Surface Acoustic Waves-Based Point-Of-Care Biosensor
Abstract
A biosensor is an analytical tool consisting of biologically active material used in close conjunction with a device that converts a biochemical signal into a quantifiable electrical signal. The early detection of the disease biomarkers can enhance the increased curability of the disease, reduce healthcare costs, and finally, improve the quality of life for patients. Thus, for the following purpose, there is always a need for an effective biosensor as a diagnostic device. The biosensor typically consists of an actuator, a bio-recognition component, and a transducer that converts captured signals into a meaningful display. The bio-recognition component uses biomolecules to interact with the analyte of interest. The biological interaction is measured by the transducer which outputs a measurable signal proportional to the presence of the target analyte or biomarker present in the sample. The biosensors are diversely classified based on the biomarkers and transducer-based components. Optical, electrochemical, piezoelectrical, magnetic, and thermometric are some commonly used transducer-based techniques for the biosensing purpose. The biosensor designing faces numerous challenges such as higher costs, uneasy accessibility, massive and complicated setups, poor reproducibility, the requirement of skilled personnel, and most of all, high sensitivity, and selectivity of the biomarker detection by the biosensor. High sensitivity is a large measurable change in the biosensor signal as a function of slight changes in the analyte or a biomarker concentration. The sensitivity in the biosensing is defined by the upper and lower limits of detection indicating the maximum and the minimum bio-analyte concentration that can be detected and measured accurately. Selectivity on the other hand is a key parameter that indicates the sensor will only respond to the target analyte ignoring all the other analytes and biomarkers present in the sample. A poor selectivity-based biosensor will lead to false positive and false negative results which will directly affect the specificity of the sensing platform irrespective of its ultra-high sensitivity. In this thesis, an ultrasensitive and highly selective tone burst-based surface acoustic wave sensor is developed for the detection of the cyanotoxins present in a water sample utilized for agricultural and human consumption purposes. The designed biosensing platform consists of novel concentric circular interdigitated electrodes as an actuator along with focused interdigitated electrodes and 5-count tone burst electrode as the sensing electrodes on top of a 36°-YX cut lithium tantalate anisotropic piezoelectric wafer for the surface acoustic waves-based sensing. The piezoelectric wafer produces shear horizontal waves which are non-dispersive and non-decaying. The orthogonal movement of particles corresponding to the direction of the wave propagation enables it to work better under liquid media. Thus, making it an excellent platform, especially for biosensing and chemical sensing. The novel biosensor utilizes different bio-specific chemicals and nanoparticles-based biosensing layers along with multiple sensing electrodes and test sites for supporting reproducibility and thus, boosting the selectivity and sensitivity. The involvement of the unique electrodes (tone burst and focused electrodes) enables access to a broader frequency range and higher amplitudes for higher sensitivity in diagnosing the cyanotoxins, unlike the conventional configuration that mostly deals with the peak central frequency. Conventional SAW-grade biosensors are only limited to phase shifts and continuous waveform signals for their detection quantification. The proposed biosensor involves tone burst signal for sensing and actuation, also includes acoustic features extracting tools and signal transformations like Fast Fourier Transform, signal enveloping, Hilbert transformation and peak count, giving a leading edge for the enhanced sensitivity and thus, lowering the limit of detection. The novel ultrasonic biosensor is designed in such a fashion that it does not require a high amount of biofluid sample unlike conventional biosensors. The sensor supports low power consumption, low material cost per sample and thus, enabling it to be lab-on-a-chip, biosensor with high sensitivity and selectivity. Last but not least, the novel biosensor is enabled with the feature of instantaneous diagnostic results which saves time and thus, delivers it to be a point-of-care (POC) biosensor which is desired worldwide. The novel tone burst biosensor successfully detects microcystin-LR which is the most toxic cogener of the harmful algal bloom, cyanobacteria and surpasses its predecessor design of conventional delay line sensing system. This is regarded both in terms of sensitivity and selectivity. The novel biosensor has the capability of the successful detection of any biomarkers and not just cyanobacteria, which makes it a powerful and robust device, especially in the field of disease diagnostics and future outbreaks which requires early detection with instant results.