An investigation into biological recognition coatings for piezoelectric sensors

The concept of harvesting chemicals from nature and employing them with piezoelectric crystals for biosensor development is investigated. Literature is reviewed for information theory relating to molecular structure, biosensors, immobilisation techniques, piezoelectric transducers and biosensor applications of quartz crystals. Three types of molecules were investigated for their biosensing potential, saccharides (pectic acid and alginic acid), an enzyme (galactose oxidase) and an antibody (specific for Botrytis cinerea). Immobilisation procedures using #gamma#-aminopropyltrimethoxy silane, polyethyleneimine and glutaraldehyde cross-linking are developed for pectic acid, alginic acid, galactose oxidase and the Botrytis antibody. These materials are immobilised onto the gold electrode area of an AT-cut quartz crystal microbalance. Operating conditions, either dip and dry batch monitoring or dynamic real-time monitoring using a flow cell are outlined. Ageing of the piezoelectric crystal sensor through erosion of coatings or during physical cleaning of crystals, prior to recoating, is featured and is particularly important to future cost effective commercial piezoelectric crystal sensor systems. Scanning tunnel microscopy is selected and an example from literature is used to evidence possible mechanisms of primary coat bonding to the gold electrodes. The associated cleaning problems and explanation of memory effects are then postulated. Calibrating data with sensitivities and limits of detection are presented for Cu"2"+ (pectic acid coating, Cu"2"+ range of 0.002mM (0.128ppm) to 0.5mM (32ppm); galactose oxidase coating, Cu"2"+ range of 0.002mM (0.128ppm) to 0.5mM (32ppm)); and for Pb"2"+ (alginic acid coating, Pb"2"+ range of 0.002mM (0.414ppm) to 0.1mM (20.7ppm)). Interference effects of Pb, Co, Ni, Zn, Ca and Mg on Cu"2"+ detection and measurement are presented. Similarly interference effects of Cu, Co, Ni, Zn and Ca on Pb"2"+ detection and measurement are presented. Sauerbrey working of the data is presented, estimating the mass change at the crystal surfaces. The worked data from the dip and dry experiments indicate the mass of analyte bound to the crystal coatings. The data from the flow cell experiments are less conclusive as the saccharide coatings changed structure on contact with divalent ions and the resulting frequency shift relates not only the change in mass at the crystal surface but also the change in structure of the coatings. The results indicate the useful and problem areas of the coatings, when integrated with a quartz crystal to form an analyte specific qualitative and quantitative micromass chemical measurement system. (author)Available from British Library Document Supply Centre- DSC:DXN058359 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo