Hydrophilic polymers biosensors

Surface-bound, neutral, hydrophilic polymers such as polyethers and polysaccharides dramatically reduce protein adsorption [26-28], The passivity of these surfaces has been attributed to steric repulsion, bound water, high polymer mobility, and excluded volume effects, all of which render adsorption unfavorable. Consequently, these polymer modified surfaces have proven useful as biomaterials. Specific applications include artificial implants, intraocular and contact lenses, and catheters. Additionally, the inherent nondenaturing properties of these compounds has led to their use as effective tethers for affinity ligands, surface-bound biochemical assays, and biosensors. 

A ferrocene modified siloxane redox polymeric electron transfer system in carbon paste electrodes for aldose biosensors using PQQ-dependent aldose dehydrogenase was reported by Smolander et al. [86]. Polymethyl(ll-ferrocenyl-4,7,10-trioxa-undecanyl)methyl(12-amino-4,7,10-trioxa-dodecyl)-siloxane (1 1 random co-polymer) (Fig. 3.6) was found to be an efficient electron transfer system yieldii better electrode operational stabiUty than those constructed with dimethylferrocene fi ee mediator. The hydrophilic nature of the pendant chain and side chain on dimethyl siloxane units favorably interact with enzjnne causing efficient electron transfer from coenzyme PQQ of aldose dehydrogenase to the electrode surface. 

In general, adsorption is achieved by applying a solution of the molecule to be immobilized to a membrane or him on the sensor transducer and allowing the molecule to adsorb to the transducer over a specified time period. The membrane or film may be hydrophilic or hydrophobic or may contain ionic groups depending on the molecule to be immobilized. Various support/surface materials have been used for adsorption but the most used are silica, cellulose acetate membranes, and polymers such as PVC and polystyrene. As shown in table 8.5, adsorption is still used in the fabrication of many chemical sensors and biosensors. 

In addition, as a hydrophilic and ftmctionalizable polymer, dextrans are used extensively for surface modification in biosensor fabrication. Dextran layers on sensor chips can effectively minimize nonspecific adsorption of analyte and facilitate surface immobilization of ligand, subsequently increasing the sensitivity of biosensors. 

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