Investigation of the electrochemical and electrocatalytic behavior of single-wall carbon nanotube film on a glassy carbon electrode

Rapid and cost-effective detection of sequence-specific DNA by monitoring the electrochemical response of 2'-deoxyguanosine 5'-triphosphate in a PCR sample

This study describes a novel strategy for rapid and cost-effective detection of sequence-specific DNA based upon the essential utility of the polymerase chain reaction (PCR) and electrochemical technologies. A dramatic enhancement of the anodic peak current (i(pa)) and a visible decrease of overpotential towards free 2'-deoxyguanosine 5'-triphosphate (dGTP) could be realized on a glassy carbon electrode modified with short single-walled carbon nanotubes (S-SWNT/GCE). Thereby, the concentration of the free dGTP in the PCR sample mixture could be determined sensitively. The i(pa) of the free dGTP decreased remarkably after a successful PCR amplification owing to the participation of the free dGTP as one of the reactive substrates for the PCR products, namely dsDNA. Based upon this response change of the free dGTP before and after incorporation in PCR, a novel method aiming at detecting PCR results was established. One transgenic maize sample as a model was successfully detected by employing the specific sequences of 35S promoter from cauliflower mosaic virus (CaMV35S) gene and nopaline synthase (NOS) gene as markers. The result was in good accordance with that obtained with gel electrophoresis.

Highly sensitive amperometric immunosensor for detection of Plasmodium falciparum histidine-rich protein 2 in serum of humans with malaria: comparison with a commercial kit

A disposable amperometric immunosensor was developed for the detection of Plasmodium falciparum histidine-rich protein 2 (PfHRP-2) in the sera of humans with P. falciparum malaria. For this purpose, disposable screen-printed electrodes (SPEs) were modified with multiwall carbon nanotubes (MWCNTs) and Au nanoparticles. The electrodes were characterized by cyclic voltammetry, scanning electron microscopy, and Raman spectroscopy. In order to study the immunosensing performances of modified electrodes, a rabbit anti-PfHRP-2 antibody (as the capturing antibody) was first immobilized on an electrode. Further, the electrode was exposed to a mouse anti-PfHRP-2 antibody from a serum sample (as the revealing antibody), followed by a rabbit anti-mouse immunoglobulin G-alkaline phosphatase conjugate. The immunosensing experiments were performed on bare SPEs, MWCNT-modified SPEs, and Au nanoparticle- and MWCNT-modified SPEs (Nano-Au/MWCNT/SPEs) for the amperometric detection of PfHRP-2 in a solution of 0.1 M diethanolamine buffer, pH 9.8, by applying a potential of 450 mV at the working electrode. Nano-Au/MWCNT/SPEs yielded the highest-level immunosensing performance among the electrodes, with a detection limit of 8 ng/ml. The analytical results of immunosensing experiments with human serum samples were compared with the results of a commercial Paracheck Pf test, as well as the results of microscopy. The specificities, sensitivities, and positive and negative predictive values of the Paracheck Pf and amperometric immunosensors were calculated by taking the microscopy results as the "gold standard." The Paracheck Pf kit exhibited a sensitivity of 79% (detecting 34 of 43 positive samples; 95% confidence interval [CI], 75 to 86%) and a specificity of 81% (correctly identifying 57 of 70 negative samples; 95% CI, 76 to 92%), whereas the developed amperometric immunosensor showed a sensitivity of 96% (detecting 41 of 43 positive samples; 95% CI, 93 to 98%) and a specificity of 94% (correctly identifying 66 of 70 negative samples; 95% CI, 92 to 99%). The developed method is more sensitive and specific than the Paracheck Pf kit.

Surface design of carbon nanotubes for optimizing the adsorption and electrochemical response of analytes

Carbon nanotubes (CNTs) from different sources were dissolved in water with high solubility by Congo red (CR) via strong noncovalent pi-stacking interactions. The resulting CNTs were capable of forming uniform, compact, stable films on various substrates. This provided a chance to explore the relationship between the surface property of CNTs and the adsorptive behavior of analytes on CNTs without considering the influence of film structures or free additives. Electrochemical behaviors of several small biomolecules and glucose oxidase (GOD) on various CR-functionalized CNT films were examined. The results showed that both the hydrophobic structural defect sites and the hydrophilic oxygen-containing groups were the electroactive sites of CNTs, which was further proven by UV-vis and FTIR spectra. Moreover, the surface properties of CNTs could be conveniently designed by simple pretreatments for optimizing the adsorption and the electrochemical response of analytes. For instance, the hydrophobic defect sites created during the growth or the workup of CNTs were favorable to the adsorption and the electrochemical response of hydrophobic analytes, whereas the hydrophilic oxygen-containing groups produced by acid treatment facilitated the stable adsorption and the direct electrochemistry of redox proteins.

Effective cell capture with tetrapeptide-functionalized carbon nanotubes and dual signal amplification for cytosensing and evaluation of cell surface carbohydrate

A novel electrochemical cytosensing strategy was designed based on the specific recognition of integrin receptors on a cell surface to arginine-glycine-aspartic acid-serine (RGDS)-functionalized single-walled carbon nanotubes (SWNTs). The covalent conjugation of the RGDS tetrapeptide to SWNTs was proved with Raman and FT-IR spectra. The conjugated RGDS showed a predominant ability to capture cells on the electrode surface by the specific combination of RGD domains with integrin receptors. With the use of BGC-823 human gastric carcinoma cells (BGC cells) as a model, the cell surface mannosyl groups could specifically bind with horseradish peroxidase labeled concanavalin A, producing an electrochemical cytosensor. On the basis of the dual signal amplification of SWNTs and enzymatic catalysis, the cytosensor could respond down to 620 cells mL (-1) of BGC cells with a linear calibration range from 1.0 x 10 (3) to 1.0 x 10 (7) cells mL (-1), showing very high sensitivity. The dual signal amplification could be further used to evaluate the mannosyl groups on the cell surface, and the mannosyl groups on a single living intact BGC cell were detected to correspond to 5.3 x 10 (7) molecules of mannose. This strategy presents a promising platform for highly sensitive cytosensing and convenient evaluation of surface carbohydrates on living cells.

Synthesis and electrochemical probing of water-soluble poly(sodium 4-styrenesulfonate-co-acrylic acid)-grafted multiwalled carbon nanotubes

Water-soluble poly(sodium 4-styrenesulfonate-co-acrylic acid)-grafted multiwalled carbon nanotubes (MWNT-g-P(SSS-co-AA)) with core-shell nanostructure were successfully synthesized by in situ free radical copolymerization of sodium 4-strenesulfonate (SSS) and acrylic acid (AA) in the presence of MWNTs terminated with vinyl groups; their structure was characterized by FTIR, (1)H NMR, Raman, TGA and TEM. The results showed that the thickness and content of the copolymer layer grafted onto the MWNT surface are about 7-12 nm and 82.3%, respectively. The P(SSS-co-AA) covalently grafted on MWNTs provides MWNT-g-P(SSS-co-AA) with good hydrophilicity and solubility in water. Then a novel MWNT-g-P(SSS-co-AA)-modified glassy carbon electrode was fabricated by coating; its electrochemical properties were evaluated by electrochemical probe of K(3)[Fe(CN)(6)], and its catalytic behaviors to the electrochemical oxidation processes of dopamine (DA) and serotonin (5-HT) were investigated. Since the MWNT-g-P(SSS-co-AA)-modified electrode possesses strong electron transfer capability, high electrochemical activity and catalytic ability, it can be used in sensitive, selective, rapid and simultaneous monitoring of biomolecules.

Part I: recent developments in nanoelectrodes for biological measurements

Biosensors are a type of analytical device that use biological molecules to monitor biorecognition events and interactions. Coupled with the progress in nanotechnologies over recent years, the development of a nanobiosensor based on individual nanoelectrodes and nanoelectrode arrays or nanoelectrode ensembles offers unprecedented avenues for screening and detection at ultrahigh sensitivities. These capabilities provide the basis for a paradigmatic change in biomedical diagnostics and treatment. In this review, we highlight recent developments in nanoelectrode platforms and their suitability for integrating with biological components for the fabrication of ultrasensitive nanobiosensors.

Assembly of polyoxometalates on carbon nanotubes paste electrode and its catalytic behaviors

Carbon nanotubes paste (CNTP) electrode was prepared with multi-walled carbon nanotubes and methyl silicone oil. Polyoxometalates (POMs) were assembled on the electrode surface with different methods, and investigated by cyclic voltammetry and Raman spectroscopy. Experiments showed that POMs/CNTP electrode prepared by direct method had better performance. K6P2Mo18O62 x 14 H2O (P2Mo18) assembled CNTP electrode (P2Mo18/CNTP) electrode possessed good reversibility and could catalyze the reduction of bromate and iodate in 0.1 M H2SO4 solution. Further, the multilayer films of P2Mo18 assembled CNTP electrodes were fabricated by layer-by-layer technique, which showed higher electrocatalytic activities. All these POMs assembled CNTP electrodes prepared exhibited good stability.

Electrocatalytic oxidation of dopamine at an ionic liquid modified carbon paste electrode and its analytical application

A room-temperature ionic liquid N-butylpyridinium hexafluorophosphate was used as a binder to construct an ionic liquid modified carbon paste electrode, which was characterized by scanning electron microscopy and electrochemical impedance spectroscopy. The ionic liquid carbon paste electrode (IL-CPE) showed enhanced electrochemical response and strong analytical activity towards the electrochemical oxidation of dopamine (DA). A pair of well-defined quasireversible redox peaks of DA appeared, with the redox peaks located at 215 mV (E (pa)) and 151 mV (E (pc)) (vs. the saturated calomel electrode, SCE) in pH 6.0 phosphate buffer solution. The formal potential (E (0')) was calculated as 183 mV (vs. SCE) and the peak-to-peak separation as 64 mV. The electrochemical behavior of DA on the IL-CPE was carefully investigated. Under the optimal conditions, the anodic peak currents increased linearly with the concentration of DA in the range 1.0 x 10(-6)-8.0 x 10(-4) mol/L and the detection limit was calculated as 7.0 x 10(-7) mol/L (3sigma). The interferences of foreign substances were investigated and the proposed method was successfully applied to the determination of DA injection samples. The IL-CPE fabricated was sensitive, selective and showed good ability to distinguish the coexisting ascorbic acid and uric acid.

Binding of acetylcholinesterase to multiwall carbon nanotube-cross-linked chitosan composite for flow-injection amperometric detection of an organophosphorous insecticide

A novel method for immobilization of acetylcholinesterase (AChE) by binding covalently to a cross-linked chitosan-multiwall carbon nanotube (MWNT) composite is described. In addition a sensitive, fast, cheap and automatizable flow injection detection of an organophosphorous insecticide was developed. The MWNTs were homogeneously distributed in the chitosan membrane which showed a homogeneous porous structure. The immobilized AChE could catalyze the hydrolysis of acetylthiocholine with a K(M)app value of 177 microM to form thiocholine, which was then oxidized to produce detectable signal in a linear range of 1.0-500 microM and fast response. MWNTs could catalyze the electrooxidation of thiocholine, thus increasing detection sensitivity. Based on the inhibition of an organophosphorous insecticide on the enzymatic activity of AChE, using Sulfotep as a model compound, the conditions for the flow-injection detection of the insecticide were optimized. Both biocompatibility of chitosan and inherent conductive properties of MWNTs favored the detection of the insecticide from 1.5 to 80 microM along with good stability and reproducibility. 95 % reactivation from inhibited AChE could be regenerated by using 2-pyridinealdoxime methiodide within 15 min for 15 times. The detection of Sulfotep samples exhibited satisfactory results. The proposed flow-injection analysis device can be applied to automated determination and characterization of enzyme inhibitors.

Amperometric glucose sensor based on catalytic reduction of dissolved oxygen at soluble carbon nanofiber

This work shows excellent catalytic activity of soluble carbon nanofiber (CNF), which was obtained with a simple nitric acid treatment, toward the electroreduction of dissolved oxygen at a low operating potential. Thus the CNF was applied in the construction of amperometric biosensors for oxidase substrates using glucose oxidase as a model. The good dispersion of CNF led to convenient preparation and acceptable repeatability of the proposed sensors. UV-vis spectra, Fourier transform infrared spectra, X-ray photoelectron spectra and titration curves demonstrated that the good dispersion resulted from the large numbers of surface oxygen-rich groups produced in the treatment process. The membrane of CNF showed good stability and provided fast response to dissolved oxygen with a linear range from 0.1 to 78 microM and detection limit of 0.07 microM. The proposed glucose biosensor could monitor glucose ranging from 10 to 350 microM with detection limit of 2.5 microM and sensitivity of 36.3 nA cm(-2) microM(-1). The coefficients of variation for intra-assay were 4.7 and 3.2% at glucose concentrations of 20 and 210 microM, respectively. The use of a low operating potential (-0.3 V) and Nafion membrane produced good selectivity toward the glucose detection. CNF-based biosensors would provide wide range of bioelectrochemical applications in different fields.