title: Isolated electrodeless high-frequency quartz crystal microbalance for immunosensors.
abstract: This paper presents a contactless technique to measure shear bulk wave resonance frequencies of an isolated quartz crystal in a flow cell. The line antenna placed outside the cell generates and detects the resonance frequencies in a wireless-electrodeless manner. It is revealed that this mechanism relies on the quasistatic electric field. A 0.3-mm-thick AT-cut quartz was used, and its overtone resonance frequencies up to 80 MHz were measured in liquids. Exact vibrational analysis was carried out for a triple-layered resonator system consisting of the adsorbed material layer, the electrode film, and the quartz plate. It predicts higher frequency sensitivity to the adsorbed material at higher modes when the electrode layer is removed. The 13th overtone (72-MHz resonance frequency) was used to detect human immunoglobulin G with concentrations between 0.1 and 20 microg/mL captured by protein A immobilized on one side of the crystal. The real-time measurement of the frequency response yielded the equilibrium constant KA=5.21 x 10(7) M(-1).
authors.affiliation: Graduate School of Engineering Science, Osaka University. Toyonaka, Osaka 560-8531, Japan. ogi@me.es.osaka-u.ac.jp
authors.forename: Hirotsugu
authors.initials: H
authors.lastname: Ogi
authors.forename: Kazuma
authors.initials: K
authors.lastname: Motoshisa
authors.forename: Takashi
authors.initials: T
authors.lastname: Matsumoto
authors.forename: Kenichi
authors.initials: K
authors.lastname: Hatanaka
authors.forename: Masahiko
authors.initials: M
authors.lastname: Hirao
mesh_terms: D015374:Biosensing Techniques; D004566:Electrodes; D006801:Humans; D007074:Immunoglobulin G / Q000032:analysis; D011791:Quartz
chemical_list: D007074:Immunoglobulin G; D011791:Quartz