Multichannel wireless-electrodeless quartz-crystal microbalance immunosensor.

We develop the wireless-electrodeless multichannel quartz-crystal microbalance (QCM) biosensor using quartz plates of slightly different thicknesses. Their shear vibrations are simultaneously excited and detected by a pair of antenna wires to perform the noncontacting measurement. Their fundamental resonance frequencies are between 43 and 55 MHz, and vibrations at up to 10 channels are measured in liquids. Owing to high affinity of naked quartz surfaces for proteins, we immobilized various receptor proteins on different quartz plates nonspecifically and detected various antigen-antibody reactions separately. The exponential coefficient of the frequency change, rather than the amount of the frequency decrease, is found to be useful for distinguishing between specific and nonspecific binding reactions.

170-MHz electrodeless quartz crystal microbalance biosensor: capability and limitation of higher frequency measurement.

We develop a highly sensitive quartz crystal microbalance (QCM) biosensor with a fundamental resonance frequency of 170 MHz. A naked AT-cut quartz plate of 9.7 microm thick is set in a sensor cell. Its shear vibration is excited by the line wire, and the vibration signals are detected by the other line wire, achieving the noncontacting measurement of the resonance frequency. The mass sensitivity of the 170 MHz QCM biosensor is 15 pg/(cm2 Hz), which is better than that of a conventional 5 MHz QCM by 3 orders of magnitude. Its high sensitivity is confirmed by detecting human immunoglobulin G (hIgG) via Staphylococcus protein A immobilized nonspecifically on both surfaces of the quartz plate. The detection limit is 0.5 pM. Limitation of the high-frequency QCM measurement is then theoretically discussed with a continuum mechanics model for a plate with point masses connected by elastic springs. The result indicates that a QCM measurement will break down at frequencies one-order-of-magnitude higher than the local resonance frequency at specific binding cites.

Replacement-free electrodeless quartz crystal microbalance biosensor using nonspecific-adsorption of streptavidin on quartz.

This paper proposes a replacement-free and surface-modification-free quartz crystal microbalance (QCM) biosensor. With the use of significant nonspecific adsorption of streptavidin on naked quartz surfaces, target analyte is detected through biotin-tagged receptors on streptavidin. The wireless-electrodeless QCM technique is developed with a 30 microm thick AT-cut quartz plate, whose fundamental resonance frequency is 55 MHz, and the naked quartz surfaces are used for the nonspecific adsorption of streptavidin. Once it is installed in the sensor cell, it can be used semipermanently; it never needs to be replaced. The equilibrium dissociation constant of streptavidin on quartz is determined to be 1.3 x 10(-7) M. The flow rate affected the number of the adsorbed streptavidin on quartz as well as the binding velocity.

Nonspecific-adsorption behavior of polyethylenglycol and bovine serum albumin studied by 55-MHz wireless-electrodeless quartz crystal microbalance.

The nonspecific binding ability of polyethylenglycol (PEG) and bovine serum albumin (BSA) on modified and unmodified surfaces is quantitatively studied by a wireless-electrodeless quartz crystal microbalance (WE-QCM). PEG and BSA are important blocking materials in biosensors, but their affinities for proteins and uncoated substrates have not been known quantitatively. The WE-QCM allows quantitative analysis of the adsorption behavior of proteins on the electrodeless surfaces. Affinities of PEG, BSA, human immunoglobulin G (hIgG), and Staphylococcus protein A (SPA) for alpha-SiO(2)(quartz), Au thin film, PEG, and BSA are systematically studied by the homebuilt flow-injection system. PEG shows low affinities for the SiO(2) surface (K(A)=4.2x10(4) M(-1)) and the Au surface (K(A)=6.6x10(4) M(-1)), but BSA shows higher affinity for the SiO(2) surface (K(A)=1.4x10(6) M(-1)). Both PEG and BSA show low affinities for hIgG (K(A) approximately 1.5x10(5) M(-1)). However, the number of binding sites of PEG to hIgG is significantly larger than that of BSA, indicating that blocking for hIgG is favorably achieved by BSA, rather than PEG.