Polymer Surface-Modified Glassy Carbon

GC material was widely modified with conducting (or nonconducting) polymers in order to obtain an improved surface for DNA adsorption and detection. The initial approaches were performed by the physical attachment of nylon or nitrocellulose membranes on GC electrodes [51]. As explained, these membranes were extensively used in classical DNA analysis due to their well-known adsorption properties [33]. Other approaches were performed by the direct adsorption of the polymeric film on the GC surface. Finally, polymeric films were electrochemically grown on the GC substrate. These conducting polymers are particularly promising for the adsorption, but also for inducing electrical signals obtained from DNA interactions. 

A chitosan oligomer film was used as an active coating for the immobihza-tion of ssDNA at a GC electrode. Chitosan oligomer is a kind of /1-1,4-linked 

Layer-by-Layer Deposited Film Modified Glassy Carbon 

Fabrication of organic thin films based on sponfaneous molecular assembly has been considered as one of fhe powerful approaches to create novel supramolecular systems. In this context, multilayer films were fabricated by layer-by-layer electrostatic deposition techniques based on the electrostatic interaction between dsDNA and the positively charged polymer poly(diallyldimethylammonium chloride) (PDDA) on GC surfaces. A uniform assembly of PDDA/DNA multilayer films was achieved, based on the adsorption of the negatively charged DNA molecules on the positively charged substrate [55]. 

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Immobilization of the DNA onto polymer modified surface can be realized by electrodeposition, which is a well-known method [25]. Application of positive potential in this process can enhance the DNA immobilization as well as the stability of immobilized DNA. Diaz-Gonzalez etal. [26] studied the DNA immobilization onto a polylysine-modified electrode at different potentials. The best results were obtained using a potential of-1-0.5 V for 120 seconds. DNA was also electrodeposited onto a poly(p-aminobenzensulfonic acid)-modified glassy carbon electrode (GCE) at -fl.5 V for 30 minutes [27] or onto overoxidized Ppy-modified electrode at -1-1.8 V for 30 minutes [28]. 

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. 

Torriero et al. [61] l-Lactate Milk L-Lactate oxidase (LOx) and peroxidase (HRP)/LOx on 3-aminopropyl-modified controlled-pore glass reactor HRP and Os-PAA were covalently immobilized on the electrode surface Glassy carbon electrode/O vs. Ag/AgCl Redox polymer... 

The adhesion power of metal electrode to perfluorosulphonic polymer is used to modify the surface of a single electrode for the analysis of electrochemical reactions of special interest. Nafion -coated electrodes have been developed by Rubinstein Bard" . Various electron-conducting materials (glassy carbon, gold, platinum) are used as support for the Teflon layer. With these coated electrodes, the mechanisms of mass and charge transfer in the perfluorosulphonic material have been investigated and also the catalytic and photochemical properties of polymer doped with various chemical species . ... 

In this article, we describe the preparation and use of amperometric electrodes for sensing the analytically significant substrate glucose based on a PEG-modified glucose oxidase (GOD) (4,5) and on a lipid-modified GOD (6). The PEG-modified GOD has been incorporated into a carbon paste (CP) electrode the modified enzyme exhibits higher activity in a hydrophobic CP matrix than hydrophilic, native GOD (7-10). The lipid-modified GOD has been immobilized on a glassy carbon (GC) electrode with a thin Nafion overcoat. The water-insoluble modified enzyme is far more stable between the electrode surface and the polymer layer than native GOD (77). 

Silica sol-gel glass-coated ferricyanide-doped Tosflex-modified screen-printed electrode used for the mediated oxidation of AA (neutral pH).The electrochemical mediation of AA is found to follow the Michaelis-Menten kinetic pathway A polymer film of N,N-dimethylaniline having a positive charge on the quaternary ammonium group in its backbone is electrochemical deposited on a glassy carbon electrode surface resulting a film-coated GC electrode... 

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