Metamaterial – based sensor for detection of biomolecules

Recently, the interest of microwave signals for biological detection applications using metamaterial structure as a biosensor element is tremendously increased due to high Q factor value and stronger electric field compared to the conventional microwave sensor. This research refers to a proof-of-concept study concerning the development of a metamaterial based sensor for biomolecule detection. The first part of this thesis is focusing on the design and characterisation of two novel planar μ-negative metamaterial structure, called Aligned Gap Split Ring Resonator (AGSRR) and Centered-Gap Split Ring Resonator (CGSRR). AGSRR is a multi-ring split ring resonator that differs from conventional split ring resonator (SRR) where the split gaps of all rings are aligned towards the same directions to obtain stronger localization of electric field at particular spots. Furthermore, Centered-Gap SRR (CGSRR) is proposed as a second design, where it combines multiple SRRs in a compact design, thus being able to miniaturize the whole structure by 64% from AGSRR structure. An investigation of the electric field distribution is conducted for AGSRR and CGSRR at resonance frequency to identify the suitable location for sensing application. The simulation results show both structures are able to obtain approximately around 400 Q factor value which lead to a better sensitivity of a sensor. In the second parts of the thesis, the proposed metamaterial structures are exploited in the designs of novel microwave sensors using Computer Simulation Technology (CST) Microwave Studio. All dimensions of the sensors are in miliscale and the operating resonance frequency is within C band. The sensing mechanism is based on perturbing the electromagnetic field around the spots, thus initiating a shift in resonance frequency that is used as an indicator of the sensor sensitivity. Sample loading with dielectric samples at these local spots is simulated and investigated in detail. By comparing to existing research works, the electric field at the occupied sensing area is strong and localized, yet required only small size of 1 mm2 sample to induce a measureable frequency shift. In the final part of this thesis, both sensors are fabricated and the sensitivity is characterised by loading several sample in solid and liquid form as well as biomolecules material with different concentrations. Both sensors demonstrate a maximum of 500 MHz frequency shift for liquid and solid sample compared to existing works by Wiwatcharagoses et al., which is around 350 MHz for maximum value of dielectric sample. Furthermore, the maximum values of frequency shifts obtained for these sensors are 70 MHz for ssDNA and 150 MHz for dsDNA compared to the reported literature by Lee et al., 20 MHz for ssDNA and 60 MHz for dsDNA. It can be concluded that, the sensitivity of these biosensors are up to 10 MHz/μMolar with the detection limit of 1μMolar are conducted during this experiment. The experiments have demonstrated that the presence of DNA can be detected at microwave frequency. Due to its simplicity of fabrication, it is expected that the proposed microwave biosensor could be a candidate for exploring cost competitive, reusable or disposable bioanalysis system.

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