Development of impedimetric biosensors for carbohydrate detection

Electrochemical impedance spectroscopy (EIS) has been employed to study protein-carbohydrate interaction using concanavalin A as a model protein. A novel biosensor based on Con A has been developed using a mixed self-assembled monolayer (mSAM) format comprising of 16- mercaptohexadecanoic acid (MHDA) and the interchelating phospholipids bearing a biotin group (biotin caproyl-DPPE) on a planar electrode. Biotinylated Con A was then linked to the layer using Neutravidin as crosslinker. Each stage in the biosensor construction and analyte detections were investigated using EIS and cyclic voltammetry (CV). Quartz crystal microbalance (QCM) and total internal reflection ellipsometry (TIRE) analysis were also carried out to follow each step of the biosensor construction. Interactions between Con A and carbohydrates of differing in chain length, ranging from monosaccharides to polysaccharides, and the glycoprotein human choriogonadtrophin (hCG) were investigated. It was found that larger oligomers could produce disruption in the impedance signa!. Data from further investigation using a series of defined oligomers with degree of polymerisation (DP) 1 to 7 (glucose to maltoheptaose respectively) implied that protein aggregation occurred at four units of glucose or more and that this was due to pinhole generation on the biosensor surface. This was indicated by a decrease in the charge-transfer resistance (Rct). However, the signal disruption was not observed when using a base layer of a copolymer of aniline and 2-aminobenzylamine (2-ABA) as the tethering template for lectin immobilisation. This suggests that a thick and rigid tethering template is required for larger glycoconjugates detection by lectins. Human blood group-specific lectins were then utilised in the copolymer system as proof-of- principle for blood typing. The biosensor was highly specific to blood group 0 sample with low detection limit of 100 erythrocytes/mlEThOS - Electronic Theses Online ServiceGBUnited Kingdo