Highly sensitive interference-free electrochemical determination of pyridoxine at graphene modified electrode: Importance in Parkinson and Asthma treatments.

To reduce the side effects in the medication of Parkinson and Asthma, pyridoxine (PY) is administered along with l-3,4-dihydroxyphenyl alanine (l-dopa) and theophylline (TP), respectively. However, excessive dosage of PY leads to nervous disorder. Thus, a sensitive and selective electrochemical method was developed for the determination of PY in the presence of major interferences including TP, l-dopa, ascorbic acid (AA) and riboflavin (RB) using electrochemically reduced graphene oxide (ERGO) film modified glassy carbon electrode (GCE) in this paper. The ERGO fabrication process involves the nucleophilic substitution of graphene oxide at basic pH on amine terminal of 1,6-hexadiamine which was pre-assembled on GCE followed by electrochemical reduction. The electrocatalytic activity of the ERGO modified electrode was examined towards the oxidation of PY. It greatly enhanced the oxidation current of PY in contrast to bare and GO modified GCEs due to facile electron transfer besides π-π interaction between ERGO film and PY. Since TP and l-dopa drugs antagonize the drug action of PY, ERGO modified GCE was also used for the simultaneous determination of PY and l-dopa and PY and TP. Further, the selective determination of PY in the presence of other water soluble vitamins such as ascorbic acid and riboflavin was also demonstrated. Using amperometry, detection of 100nM PY was achieved and the detection limit was found to be 5.6×10(-8)M (S/N=3). The practical application of the present method was demonstrated by determining the concentration of PY in human blood serum and commercial drugs.

Formation of electrochemically reduced graphene oxide on melamine electrografted layers and its application toward the determination of methylxanthines.

The current study describes the electrografting of 2,4-diamino-1,3,5-triazine (AT) groups at the surfaces of glassy carbon electrode (GCE) and indium tin oxide (ITO) through in situ diazotization of melamine. The presence of AT groups at the surface of the electrode was confirmed by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). Furthermore, graphene oxide (GO) was self-assembled on AT grafted GCE. The oxygen functional groups present on the surface of GO were electrochemically reduced to form an electrochemically reduced graphene oxide (ERGO) on AT grafted electrode surface. Raman spectra show the characteristic D and G bands at 1340 and 1605 cm(-1), respectively, which confirms the successful attachment of GO on AT grafted surface, and the ratio of D and G bands was increased after the electrochemical reduction of GO. EIS shows that the electron transfer reaction of [Fe(CN)6](3-/4-) was higher at the ERGO modified electrode than at bare, AT grafted, and GO modified GCEs. The electrocatalytic activity of ERGO was investigated toward the oxidation of methylxanthines. It shows excellent electrocatalytic activity toward these methylxanthines by not only shifting their oxidation potentials toward less positive potentials but also enhancing their oxidation currents.

Simultaneous determination of uric acid, xanthine, hypoxanthine and caffeine in human blood serum and urine samples using electrochemically reduced graphene oxide modified electrode.

This paper describes the fabrication of graphene on glassy carbon electrode (GCE) by electrochemical reduction of graphene oxide (GO) attached through 1,6-hexadiamine on GCE and the simultaneous determination of structurally similar four purine derivatives using the resultant electrochemically reduced GO (ERGO) modified electrode. The electrocatalytic activity of ERGO was investigated toward the oxidation of four important purine derivatives, uric acid (UA), xanthine (XN), hypoxanthine (HXN) and caffeine (CAF) at physiological pH. The modified electrode not only enhanced the oxidation currents of the four purine derivatives but also shifted their oxidation potentials toward less positive potentials in contrast to bare GCE. Further, it successfully separates the voltammetric signals of the four purine derivatives in a mixture and hence used for the simultaneous determination of them. Selective determination of one purine derivative in the presence of low concentrations other three purine derivatives was also realized at the present modified electrode. Using differential pulse voltammetry, detection limits of 8.8×10(-8)M, 1.1×10(-7)M, 3.2×10(-7)M and 4.3×10(-7)M were obtained for UA, XN, HXN and CAF, respectively. The practical application of the modified electrode was demonstrated by simultaneously determining the concentrations of UA, XN, HXN and CAF in human blood plasma and urine samples.

Synthesis, characterization and modification of functionalized pyrimidine stabilized gold nanoparticles on ITO electrode for the determination of tannic acid.

This paper describes the synthesis of 4-amino-6-hydroxy-2-mercaptopyrimidine capped gold nanoparticles (AHMP-AuNPs) in aqueous medium and their immobilization on indium tin oxide (ITO) electrode modified with (3-mercaptopropyl)trimethoxysilane (MPTS) sol-gel for the determination of tannic acid (TA). The high resolution transmission electron microscopy (HR-TEM) images show that the particles are spherical in shape with a diameter of ~6 nm. The heterogeneous electron transfer rate constant (k(et)) of [Fe(CN)6]³â»/4⁻ at ITO/MPTS/AHMP-AuNPs electrode was found to be 1.14×10⁻7 m/s. This value was much higher than the values obtained at ITO/MPTS (4.94×10⁻9 m/s) and bare ITO (8.79×10⁻8 m/s) electrodes, indicating that the electron transfer reaction was faster at AuNPs modified electrode. Further, the ITO/MPTS/AHMP-AuNPs electrode shows excellent electrocatalytic activity toward TA oxidation when compared to bare ITO electrode. This was understood from the obtained higher heterogeneous rate constant (k(s)) value at AuNPs modified electrode (7.35×10⁻5 m/s) than at bare ITO electrode (5.45×10⁻6 m/s). Using the amperometry method, detection of 20 nmol/L TA was achieved. The practical application of the present method was demonstrated by determining the concentration of TA in commercial beer samples.

Selective determination of 3,4-dihydroxyphenylacetic acid in the presence of ascorbic acid using 4-(dimethylamino)pyridine capped gold nanoparticles immobilized on gold electrode.

4-(Dimethylamino)pyridine capped gold nanoparticles (DMAP-AuNPs) were synthesized in aqueous medium and then immobilized on 1,6-hexanedithiol (HDT) modified Au electrode for the selective determination of 3,4-dihydroxyphenylacetic acid (DOPAC) in the presence of ascorbic acid (AA). The synthesized DMAP-AuNPs were characterized by UV-visible spectroscopy and high resolution-transmission electron microscopy (HR-TEM). The HR-TEM images showed that the nanoparticles are spherical in shape with a diameter of ∼12 nm. The DMAP-AuNPs immobilized on HDT modified electrode was characterized by cyclic voltammetry and impedance spectroscopy. Impedance spectra show that the electron transfer reaction was more facile at the AuNPs modified electrode when compared to bare and HDT modified Au electrodes. The application of DMAP-AuNPs modified electrode was demonstrated by selective determination of DOPAC in the presence of high concentration of AA at pH 4. Using amperometry method, 40 nM detection of each AA and DOPAC was achieved. The current response was increased linearly with increasing AA and DOPAC in the concentration range of 40×10(-9) to 10×10(-5) M and a detection limit was found to be 5.6×10(-10) M and 3.7×10(-10) M (S/N=3) for AA and DOPAC, respectively. The present modified electrode was also successfully used for the determination of 40 nM DOPAC in the presence of 2500-fold excess of common interferents such as Na(+), Mg(2+), Cu(2+), Ca(2+), NH(4)(+) urea and glucose.