A new affinity biosensor: Self-assembled thiols as selective monolayer coatings of quartz crystal microbalances

We report on the use of quartz crystal microbalances (QCMs) for on-line detection of bioaffinity interactions. The QCM transducer is of reasonable simplicity as compared to other transducers used in direct affinity sensing. However, the performance achieved with QCMs in liquids is in many cases inferior to the performance achieved in air. We have investigated the influence of several experimental parameters to improve the stability and performance of QCM in liquids. With the aim of achieving a densely packed sensitive layer the Au substrates were examined first with X-ray photoelectron spectroscopy (XPS) and scanning force microscopy (SFM). The successful immunological reaction of the subsequently immobilized antigen and antibody was demonstrated by an enzyme linked immunosorbent assay (ELISA) experiment. The same immunological reaction [determination of antibodies against the foot-and-mouth-disease virus (FMDV)] was then monitored with a QCM mounted in a flow-through cell. The sensitive coating of the QCM could be regenerated for successive use as mass sensitive biosensor.