Self-assembly of biotin and thio-functionalized carboxymethyl celluloses on gold and molecular recognition of streptavidin detected by surface plasmon resonance

Biotin was attached via a spacer group to thiomethyl and thiosulfate derivatives of carboxymethylcellulose (CMC) by DCC coupling. A degree of substitution (DS) 0.3 per modified anhydroglucose unit was reached for the biotin moieties. These biotinylated CMCs are able to recognize the receptor protein streptavidin in aqueous solution as demonstrated by gel electrophoresis. Furthermore, they spontaneously form stable monolayers of 1-2 nm thickness on planar gold surfaces as evidenced by surface plasmon resonance (SPR). These monolayers irreversibly bind streptavidin. The observed increase of layer thickness of 6 nm resembles the size of a single streptavidin molecule. Consequently, dense streptavidin monolayers must have been formed. The resulting functional monolayers of CMC derivatives on gold are interesting platforms for biosensors, because they are very stable, hydrophilic, and formed in a reproducible way.