Ultrasensitive quartz crystal microbalance sensors for detection of M13-Phages in liquids

Quartz crystal microbalance (QCM) sensors are widely used for determining l iquid properties or probing interfacial processes. For some applications th e sensitivity of the QCM sensors typically used (5-20 MHz) is limited compa red with other biosensor methods. In this study ultrasensitive QCM sensors with resonant frequencies from 39 to 110 MHz for measurements in the liquid phase are presented. The fundamental sensor effect of a QCM is the decreas e of the resonant frequency of an oscillating quartz crystal due to the bin ding of mass on a coated surface during the measurement. The sensitivity of QCM sensors increases strongly with an increasing resonant frequency and, therefore, with a decreasing thickness of the sensitive area. The new kind of ultrasensitive QCM sensors used in this study is based on chemically mil led shear mode quartz crystals which are etched only in the center of the b lank. forming a thin quartz membrane with a thick, mechanically stable oute r ring. An immunoassay using a virus specific monoclonal antibody and a M13 -Phage showed an increase in the signal to noise ratio by a factor of more than 6 for 56 MHz quartz crystals compared with standard 19 MHz quartz crys tals, the detection limit was improved by a factor of 200. Probing of acous tic properties of glycerol/water mixtures resulted in an increase in sensit ivity, which is in very good agreement with theory. Chemically milled QCM s ensors strongly improve the sensitivity in biosensing and probing of acoust ic properties and, therefore, offer interesting new application fields for QCM sensors. (C) 2001 Elsevier Science B.V. All rights reserved.