous nanoporous structures possesses tremendously large specific area, clean surface, high stability and biocompatibility, bringing about significant advantages in both molecular recognition and signal response. As paradigms, two analytes of bisphenol A (BPA) and ochratoxin A (OTA) were selected to demonstrate the superiority and versatility of designed aptasensors. Trace amounts of mDNA (associated with BPA or OTA concentration) hybridized with cDNA strands assembled on np-Au microelectrode, activating the cleavage reaction with Exo III. Thus, cDNA was digested and mDNA was released to undergo a new hybridization and cleavage cycle. Finally, residual cDNA strands were recognized by methylene blue labelled rDNA/AuNPs with the assistance of hDNA to generate the electrochemical signals, which were used to quantitatively monitor targets. Under the optimized conditions, prepared aptasensors exhibited wide linear ranges (25 pg/mL to 2 ng/mL for BPA, 10 pg/mL to 5 ng/mL for OTA) with ultralow detection limits (10 pg/mL for BPA, 5 pg/mL for OTA), excellent selectivity and stability, and reliable detection in real samples. This work opens a new horizon for constructing promising electrochemical aptasensors for environmental monitoring, medical diagnostics and food safety. [ABSTRACT FROM AUTHOR]

This paper describes the synthesis of organically-modified silicates (ormosils) with phosphomolybic acid (HPMo), and their use to detect ametryn. Gold electrodes coated with an ormosil film made of 3-cyanopropyltriethoxysilane (CPTS) and HPMo were used to detect ametryn between 3.5 and 24 µmol L −1 in an acidic medium. There was no evidence of electroreduction of ametryn when ormosils with HPMo and (3-glycidyloxypropyl)trimethoxysilane (GLPTS) or 3-aminopropyltriethoxysilane (APTS) were used. This difference in behavior is ascribed to aggregation in CPTS ormosil, while GLPTS and APTS ormosils displayed homogeneous surfaces, according to scanning electron microscopy. HPMo had its structure preserved in CPTS ormosil as indicated by 31 P solid-state nuclear magnetic resonance spectra. Using polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS), we inferred that the functional group dipole moments in all ormosils are oriented parallel to the interface. Control of morphology thus seems essential for applications of ormosil films, being particularly promising to monitor environmentally-relevant herbicides. [ABSTRACT FROM AUTHOR]

A novel electrochemical PNA-based biosensor for the determination of Hg 2 + is described. The receptor layer, containing single strands of polythymine PNA (peptide nucleic acid), was formed at the surface of gold electrode. Due to the presence of thymine bases and peptide bonds, an interaction between Hg 2 + ion and receptor layer occurs. The influence of chain modification – PNA vs. DNA – and type of redox marker – anionic AQMS-Na (sodium salt of anthraquinone-2-sulfonic acid) and Fe II/III (potassium ferri/ferrocyanide) or cationic MB (methylene blue) and RuHex (hexaammineruthenium(III) chloride) – were studied. Proposed PNA-based biosensor with anionic AQMS-Na as a redox marker demonstrated significantly better analytical parameters, as compared to results obtained for other tested redox markers (for measurements at pH 6.0). The linear response towards Hg 2 + was in the range from 5 to 500 nmol·L − 1 with the detection limit of 4.5 nmol·L − 1 . The developed sensor distinguishes itself with high selectivity towards Hg 2 + , even for solutions containing several interfering cations. Interactions between Hg 2 + and PNA receptor layer were studied using square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS). [ABSTRACT FROM AUTHOR]

The analysis of antioxidants in foodstuffs has become an active area of research, leading to the recent development of numerous methods for assessing antioxidant capacity. Here we described the fabrication and validation of a novel and simple cell-based electrochemical biosensor for this purpose. The biosensor is used to assess the antioxidant capacity of cell-free extracts from Lactobacillus plantarum strains isolated from Chinese dry-cured ham. The biosensor relies on the determination of cellular reactive oxygen species (ROS) (the flux of H 2 O 2 released from RAW 264.7 macrophage cells) to indirectly assess changes in intracellular oxidative stress level as influenced by L . plantarum strains. A one-step acidified manganese dioxide (a-MnO 2 ) modified gold electrode (GE) was used to immobilize RAW 264.7 macrophage cells, which were then encapsulated in a 3D cell culture system consisting of alginate/ graphene oxide (NaAlg/GO). The biosensor exhibited a rapid and sensitive response for the detection of H 2 O 2 released from RAW264.7 cells. The detection limit was 0.02 μM with a linear response from 0.05 μM to 0.85 μM and the biosensor was shown to have good stability and outstanding repeatability. This technique was then used for evaluating the antioxidant ability of extracts from L. plantarum NJAU-01. According to the electrochemical investigations and assays of SEM, TEM, and ROS, these cell-free extracts effectively reduced the oxidative stress levels in RAW264.7 cells under external stimulation. Extracts from L. plantarum strains at a dose of 10 10 CFU/mL showed the highest antioxidant activities with a relative antioxidant capacity (RAC) rate of 88.94%. Hence, this work provides a simple and efficient electrochemical biosensing platform based on RAW264.7 cells for fast, sensitive and quantitative assessment of antioxidant capacity of L. plantarum strains. The method demonstrates its potential for rapid screening for evaluating antioxidant properties of samples. [ABSTRACT FROM AUTHOR]

Altering a material’s catalytic properties requires identifying structural features that give rise to active surfaces. Grain boundaries create strained regions in polycrystalline materials by stabilizing dislocations and may provide a way to create high-energy surfaces for catalysis that are kinetically trapped. Although grain-boundary density has previously been correlated with catalytic activity for some reactions, direct evidence that grain boundaries create surfaces with enhanced activity is lacking. We used a combination of bulk electrochemical measurements and scanning electrochemical cell microscopy with submicrometer resolution to show that grain-boundary surface terminations in gold electrodes are more active than grain surfaces for electrochemical carbon dioxide (CO2) reduction to carbon monoxide (CO) but not for the competing hydrogen (H2) evolution reaction. The catalytic footprint of the grain boundary is commensurate with its dislocation-induced strain field, providing a strategy for broader exploitation of grain-boundary effects in heterogeneous catalysis. [ABSTRACT FROM AUTHOR]

para-Nitrophenol (p-NP) is a high priority environmental pollutant. For the sake of safety, sensitive detection of its presence in water resources and food is highly important. The present article describes the use of copper metal nanoparticles for selective and sensitive electrochemical detection of p-NP in pure and real sample. For this the gold electrode was fabricated by polyvenylpyrrolidone stabilized copper metal nanoparticles ( ca. 4 nm d.) via self-assembled 4,4′-bipyridine monolayer and characterized by microscopic and electrochemical techniques. The newly developed sensor permits for sensitive detection of p-NP in a linear concentration range of 1-500 μM with lowest detection limit of 0.34 nM and high sensitivities 247.1 μA cm−2 μM−1. The sensor electrode exhibited high stability, reproducibility, good selectivity in the presence of potential interfering agents and had an excellent capability for the selective determination of p-NP in river water without preliminary treatments. [ABSTRACT FROM AUTHOR]

The aim of this work is to highlight the potential of using a modified gold electrode with controlled quantity of silver nanoparticles as a working electrode to detect low concentrations of nitrate in chloride solutions. Optimal charge for silver deposition has been determined to obtain the highest signal for the nitrate reduction as the electrocatalytic properties of the bimetallic electrode were directly influenced by its composition. According to the Volcano plot obtained the charge chosen was −52 μC for a 3 mm diameter electrode, corresponding to 4.6×1015 Ag atoms cm−2. It has been shown that dioxygen did not participate to the nitrate reduction mechanism. In order to decrease the limit of quantification, square wave voltammetry was preferred to less sensitive cyclic voltammetry. Nitrate was quantified in chloride solutions in the concentration range found in the open ocean, i. e. 0.39-50 μmol L−1 with a good linear regression (R2=0.9969). The stability of the bimetallic Au−Ag systems has been evaluated and showed almost no difference on the signal recorded over a 26 days period which is suitable to consider an in situ sensor development for marine applications. [ABSTRACT FROM AUTHOR]

The electrochemical behaviour of a bismuth-containing gold thick-film, which was screen-printed and co-fired on low temperature co-fired ceramic (LTCC), has been investigated in 1 M nitric acid. After potentiostatic polarisation the material was electrochemically studied by voltammetry to determine the degradation kinetics and the role of elements of the glass-ceramic compounds. Field emission scattering electron microscopy (FESEM) examinations and energy dispersive X-ray (EDX) analyses confirm the electrochemically driven degradation of the composite: The interphase between the thick-film and the LTCC substrate was selectively attacked around the conductive gold layer. Elementary bismuth was reductively formed within the attacked area. Inverse voltammetric analyses of the electrolyte solution show that the electrochemical degradation is superimposed by chemical degradation of bismuth-containing glass-phases. The reductively formed bismuth was removed from the screen-printed electrode (SPE) due to the subsequently performed anodic polarisation. The amount of anodically dissolved bismuth is comparable with the coulometrically determined value of the anodic polarisation sweep. [ABSTRACT FROM AUTHOR]

A Ni(OH) 2 /nanoporous gold (NPG) hybrid electrode was one-step obtained by anodizing gold in NiCl 2 solution for 100 s. The as-prepared electrode is self-supported due to the nature of the synthesis method. Under the optimal condition, it showed an ultrahigh sensitivity (3286.1 μA mM −1 cm −2 ) in a linear range from 0.2 μM to 1.1 mM, a low detection limit (170 nM) and a fast response time (< 2 s) towards nonenzymatic glucose detection in NaOH solution. The provided strategy is applicable in most laboratories to prepared transition metal hydroxide (MOH x (M = Ni, Co, Cu, Fe, etc.)) modified NPG. [ABSTRACT FROM AUTHOR]

Electrowetting of a Au/aqueous solution interface with hexadecane (HD) was largely affected by specific adsorption of Br − on the Au surface. The adsorption distinctly changed the potential dependence of the contact angle (θ) of HD droplets on a Au(1 1 1) electrode surface in line with electrocapillary relationship. Measurements of θ as a macroscopic observable, being sensitive to the atomic level change of the electrode surface such as surface reconstruction and Br − adsorption, allowed us to monitor the state of the Au/aqueous solution interface as demonstrated by pinpointing the Br − desorption potential. The amplitude of potential-controlled reshaping of a HD 1.0 μL droplet was enhanced by specific adsorption of Br − . The specific adsorption also affected HD microdroplets (<50 μm diameter ≈ 33 pL volume) in the same way as 1.0 μL droplets as revealed by in situ electrochemical fluorescence imaging measurements. Overall, ionic adsorption provides us with opportunities of fine control of the dynamics of oil droplet in an electrode potential range narrower than 1.5 V. [ABSTRACT FROM AUTHOR]

We report a new multiplexed strategy for the electrochemical detection of regional DNA methylation across multiple regions. Using the sequence dependent affinity of bisulfite treated DNA towards gold surfaces, the method integrates the high sensitivity of a micro-fabricated multiplex device comprising a microarray of gold electrodes, with the powerful multiplexing capability of multiplex-PCR. The synergy of this combination enables the monitoring of the methylation changes across several genomic regions simultaneously from as low as 500 pg μl−1 of DNA with no sequencing requirement. [ABSTRACT FROM AUTHOR]

This article explains a step-wise protocol to develop an electrochemical sensor to quantify serum levels of C-telopeptide (CTX) crosslinks also known as crosslaps in a matter of minutes and with high level of accuracy. The technique needs only one-step (incubation) and can thus be used for point of care screening. Due to the excellent electrical properties of the as-prepared immunosensor, CTX levels were successfully measured from 1 to 1000 pg/mL. This is while the normal reference of the marker is 50-450 pg/mL, suggesting that the sensor can acceptably detect CTX. The results also showed a good correlation with ECLIA in measuring serum levels of CTX. [ABSTRACT FROM AUTHOR]

Electrochemical surface activity arises from the interaction and geometric arrangement of molecules at electrified interfaces. We present a novel electrochemical tip-enhanced Raman spectroscope that can access the vibrational fingerprint of less than 100 small, non-resonant molecules adsorbed at atomically flat Au electrodes to study their adsorption geometry and chemical reactivity as a function of the applied potential. Combining experimental and simulation data for adenine/Au(111), we conclude that protonated physisorbed adenine adopts a tilted orientation at low potentials, whereas it is vertically adsorbed around the potential of zero charge. Further potential increase induces adenine deprotonation and reorientation to a planar configuration. The extension of EC-TERS to the study of adsorbate reorientation significantly broadens the applicability of this advanced spectroelectrochemical tool for the nanoscale characterization of a full range of electrochemical interfaces. [ABSTRACT FROM AUTHOR]

The authors describe a three-dimensional (3D) structure composed of graphene and DNA for use in a voltammetric dopamine (DA) sensor. The material was deposited on a gold electrode, and the enhanced charge-transfer performance and deposition of DNA were confirmed by electrochemical analysis. Atomic force microscopy shows the graphene-DNA composite to have been assembled on the modified gold electrode. The modified gold electrode possesses excellent electrocatalytic activity for determination of DA, best at a working voltage of 0.1 V (vs. SCE). Ascorbic acid does not interfere. Response to DA is linear in the 0.1 to 100 μM concentration range, with a 30 nM detection limit even in the presence of 1.0 mM of ascorbic acid. [ABSTRACT FROM AUTHOR]

Electrochemical and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) techniques were employed to study the ion channel properties of gramicidin A (gA) in tethered bilayer lipid membranes (tBLMs) with varying concentrations of gA added to the outer leaflet of the bilayer. The electrochemical impedance spectroscopy (EIS) results demonstrate that gA forms conductive ion channels in tBLM systems even at concentrations as low as 0.5 mol%. The impedance of the membrane depended on the gA concentration where a minimum was observed at 10 mol%. When the amount of gA in the bilayer is increased to a concentration above 10%, the ion channels appear to arrange into a non-conducting state. PM-IRRAS spectra suggest that the gA molecules adopt a tilt angle of ∼29 ± 4° in the conductive ion channel state. In the non-conducting state, the average tilt angle of the gA molecules is ∼52 ± 3°, which implies that gA peptides assume a random orientation in the tBLM. [ABSTRACT FROM AUTHOR]

A high surface area nanoporous gold film electrode (NPGF) was prepared by a simple electrochemical route instead of the well-known alloying/dealloying method. Field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray analysis (EDX) were used to investigate the surface morphology and elemental composition of the as-prepared NPGF electrode. The electrocatalytic activity and sensing behaviour of the developed non-enzymatic NPGF electrode was demonstrated towards hydrogen peroxide (H 2 O 2 ) reduction employing cyclic voltammetry and amperometry techniques. Cyclic voltammetric measurements confirmed the excellent catalytic activity of the NPGF electrode as a shift in the overpotential (~ 0.4 V) towards less negative direction along with increased current signal compared to the unmodified bare Au electrode were noticed. Additionally, the H 2 O 2 reduction on the NPGF electrode takes place at less negative potential values in comparison with those found for existing NPG electrodes prepared by alloying/dealloying method. The electrochemical sensing of H 2 O 2 at the NPGF electrode was evaluated through amperometric mode by applying a constant potential of − 0.2 V in the linear range 10 × 10 − 6 mol L − 1 –1 × 10 − 3 mol L − 1 . The lower detection limit (LOD) was found to be 3.7 × 10 − 6 mol L − 1 (S/N = 3) and a remarkable selectivity was observed in the presence of major interfering molecules like glucose, ascorbic acid, dopamine and uric acid with high sensitivity (400 μA mM − 1 cm − 2 ). Other analytical parameters such as reproducibility and stability were well-studied and satisfactory results were obtained. The developed NPGF was used as a sensor probe for H 2 O 2 detection in real samples. [ABSTRACT FROM AUTHOR]