Carbon Nanotubes Modified Edge Plane Research Articles

A novel nanogold–single wall carbon nanotube modified sensor for the electrochemical determination of 8-hydroxyguanine, a diabetes risk biomarker

An electrochemical study of the oxidation of 8-hydroxyguanine (8-OH-Gua) at gold nanoparticles attached to single walled carbon nanotube modified edge plane pyrolytic graphite electrode (AuNP-SWCNT/EPPGE) has been carried out to develop a method for the self diagnosis of diabetes. The level of 8-OH-Gua, an important biomarker of oxidative DNA damage, is higher in urine of diabetic patients than control subjects. A detailed comparison has been made between the square wave voltammetric (SWV) response of SWCNT/EPPGE and AuNP-SWCNT/EPPGE towards the oxidation of 8-OH-Gua in respect of several essential analytical parameters viz. sensitivity, detection limit, peak current and peak potential. The AuNP-SWCNT/EPPGE exhibited a well defined anodic peak at potential of ~221mV for the oxidation of 8-OH-Gua as compared to ~312mV using SWCNT/EPPGE at pH=7.2. Under optimized conditions linear calibration curve for 8-OH-Gua is obtained over a concentration range of 0.01–10.0nM in phosphate buffer solution (PBS) of pH=7.2 with detection limit and sensitivity of 5.0 (±0.1) pM and 4.9 (±0.1) μAnM−1, respectively. The oxidation of 8-OH-Gua occurred in a pH dependent process and the electrode reaction followed adsorption controlled pathway. The electrode exhibited an efficient catalytic response with good reproducibility and stability. The method has been found selective and successfully implemented for the determination of 8-OH-Gua in urine samples of diabetic patients.

Electrochemical mechanism and sensitive assay of antiretroviral drug Abacavir in biological sample using multiwalled carbon nanotube modified pyrolytic graphite electrode

Multiwalled carbon nanotube modified edge plane pyrolytic graphite electrode (MWCNT/EPPGE) was developed and implemented for the determination of antiretroviral drug Abacavir using differential pulse adsorptive stripping voltammetry (DP AdSV). Cyclic voltammogram showed two oxidation peaks located at+0.91V and+1.10V on (MWCNT/EPPGE). Dependency of peak potential and peak current on pH was investigated as details. The oxidation potentials affected by the pH indicating protons are involved in the electrochemical oxidation of Abacavir. Mass transport to the electrode surface was found as a combination of diffusion and adsorption which was concluded by studying the potential scan rate dependency of both peak currents. The oxidation mechanism was proposed using the obtained data and discussed. A large enhancement in both of the peak currents was observed with applying an accumulation step presenting the effect of adsorption. Peak currents showed a linear relation upon the Abacavir concentration within a range of 1×10−7–2×10−5M with (r=0.999) for both peak responses. The method was fully validated related with selectivity, sensitivity, precision and accuracy studies. Abacavir was also determined with the proposed method in its pharmaceutical dosage forms and human serum samples. No interferences from the excipients of the dosage form or endogenous substances from biological material were found.

Simultaneous determination of epinephrine and norepinephrine in human blood plasma and urine samples using nanotubes modified edge plane pyrolytic graphite electrode

The simultaneous determination of catecholamines – epinephrine and norepinephrine by square wave voltammetry (SWV) at physiological pH 7.2 is reported using multi-walled carbon nanotubes modified edge plane pyrolytic graphite electrode (MWNT/EPPGE). A broad bump at ∼250 mV is appeared for the oxidation of epinephrine (EP) and norepinephrine (NE) at bare EPPGE whereas at MWNT/EPPGE two well-separated peaks at ∼150 and ∼215 mV are appeared for the oxidation of EP and NE, respectively. The oxidation peak current of both the neurotransmitters also increased significantly along with the negative shift of peak potentials using MWNT/EPPGE. The oxidation of both compounds occurred in a pH dependent, 2e and 2H + process and the electrode reaction followed diffusion controlled pathway. Linear calibration curves were obtained for epinephrine and norepinephrine in the range 0.5–100 nM with limits of detection 0.15 × 10 −9 and 0.90 × 10 −10 M, respectively. The developed protocol is implemented for the simultaneous determination of epinephrine and norepinephrine in blood plasma and urine samples of smokers as well as in athletes.

A Sensitive Voltammetric Sensor for Detecting Betamethasone in Biological Fluids

A rapid and sensitive voltammetric sensor based on reduction of betamethasone has been developed using single wall carbon nanotube modified edge plane pyrolytic graphite electrode (SWNT/EPPGE). The reduction of betamethasone occurred in a well-defined, pH dependent peak. Linear calibration curve was obtained in the range 1 to 25 nM in 1.0 M phosphate buffer solution (PBS) of pH 7.2 with the limit of detection (3sigma / slope) as 0.50 nM. The analytical utility of the developed method has been demonstarted by sensing the drug in human body fluids and for the determination of betamethasone content in several commercially available pharmaceutical preparations. Interfering effect of some common metabolites including ascorbic acid, uric acid, albumin and hypoxanthine has also been evaluated. A comparison of the observed results of proposed method with HPLC clearly indicates that the results of both methods are essentially similar.

Sensitive voltammetric sensor for the determination of oxidative DNA damage in calf thymus DNA

A simple and reliable method based on voltammetry is proposed for the determination of oxidative DNA damage by the simultaneous determination of guanine and 8-hydroxygunine using single-walled carbon nanotubes modified edge plane pyrolytic graphite electrode (SWNT/EPPGE). In acid-hydrolyzed calf thymus DNA, two well-defined peaks at ∼312 and ∼502 mV corresponding to the oxidation of 8-hydroxyguanine and guanine, respectively in phosphate buffer solution (PBS) of pH 7.2 were observed in square wave voltammetry. Remarkable enhancement in the oxidation peak current of both the compounds was observed along with the negative shift of peak potentials using SWNT/EPPGE as compared to bare EPPGE. The detection limits of guanine and 8-hydroxyguanine were calculated to be 0.05 × 10 −9 and 0.01 × 10 −9 mol L −1, respectively. The limits of quantification were found as 0.17 × 10 −9 and 0.34 × 10 −10 mol L −1 for guanine and 8-hydroxyguanine, respectively.

Voltammetric determination of amlodipine besylate in human urine and pharmaceuticals

Electrochemical determination of amlodipine besylate (ADB) using single and multi-walled carbon nanotubes modified edge plane pyrolytic graphite electrodes (SWNT/EPPGE and MWNT/EPPGE) is described by using cyclic and square wave voltammetries at physiological pH 7.2. An increased peak current with a shift of peak potential to less positive value was observed using carbon nanotubes modified EPPGE as compared to bare electrode. The effect of pH, scan rate and analyte concentration has been examined. Under the optimum conditions the peak current was linear to the concentration of amlodipine in the range 5.0 × 10 − 9 to 1.0 × 10 − 6 mol L − 1 for SWNT/EPPGE and the detection limit was found to be 1.0 × 10 − 9 mol L − 1 whereas, for MWNT/EPPGE the detection limit was found to be 5.0 × 10 − 9 mol L − 1 . The method was successfully used to determine the content of amlodipine in the pharmaceutical preparations and human urine samples of angina patients undergoing treatment with amlodipine. A comparison of electrocatalytic activities of SWNT and MWNT modified electrodes indicated that SWNT modified EPPGE is ∼ 1.8 times more sensitive in comparison to MWNT/EPPGE. Biological relevance of the developed method has been described by the determination of amlodipine in human body fluids. Amlodipine can be determined without any interference from common urine metabolites such as uric acid, ascorbic acid and xanthine.

A single-wall carbon nanotubes modified edge plane pyrolytic graphite sensor for determination of methylprednisolone in biological fluids

An electrochemical protocol based on reduction is developed to determine methylprednisolone using single-wall carbon nanotubes (SWNTs) modified edge plane pyrolytic graphite electrode (EPPGE). To obtain a good sensitivity, instrumental variables were studied using Square Wave Voltammetry (SWV). The voltammetric results indicate that SWNTs modified EPPGE remarkably enhances the reduction of methylprednisolone which leads to considerable improvement of peak current with shift of peak potential to less negative values. The voltammetric current showed a linear response for methylprednisolone concentration in the range 5–500 nM with a sensitivity of 98 nA nM −1. The limit of detection was estimated to be 4.5 × 10 −9 M. The developed method is used for the determination of methylprednisolone in pharmaceutical dosages and human blood plasma samples of patients undergoing treatment with methylprednisolone. The major metabolites present in blood plasma did not interfere with the present investigation as they did not exhibit reduction peak in the experimental range used. A comparison of results with high performance liquid chromatography (HPLC) indicates a good agreement.