A Modus Operandi of One-port Surface Acoustic Wave (SAW)Resonator Sensing System to Characterize Liquids and Biomolecular Interactions.

Surface acoustic wave (SAW) devices have been utilized in sensing applications to detect a particular analyte and liquid characterization primarily based on mass of the target. Line up of common SAW device configuration employed as sensor includes SAW delay line, two-port SAW resonator and one-port SAW resonator.
   
   Among the configurations, one-port SAW resonator holds an upper-hand on responsiveness, compactness and sensitivity. However, the configuration of one port does not offer an explicit cavity or open area for liquid sensing and hence signal measured immediately attenuated when target liquid is in contact with interdigital transducer (IDT) of the device. Further credit to absence of cavity, there is a necessity for much delicate microfluidic channel to pass the liquid to the resonator.
   
   Hence, presenting one-port SAW resonator as practical liquid sensor is equivalent as introducing a highly responsive, compact and sensitive sensor in the field of liquid detection. However, work established on using the device for practical liquid sensing is rarely reported and document detailing the fundamental theory to operate the device in liquid environment is singular. Because of this, it is both stimulating and essential to explore resolution to the addressed stumble block.
   
   This thesis proposes approaching one-port SAW resonator to operate in liquid environment. Furthermore, to promote the configuration as potential liquid sensor, the application of one-port SAW resonator is suggested as well for chemical and biosensing. For the later application, surface of the device has to be functionalized to immobilize target of interest. The material selected for surface functionalization is carboxymethyl cellulose (CMC) due to its biocompatibility, availability and simplicity in coating. By date, there is always an immense interest of using CMC modified cellulose in diagnostic platform and the material was recently applied in biosensing application.
   
   In view of the aforementioned matter, the foremost aim of this thesis is to approach one-port SAW resonator to characterize liquid and biomolecular interaction. Firstly, one-port SAW resonator was designed and fabricated, following is the experimental setup for liquid injection which involves the design and fabrication of microfluidic housing for the device, packaging of the flow cell for measurement and microfluid dispensing system. The key findings of this work comprises original microcontroller based microfluid injection system, flow cell packaging and shear horizontal displaced one-port SAW resonator operated at radio frequency.
   
   Secondly, phosphate buffer saline (PBS) as liquid model was injected to the flow cell enclosing one-port SAW resonator for liquid characterization. To exploit possible region of one-port SAW resonator as potential detection zone, the liquid was passed across surface of the resonator in such that the liquid streamed through 1 feature size of electrode per second. Changes of signal response were carefully observed as liquid flow through the flow cell and the result was analysed to address possible liquid sensing region of the device. The key finding of this work is derivation of an approach to characterize liquid using one-port SAW resonator without additional coating layer for insulation purpose.
   
   Thirdly, surface of the one-port SAW resonator was functionalized with cellulose model layer and further modified via reversible adsorption of CMC to the cellulose surface. The surface foundation was allowed to bind with bovine serum albumin (BSA) to function the device for basic biosensing objective. Performance characterization of the device for both chemisorption and physisorption of the protein on the surface was conducted and analysed. Novelty of this work is features on capability of the one-port SAW resonator to discriminate strong and weak binding of BSA on surface of CMC modified cellulose using the methodology for liquid sensing derived earlier.
   
   Overall, the main contribution of the work is derivation of an approach to realize an operational one-port SAW resonator readily employed for characterization of liquids and biomolecular interaction. The sensor features defined resonant frequency and signal of high responsiveness without application of complicated electronic filters and impedance matching circuit.