Abstract
The frequency shift of a shear-horizontal surface-acoustic-wave (SH-SAW) biosensor in which the concentration of biomolecule is determined by the amount of its adsorption on the sensing film was studied. Simulation results were compared with experimental results to investigate its sensitivity and to develop a model to estimate the concentration of a cancer-related biomarker antigen epidermal growth factor (EGF) in the sample, with two types of sensing films, 3-aminopropyltriethoxysilane (APTES) and glutaraldehyde. With the concentration of the targeted biomarker varying from 0.2 to 5 ng/mL, a typical exponential relationship was found between the concentration and the frequency shift of the SH-SAW sensor. Measurement results showed a clear response of this immunosensor to the mass-loading effects of the antibody–antigen. The sensitivity of the glutaraldehyde film is greater than that of the APTES film owing to the chemisorption of the antibody. In the simulation, a shift of the SH-SAW resonant frequency due to added mass occurred on applying an incremental surface mass density on the sensing film, while in real applications, the concentration of the targeted biomarker to be absorbed in the sensing film is demanded. An empirical model was proposed to calculate the frequency shift in the simulation of the SH-SAW biosensor, corresponding to the concentration of specific biomolecules absorbed on a specific film. From the semi-empirical model, the sensitivity level is found to be 0.641 and 1.709 kHz/(ng/mL) for APTES and glutaraldehyde sensing films, respectively, at a biomarker concentration of less than 1 ng/mL. The developed method is useful for quickly estimating the frequency shift with respect to the concentration of the target molecules in the simulation for SH-SAW sensors.
Highlights
Surface-acoustic-wave (SAW) sensors, with their advantages of high sensitivity, low cost, low power requirement and real-time monitoring, have great potential in the application of immune sensing, environmental monitoring and biotechnology
Most SAW biosensors are composed of a delay-line configuration that consists of interdigital transducers (IDTs) placed on a piezoelectric substrate, with a sensing film between the input and output IDTs
Biosensors 2020, 10, 92 a periodic strain field is generated along the surface, due to the inverse piezoelectric effect, that leads to the propagation of surface waves through the sensing film to be detected on the output IDTs [2]
Summary
Surface-acoustic-wave (SAW) sensors, with their advantages of high sensitivity, low cost, low power requirement and real-time monitoring, have great potential in the application of immune sensing, environmental monitoring and biotechnology. In the current study, we focused on investigating and demonstrating the feasibility of applying SH-SAW for detecting EGF at a concentration that is compatible with biofluids. The sensitivity of these two sensing films was measured and discussed. Most previous numerical studies for SH-SAW devices have focused on the determination of the optimal thickness of the guiding layer to increase the sensitivity [14,26,27]. Proposed model, which was modified from the concept of the Sauerbrey equation, provides a useful approach to effectively and accurately analyzing the frequency shift corresponding to the concentration of sensed molecules while greatly reducing the complexity of the mass transport analysis in the sensing film
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