Research on the Sensitivity Enhancement by Varifocal Electrowetting Effect in Surface Plasmon Resonance Waveguide Sensor

Abstract

As science and technology are developed in modern times, people are becoming exposed to many diseases. Because of this, research and development on the biosensor are getting a great attention. Among many researches on the biosensor, recent researches have focused on the application of Point-of-Care (POC) system, which is defined as simple medical diagnosis that can be conducted at the bedside. So as to exploit the biosensor for POC system, several characteristics such as real time measure-ment, portability, and ease-of-use are required. These features can be achieved by utilizing surface plasmon resonance (SPR) technology. There are many different types of biosensor using SPR technology. In this thesis, a study on the waveguide type SPR sensor is included because this type has many advantages including min-iaturization and cost effective fabrication process. Previously developed waveguide type SPR sensors are only based on the spectral modulation with keeping the incident angle of the light constant. That is because it is difficult to change the incident angle in a waveguide structure. These sensors have critical limitations in terms of the sensitivity because the incident angle is important parameter in surface plasmon resonance condition. However, this limitation can be easily overcome by using varifocal electrowetting effect of electrowetting (EW) lens. Therefore, in this research, a novel SPR waveguide sensor using both the spectral modulation and the angular modulation is proposed. Firstly, numerical simulations are conducted for optimization of structure and analysis of angular properties. Subsequently, the SPR waveguide sensor is fabricated in accordance with optimization results and evaluated by measuring and calculating the normalized intensity, the operating range, and the sensitivity. The proposed SPR waveguide sensor shows that the minimum value of the normalized intensity is 0.1 ？ 0.3, the operating range is 511.4 ？ 576.2nm, and the sensitivity is 2160nm/RIU. Compared to the sensitivity of the conventional sensing system based only on the spectral modula-tion, the sensitivity of the proposed sensing system is enhanced by up to 169.7%. This result demonstrates that the performance of the sensor can be further improved when using both the spectral modulation and the angular modulation.