Electrochemical Pretreatment of Carbon Electrodes as a Function of Potential, pH, and Time

Non-invasive electrochemical immunosensor for reverse iontophoretic determination of cardiac troponins (cTnT & cTnI) in a simulated artificial skin model. Significance of raw DPV and CV data for chemometric discrimination

Electrochemical immunosensors coupled with reverse iontophoresis (RI) for noninvasive determination of cardiac troponins were developed and validated according to ICH Q2 (R1) guideline. Linearity was in 0.01-10 and 100-500 ng/mL ranges. LODs (ng/mL) were in 6-25 × 10-4, while LOQs (μg/mL) were in 18-7.5 × 10-4 range. Chemometric evaluation was performed on raw data simply by principle component analysis and cluster analysis to discriminate stages of immunosensors. This is the first demonstration of RI determination of cardiac troponins so far. Findings of the current manuscript have great potential to develop point of care diagnostic systems for major cardiac events, where high sensitivity and specificity are required.

Graphitic Carbon Electrodes on Flexible Substrate for Neural Applications Entirely Fabricated Using Infrared Nanosecond Laser Technology

Neural interfaces for neuroscientific research are nowadays mainly manufactured using standard microsystems engineering technologies which are incompatible with the integration of carbon as electrode material. In this work, we investigate a new method to fabricate graphitic carbon electrode arrays on flexible substrates. The devices were manufactured using infrared nanosecond laser technology for both patterning all components and carbonizing the electrode sites. Two laser pulse repetition frequencies were used for carbonization with the aim of finding the optimum. Prototypes of the devices were evaluated in vitro in 30 mM hydrogen peroxide to mimic the post-surgery oxidative environment. The electrodes were subjected to 10 million biphasic pulses (39.5 μC/cm²) to measure their stability under electrical stress. Their biosensing capabilities were evaluated in different concentrations of dopamine in phosphate buffered saline solution. Raman spectroscopy and x-ray photoelectron spectroscopy analysis show that the atomic percentage of graphitic carbon in the manufactured electrodes reaches the remarkable value of 75%. Results prove that the infrared nanosecond laser yields activated graphite electrodes that are conductive, non-cytotoxic and electrochemically inert. Their comprehensive assessment indicates that our laser-induced carbon electrodes are suitable for future transfer into in vivo studies, including neural recordings, stimulation and neurotransmitters detection.

Substrate selection for fundamental studies of electrocatalysts and photoelectrodes: inert potential windows in acidic, neutral, and basic electrolyte

The selection of an appropriate substrate is an important initial step for many studies of electrochemically active materials. In order to help researchers with the substrate selection process, we employ a consistent experimental methodology to evaluate the electrochemical reactivity and stability of seven potential substrate materials for electrocatalyst and photoelectrode evaluation. Using cyclic voltammetry with a progressively increased scan range, we characterize three transparent conducting oxides (indium tin oxide, fluorine-doped tin oxide, and aluminum-doped zinc oxide) and four opaque conductors (gold, stainless steel 304, glassy carbon, and highly oriented pyrolytic graphite) in three different electrolytes (sulfuric acid, sodium acetate, and sodium hydroxide). We determine the inert potential window for each substrate/electrolyte combination and make recommendations about which materials may be most suitable for application under different experimental conditions. Furthermore, the testing methodology provides a framework for other researchers to evaluate and report the baseline activity of other substrates of interest to the broader community.

Electrochemical determination of antioxidant capacities in flavored waters by guanine and adenine biosensors

The immobilization and electro-oxidation of guanine and adenine as DNA bases on glassy carbon electrode are evaluated by square wave voltammetric analysis. The influence of electrochemical pretreatments, nature of supporting electrolyte, pH, accumulation time and composition of DNA nucleotides on the immobilization effect and the electrochemical mechanism are discussed. Trace levels of either guanine or adenine can be readily detected following short accumulation time with detection limits of 35 and 40 ngmL(-1) for guanine and adenine, respectively. The biosensors of guanine and adenine were employed for the voltammetric detection of antioxidant capacity in flavored water samples. The method relies on monitoring the changes of the intrinsic anodic response of the surface-confined guanine and adenine species, resulting from its interaction with free radicals from Fenton-type reaction in absence and presence of antioxidant. Ascorbic acid was used as standard to evaluate antioxidant capacities of samples. Analytical data was compared with that of FRAP method.

Nitric oxide sensor based on carbon fiber covered with nickel porphyrin layer deposited using optimized electropolymerization procedure

Electropolymerization regime of meso-tetrakis(3-methoxy-4-hydroxyphenyl) porphyrin is optimized to yield films possessing both electrocatalytical and permselective properties towards nitric oxide oxidation. The sensor composed of electrochemically oxidized carbon fiber, covered solely with nickel porphyrin derivative layer electropolymerized using our method, is characterized by high selectivity towards nitrite (1:600), ascorbate (1:8000) and dopamine (>1:80), determined by constant potential amperometry at 830 mV (vs. Ag/AgCl). Selectivity for ascorbate and dopamine as well as detection limit for NO (1.5 nM at S/N=3) is 5-10 times better than parameters usually reported for Nafion coated porphyrinic sensors. Nafion coating can further enhance selectivity properties as well as aids to the stability of the sensors' responses.

Nanocomposite and Nanoporous Polyaniline Conducting Polymers Exhibit Enhanced Catalysis of Nitrite Reduction

Nanostructured polyaniline (PANI) conducting polymer films were prepared on electrochemically pretreated glassy carbon electrodes, which were previously modified with multilayers of polystyrene (PS) nanoparticles with a diameter of 100 nm. PANI was electropolymerised and grown through the interstitial spaces between the PS nanoparticles, which formed a nanocomposite film of PANI and PS nanoparticles on the electrode surface. Furthermore, a nanoporous PANI film was fabricated through the removal of the PS nanoparticles by dissolution in toluene. As a result of their nanostructure, both of the PANI films (before and after removal of the PS nanoparticles) exhibited enhanced electrocatalytic behaviour towards the reduction of nitrite relative to bulk-PANI films; however, partial collapse or shrinkage may have occurred with the removal of the nanoparticles and could have resulted in a less enhanced response. Under optimised conditions, the nanocomposite-film-modified electrode exhibited a fast response time of 5 s and a linear range from 5.0 x 10(-7) to 1.4 x 10(-3) M for the detection of nitrite; the detection limit was 2.4 x 10(-7) M at a signal-to-noise ratio of 3.

Electrochemical characterization of parylene-embedded carbon nanotube nanoelectrode arrays

A novel parylene-embedded carbon nanotube nanoelectrode array is presented for use as an electrochemical detector working electrode material. The fabrication process is compatible with standard microfluidic and other MEMS processing without requiring chemical mechanical polishing. Electrochemical studies of the nanoelectrodes showed that they perform comparably to platinum. Electrochemical pretreatment for short periods of time was found to further improve performance as measured by cathodic and anodic peak separation of K(3)Fe(CN)(6). A lower detection limit below 0.1 µM was measured and with further fabrication improvements detection limits between 100 pM and 10 nM are possible. This makes the nanoelectrode arrays particularly suitable for trace electrochemical analysis.

Electrochemical processing of fibrinogen modified-graphite surfaces: Effect on plasmin generation from adsorbed plasminogen

With the aim to improve the fibrinolytic properties of carbons by different biological and electrochemical treatments, we modified graphite surfaces by fibrinogen adsorption and subsequent application of various constant potentials before submitting them to plasminogen adsorption. First, we verified that plasminogen (purified or present in human plasma) could adsorb onto these modified surfaces and that adsorbed plasminogen could be converted by t-PA (the principal physiological activator of plasminogen) to adsorbed plasmin. The catalytic properties of the generated enzyme were characterized in assay solutions containing t-PA, fibrinogen and the chromogenic substrate S-2403 (pyroGlu-Phe-Lys-p-nitroaniline, HCl). Experiments showed that the application of electrical potentials to the fibrinogen coating could indirectly affect the properties of the material. In the case of anodic potentials, the amidolytic activity of the generated plasmin was significantly enhanced. Especially, this activity was 10 times higher at a particular potential value.

Interaction of echinomycin with guanine: electrochemistry and spectroscopy studies

The interaction of antitumor antibiotic, echinomycin (Echi) with guanine (Gua) was thoroughly investigated by adsorptive transfer stripping cyclic voltammetry, ultraviolet and visible adsorption spectra (UV/Vis) and Fourier-transform infrared spectroscopy (FTIR). Electrochemistry provided a simple tool for verifying the occurrence of interaction between Echi and Gua. Echi could be accumulated from the solution and give well-defined electrochemical signals in 0.1 M phosphate buffer solution (pH 7.0) only when Gua was present on the surface of the electrochemically pretreated glass carbon electrode (GCE), suggesting a strong binding of Echi to Gua. All the acquired spectral data showed that a new adduct between Echi and Gua was formed, and two pairs of adjacent intermolecular hydrogen bonds between the Ala backbone atoms in Echi and Gua (Ala-NH to Gua-N3 and Gua-NH2 to Ala-CO) played a dominating role in the interaction. Electrochemistry coupled with spectroscopy techniques could provide a relatively easy way to obtain useful insights into the molecular mechanism of drug-DNA interactions, which should be important in the development of new anticancer drugs with specific base recognition.

Determination of chlorite in drinking water by differential pulse voltammetry on graphite

The chlorite ion is an unavoidable by-product of the disinfection of drinking water by means of chlorine dioxide. The maximum concentration values of chlorite accepted in many countries' regulations range from 0.2 to 1.0 mg L(-1). A simple, inexpensive and quickly set up voltammetric procedure for the on-site determination of chlorite in drinking water networks is described. This procedure is suitable for the whole range of applications in drinking water plants. A useful cell for on-field analysis has been developed. Surface morphology and behaviour of carbon-based working electrodes have been investigated by voltammetry and atomic force microscopy (AFM). Actual samples of different types of water networks have been analysed for chlorite concentration.

Electrochemical activation of electrodes for amperometric detection of nitric oxide

An open question in the literature of nitric oxide detection was investigated: does electrochemical activation account for the enhanced properties of certain presumed chemically-modified electrodes? Uniform electrodes of graphite, iridium, palladium, platinum, and ruthenium were exposed to potential cycling and then tested for amperometric response to nitric oxide to identify principles that govern electrochemical activation of nitric oxide electrodes. These electrodes were compared to similar electrodes that were not cycled. Only cycled graphite and ruthenium showed significantly increased responses. Graphite demonstrated enhanced performance after exposure to cycling potentials at which oxygen, CO(2), and soluble carbonates form, suggesting that erosion of the electrode enhanced its response by increasing the surface area accessible to nitric oxide. This may explain the performance of carbon fibers cycled to the same potentials in solutions containing metalloporphyrins. The response of ruthenium was enhanced after cycling to less extreme potentials at which soluble species do not form and at which a metallic conductive oxide, RuO(2), could lay down a stable, adherent layer on the electrode surface. Cycled ruthenium also exhibited a much greater increase in capacitance after cycling, consistent with the formation of a conductive surface layer.