Carbon-based quantum particles, especially spherical carbon quantum dots (CQDs) and nanosheets like graphene quantum dots (GQDs), are an emerging class of quantum dots with unique properties owing to their quantum confinement effect.

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Differential pulse and cyclic voltammetry were applied for the oxidation of mixture of uric acid and ascorbic acid at the surface of carbon paste/cobalt Schiff base composite electrode. The electrooxidation of these compounds at bare electrode is sluggish, and there is no suitable peak separation between them. However, using cobalt methyl salophen as modifier, two well-defined anodic waves with a considerable enhancement in the peak current and a remarkable peak potential separation near 315 mV are obtained. It can improve the kinetics of electron transfer for both compounds remarkably. All these improvements are created because of the electrocatalytic property of cobalt Schiff base complex. The effect of some parameters such as pH and scan rates were studied. All the anodic peak currents for the oxidation of ascorbic acid and uric acid shifted toward more negative potential with an increase in pH, revealing that protons have taken part in their electrode reaction processes. The best peak separation with appropriate current was obtained for pH 4.0. A linear range of 5.0× 10 −4 to 1.0×10 −8 and 1.0×10 −3 to 1.0×10 −8 M with detection limit of 8.0×10 −9 and 8.0×10 −9 M was obtained for ascorbic acid and uric acid using differential pulse voltammetry at the surface of modified electrode, respectively. Analytical utility of the modified electrode has been examined successfully using human urine samples and vitamin C commercial tablets.

In this approach, flower-like cobalt with a hierarchical structure was applied as modifier for voltammetric determination of chlorpheniramine, which is an antihistaminic drug. The flower-like cobalt nanostructures were synthesized by using a simple chemical method. They have been characterized by using scanning electron microscopy and cyclic voltammetry. The carbon paste electrode modified with cobalt nanostructures shows an excellent electrocatalytic activity and sensitivity toward chlorpheniramine due to its unique properties such as high specific surface area and large pore volume. Potential sweep rate and pH effects on the response of the electrode for the oxidation of chlorpheniramine were investigated. Differential pulse voltammetry has been applied for quantitative determination of chlorpheniramine. A dynamic linear range was obtained in the range of 1.0 × 10 −7 −1.0 × 10 −5 mol L −1 , and the detection limit was estimated to be 8.0 × 10 −8 mol L −1 .

Covalently grafted KolliphorEL (a poly(ethylene glycol)-based transporter molecule for hydrophobic water-insoluble drugs; MW, ca. 2486; diameter, ca. 3 nm) at the surface of a glassy-carbon electrode strongly affects the rate of electron transfer for aqueous redox systems such as Fe(CN)6(3-/4-). XPS data confirm monolayer grafting after electrochemical anodization in pure KolliphorEL. On the basis of voltammetry and impedance measurements, the charge transfer process for the Fe(CN)6(3-/4-) probe molecule is completely blocked after KolliphorEL grafting and in the absence of a "guest". However, in the presence of low concentrations of suitable ferrocene derivatives as guests, mediated electron transfer across the monolayer via a shuttle mechanism is observed. The resulting amplification of the ferrocene electroanalytical signal is investigated systematically and compared for five ferrocene derivatives. The low-concentration electron shuttle efficiency decreases in the following sequence: (dimethylaminomethyl)ferrocene > n-butyl ferrocene > ferrocene dimethanol > ferroceneacetonitrile > ferroceneacetic acid.