Silicomolybdate-doped-glutaraldehyde-cross-linked poly-l-lysine (PLL-GA-SiMo) film modified glassy carbon electrode was prepared by means of electrostatically trapping the silicomolybdate anion in the cationic film. The PLL-GA-SiMo film was stable and the charge transport through the film was fast. The modified electrode shows excellent electrocatalytic activity towards hydrogen peroxide reduction with significant reduction of overpotential, however, not responded to potential interferrents such as dopamine, ascorbic acid and uric acid. This unique feature of PLL-GA-SiMo modified electrode allowed for the development of a highly selective method for the determination of H 2 O 2 in the presence of interferents. The selective and sensitive detection of hydrogen peroxide (H 2 O 2 ) has been an important topic of research for decades due to its wide use in many fields, which includes food production [1 -3], clinical applications [4,5], oxidation of organic compounds [6 -8] and fuel cells [9 -13]. In addition, hydrogen peroxide is the product of reactions catalyzed by a large number of oxidases. Therefore, determination of H 2 O 2 concentration is practically important in the field of biosensor development in order to correlate its concentration to the concentration of target molecules [14 -18].Different methods and analytical techniques have been reported in the literature for the determination of H 2 O 2 , including titrimetry, spectrophotometry, fluorometry, electrochemical methods and chemiluminescence [19 -36]. Among these, electrochemical methods have been considered to be an effective way for H 2 O 2 determination because they possess quick response, low cost, simple of instrumentation, high sensitivity and possibility of miniaturization. However, the direct reduction or oxidation of H 2 O 2 at bare electrode is not suited for analytical application due to slow electrode kinetics on many electrodes materials. Hence, numerous attempts have been made to reduce the large overpotential in the electrochemical reduction of hydrogen peroxide. A number of electrochemical sensors based on using different electron transfer mediators such as complexes of transition metals, water soluble dyes, metal and metal oxide nanoparticles have been used for determination of H 2 O 2 [37 -41]. Polyoxometalates (POMs) are useful and attractive for the modification of electrode surfaces due to their reversible redox activities and good chemical stability. Sadakane and Steckhan [42] have presented detailed accounts of electrocatalytic applications of POMs and various methods used for the immobilization of POMs onto electrode surfaces. There are three main strategies used to modify electrode surfaces with a variety of POMs, including electrodeposition [43] adsorption [44] and incorporation into polymers [45]. In many cases, heteropolyanion immobilized in a polymer matrix is efficient towards electrocatalytic reactions than the homogeneously dissolved one. Hence, these systems are especially interesting for sensor applications.In...
The present work describes preparation, characterization, and electrocatalytic behavior of a hexacyanoferrate-dopedglutaraldehyde-cross-linked poly-l-lysine (PLL-GA-Fe(CN) 4À 6 Þ film modified glassy carbon electrode. The modified electrode has been successfully prepared by electrostatically binding negatively charged Fe(CN) 4À 6 mediator into cross-linked poly-l-lysine cationic film. The dependence of the peak current of the modified electrode in pure supporting electrolyte (pH 6.8 phosphate buffer solution; PBS) shows that the charge transport in the film is fast and relatively unimpeded at lower scan rates. Cyclic voltammetry and rotating disk electrode (RDE) techniques are used to investigate the electrocatalytic activity of modified electrode towards oxidation of ascorbic acid. The rate constant (k), of catalytic reaction between electrogenerated Fe(CN) 3À 6 ions and ascorbic acid, obtained from RDE analysis was found to be 5.53 Â 10 5 cm 3 mol À1 s À1. Finally, the PLL-GA-Fe(CN) 4À 6 film electrodes are successfully used for the individual estimation of ascorbic acid in the concentration range of physiological interest.
Silicomolybdate-doped-glutaraldehyde-cross-linked poly-l-lysine (PLL-GA-SiMo) film modified glassy carbon electrode was successfully prepared by means of electrostatically trapping the silicomolybdate anion in PLL-GA cationic coating. The PLL-GA-SiMo film was stable and the charge transport through the film was fast. The modified electrode shows excellent electrocatalytic activity towards bromate reduction with significant reduction of overpotential. In amperometric determination of bromate, the calibration plot was linear over the concentration range of 5 Â 10 À5 to 1.2 Â 10 À3 M with a sensitivity of 3.6 mA mM À1. Furthermore, PLL-GA-SiMo film electrode showed fast response and good stability. [39]. In many cases, heteropolyanion immobilized in a polymer matrix is efficient towards electrocatalytic reactions than the homogeneously dissolved one. Hence, these systems are especially interesting for sensor applications. KeywordsIn the present investigation, silicomolybdate-doped-glutaraldehyde-cross-linked poly-l-lysine film modified electrodes are prepared by electrostatically binding the negatively charged SiMo 12 O 4À 40 (SiMo) mediator into positively charged PLL-GA coatings, and its application in the electrocatalytic reduction of bromate is studied. The SiMo-doped-PLL-GA modified electrode showed electrocatalytic activity towards bromate reduction and also served as an electrochemical sensing platform for sensitive amperometric determination of bromate. Thus, PLL-GA-SiMo film electrode has great potentiality in sensor development.As silicomolybdate anion is unstable in neutral and basic aqueous solution and undergoes a series of hydrolysis process [40], studies are carried out in 0.1 M H 2 SO 4 solution. Figure 1 illustrates the incorporation of SiMo 12 molecules
Highly stable Nafion-covered hexacyanoferrate-doped-glutaraldehyde-cross-linked poly-l-lysine (PLL-GA-Fe(CN) 6 4À /Naf) film modified glassy carbon electrode (GCE), for the selective detection of dopamine (DA) in the presence of ascorbic acid (AA), was prepared by first ion-exchanging Fe(CN) 6 4À into PLL-GA coating on GCE then sealing it with a Nafion outer layer. The Nafion over layer is crucial in preventing leaching of Fe(CN) 6 4À ions from the inner layer. The first layer was acting as electrocatalyst for DA oxidation and the outer coating acted as discriminating layer for selective permeation of DA in the presence of interfering anionic species. More than 90% of the initial response was retained after coating with the Nafion protecting layer compared to a huge loss (> 60%) without Nafion outer layer. 5% Nafion coating was identified as optimum thickness for the selective detection of DA in the presence of AA.
The present work describes oxidation of ascorbic acid (AA) at octacyanomolybdate-doped-glutaraldehyde-crosslinked poly-l-lysine (PLL-GA-Mo(CN) ). Cyclic voltammetry and rotating disk electrode (RDE) techniques are used to investigate the electrocatalytic oxidation of ascorbic acid and compared with its oxidation at bare and undoped PLL-GA film coated electrodes. The rate constant of catalytic reaction k obtained from RDE analysis was found to be 9.5 Â 10 5 cm 3 mol À1 s À1. The analytical determination of ascorbic acid has been carried out using RDE technique over the physiological interest of ascorbic acid concentrations with a sensitivity of 75 mA mM
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