Gustavo A. Rivas

Carbon nanotubes for electrochemical biosensing.

The aim of this review is to summarize the most relevant contributions in the development of electrochemical (bio)sensors based on carbon nanotubes in the last years. Since the first application of carbon nanotubes in the preparation of an electrochemical sensor, an increasing number of publications involving carbon nanotubes-based sensors have been reported, demonstrating that the particular structure of carbon nanotubes and their unique properties make them a very attractive material for the design of electrochemical biosensors. The advantages of carbon nanotubes to promote different electron transfer reactions, in special those related to biomolecules; the different strategies for constructing carbon nanotubes-based electrochemical sensors, their analytical performance and future prospects are discussed in this article.

Carbon nanotubes paste electrode

Abstract The performance of carbon nanotubes paste electrodes (CNTPE) prepared by dispersion of multi-wall carbon nanotubes (MWNT) within mineral oil is described. The resulting electrode shows an excellent electrocatalytic activity toward ascorbic acid, uric acid, dopamine, 3,4-dihydroxyphenylacetic acid (dopac) and hydrogen peroxide. These properties permit an important decrease in the overvoltage for the oxidation of ascorbic acid (230 mV), uric acid (160 mV) and hydrogen peroxide (300 mV) as well as a dramatic improvement in the reversibility of the redox behavior of dopamine and dopac, in comparison with the classical carbon (graphite) paste electrodes (CPE). The substantial decrease in the overvoltage of the hydrogen peroxide reduction (400 mV) associated with a successful incorporation of glucose oxidase (GOx) into the composite material, allow the development of a highly selective and sensitive glucose biosensor without using any metal, redox mediator or anti-interference membrane. No interference was observed at −0.100 V even for large excess of ascorbic acid, uric acid and acetaminophen. A linear response up to 30 mM (5.40 g l −1 ) glucose with a detection limit of 0.6 mM (0.11 g l −1 ) were obtained with the CNTPE modified with 10% w/w GOx. Such an excellent performance of CNTPE toward hydrogen peroxide, represents a very good alternative for developing other enzymatic biosensors.

Glucose biosensors based on the immobilization of copper oxide and glucose oxidase within a carbon paste matrix

The performance of amperometric glucose biosensors based on the dispersion of glucose oxidase (GOx) and copper oxide within a classical carbon (graphite) paste composite is reported in this work. Copper oxide promotes an excellent electrocatalytic activity towards the oxidation and reduction of hydrogen peroxide, allowing a large decrease in the oxidation and reduction overpotentials, as well as an important enhancement of the corresponding currents. Therefore, it is possible to perform the glucose biosensing at low potentials where there is no interference even in large excess of ascorbic acid, uric acid or acetaminophen. The influence of the copper oxide and glucose oxidase content in the paste on the analytical performance of the bioelectrode is discussed. The resulting biosensor shows a fast response, a linear relationship between current and glucose concentration up to 1.35 x 10(-2) M (2.43 g L(-1)) and a detection limit of 2.0 x 10(-5) M. The effect of the presence of the enzyme in the composite material on the dispersion of the copper oxide particles is also discussed.

Amperometric determination of dopamine on an enzymatically modified carbon paste electrode

The amperometric determination of dopamine under controlled convective conditions on an enzymatically modified carbon paste electrode was studied using potato tissue as a source of polyphenol oxidase. Enzymatic kinetic constants and substrate diffusional-resistance parameters were determined and an analysis of the most common interferents was made. It is concluded that the electrode is suitable for the quantification of dopamine with a detection limit as low as 2.5 × 10−6 M when the hydrodynamic conditions are carefully controlled. The electrode is active towards dopac, ascorbic acid and pyrocatechol but not l-tyrosine, l-dopa, homovanillic acid, adrenaline, normetanephrine and vanilmandelic acid.

Label-free electrochemical aptasensor for the detection of lysozyme

This work reports the advantages of a label free electrochemical aptasensor for the detection of lysozyme. The biorecognition platform was obtained by the adsorption of the aptamer on the surface of a carbon paste electrode (CPE) previously blocked with mouse immunoglobulin under controlled-potential conditions. The recognition event was detected from the decrease in the guanine and adenine electro-oxidation signals produced as a consequence of the molecular interaction between the aptamer and lysozyme. The biosensing platform demonstrated to be highly selective even in the presence of large excess (9-fold) of bovine serum albumin, cytochrome C and myoglobin. The reproducibility for 10 repetitive determinations of 10.0 mg L(-1) lysozyme solution was 5.1% and 6.8% for guanine and adenine electro-oxidation signals, respectively. The detection limits of the aptasensor were 36.0 nmol L(-1) (if considering guanine signal) and 18.0 nmol L(-1) (if taking adenine oxidation current). This new sensing approach represents an interesting and promising alternative for the electrochemical quantification of lysozyme.

Amperometric determination of dopamine on vegetal-tissue enzymatic electrodes. Analysis of interferents and enzymatic selectivity

Abstract The amperometric determination of phenol and catechol derivatives in general, and dopamine in particular, is studied, using enzymatically modified carbon paste electrodes. Both the electrochemical behaviour of the substrates and the enzymatic selectivity of polyphenol oxidase (PPO) according to the source are taken into account. In this way, the quantification of dopamine in the presence of metabolically related compounds is carried out with reasonable accuracy. Fresh tissues of pear, peach, mushroom and potato are used as the enzymatic source. For fresh mushroom PPO, apparent Michaelis-Menten constants ( K ′ M ) for each substrate are determined electrochemically. Purified mushroom PPO is used for comparative purposes. The effect of the substituent group of catechol derivatives on the enzymatic affinity was also analysed.

Analytical Performance of a Glucose Biosensor Prepared by Immobilization of Glucose Oxidase and Different Metals into a Carbon Paste Electrode

Enzymatic metallized carbon paste electrodes prepared by incorporation of mixtures of different metals into the paste offer a substantial decrease in the overvoltage for hydrogen peroxide oxidation and reduction. Dramatic improvements in the sensitivity and selectivity for glucose determination were obtained after the addition of iridium into carbon paste electrodes (CPE) containing glucose oxidase and palladium, copper or ruthenium. In all cases a synergistic effect was observed with a large enhancement in sensitivity obtained specially in the case of palladium-composite materials. The improvement in selectivity was more evident in the case of copper and palladium carbon paste enzymatic electrodes containing iridium where even in the presence of large excess of ascorbic acid, uric acid and acetaminophen, no interference was observed. A linear relationship between current and glucose concentration was obtained up to 1.5×10−2 M (2.7 g/L) glucose in the case of Pd(2.65%)-Ir(8.00%)-GOx(7.00%)-CPE. The effect of metals and enzyme content on the analytical performance of the bioelectrodes is analyzed.

New biosensing platforms based on the layer-by-layer self-assembling of polyelectrolytes on Nafion/carbon nanotubes-coated glassy carbon electrodes.

We are proposing for the first time the use of a Nafion/multi-walled carbon nanotubes dispersion deposited on glassy carbon electrodes (GCE) as a new platform for developing enzymatic biosensors based on the self-assembling of a chitosan derivative and different oxidases. The electrodes are obtained by deposition of a layer of Nafion/multi-wall carbon nanotubes dispersion on glassy carbon electrodes, followed by the adsorption of a chitosan derivative as polycation and glucose oxidase, l-aminoacid oxidase or polyphenol oxidase, as polyanions and biorecognition elements. The optimum configuration for glucose biosensors has allowed a highly sensitive (sensitivity=(0.28+/-0.02)muAmM(-1), r=0.997), fast (4s in reaching the maximum response), and highly selective (0% interference of ascorbic acid and uric acid at maximum physiological levels) glucose quantification at 0.700V with detection and quantification limits of 0.035 and 0.107mM, respectively. The repetitivity for 10 measurements was 5.5%, while the reproducibility was 8.4% for eight electrodes. The potentiality of the new platform was clearly demonstrated by using the carbon nanotubes/Nafion layer as a platform for the self-assembling of l-aminoacid oxidase and polyphenol oxidase. Therefore, the platform we are proposing here, that combines the advantages of nanostructured materials with those of the layer-by-layer self-assembling of polyelectrolytes, opens the doors to new and exciting possibilities for the development of enzymatic and affinity biosensors using different transdution modes.

Immobilization of DNA on glassy carbon electrodes for the development of affinity biosensors

The adsorption and electrooxidation of nucleic acids on glassy carbon electrodes are evaluated by using chronopotentiometric stripping analysis. The influence of electrochemical pretreatments, supporting electrolyte, halides and monovalent cations levels as well as the role of the oligonucleotide length and composition, accumulation potential and time on the adsorption and further electrooxidation of oligo(dG)(11) and oligo(dG)(21) are discussed. The adsorption behavior of single and double stranded calf thymus DNA on untreated glassy carbon electrodes is also evaluated. Trace (microg/l) levels of the oligonucleotides and polynucleotides can be readily detected following short accumulation periods with detection limits of 25, 60, 126 and 219 microg/l for oligo(dG)(21), oligo(dG)(11), ss and ds calf thymus DNA, respectively. The confined DNA layers demonstrated to be stable in air, in 0.200 M acetate buffer pH 5.00 and in 0.020 M phosphate buffer pH 7.40+0.50 M NaCl.

Selective detection of dopamine in the presence of ascorbic acid using carbon nanotube modified screen-printed electrodes

This work reports on the performance of carbon nanotube modified screen-printed electrodes (SPE-MWCNT) for the selective determination of dopamine (DA) in the presence of ascorbic acid (AA) by adsorptive stripping voltammetry (AdSV). Several operating conditions and parameters were examined including the electrochemical pre-treatment and the previous AA interaction and DA accumulation in the presence AA at physiological conditions. Under the chosen conditions, DA peak current of differential pulse voltammograms increases linearly with DA concentration in the range of 5.0 x 10(-8) to 1.0 x 10(-6) mol L(-1) with a limit of detection of 1.5 x 10(-8) mol L(-1) in connection with 600s accumulation time. The sensitivity obtained for DA was independent from the presence or absence of AA; therefore, the proposed method can be readily applied to detect DA in real samples. The proposed methodology was successfully used for the quantification of DA in urine samples.