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Neuroblastoma is a pediatric neuroblastic tumor arising in the sympathetic nervous crest cells. A high grade of Neuroblastoma is characterized by a high urinary excretion of homovanillic acid and dopamine. In this work l-leucine modified Sol-Gel-Carbon electrode was used for a sensitive voltammetric determination of homovanillic acid and dopamine in urine. The electrochemical response characteristics were investigated by cyclic and differential pulse voltammetry; the modified electrode has shown an increase in the effective area of up to 40%, a well-separated oxidation peaks and an excellent electrocatalytic activity. High sensitivity and selectivity in the linear range of 0,4-100μML -1 of homovanillic acid and 10-120μML -1 of dopamine were also obtained. Moreover, a sub-micromolar limit of detection of 0.1μM for homovanillic acid and 1.0μM for the dopamine was achieved. Indeed, high reproducibility with simple preparation and regeneration of the electrode surface made this electrode very suitable for the determination of homovanillic acid and dopamine in pharmaceutical and clinical preparations. The mechanism of homovanillic acid and the electrochemical oxidation at l-leucine modified Sol-Gel-Carbon electrode is described out the B3P86/6-31+G(d,p) level of theory as implemented in Gaussian software., (Copyright © 2016 Elsevier B.V. All rights reserved.)

The Sonogel-Carbon electrode is a special class of sol-gel electrode that exhibits favourable mechanic and electric properties to be used as electrochemical sensor. In this study, Sonogel-Carbon modified with L-Cysteine was used to prepare a novel electrochemical sensor. The objective of this novel electrode modification was to seek new electrochemical performances for detection of epinephrine in the presence of uric acid. The response of catalytic current with epinephrine concentration shows a linear relation in the range from 1 x 10(-7) to 5 x 10(-4)M with a correlation coefficient of 0.998, and a detection limit of 8.7 x 10(-8)M. The modified electrode had also been applied to the determination of epinephrine and uric acid in biological samples with satisfactory results. A surface characterisation of this modified electrode was carried out helped by scanning electron microscopy (SEM) and X-Ray energy dispersive spectroscopy (EDS).

The detection and quantification of uric acid (UA) and ascorbic acid (AA) in different biological fluids such as serum is very important in clinical diagnosis. In this study, a sonogel–carbon electrode modified with l -cysteine was used for detection and quantification of these molecules by cyclic voltammetry (CV) and square wave voltammetry (SWV). These two methods are known for their suitability for monitoring of bioactive molecules in biological samples. Optimization of parameters affecting selectivity and sensitivity of these two methods is included. The peak current showed a linear relationship with the concentrations of UA and AA in the range of 10 − 5 M to 10 − 4 M for UA and 5 × 10 − 5 M respectively. The detection limit was of 10 − 5 M for UA and 5 × 10 − 5 M for AA. In addition, the interference of UA and AA was also studied. A neat separation of the oxidation peaks of these two compounds with a peak-to-peak separation of 295 mV was registered. The results indicate that carbon electrode modified with l -cysteine can successfully be used for a selective and sensitive simultaneous determination of UA and AA in the serum. [ABSTRACT FROM AUTHOR]