Electroanalytical Performance Research Articles

Amperometric cholesterol biosensors based on carbon nanotube–chitosan–platinum–cholesterol oxidase nanobiocomposite

Abstract A highly sensitive and fast responsed biosensor was successfully fabricated in this work. Platinum nanoparticles were electrochemically deposited in multiwalled carbon nanotube (MWCNT)–chitosan matrix by a cyclic voltammetry method. A Pt(IV) complex was reduced to Pt on the surface of MWCNTs. The Pt nanoparticles in the MWCNT–chitosan film were identified with transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). The doped Pt nanoparticles demonstrate the abilities to electrocatalyze the oxidation of hydrogen peroxide and substantially raise the response current. The results indicated that the Pt nanoparticles exhibited efficiently electrocatalytic activity. The influence of enzyme loading within the MWCNT–chitosan–Pt–cholesterol oxidase nanobiocomposite was explored to optimize the electroanalytical performance of the cholesterol biosensor. The optimized cholesterol biosensor shows a sensitivity of 0.044 A M−1 cm−2 and a response time of about 8 s. No response currents were observed at the MWCNT–chitosan–Pt–cholesterol oxidase nanobiocomposite modified electrode after the additions of 100 μM glucose and 1 μM ascorbic acid to 100 μM cholesterol in 0.1 M phosphate buffer solution (pH 7) in the interference study. The prepared cholesterol biosensor retained 60% of initial activity after 7 days when stored in 0.1 M phosphate buffer solution at 4 °C.

Bismuth Film Microelectrode Modified with Overoxidized Poly‐1‐Naphtylamine Protective Membrane for Enhanced Stripping Voltammetric Detection

AbstractThe application of protective overoxidized poly‐1‐naphtylamine membrane (ONAP) is demonstrated in combination with bismuth film microelectrode (ONAP‐BiFME) for anodic stripping voltammetric measurement of trace heavy metals in the presence of some selected surfactants. The ONAP membrane was electrochemically deposited on the surface of bare single carbon fiber microelectrode followed by the in situ or ex situ preparation of the bismuth film. The key operational parameters influencing the stripping performance of the ONAP‐BiFME were optimized and its electroanalytical performance was examined in the model solution containing Cd(II) and Pb(II) as test metal ions. The ONAP‐BiFME exhibited significantly enhanced stripping voltammetric response (approximately 70% for Cd(II) and 45% for Pb(II)) in comparison with unmodified BiFME in the absence of surfactants. In the presence of high concentrations, e.g., 20 mg L−1, of anionic or cationic surfactants, the stripping signal for, e.g., Cd(II) decreased for less than 6% at the ONAP‐BiFME, whereas at the unmodified BiFME the signal attenuated considerably (approximately 38%). Moreover, in the presence of 10 mg L−1 of nonionic surfactant Triton X‐100, the stripping signals at the bare BiFME were almost completely suppressed, whereas at the ONAP‐BiFME exhibited linear concentration behavior in the examined concentration range from 10 to 120 μg L−1, with the calculated limit of detection of 5.0 μg L−1 and 3.4 μg L−1 for Cd(II) and Pb(II), respectively in connection with 60 s accumulation time. The attractive behavior of ONAP‐modified BiFME expands the applicability of bismuth‐based electrodes for measurement of trace heavy metals in real environments, where the presence of more complex matrix can be expected.

Electroanalytical performance of a terbium(III)-selective sensor based on a neutral ionophore in environmental and medicinal samples

A new highly selective terbium(III) electrode was prepared with a polymeric film doped using S-2-benzothiazolyl-2-amino-alpha-(methoxyimino)-4-thiazolethiol acetate as an electroactive material, benzyl acetate (BA) as a plasticizer, and potassium tetrakis(4-chlorophenyl) borate (KTpClPB) as an anionic site in the percentage ratio 3.17:1.58:63.4:31.7 (ionophore-KTpClPB-BA-PVC, w/w). The electrode exhibited a linear response with a near Nernstian slope of 19.5 mV/decade within the concentration range 1.5 x 10(-7)-1.0 x 10(-2) M terbium ions, with a working pH range from 2.0 to 8.0, and a fast response time of 10 s and presented satisfactory reproducibility. The limit of detection was 9.3 x 10(-8) M. The results show that this electrode can be used in ethanol media up to 30% (v/v) concentration without interference. It can be used for 3 months without any considerable divergence in the potentials. Selectivity coefficients for terbium(III) with respect to many cations were investigated. The electrode is highly selective for terbium(III) ions over a large number of monovalent, bivalent, and trivalent cations. This shows the valuable property of the proposed electrode. The stability constant of the ionophore towards Tb(3+) ions was determined with the sandwich membrane method. It was successfully used as an indicator electrode in potentiometric determination of terbium(III) ions with EDTA and in direct determination in tap water and binary mixtures with quantitative results. The utility of the proposed electrode was also determined in the presence of ionic and nonionic surfactants and in the presence of fluoride ions in four pharmaceutical (mouthwash) preparations. [figure: see text]

Comparative study of multi walled carbon nanotubes-based electrodes in micellar media and their application to micellar electrokinetic capillary chromatography

This work reports on a comparative study of the electrochemical performance of carbon nanotubes-based electrodes in micellar media and their application for amperometric detection in micellar electrokinetic capillary chromatography (MEKC) separations. These electrodes were prepared in two different ways: immobilization of a layer of carbon nanotubes dispersed in polyethylenimine (PEI), ethanol or Nafion onto glassy carbon electrodes or preparation of paste electrodes using mineral oil as binder. Scanning electron microscopy (SEM) was employed for surface morphology characterization while cyclic voltammetry of background electrolyte was used for capacitance estimation. The amperometric responses to hydrogen peroxide, amitrol, diuron and 2,3-diclorophenol (2,3CP) in the presence and in the absence of sodium dodecylsulphate (SDS) were studied by flow injection analysis (FIA), demonstrating that the electrocatalytic activity, background current and electroanalytical performance were strongly dependent on the electrodes preparation procedure. Glassy carbon electrodes modified with carbon nanotubes dispersed in PEI (GC/(CNT/PEI)) displayed the most adequate performance in micellar media, maintaining good electrocatalytic properties combined with acceptable background currents and resistance to passivation. The advantages of using GC/(CNT/PEI) as detectors in capillary electrophoresis were illustrated for the MEKC separations of phenolic pollutants (phenol, 3-chlorophenol, 2,3-dichlorophenol and 4-nitrophenol) and herbicides (amitrol, asulam, diuron, fenuron, monuron and chlortoluron).

Flow Injection Analysis of Maleic Hydrazide Using an Electrochemical Sensor Based on Palladium‐Dispersed Carbon Paste Electrode

AbstractA new analytical methodology for the electrochemical detection of the herbicide maleic hydrazide (3,6‐dihydroxypyridazine) by flow injection analysis is presented. This method is supported by the novel application of a palladium‐dispersed carbon paste electrode as an amperometric sensor for this herbicide. Maleic hydrazide shows anodic electrochemical activity on carbon‐based electrodes (glassy carbon or carbon paste electrodes) in all the pH range. This electrochemical activity is enhanced using metal‐dispersed carbon paste electrodes, especially at Pd‐dispersed CPE which displays good oxidation signals at 690 mV (0.050 M phosphate buffer pH 7.0), 140 mV lower than at unmodified electrodes. Under the optimized conditions, the electroanalytical performance of Pd‐dispersed CPE in flow injection analysis was excellent, with good reproducibility (RSD 3.3%) and a wide linear range (1.9×10−7 to 1.0×10−4 mol L−1). A detection limit of 1.4×10−8 mol L−1 (0.14 ng maleic hydrazide) was obtained for a sample loop of 100 μL at a fixed potential of 700 mV in 0.050 M phosphate buffer solution at pH 7.0 and a flow rate of 2.0 mL min−1. The proposed method was applied for the maleic hydrazide detection in natural drinking water samples.

Immobilization of lactate dehydrogenase within multiwalled carbon nanotube-chitosan nanocomposite for application to lactate biosensors

A composite of multiwalled carbon nanotubes-chitosan (MWCNT-CHIT) was used as a matrix for entrapment of lactate dehydrogenase (LDH) onto a glassy carbon electrode in order to fabricate amperometric biosensor. The homogeneity of the resulting multiwalled carbon nanotubes-chitosan-lactate dehydrogenase (MWCNT-CHIT-LDH) nanobiocomposite film was investigated by atomic force microscopy (AFM). It shows that the enzyme is homogeneously immobilized within MWCNT-CHIT-LDH. The inclusion of MWCNT within MWCNT-CHIT-LDH exhibits the abilities to raise the current responses, to decrease the electrooxidation potential of β-nicotinamide adenine dinucleotide, reduced form (NADH), and to prevent the electrode surface fouling. The influence of several experimental parameters such as applied potential, solution pH value, NAD+ concentration, and enzyme loading was explored to optimize the electroanalytical performance of the biosensor. The optimized biosensor for the determination of lactate shows a sensitivity of 0.0083AM−1cm−2 and a response time of about 3s. The proposed biosensor retained 65% of its original response after 7 days.

A PVC/TTF‐TCNQ Composite Electrode for Use as a Detector in Flow Injection Analysis

AbstractA new polyvinyl chloride (PVC)/tetrathiafulvalene‐tetracyanoquinodimethane (TTF‐TCNQ) composite electrode was prepared and tested for electroanalytical performance. Different PVC/TTF‐TCNQ–graphite proportions were used in order to obtain the best possible detector for accommodation in a wall‐jet electrochemical cell of use in flow injection analysis. A PVC/TTF‐TCNQ w/w ratio of 1/10 provided the best results in terms of sensitivity, coefficients of variation and mechanical resistance. The voltammetric and flow‐injection amperometric detection responses of the electrode to ascorbic acid (AA) were measured and compared with those of a PVC–graphite electrode. The resulting electrode provided good electrode kinetics with a low background current and a relatively reproducible signal. In addition, the electrode can be readily prepared and its surface readily renewed.

Electrochemical immunosensor array using a 96-well screen-printed microplate for aflatoxin B1 detection

A novel analytical immunosensor array, based on a microtiter plate coupled to a multichannel electrochemical detection (MED) system using the intermittent pulse amperometry (IPA) technique, is proposed for the detection of aflatoxin B1 (AFB1). In the present work, the electrochemical behaviour and electroanalytical performance of the thick-film carbon sensors (also designated as screen-printed electrodes) incorporated in the multichannel electrochemical plate were first evaluated. Then the 96-well screen-printed microplate was modified in accord with a competitive indirect enzyme-linked immunoassay (ELISA) format for aflatoxin B1 detection. The measurements were performed using both spectrophotometric and electrochemical procedures and the results of the calibration curves, detection limit (LOD), sensitivity and reproducibility of the respective assay systems were evaluated. The immunoassay was then applied for analysis of corn samples spiked with AFB1 before and after the extraction treatment, in order to study the extraction efficiency and the matrix effect, respectively. These studies have shown that using this system, AFB1 can be measured at a level of 30 pg/mL and with a working range between 0.05 and 2 ng/mL. Good recoveries (103+/-8%) were obtained, demonstrating the suitability of the proposed assay for accurate determination of the AFB1 concentration in corn samples. The specificity of the assay was assessed by studying the cross-reactivity of PAb relative to AFB1. The results indicated that the PAb could readily distinguish AFB1 from other aflatoxins, with the exception for AFG1.

Bismuth film electrode for anodic stripping voltammetric determination of tin

The bismuth film electrode (BiFE), in combination with anodic stripping voltammetry, offers convenient measurement of low concentrations of tin. The procedure involves simultaneous in situ formation of the bismuth film electrode on a glassy carbon substrate electrode, together with electrochemical deposition of tin, in a non-deaerated model solution containing bismuth ions, catechol as complexing agent and the metal analyte, followed by an anodic stripping scan. The BiFE is characterized by an attractive electroanalytical performance, with two distinct voltammetric stripping signals corresponding to tin, accompanied with low background contributions. Several experimental parameters were optimized, such as concentration of bismuth ions and catechol, deposition potential, deposition time and pH of the model solution. In addition, a critical comparison is given with bare glassy carbon and mercury film electrodes, revealing the superior characteristics of BiFE for measurement of tin. BiFE exhibited highly linear behavior in the examined concentration range from 1 to 100 μg L −1 of tin ( R 2 = 0.997), an LoD of 0.26 μg L −1 tin, and good reproducibility with a calculated R.S.D. of 7.3% for 10 μg L −1 tin ( n = 10). As an example, the practical applicability of BiFE was tested with the measurement of tin in a real sample of seawater.

Recent Advances in Anodic Stripping Voltammetry with Bismuth-Modified Carbon Paste Electrodes

In this article, the results of some recent investigations on two types of bismuth-modified carbon paste electrodes are presented. In the first study, the bismuth-film carbon paste electrode (BiF-CPE) operated in situ and employed in anodic stripping voltammetry of Cd(II) and Pb(II) at the low μg L−1 level was of interest in view of choosing the proper Bi(III)-to-Me(II) concentration ratios (where Me: Pb or Cd). Such optimization has resulted in significant improvement of detection limits down to 1.0 μg L−1 Cd and 0.8 μg L−1 for Pb, which allowed us to apply the BiF-CPE for analysis of selected real samples of tap and sea water. The BiF-CPE was also further investigated for its application in highly alkaline media. In this case, attention was focused on the complex-forming capabilities of the OH – ions and their effect on the anodic stripping characteristics of some heavy metals (i.e. Cd, Pb, Tl) as well as upon the formation of the bismuth film itself. The last example deals with the continuing characterization of the recently introduced carbon paste electrodes modified with bismuth powder (Bi-CPEs) which combine the advantageous properties of carbon paste material with the favorable electrochemical properties of bismuth. Three series of electrodes, differing either in the content of metallic bismuth (from 8 to 50% w/w) or in the type of the carbon powder used (two spectroscopic types of graphite and powdered glassy carbon), were compared and the respective relations to the optimal carbon paste composition evaluated. Attractive electroanalytical performance of the Bi-CPE in anodic stripping voltammetry is demonstrated for selected model mixtures of heavy metals (Mn, Zn, Cd, Pb, Tl, and In).

Novel electrode for electrochemical stripping analysis based on carbon paste modified with bismuth powder

Bismuth-powder modified carbon paste electrode (Bi-CPE) is presented as an attractive “mercury-free” sensor applicable in electrochemical striping analysis of selected heavy metals. The electrode paste was prepared as a mixture of finely powdered metallic bismuth together with graphite powder and silicon oil. The Bi-CPE was characterized in nondeaerated solutions containing Cd(II) and Pb(II) at the μg/L level in conjunction with square-wave anodic stripping voltammetry. The electrode exhibited well-defined and separated stripping signals for both metals accompanied with a low background contribution, and a reproducibility of 5.6 and 6.0% ( n = 12) for 20 μg/L Cd(II) and Pb(II), respectively. The Bi-CPE exhibited superior performance in comparison to the bare carbon paste electrode (CPE) and the bismuth paste electrode (BiPE) and surprisingly, yielded a higher response than the in situ prepared bismuth-film carbon paste electrode. The electrode displayed excellent linear behavior in the examined concentration range from 10 to 100 μg/L Cd(II) + Pb(II) ( R 2 = 0.998 for both), with limits of detection of 1.2 μg/L for Cd(II) and 0.9 μg/L for Pb(II). The electroanalytical performance of Bi-CPE was successfully tested in a real sample of tap water spiked with Cd(II) and Pb(II).

Carbon Nanotube Modified Microelectrode for Enhanced Voltammetric Detection of Dopamine in the Presence of Ascorbate

AbstractA single carbon fiber microelectrode modified with multi‐wall carbon nanotubes (MWCNT) and Nafion exhibits an attractive electroanalytical performance for enhanced voltammetric detection of dopamine in the presence of ascorbate at physiological pH. The fast and simple preparation protocol involves dipping a single carbon fiber microelectrode into a modification solution containing Nafion and MWCNT. The resulting surface modification couples the sensitivity improvement associated with the MWCNT with the permselectivity of Nafion films. The microsensor displays highly linear behavior over the 2 to 20 μM dopamine range examined (R of 0.997), with a detection limit of 70 nM. A highly reproducible response was observed for 50 repetitive measurements with a RSD of 1.6%, while the effect of ascorbate upon the voltammetric signal for dopamine was negligible. In addition, some more insights are given into the electroanalytical performance of the MWCNT/Nafion modified microelectrode. Such a disposable dopamine microsensor holds great promise for convenient detection of dopamine in the presence of ascorbate at physiological concentrations in microvolume samples and at microlocations (e.g., measurement of dopamine under physiological conditions).

Ex situ preparation of bismuth film microelectrode for use in electrochemical stripping microanalysis

A study on the preparation and characterisation of ex situ formed bismuth film microelectrodes (BiFMEs) is presented, focusing in particular on their stable and reliable stripping electroanalytical performance. The potentiostatic pre-plating of the bismuth film onto a single carbon fibre substrate microelectrode was investigated and optimised with the aim of achieving long-term electrochemical and mechanical film stability. Several important film preparation parameters, such as plating agent, potential and time, and composition of the plating solution were examined with respect to the current signals of 40 consecutive adsorptive cathodic stripping voltammetry (AdCSV) measurements of trace Co(II) as model analyte. A comparison, also presented, of the stripping performance between bismuth and mercury film microelectrodes revealed a distinct practical advantage of the BiFME. The resulting optimised BiFME exhibited, besides excellent long-term film functional stability, attractive stripping analytical performance. Employing AdCSV with square-wave voltammetric detection, highly linear behaviour was obtained in the examined concentration range, with limits of detection of 70 and 90 ng/l and excellent reproducibility with 2.4 and 2.9% relative standard deviation at the 1 μg/l level ( n = 10), for Co(II) and Ni(II), respectively, achieved using only 2 min preconcentration time in the presence of dissolved oxygen. In addition, the performance of the proposed ex situ prepared BiFME in both anodic stripping voltammetry (ASV) of Cd(II) and Pb(II) and in AdCSV of Co(II) and Ni(II) from the same test solution is demonstrated. The ex situ prepared BiFME represents a promising non-toxic, environmentally friendly microsensor for detection at microlocations and in microvolumes, in particular where in situ bismuth film electrode preparation is inappropriate, inconvenient or impossible.

Comparison of the Electrochemical Reactivity of Electrodes Modified with Carbon Nanotubes from Different Sources

AbstractThe electrochemical activity of five different commercial carbon nanotubes (CNT), prepared by the ARC discharge and chemical vapor deposition (CVD) methods, has been assessed and compared. The various multi‐walled CNT were immobilized onto a glassy carbon electrode using three different dispersing agents (Nafion, concentrated nitric acid and dimethylformamide (DMF)) and their voltammetric response to ferricyanide, NADH and hydrogen peroxide examined. SEM was used to characterize the surface morphology. The corresponding cyclic voltammetry and amperometric data showed that the electrocatalytic activity, the background current and the electroanalytical performance are strongly depended on the preparation of the CNT and on the dispersing agent used. The most favorable amperometric detection of NADH and hydrogen peroxide is observed at the NanoLab CVD‐produced CNT in connection to a DMF‐surface dispersion. ARC‐produced CNT display a smaller capacitance, particularly in connection to the DMF dispersion. Such differences in the electrochemical reactivity are attributed to the different surface chemistries (primarily defect densities) of the corresponding CNT layers, associated with the different production and dispersion protocols.

Nickel hexacyanoferrate modified screen-printed carbon electrode for sensitive detection of ascorbic acid and hydrogen peroxide

Electrochemically modified screen-printed carbon electrode (SPCE) has been prepared by electrodepositing nickel hexacyanoferrate(III) (NiHCF) onto the electrode surface using cyclic voltammetry (CV). The performance of NiHCF-SPCE sensor was characterized and optimized by controlling several operational parameters. The NiHCF film has been proven to remain stable after CV scanning from 0 to +1.0 V vs. Ag/AgCl in the pH range of 3 to 10 and is re-useable. The most favourable supporting electrolyte solution exhibiting the optimum electroanalytical performance of the NiHCF-SPCE sensor was found to be 0.2 mol/L sodium nitrate. The electrochemical response toward ascorbic acid (AA) and H2O2 in 0.2 mol/L sodium nitrate solution was studied by using CV and the results showed that both analytes were electrocatalytically oxidized at approximately +0.4 V, while H2O2 also revealed a reduction signal at -0.8 V vs. Ag/AgCl. The NiHCF-SPCE sensor exhibited highly linear response for AA and H2O2 in the examined concentration range from 5.0x10-5 to 1.5x10-3 mol/L and from 2.0x10-5 to 1.0x10-3 mol/L (at +0.4 V), with the correlation coefficients of 0.999 and 0.998, respectively. The reproducibility of the NiHCF-SPCE sensor was followed for the determination of AA by using four individual electrodes, and the relative standard deviation of CV peak currents varied between 0.9 % and 2.2 %. The proposed NiHCF-SPCE has been shown to be a very attractive electrochemical sensor for AA and H2O2, also in a view of inexpensive mass production of disposable single-use sensors. The NiHCF-SPCE sensor was tested by measuring AA in multivitamin tablets, with recoveries obtained between 94.4 % and 108.2 % (n=5).

Amino-polysiloxane hybrid materials as carbon composite electrodes for potentiometric detection of anions

Hybrid organic–inorganic polysiloxane materials functionalised with amino groups have been prepared and studied as active phases of potentiometric sensors for anion detection. The aminopolysiloxane matrix is obtained via sol–gel using 3-(trimethoxysilyl)propyl methacrylate (MAPTS) and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AETAPTS) as alkoxysilane precursors and allowing the amino groups to act as basic catalysts for the hydrolysis and polycondensation processes at room temperature. Graphite powder was added during the synthesis process in order to obtain electronically conductive composites for the preparation of the electrochemical sensors. Acid–base properties of the amino groups in the electrode surface allow the sensors to be applied in the electrochemical detection of several anions in aqueous solution. These sensors exhibit a long-time stability, robustness and a suitable electroanalytical performance in the potentiometric detection of anions in solution.

Carbon composite microelectrodes: charge percolation and electroanalytical performance.

Microelectrodes based on two different epoxy-graphite composites (Araldite-M/HY5162 and Araldite-PY302-2/HY943) that are compatible with organic solvents have been developed and characterized. The variation in the bulk conductivity with graphite particle loading is described by percolation theory and indicates that the particles interact strongly with one another. The percolation threshold is 52% v/v loading of graphite, and this composite exhibits a bulk conductivity of 15 S m(-1). Microdisk electrodes of 25-microm diameter were produced by first etching a microcavity at the tip of a platinum microelectrode, which was then packed with a composite containing 60% v/v graphite so as to optimize both electrical conductivity and the electrode stability in acetonitrile and methanol solutions. Solution phase voltammetry of ferrocene is nearly ideal, and the responses are dominated by radial diffusion (slow scan rates) and semi-infinite linear diffusion (fast scan rates). The microelectrodes display high signal-to-noise ratios, good sensitivity, and low detection limits. The response times given by the product of the resistance, R, and capacitance, C, are 7.5 x 10(-4) and 1.4 x 10(-1) s for the Araldite M and PY302-2 composites, respectively. Although these response times are significantly slower than those associated with microelectrodes based on carbon fibers or metal wires, they are sufficient for time-resolved electroanalytical applications. The long response times arise from the large composite resistances, 3.1 x 10(11) and 8.3 x 10(11) Omega cm(-2) for Araldite M and PY302-2, respectively. Voltammetry of ferrocene in the absence of deliberately added supporting electrolyte is also reported. Significantly, indistinguishable slopes and intercepts for a calibration curve of peak current vs ferrocene concentration where 2 < [ferrocene] < 50 microM are obtained in the presence and absence of supporting electrolyte.

Hybrid materials based on lichen–polysiloxane matrices: application as electrochemical sensors

Chemically modified electrodes based on the incorporation of lichens in a rigid matrix obtained by sol–gel process show higher ruggedness and stability than conventional carbon paste electrodes. The lichen ion-exchange properties in the uptake of metal ions are combined with the improved physical characteristics of the synthesized materials. SEM, EIS and AS-LSV techniques have been applied to characterize the sol–gel/lichen materials and to evaluate their ability in the construction of electrochemical devices. The coating of solid graphite electrodes with the lichen–polysiloxane materials by means of a spin-coating process allows the development of robust electrochemical sensors. Such devices exhibit a long-time stability and a suitable electroanalytical performance in the amperometric determination of heavy metal ions in water samples. The impedancimetric response of the sensor towards sodium ions has been also demonstrated.

Effect of the Microelectrode Geometry on the Diffusion Behavior and the Electroanalytical Performance of Hg-Electroplated Iridium Microelectrode Arrays Intended for the Detection of Heavy Metal Traces

Mercury-electroplated iridium microband arrays intended for heavy metal determination purposes were successfully fabricated by means of microelectronic processing techniques. Iridium microbands of 5 μm width each and lengths of 50 μm, 100 μm and 5 mm were investigated and their diffusion behavior and analytical performance compared with those of 5 μm microdisk arrays. The limiting current responses of disk arrays and 5 mm length microband arrays were found to be in good agreement with the radial and hemicylindrical flux expressions, respectively. In contrast, microband arrays having an aspect ratio (length/width) below 50 exhibit diffusion profiles that are characterized by a mixture of both radial and hemicylindrical diffusion components. Such a behavior is thought to be a consequence of edge effects at the extremity of the bands. To perform square-wave anodic stripping voltammetry (SWASV) analysis, the iridium microelectrode arrays were successfully Hg-electroplated and a complete surface coverage was obtained even on microbands having an aspect ratio as high as 1000. The electroanalytical performance of the various Hg-electroplated iridium microelectrode array geometries was evaluated by measuring Cd and Pb ion concentrations in synthetic solutions by means of SWASV over a concentration range as wide as 0.1 to 50 μg L−1. Their detection efficiency (as expressed by the redissolution current normalized to the microelectrodes surface) is shown to be significantly lower than that of microdisk arrays having the same critical dimension (5 μm). Moreover, not only the detection efficiency but also the detection limits were found to decrease as the length of the microbands increases.

Electroanalytical performance of carbon films with near-atomic flatness.

Physicochemical and electrochemical characterization of carbon films obtained by pyrolyzing a commercially available photoresist has been performed. Photoresist spin-coated on to a silicon wafer was pyrolyzed at 1,000 degrees C in a reducing atmosphere (95% nitrogen and 5% hydrogen) to produce conducting carbon films. The pyrolyzed photoresist films (PPF) show unusual surface properties compared to other carbon electrodes. The surfaces are nearly atomically smooth with a root-mean-square roughness of <0.5 nm. PPF have a very low background current and oxygen/carbon atomic ratio compared to conventional glassy carbon and show relatively weak adsorption of methylene blue and anthraquinone-2,6-disulfonate. The low oxygen/carbon ratio and the relative stability of PPF indicate that surfaces may be partially hydrogen terminated. The pyrolyzed films were compared to glassy carbon (GC) heat treated under the same conditions as pyrolysis to evaluate the electroanalytical utility of PPF. Heterogeneous electron-transfer kinetics of various redox systems were evaluated. For Ru(NH3)6(3+/2+), Fe(CN)6(3-/4-), and chlorpromazine, fresh PPF surfaces show electron-transfer rates similar to those on GC, but for redox systems such as Fe3+/2+, ascorbic acid, dopamine, and oxygen, the kinetics on PPF are slower. Very weak interactions between the PPF surface and these redox systems lead to their slow electron-transfer kinetics. Electrochemical anodization results in a simultaneous increase in background current, adsorption, and electron-transfer kinetics. The PPF surfaces can be chemically modified via diazonium ion reduction to yield a covalently attached monolayer. Such a modification could help in the preparation of low-cost, high-volume analyte-specific electrodes for diverse electroanalytical applications. Overall, pyrolysis of the photoresist yields an electrode surface with properties similar to a very smooth version of glassy carbon, with some important differences in surface chemistry.