S. Brillians Revin

Highly sensitive determination of uric acid in the presence of major interferents using a conducting polymer film modified electrode

This paper describes the sensitive and selective determination of uric acid (UA) in the presence of important interferences, ascorbic acid (AA), dopamine (DA), tyrosine (Tyr) and methionine (Met) at physiological pH using an electropolymerized film of 3-amino-5-mercapto-1,2,4-triazole on glassy carbon (p-AMTa) electrode. The p-AMTa electrode shows an excellent electrocatalytic activity towards UA. This was understood from the observed higher oxidation current and heterogeneous rate constant (3.24×10(-5)ms(-1)) for UA when compared to bare GC electrode (4.63×10(-6)ms(-1)). The selective determination of UA in the presence of 1000-fold excess of AA was achieved using p-AMTa electrode. Further, the p-AMTa electrode was successfully used for the simultaneous and selective determination of UA in the presence of important interferences, DA, Tyr and Met. Using amperometric method, 40nM UA was detected for the first time. The current response of UA was increased linearly while increasing its concentration from 40nM to 0.1mM and a detection limit was found to be 0.52nM (S/N=3). Finally, the practical application of the present method was demonstrated by determining UA in human urine and blood serum samples.

Fabrication, characterization and application of a grafting based gold nanoparticles electrode for the selective determination of an important neurotransmitter

β-D-Glucose capped gold nanoparticles (Glu-AuNPs) were synthesized and then immobilized on an aminophenyl grafted GC electrode for the selective determination of norepinephrine (NEP) in the presence of uric acid (UA). 1,4-Diaminobenzene (DAB) was used to graft the GC surface and the resulting grafted GC electrode was characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV) and impedance spectroscopy. Glu-AuNPs were immobilized on a grafted GC electrode (Glu-AuNPs electrode) and it was confirmed by SEM, UV-visible spectroscopy and electrochemical techniques. Impedance studies show that the electron transfer reaction of [Ru(NH3)6]3+/2+ was higher at the Glu-AuNPs electrode (7.49 × 10−4 cm s−1) than at bare (5.64 × 10−4 cm s−1) and grafted (1.67 × 10−6 cm s−1) GC electrodes. The Glu-AuNPs electrode shows an excellent electrocatalytic activity towards NEP and UA when compared to grafted and bare GC electrodes. Further, the Glu-AuNPs electrode was successfully used for the selective determination of NEP in the presence of 50-fold excess UA at physiological pH.

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.

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]³⁻/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.

Simultaneous determination of two important dopamine metabolites at physiological pH by voltammetry

Simultaneous determination of two important dopamine metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), at physiological pH was demonstrated for the first time using the electropolymerized film of a 3-amino-5-mercapto-1,2,4-triazole modified glassy carbon electrode.

Selective determination of inosine in the presence of uric acid and hypoxanthine using modified electrode

This article describes the selective determination of inosine (INO) in the presence of important physiological interferents, uric acid (UA) and hypoxanthine (HXN), by differential pulse voltammetry at physiological pH (7.2) using the electropolymerized film of 3-amino-5-mercapto-1,2,4-triazole (p-AMTa) modified glassy carbon (GC) electrode. The electropolymerization of AMTa was carried out by the potentiodynamic method in 0.1M H(2)SO(4). An atomic force microscopy image shows that the p-AMTa film contains a spherical-like structure. Bare GC electrode fails to resolve the voltammetric signal of INO in the presence of UA and HXN due to the surface fouling caused by the oxidized products of UA and HXN. However, p-AMTa film modified GC electrode (p-AMTa electrode) not only separates the voltammetric signals of UA, HXN, and INO, with potential differences of 730 mV between UA and HXN and 310 mV between HXN and INO, but also shows enhanced oxidation current for them. The selective determination of INO in the presence of UA and HXN at physiological pH was achieved for the first time. Using the amperometric method, we achieved the lowest detection of 50 nM for INO. The practical application of the current modified electrode was demonstrated by determining the concentration of INO in human blood serum and urine samples.