A Novel Kinetic Spectrophotometric Method for the Determination of Dopamine in Biological and Pharmaceutical Samples

A sensitive and accurate method for quantitative determination of dopamine was introduced. The proposed method is based on inhibitory effect of dopamine on the oxidation of thionine by bromate in acidic media. The change in absorbance was followed spectrophotometrically at 601 nm. The dependence of sensitivity on the reaction variables was investigated and optimized to obtain the maximum sensitivity. Under optimum experimental conditions, calibration curve was linear over the range 0.2–103.3 μg mL−1 of dopamine. The relative standard deviations () of 0.5, 1.0, 5.0, and 30.0 μg mL−1 of dopamine were 1.13, 1.02, 0.99, and 0.97%, respectively. The limit of detection was 0.057 μg mL−1 of dopamine. The effect of diverse species was also investigated. The developed method was successfully applied for the determination of dopamine in pharmaceutical and biological samples

Development of an electrochemical nanosensor for the determination of gallic acid in food

In the present work, a silver nanoparticle/delphinidin modified glassy carbon electrode (AgNP/Delph/GCE) was fabricated as a highly sensitive electrochemical sensor for gallic acid (GA) determination. Cyclic voltammetry experiments indicated a higher sensitivity and better selectivity for gallic acid when using the AgNP/Delph/GCE as compared with the bare GCE surface, which were attributed to AgNPs and delphinidin, respectively. Moreover, the calculated surface electron transfer rate constant (ks), and the electron transfer coefficient (\u3b1) between the GCE and the electrodeposited delphinidin demonstrated that delphinidin is an excellent electron transfer mediator for the electrocatalytic process. The average catalytic rate constant (k\u2032) of the overall process was also estimated to be 7.40 7 10-4 cm s-1 for the AgNP/Delph/GCE in the presence of 1.50 mmol L-1 of GA. Amperometry experiments were used to determine the limit of detection of the AgNP/Delph/GCE electrochemical sensor, which was 0.28 \u3bcmol L-1 of GA. Finally, two linear ranges were found, i.e. 0.60-8.68 \u3bcmol L-1 and 8.68-625.80 \u3bcmol L-1 for GA. The activity of the modified electrode was eventually investigated to assess the potential quantification of GA in real foods

Polymers in biosensors

Polymers can be conductive or nonconductive, natural or synthetic, and have been widely used in the development of biosensors; polymers can be processed at a large scale at a relatively low cost. Poly (3, 4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), PANI, and PPy are widely used in fabricating biosensors owing to their intrinsic conductive property. Although conductivity is crucial in developing biosensors, a large number of nonconductive polymers such as chitin, chitosan, gelatin, dextran, cellulose, and polystyrene also attract interest for their function as support matrices for the immobilization of biomolecules. The non- conductive polymers can be classified into two categories: natural and synthetic. This chapter focuses on the potential use of polymer composites in biosensors