Pristine multi-walled carbon nanotubes/SDS modified carbon paste electrode as an amperometric sensor for epinephrine.

An amperometric sensor for the determination of epinephrine (EP) was fabricated by modifying the carbon paste electrode (CPE) with pristine multi-walled carbon nanotubes (pMWCNTs) using bulk modification followed by drop casting of sodium dodecyl sulfate (SDS) onto the surface for its optimal potential application. The modified electrode showed an excellent electrocatalytic activity towards EP by decreasing the overpotential and greatly enhancing the current sensitivity. FE-SEM images confirmed the dispersion of pMWCNTs in the CPE matrix. EDX analysis ensured the surface coverage of SDS. A comparative study of pMWCNTs with those of oxidized MWCNTs (MWCNTsOX) modified electrodes reveals that the former is the best base material for the construction of the sensor with advantages of lower oxidation overpotential and the least background current. The performance of the modified electrode was impressive in terms of the least charge transfer resistance (Rct), highest values for diffusion coefficient (DEP) and standard heterogeneous electron transfer rate constant (k°). Analytical characterization of the modified electrode exhibited two linear dynamic ranges from 1.0×10(-7) to 1.0×10(-6)M and 1.0×10(-6) to 1.0×10(-4)M with a detection limit of (4.5±0.18)×10(-8)M. A 100-fold excess of serotonin, acetaminophen, folic acid, uric acid, tryptophan, tyrosine and cysteine, 10-fold excess of ascorbic acid and twofold excess of dopamine do not interfere in the quantification of EP at this electrode. The analytical applications of the modified electrode were demonstrated by determining EP in spiked blood serum and adrenaline tartrate injection. The modified electrode involves a simple fabrication procedure, minimum usage of the modifier, quick response, excellent stability, reproducibility and anti-fouling effects.

Multi-walled carbon nanotube/poly(glycine) modified carbon paste electrode for the determination of dopamine in biological fluids and pharmaceuticals.

A modified carbon paste electrode (CPE) for the selective detection of dopamine (DA) in presence of large excess of ascorbic acid (AA) and uric acid (UA) at physiological pH has been fabricated by bulk modification of CPE with multi-walled carbon nanotubes (MWCNTs) followed by electropolymerization of glycine (Gly). The surface morphology is compared using SEM images. The presence of nitrogen was confirmed by the energy dispersion X-ray spectroscopy (EDS) indicating the polymerization of Gly on the surface of the modified electrode. The impedance study indicates a better charge transfer kinetics for DA at CPE modified with MWCNT/polyglycine electrode. The presence of MWCNTs in carbon paste matrix triggers the extent of electropolymerization of Gly and imparts more selectivity towards DA by electrochemically not sensing AA below a concentration of 3.1×10(-4)M. Due to the exclusion of the signal for AA, the interference of AA in the determination of DA is totally ruled out by DPV method which is used for its detection at lower concentrations. Large peak separation, good sensitivity, reproducibility and stability allow this modified electrode to analyze DA individually and simultaneously along with AA and UA. Detection limit of DA was determined from differential pulse voltammetric (DPV) study and found to be 1.2×10(-8)M with a linear dynamic range of 5.0×10(-7)M to 4.0×10(-5)M. The practical analytical application of this electrode was demonstrated by measurement of DA content in dopamine hydrochloride injection and human blood serum.

Multi-walled carbon nanotube modified carbon paste electrode as a sensor for the amperometric detection of L-tryptophan in biological samples.

An electrochemical sensor for the amperometric determination of L-tryptophan (Trp) was fabricated by modifying the carbon paste electrode (CPE) with multi-walled carbon nanotubes (MWCNTs) using drop cast method. 4.0 µL of the dispersion containing 2.0 mg of MWCNTs in 1.0 mL of ethanol was drop cast onto the electrode surface and dried in hot air oven to form a stable layer of MWCNTs. The electro-catalytic activity of the modified electrode towards the oxidation of Trp was thoroughly investigated. The modification with MWCNTs has greatly improved the current sensitivity of CPE for the oxidation of Trp. A very minimal amount of the modifier was required to achieve such a high sensitivity. The field emission scanning electron microscopy (FESEM) images revealed a uniform coverage of the surface of CPE by MWCNTs. Nyquist plots revealed the least charge transfer resistance for the modified electrode. The analytical performance of the modified electrode was examined using amperometry under hydro-dynamic conditions. The two linear dynamic ranges observed for Trp were 0.6-9.0 µM and 10.0-100.0 µM. The amperometric determination of Trp did not suffer any interference from other biomolecules. The detection limit of Trp at modified electrode was (3.30±0.37)×10(-8)M (S/N=3). The analytical applications of the modified electrode were demonstrated by estimating Trp in the spiked milk and biological fluid such as blood serum. The modified electrode showed good reproducibility, long-term stability and anti-fouling effects.

Multi-walled carbon nanotube modified carbon paste electrode as an electrochemical sensor for the determination of epinephrine in the presence of ascorbic acid and uric acid.

A biocompatible electrochemical sensor for selective detection of epinephrine (EP) in the presence of 1000-fold excess of ascorbic acid (AA) and uric acid (UA) was fabricated by modifying the carbon paste electrode (CPE) with multi-walled carbon nanotubes (MWCNTs) using a casting method. The electro-catalytic activity of the modified electrode for the oxidation of EP was investigated. The current sensitivity of EP was enhanced to about five times upon modification. A very minimum amount of modifier was used for modification. The voltammetric response of EP was well resolved from the responses of AA and UA. The electrochemical impedance spectroscopic (EIS) studies reveal the least charge transfer resistance for the modified electrode. The AA peak that is completely resolved from that of EP at higher concentrations of AA and the inability of the sensor to give an electrochemical response for AA below a concentration of 3.0×10(-4)M makes it a unique electrochemical sensor for the detection of EP which is 100% free from the interference of AA. Two linear dynamic ranges of 1.0×10(-4)-1.0×10(-5) and 1.0×10(-5)-5.0×10(-7)M with a detection limit of 2.9×10(-8)M were observed for EP at modified electrode. The practical utility of this modified electrode was demonstrated by detecting EP in spiked human blood serum and EP injection. The modified electrode is highly reproducible and stable with anti fouling effects.

Poly(Patton and Reeder's reagent) modified carbon paste electrode for the sensitive detection of acetaminophen in biological fluid and pharmaceutical formulations.

An electrochemical sensor for sensitive detection of acetaminophen (AAP) was developed by electropolymerizing Patton and Reeder's reagent at carbon paste electrode (CPE). Modification improves the redox kinetics of AAP with increased current sensitivity. A similar modification at multiwall carbon nanotube (MWCNT) modified CPE did not result in an impressive charge transfer. Electrochemical impedance spectroscopy (EIS) of the bare and modified electrodes investigated imply a least charge transfer resistance at Patton and Reeder's reagent modified carbon paste electrode (MCPE/PR) as compared to bare CPE and MWCNT modified electrode. Differential pulse voltammetric (DPV) study at MCPE/PR electrode did not suffer any interference from its hydrolytic degradation product 4-aminophenol (4-AP) even in 1000-fold excess of its concentration and enables its detection simultaneously. A linear dynamic range of 0.7-100 µM with detection limit (S/N=3) of 0.53 µM was obtained for AAP. This modified electrode is easy to prepare, cheap, and having good reproducibility and stability. The analytical performance of the modified electrode is assessed by successfully applying it for the estimation of acetaminophen in different pharmaceutical samples and spiked biological fluid.