Surface composition glassy carbon electrodes

Due to their small size and high surface area, nanoparticles can be applied to modify electrode surface property. Convenient and sensitive electrochemical sensors to various targets have been set up by using nanoparticle modification. The determination of acetaminophen in a commercial paracetamol oral solution was reported using a multiwall CNTs composite film-modified glassy carbon electrode with a detection limit of 50 nM (Li etal. 2006a). Heavy metal ions, such as ar-senite (Dai and Compton 2006 Majid et al. 2006) and lead ion (Cui et al. 2005),... 

This move from the modification of electrodes to the modification of nonconducting surfaces in contact with electrodes is also seen in systems in which electrodes are modified using nonconduct ive particles. For example, Zak and Kuwana showed that the basic surface of alpha-alumina imbedded in glassy carbon electrodes caused catalysis of the electrooxidation of catechol and other organic species requiring loss of a proton for their oxidation JJ ), Similar results were obtained by Shaw and Creasy (78) using alumina or layered-double hydroxides in composite electrodes (vide infra). 

A composite electrode composed of graphite and carbon nanotube was fabricated by Zhu et al. [65]. The redox reactimis are reversible on graphite but not on carbon nanotube, but carbon nanotube was able to improve on the low ciurents of graphite. Recently, Li et al. [66] reported multiwaUed carbon nanotubes (MWCNTs) and functional MWCNTs as electrodes in RFBs. Different MWCNTs were used to modify glassy carbon electrodes, resulting in improved electrochemical activity of the redox couple and battery performance. The increased activities of modified electrodes were attributed to an increased electrode surface area and the introduction of oxygen functional groups. 

Composites of gold and PANl on a glassy carbon electrode were also used by Xiang et al. [52] for the development of a glucose biosensor. They used a bienzy-matic approach where glucose was oxidized thereby producing H2O2, which was reduced by cytochrome oxidase c, absorbed on the surface of the nanocomposites. This sensor enabled a direct electron transfer to the electrode material. The sensor has a detection limit of 0.01 mM. 

Another important electroanalytieal application of modified electrodes is DNA detection [34-40]. Zhang et al. [39] produced an electrochemical DNA sensor based on silver nanoparticles/poly(trans-3-(3-pyridyl) aciylic acid) (PPAA)/multiwalled carbon nanotubes with carboxyl groups (MWCNTs-COOH) modified glassy carbon electrode (GCE). The polymer film was electropolymerized onto MWCNTs-COOH modified electrode by cyclic voltammetry, and then silver nanoparticles were electrodeposited on the surface of PPAA/MWCNTs-COOH composite film. The novel electrochemical detection method of DNA hybridization-based modified electrode has been developed with high sensitivity and selectivity. Furthermore the results of the experiment indicated that the DNA sensor is of excellent reusability. 

An environmentally friendly sensor was developed by fabricating a nickel-copper (NiCu) alloy electrode to determine the chemical oxygen demand. The NiCu alloy film was applied to modify the surface of a glassy carbon electrode which led to a very stable detecting element. The surface morphology of NiCu alloy was investigated by atomic force microscopy which confirmed its continuity and uniform thickness over the entire electrode. The chemical composition of the developed NiCu film was evaluated by energy-dispersive X-ray spectrometry which revealed 69 % presence of Ni in the alloy. 

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