Signal Enhancement by Dynamic Polymers in Quartz Crystal Microbalance Applications

Abstract:  This licentiate thesis presents studies of signal enhancement by dynamic polymers in quartz crystal microbalance (QCM) applications. The aim of the study has been to determine the potential for the use of polymers on QCM sensors for signal enhancement in molecular interaction studies. A method for synthesis of polymer sensor surfaces on QCM substrates was developed based on an iniferter photo polymerization technique. Polymerized poly(acrylic acid) and poly(acryl amide) surfaces were extensively characterized with electron spectroscopy for chemical analysis (ESCA), infrared reflection absorption spectroscopy (IRAS) and atomic force microscopy (AFM). The QCM response dynamics of these surfaces to pH changes was studied and the carboxyl containing surfaces exhibited large, reversible and highly reproducible frequency shifts due to expansion of deprotonated polymer chains. Surface acid dissociation constants (pKa) were determined for poly(acrylic acid) surfaces, carboxymethyldextran surfaces and self-assembled monolayer carboxyl surfaces by means of pH titration in QCM flow-through instrumentation. Surface pKa data was consistent with available literature data. The sensitivity enhancement for molecular interaction studies was investigated for poly(acrylic acid) coated QCM sensors with a model system consisting of immobilized biotin and an anti-biotin Fab fragment. Binding responses of antibiotin Fab to immobilized biotin was revealed to be 11 times higher than the corresponding results for a carboxylated SAM surface.