Affinity biosensor for avidin using a double functionalized dendrimer monolayer on a gold electrode

We have developed an affinity biosensor system based on avidin-biotin inter action on a gold electrode. As the building block of an affinity-sensing mo nolayer, a fourth-generation (G4) poly(amidoamine) dendrimer having partial ferrocenyl-tethered surface groups was prepared and used. The unmodified s urface amine groups from dendrimers were functionalized with biotinamidocap roate, and the biotinylated and electroactive dendritic monolayer was const ructed on a gold electrode for the affinity-sensing surface interacting wit h avidin. An electrochemical signal from the affinity biosensor was generat ed by free glucose oxidase in electrolyte, depending on the degree of cover age of the sensing surface with avidin. The sensor signal decreased correla tively with increasing avidin concentration and approached a minimum level when the sensing surface was fully covered with avidin. The detection limit of avidin was about 4.5 pM, and the sensor signal was linear ranging from 1.5 pM to 10 nM under optimized conditions. From the kinetic analysis using the biotinylated glucose oxidase, an active enzyme coverage of 2.5 x 10(-1 2) mol/cm(2) on the avidin-pretreated surface was registered, which demonst rates the formation of a spatially ordered and compact protein layer on the derivatized electrode surface. (C) 2000 Academic Press.