Carboxymethyl Dextran – Poly(ethyleneglycol) Composite Material as a Matrix for

D. PALLAROLA; L. DOMENIANNI; G. PRIANO; F. BATTAGLINI

Burdeos

Congreso; 11th International Conference on Electroanalysis; 2006

Society for Electroanalytical Chemistry

Biosensors for detecting specific biomolecular interactions such as antigen/antibody recognition and DNA hybridization play a significant role as a tool in the biochemical and medical fields. In many cases gold serves as the interface between the recognition element and the transduction system; it may even be the only useful interfase , such as in the case of surface plasmon resonance and quartz crystal microbalance. For other methods, e.g.: impedance and amperommetry, is highly recommended. Generally, the recognition element is attached to the gold surface through the formation of a self-assembled layer of a mercaptan derivative, which afterward is modified with an hydrophilic polymer to form a matrix that avoid protein non-specific adsorption. Among the most successful polymers are dextran and its derivatives, due its low interactions with proteins. For example, carboxymethyl dextran (CMDex) was used in the surface modification of gold in SPR transductors and currently is commercially exploited by BIACORE in its SPR sensor model CM5. One of the advantages of CMDex is the fact that it can be easily modified on the carboxylate groups present in its structure; yielding an interface useful for the construction of biosensors. On the other hand, depending on the way it is attached to the surface, it can yield an open structure plenty of water where proteins can diffuse and be adsorbed onto the un-reacted mercaptan derivatives. This process becomes important when the biosensor is used close to the detection limit and other biocomponents of the sample, at higher concentrations, may be non-specifically adsorbed, or in a sandwich assay where the labelling indicating molecule is at a relative high concentration and can be non-specifically adsorbed. In this work, gold surfaces modified with CMDex combined with different oligo- and poly(ethyleneglycol) derivatives (PEG) are studied for its application in amperometric sensors. The non-specific adsorption of neutravidin-horseradish peroxidase (NHRP), a common labelling indicating molecule, on the different electrodes is analyzed considering the orientation that CMDex adopts on the surface based on results obtained by ellipsometry and amperommetry. The combination of CMDex with Methoxypolyethylene glycol succinate N-hydroxysuccinimide ester (MW: 5000 D) yields the best surface to reduce non-specific interactions. Also, CMDex was modified with biotin to establish the specific binding of NHRP and the effect of the tridimensional structure in the electrode response.