Indium tin oxide electrodes modified with tris(2,2'-bipyridine-4,4'-dicarboxylic acid) iron(II) and the catalytic oxidation of tris(4,4'-di-tert-butyl-2,2'-bipyridine) cobalt(II)

Indium tin oxide (ITO) electrodes modified by attachment of tris(2,2'-bipyridine-4,4'-dicarboxylic acid) iron(II) are examined. The mode of attachment is believed to be via the COOH functions in a manner similar to attachment of similar carboxylate-containing compounds to TiO2 surfaces. On the surface the complex resides as a stable electrochemically active monolayer. These modified electrodes can efficiently catalyze the oxidation of certain cobalt complexes, specifically, tris(4,4'-di-tert-butyl-2,2'-bipyridine) cobalt(II). On the unmodified ITO surfaces this cobalt complex is essentially electrochemically inert. The catalytic process approaches diffusional control at very slow scan speeds. Also, the electro-catalysis is sufficiently efficient that the peak oxidation current for Co2+, under certain conditions, exceeds the i(p) for the surface oxidation of the adsorbed Fe2+ by >x100 and the current for the uncatalyzed oxidation of Co2+ by considerably more than that.     

Iridium Oxide Film-Enhanced Impedance Immunosensor for Rapid Detection of Carcinoembyronic Antigen

A simple, rapid and sensitive impedance immunosensor based on iridium oxide （IrOx） thin film for the detection of carcinoembyronic antigen （CEA） in human sera has been proposed. Gold electrode was electrochemically modified with IrOx thin film and simultaneously functionalized with protein A （PA） to bind anti-CEA antibodies in an orientated way. It has been found that the antibody loading amount was dependent on the PA concentration and the deposition time of IrOx matrix. Under the optimized experimental conditions, the electron transfer resistances obtained were linearly related to the CEA concentration ranging from 36.2 to 460.0 ng/mL, with a detection limit of 28.0 ng/mL. Analytical results of clinical samples from cancer patients show that the proposed immunoassay is reasonably comparable with the chemiluminescence immunoassay （CLIA）, indicating the feasibility of using the proposed method for CEA immunoassay in clinical laboratory.     

Preparation of a Novel NH2 + Ion Implantation Modified Electrode and Its Study of the Electrochemical Behavior of Hemoglobin

Abstract

A novel functional electrode was obtained by implanting NH₂ ⁺ into ITO film (NH₂/ITO) for the first time. The NH₂/ITO surface showed a better affinity to gold nanoparticles than bare ITO. Gold nanoparticles were deposited on the surface of NH₂/ITO electrode (Au/NH₂/ITO). The Au/NH₂/ITO and NH₂/ITO electrodes were used to observe the electrochemical behavior of Hemoglobin (Hb) immobilized on the electrodes surfaces. The peak current value of Hb immobilized on NH₂/ITO increased compared with on bare ITO while peak current value of Hb immobilized on Au/NH₂/ITO increased compared with on Au/ITO. Linkage between the ‐NH₂ implanted into the ITO film and the ‐COOH of Hb was thought to be the reason for the increase of active Hb coverage on NH₂/ITO compared with bare ITO. Increase of active Hb coverage on Au/NH₂/ITO compare with Au/ITO was attributed to the different amount of gold nanoparticles deposited. Results showed the novel NH₂/ITO and Au/NH₂/ITO electrodes exhibited good stability, reproducibility besides selectivity and sensitivity. The electrode process of Hb immobilized on Au/NH₂/ITO was quasi‐reversible with adsorption. The electrode reaction rate constant k_s and other related constants were determined. X‐ray photoelectron spectroscopy (XPS), field‐emission scanning electron microscopy (FE‐SEM), and impedance spectra were used to characterize the different surfaces.     

Development of an Electrochemical Immunoassay Based on the Use of an Eight‐Electrodes Screen‐Printed Array Coupled with Magnetic Beads for the Detection of Antimicrobial Sulfonamides in Honey

In this work an electrochemical immunoassay, based on a direct competitive assay, was developed using magnetic beads as solid phase and carbon screen‐printed arrays as transducers for the detection of sulfonamides in food matrices such as honey. Magnetic beads coated with protein A were modified by immobilisation of specific antibodies and then the competition between the target analyte and the corresponding analyte‐labelled with an enzyme was carried out; after the immunosensing step, beads were captured by a magnet onto the working surfaces of a screen‐printed eight‐electrodes array for a multiple electrochemical detection. Screen‐printed eight‐electrodes arrays were chosen as transducers due to the possibility to repeat multiple analysis and to test different samples simultaneously. Alkaline Phosphatase (AP) was used as enzyme label and Differential Pulse Voltammetry (DPV) as fast electrochemical technique. Calibration curves demonstrate that the developed electrochemical immunoassay was able to detect this class of drugs in standard solutions at low concentrations (ng/mL levels). The short incubation times (25 min) and the fast electrochemical measurement (10 sec) make of these systems a possible alternative to classic ELISA tests.     

Approaching charge balance in organic light-emitting diodes by tuning charge injection barriers with mixed monolayers

Self-assembled monolayers (SAMs) of binary mixtures of 1-butylphosphonic acid and the trifluoromethyl-terminated analogue (4,4,4-trifluoro-1-butylphosphonic acid) were formed on ITO surfaces to tune the work function of ITO over a range of 5.0 to 5.75 eV by varying the mixing ratio of the two adsorbents. The mixed SAM-modified ITO surfaces were used as the anode in the fabrication of OLED devices with a configuration of ITO/SAM/HTL/Alq3/MX/Al, where HTL was the NPB or BPAPF hole-transporting layer and MX was the LiF or Cs(2)CO(3) injection layer. It was shown that, depending on the HTL or MX used, the maximum device current and the maximum luminance efficiency occurred with anodes of different modifications because of a shift in the point of hole/electron carrier balance. This provides information on the charge balance in the device and points to the direction to improve the performance.     

Label‐free Electrochemical Sensor for Ex‐vivo Monitoring of Alzheimer's Disease Biomarker

The beta‐amyloid (Aβ) peptide was used as an important biomarker for Alzheimer's disease (AD) diagnosis. The development of an accurate, selective, rapid, and highly sensitive technique for detecting of Aβ level is an important issue in biology, and medicine to assess human health risks. Here, gold nanoparticles (Au NPs) with different size were electrochemically deposited onto the indium tin oxide (ITO) substrate in the presence of different molecular weights of surfactants. The modified substrates were used as a high sensitive electrochemical sensor of in‐vitro as well as ex‐vivo monitoring of Aβ based on cyclic voltammetry and square wave voltammetry techniques. Our findings revealed that the modification of ITO electrode with Au NPs could enhance its sensor performance with high sensitivity for low concentration levels of Aβ over a wide linear range with a detection limit of about 20.7 ng/g, which is less than the concentration of insoluble Aβ40 (105.4±40.2 μg/g) in brain of AD induced. In addition, Au NPs/ITO modified electrodes have demonstrated ability to monitor Aβ in the brain extracted samples without any potential interference with other components. Raman spectroscopy has been used to confirm the presence of Aβ in the AD‐induced samples. Thus, it is applicable for analyzing ex‐vivo samples.     

XPS study of the Li intercalation process in sol–gel‐produced V2O5 thin film: influence of substrate and film synthesis modification

We report on the process of lithium intercalation in V₂O₅ thin films deposited onto standard ITO‐coated glass substrates. The films were deposited via a well‐established sol–gel route, and the samples were examined as working electrodes in a range of potentials versus lithium reference electrode. This paper follows up issues arising from parallel spectroscopic characterizations of the films by X‐ray photoelectron spectroscopy (XPS). Specifically, the XPS examination showed that not all of the Li‐ion charge inserted was accounted for by the V(5) to V(4) reduction, but the stoichiometric balance could be maintained only by considering additional oxygens arising from the intercalation procedure, leading to Li₂O formation. In this work, we have examined the possibility that the source of oxygen is the ITO substrate. To this purpose, films of V₂O₅ deposited on silicon substrates have been prepared using the sol–gel process and examined by XPS after electrochemical intercalation/de‐intercalation cycles. We show that in this case a perfect balance between electrochemical charge, inserted Li and reduced vanadium is obtained. A further indication of ITO‐substrate effects was obtained from examination, by the same methods, of some unconventional V₂O₅ films that had been co‐precipitated with a siloxane, designed to provide a template structure. The results obtained from this material imply that a barrier layer is formed at the ITO interface and, therefore, the formation of Li₂O is avoided. The results are discussed in terms of the possible degradation of conventional V₂O₅ on ITO as a result of electrochemically induced interface reactions. Copyright © 2005 John Wiley & Sons, Ltd.     

Electrochemical immunosensor for carcinoembryonic antigen based on antigen immobilization in gold nanoparticles modified chitosan membrane.

A disposable electrochemical immunosensor for carcinoembryonic antigen (CEA) was proposed based on the antigen immobilized in a colloidal gold nanoparticles modified chitosan membrane on the surface of an indium-tin oxide (ITO) electrode. The different membranes were characterized by scanning electron microscope and electrochemical methods. Based on a competitive immunoassay format, the immobilized antigen of the immunosensor was incubated with a horseradish peroxidase (HRP) labeled antibody and sample CEA antigen, and the formed immunoconjugate in the immunosensor was detected by an o-phenylenediamine-H(2)O(2)-HRP electrochemical system. Under the optimal experimental conditions, the electrocatalytic current decreased linearly with the competitive mechanism. CEA could be determined in the linear range from 2.0 to 20 ng/ml with a detection limit of 1.0 ng/ml. The prepared CEA immunosensor is not only economic due to the low-cost ITO electrode obtained from industrial mass production, but is also capable with good stability and reproducibility for batch fabrication.     

Electrochemical immunoassay combined with column liquid chromatography: determination of phenytoin in human serum

A new electrochemical immunoassay combined with column liquid chromatography has been developed for the determination of phenytoin in human serum. Phenytoin was labelled with the electrochemically active nitroxide, and the separation of the free labelled antigen from other electrochemically active compounds in serum was accomplished by the use of gel chromatography. Serum samples were mixed with the antibody and the labelled antigen, incubated for 90 min, and then a 100-microliter aliquot of the mixture was directly injected to the column, which was equipped with an electrochemical detector. With 10 microliter of serum, the smallest detectable concentration of phenytoin was 2 micrograms/ml.     

Different types of electrospun nanofibers and their effect on microfluidic‐based immunoassay

Protein capturing on polymeric substrate of microfluidic devices is a key factor for the fabrication of immunoassay with high sensitivity. In this work, simple and versatile technique of electrospinning was used to produce electrospun nanofibrous membranes (e.NFMs) with high surface area as a substrate for microfluidic‐based immunoassay to increase sensitivity. It was found that the simultaneous use of e.NFM and 1‐Ethylethyl‐3‐(3‐dimethylaminopropyl)‐carbodiimide/N‐Hydroxysuccinimide hydroxysuccinimide as coupling agent has synergic effect on antigen immobilization onto the microchannels. It was found that the oxygen plasma technique for the creation of oxygen containing functional group like carboxyl and hydroxyl causes extreme leakage of solution through the microchannels. Thus, due to capillary effect, it is impossible to use hydrophilic substrate to modify microchannels. In order to compensate this problem, it is propose to utilize other type of polymer for the fabrication of nanofiber to answer this important question that if it is possible to enhance the sensitivity of immunoassay just by changing the polymer type? For this purpose, four different polymers, namely, polycaprolactone, poly lactic‐co‐glycolic acid, poly L‐lactic acid, and polyethersolfone were used as the based material for e.NFM fabrication. Results showed that compared with plain poly (dimethylsiloxane) surface of microchannels, poly lactic‐co‐glycolic acidand poly L‐lactic acid, which inherently contain end‐group of carboxyl in their chemical structure, can improve the protein immobilization, which leads to immunoassay signal enhancement through 1‐ethyl‐3‐(3‐dimethylaminopropyl)‐carbodiimide/N‐hydroxysuccinimide coupling chemistry, significantly.     

Characterization of transparent conducting oxide surfaces using self-assembled electroactive monolayers

The electronic properties of various transparent conducting oxide (TCO) surfaces are probed electrochemically via self-assembled monolayers (SAMs). A novel graftable probe molecule having a tethered trichlorosilyl group and a redox-active ferrocenyl functionality (Fc(CH2) 4SiCl3) is synthesized for this purpose. This molecule can be self-assembled via covalent bonds to form monolayers on various TCO surfaces. On as-received ITO, saturation coverage of 6.6 x 10(-10) mol/cm2 by a close-packed monolayer and an electron-transfer rate of 6.65 s(-1) is achieved after 9 h of chemisorption, as determined by cyclic voltammetry (CV) and synchrotron X-ray reflectivity. With this molecular probe, it is found that O2 plasma-treated ITO has a significantly greater electroactive coverage of 7.9 x 10 (-10) mol/cm2 than as-received ITO. CV studies of this redox SAM on five different TCO surfaces reveal that MOCVD-derived CdO exhibits the greatest electroactive coverage (8.1 x 10(-10) mol/cm2) and MOCVD-derived ZITO (ZnIn2.0Sn1.5O) exhibits the highest electron transfer rate (7.12 s(-1)).     

Sensitive electrochemical immunosensor array for the simultaneous detection of multiple tumor markers

A novel electrochemical immunosensor array for the simultaneous detection of multiple tumor markers was developed by incorporating electrochemically addressing immobilization and one signal antibody strategy. As a proof-of-principle, an eight-electrode array including six carbon screen-printed working electrodes was used as a base array for the analysis of two important tumor markers, carcinoembryonic antigen (CEA) and α-fetoprotein (AFP) and a horseradish peroxidase-labeled antibody was employed as a signal antibody. The immunosensor in the array was fabricated in sequence by covalently coupling the capture antibody onto the surface of the desired working electrode, which was firstly electrochemically addressably grafted with an aminophenyl group by reduction of in situ generated aminophenyl diazonium cation generated from p-phenylenediamine, using glutaraldehyde as cross-linker. This allowed the selective immobilization of the capture antibody at the desired position on a single array via an electrochemical operation. The immunoassay in sandwich mode was performed by specifically binding the targets, second antibodies and one signal antibody to the immunosensor array. The result showed that the steady current density was directly proportional to the concentration of target CEA/AFP in the range from 0.10 to 50 ng mL(-1) with a detection limit of 0.03 ng mL(-1) for CEA and 0.05 ng mL(-1) for AFP (S/N = 3), respectively. This work demonstrates that the employment of an electrochemically addressing method for the fabrication of an immunosensor array and one signal antibody is a promising approach for the determination of multiple tumor markers in clinical samples.     

ITO pattern fabrication of glass platforms for electropolymerization of light sensitive polymer for its conjugation to bioreceptors on a micro-array

We present herein an effective and versatile method to fabricate a micro-patterned structure of conductive polymer, poly(pyrrole-benzophenone), on Indium Tin Oxide (ITO) glass chips for the subsequent photo-immobilization of various bioreceptor, antigens. Such methodologies are based on photolithography of ITO pattern fabrication on non-conductive surfaces, glass slides, and on a photo-active electrogenerated polymer films. The photo-active polymer serves as a substrate platform for the photo-immobilization of the bioreceptor reagents used for subsequent immunoreactions. We were able to show the resolution of electropolymerization on an ITO pattern as well as immobilization of more than one bioreceptor for the simultaneous detection of several analytes. The antigen micro-arrays were tested for sensitivity, specificity, and overall practicality for the simultaneous detection of analyte anti-Cholera Toxin B, anti-Hepatitis B virus surface and core protein antibodies. In addition we used our pattern ITO-poly(pyrrole-benzophenone) micro-array for the detection of serum samples of Hepatitis B virus patients previously screened by a standard hospital detection method.     

Selective response of antigen‐antibody reactions on chiral surfaces modified with 1,2‐diphenylethylenediamine enantiomers

This work reported a comparative analysis of the amperometric responses of antigen‐antibody reactions on two stable chiral surfaces which were modified with 1,2‐diphenylethylenediamine enantiomers. Alpha‐fetoprotein antibody and antigen (anti‐AFP and AFP) were selected as model systems. First, (1R,2R)‐1,2‐diphenylethylenediamine or (1S,2S)‐1,2‐diphenylethylenediamine was modified on the gold surface of the electrode through amide linkage to construct chiral surfaces. Then, anti‐AFP was immobilized on the chiral electrode surface by electrostatic and hydrogen bonding interactions. The electrochemical characteristics of the modified electrodes were studied via cyclic voltammetry. The selective current responses of antigen‐antibody reactions on chiral electrode surfaces for different incubation time and varying AFP concentrations were monitored. The antigen‐antibody reactions were greatly influenced by the chirality of 1,2‐diphenylethylenediamine enantiomers, and the amperometric responses obtained from the (1S,2S)‐1,2‐diphenylethylenediamine modified electrode was obviously stronger than that from the (1R,2R)‐1,2‐diphenylethylenediamine modified electrode. Such work may not only offer valuable reference to the research of chiral drugs, but also help to comprehend the high selectivity of chiral molecular species in biosystems. Copyright © 2011 John Wiley & Sons, Ltd.     

Electrochemical Synthesis of Chitosan‐co‐polyaniline/WO3⋅nH2O Composite Electrode for Amperometric Detection of NO2 Gas

An electrode of hydrated tungsten oxide (WO₃?nH₂O) embedded chitosan‐co‐polyaniline (CHIT‐co‐PANI) composite was electrochemically prepared on an indium tin oxide (ITO) coated glass surface using mineral acid as a supporting electrolyte. The resulting CHIT‐co‐PANI/WO₃?nH₂O/ITO electrode was characterized using ultraviolet‐visible spectroscopy (UV‐vis), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV), and scanning electron microscopy (SEM). The composite electrode exhibited a three‐dimensional nanofibrous structure with the diameter of the nanofibers ranging from 20 to 100 nm. The CHIT‐co‐PANI/WO₃?nH₂O/ITO electrode allowed for the low potential detection of NO₂ gas in acidic medium. The NO₂ gas sensing characteristics were studied by measuring change in the current with respect to concentration and time. Using the CHIT‐co‐PANI/WO₃?nH₂O/ITO electrode, NO₂ gas was detected electrochemically without interference at pH 2.0 and 0.25 V vs. Ag/AgCl. The current of the electrochemical cell with the CHIT‐co‐PANI/WO₃?nH₂O/ITO electrode decreased linearly with an increase in NO₂ gas concentration in a range from 100 to 500 ppb with a response time of eight seconds.     

Surface modification and characterization of indium-tin oxide for organic light-emitting devices

In this work, we used different treatment methods (ultrasonic degreasing, hydrochloric acid treatment, and oxygen plasma) to modify the surfaces of indium-tin oxide (ITO) substrates for organic light-emitting devices. The surface properties of treated ITO substrates were studied by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), sheet resistance, contact angle, and surface energy measurements. Experimental results show that the ITO surface properties are closely related to the treatment methods, and the oxygen plasma is more efficient than the other treatments since it brings about smoother surfaces, lower sheet resistance, higher work function, and higher surface energy and polarity of the ITO substrate. Moreover, polymer light-emitting electrochemical cells (PLECs) with differently treated ITO substrates as device electrodes were fabricated and characterized. It is found that surface treatments of ITO substrates have a certain degree of influence upon the injection current, brightness, and efficiency, but hardly upon the turn-on voltages of current injection and light emission, which are in agreement with the measured optical energy gap of the electroluminescent polymer. The oxygen plasma treatment on the ITO substrate yields the best performance of PLECs, due to the improvement of interface formation and electrical contact of the ITO substrate with the polymer blend in the PLECs.     

Electroanalytical Properties of ITO Electrodes Modified with Environment‐Sensitive Poly(N‐isopropylacrylamide) Gel and Prussian Blue

It has been shown that ITO electrodes could be modified with a volume‐phase‐transition gel based on poly(N‐isopropylacrylamide) cross‐linked with N,N′‐methylenebisacrylamide. Prussian blue (PB) was deposited electrochemically inside the gel while glucose oxidase was added at the time of electropolymerization. The electrocatalytic activity of glucose oxidase towards the oxidation of glucose (measured as the reduction current of hydrogen peroxide) was strongly depressed by the shrinking process. Since the volume phase transition triggered by the temperature change is reversible the obtained change in the enzyme activity may be useful for getting a switchable system.     

Preparation and characterization of dense films of poly(amidoamine) dendrimers on indium tin oxide

Indium tin oxide (ITO) substrates were modified with a layer of poly(amidoamine) (PAMAM) dendrimers to change their surface properties and, in particular, the substrates' work function. The functionalization procedure involved the electrostatic adsorption of positively charged PAMAM dendrimers of generation five onto negatively polarized ITO surfaces. Three different PAMAM dendrimers were used: PAMAM-NH2 and PAMAM-OH with terminal amine and hydroxyl groups, respectively, as well as Q-PAMAM-NH2, which had been prepared from PAMAM-NH2 by quaternization of the dendrimer's terminal and internal amine groups with methyl iodide. The resulting organic films were analyzed by contact angle goniometry, X-ray photoelectron spectroscopy, ellipsometry, and Kelvin probe force microscopy to confirm the presence of a dense layer. A Langmuir isotherm was derived from surface densities of fluorescence-labeled PAMAM-NH2 dendrimers from which we deduced an equilibrium binding constant, K(eq), of (1.3 +/- 0.3) x 10(5) M(-1). Kelvin probe measurements of the contact potential difference revealed a high reduction of the work function from 4.9 eV for bare ITO to 4.3 eV for ITO with a dense film of PAMAM-NH2 of generation five. PAMAM-OH and Q-PAMAM-NH2 resulted in slightly smaller work function changes. This study illustrates that the work function of ITO can be tuned by adlayers composed of PAMAM dendrimers.     

Homogenous electrogenerated chemiluminescence immunoassay for human immunoglobulin G using N-(aminobutyl)-N-ethylisoluminol as luminescence label at gold nanoparticles modified paraffin-impregnated graphite electrode

A homogeneous electrogenerated chemiluminescence (ECL) immunoassay for human immunoglobulin G (hIgG) has been developed using a N-(aminobutyl)-N-ethylisoluminol (ABEI) as luminescence label at gold nanoparticles modified paraffin-impregnated graphite electrode (PIGE). ECL emission was electrochemically generated from the ABEI-labeled anti-hIgG antibody and markedly increased in the presence of hIgG antigen due to forming a more rigid structure of the ABEI moiety. The concentration of hIgG antigen was determined by the increase of ECL intensity at a gold nanoparticles modified PIGE. It was found that the ECL intensity of ABEI in presence of hydrogen peroxide was dramatically enhanced at gold nanoparticles modified PIGE in neutral aqueous solution and the detection limit of ABEI was 2 x 10(-14)mol/L (S/N=3). The integral ECL intensity was linearly related to the concentration of hIgG antigen from 3.0 x 10(-11) to 1.0 x 10(-9)g/mL with a detection limit of 1 x 10(-11)g/mL (S/N=3). The relative standard deviation was 3.1% at 1.0 x 10(-10)g/mL (n=11). This work demonstrates that the enhancement of the sensitivity of ECL and ECL immunoassay at a nanoparticles modified electrode is a promising strategy.     

Evaluation of the adhesion properties of inorganic materials with high surface energies

With the aim of checking the validity of methods for characterizing the adhesion between inorganic materials with high surface energies, the properties of the adhesion between an inorganic material (indium tin oxide (ITO)) and model surfaces with various surface energies (Cl-, NH2-, CH(3)-, and CF3-functionalized surfaces) were evaluated using atomic force microscopy (AFM) and the Johnson-Kendall-Roberts (JKR) apparatus. For this purpose, the AFM tip and the JKR lens were modified with ITO using radio frequency (rf) magnetron sputtering. The work of adhesion between the ITO coating and each model surface was estimated using AFM and the JKR apparatus and compared with the result obtained from contact angle measurements. The adhesion forces determined from the force-displacement curves (AFM) were found to agree with the predictions of the Derjaguin-Muller-Toporov (DMT) theory. The JKR equation used in the interpretation of the JKR experiments was modified by taking into account the differences between the surface and bulk moduli of the ITO-coated poly(dimethylsiloxane) (PDMS) lens. The ratio of the surface modulus to the bulk modulus we used in this modified JKR equation was obtained by determining the slope of the attracting part of the force-displacement curve. The values of the work of adhesion calculated using the modified JKR equation were also found to agree with the values obtained from contact angle measurements. We conclude that the two methods using AFM and the JKR apparatus can be used in the evaluation of the work of adhesion between inorganic materials with high surface energies such as metal and metal oxide surfaces.