Abstract
We investigate a immunoassay biosensor that employs a Quartz Crystal Microbalance (QCM) to detect the specific binding reaction of the (Human IgG1)-(Anti-Human IgG1) protein pair under physiological conditions. In addition to experiments, a three dimensional time domain finite element method (FEM) was used to perform simulations for the biomolecular binding reaction in microfluidic channels. In particular, we discuss the unsteady convective diffusion in the transportation tube, which conveys the buffer solution containing the analyte molecules into the micro-channel where the QCM sensor lies. It is found that the distribution of the analyte concentration in the tube is strongly affected by the flow field, yielding large discrepancies between the simulations and experimental results. Our analysis shows that the conventional assumption of the analyte concentration in the inlet of the micro-channel being uniform and constant in time is inadequate. In addition, we also show that the commonly used procedure in kinetic analysis for estimating binding rate constants from the experimental data would underestimate these rate constants due to neglected diffusion processes from the inlet to the reaction surface. A calibration procedure is proposed to supplement the basic kinetic analysis, thus yielding better consistency with experiments.
Highlights
Efficient, accurate, and real-time monitoring of chronic diseases becomes more and more important for an aging society
In 1959, Sauerbrey [2] derived an equation to relate the change of the resonance frequency shift to the change of loaded mass on the crystal surface; namely, ∆f = −2f0 ∆M/A μQ ρQ, where ∆f is the frequency shift, ∆M is the change of the load mass, f0 is the oscillating frequency of the quartz without loaded mass, μQ is the elastic modulus of the quartz, ρQ is the density of the quartz and A is the area of the electrode
The conventional analysis yields the “apparent” association and dissociation rate constants k'a and k'd, but not the “true” ones. To remedy this deficiency in the basic kinetic analysis, in the following we propose a modified method, which calibrates the calculation of the conventional kinetic analysis, to recover the “true” reaction rate constants
Summary
Accurate, and real-time monitoring of chronic diseases becomes more and more important for an aging society. Biosensors provide a quick and convenient technology for real-time surveillance in health-care. When the specific target molecules (the analyte) carried by the buffer solution flow over the reaction surface of a biosensor, a specific binding reaction occurs between the analyte molecules and the immobilized ligand molecules. A variety of physical mechanisms have been used in the transducer to record the specific binding and the subsequent real-time examination takes place by amplifying these signals [1]. With its superior characteristics of timely reaction and high sensitivity, the Quartz Crystal Microbalance (QCM) has recently become a commonly used biosensor. The QCM uses the indirect piezoelectric effect as a way of energy transformation to timely record the resonance frequency shifts with a tiny mass loading. QCM was applied as a gas-sensing device [3]; nowadays, it is widely used in research on bioimmune tests [4,5]
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