硅纳米柱光波导级联微环谐振器的超灵敏生物传感机理研究

Silicon optical waveguide microring biosenor has great potential for life science research, disease diagnosis and drug development, for its advantages of ultracompact size, high quality-factor, compatible with CMOS technology, and easiness to large scale integration. However, the cladding evanescent field-biomolecules overlap in normal silicon waveguide is relatively small, which limit its sensitivity. Even though silicon slot waveguide can largely increase this overlap, the big scattering loss at the sidewall of slot deteriorates the detection limit level of microring. In this project, we propose a new optical waveguide composed by periodic silicon nanopillars, in which the light-biomolecules interaction can be greatly enhanced. And upon this, by cascaded microring design, the detecting sensitivity can be further greatly improved by the "Vernier effect" brought by spectra overlap of these two microrings. We plan to explore the physical mechanism for enhancing mode field-biomolecules interaction in this waveguide. And the biosensor will be fabricated by E-beam lithography and silicon dry etching. At last, the DNA molecules will be detected by this sensor and the high sensitivity and low detection limit will be demonstrated. Through this project we can break through the sensitivity limit of silicon waveguide biosensor. Two order of magnitudes improvement on the sensitivity would be attained. The results of this project would also provide a powerful theoretical instruction and experimental demonstration for constructing highly integrated and supersensitive biosensing chips.

硅基光波导微环谐振生物传感器具有体积小、品质因子高、制作工艺与CMOS技术兼容、易规模集成等优点，对生命科学研究、疾病诊断、新药开发等具有重要意义和价值。但传统硅波导依赖较弱的包层倏逝场与被探测生物分子相互作用，导致传感灵敏度较低。而硅狭缝波导虽可提高光与生物分子相互作用，但侧壁散射损耗较大，使得微环检测极限变差。本项目创新性的提出一种周期排列硅纳米柱光波导，可显著增强光与生物分子相互作用。在此基础上，通过级联微环设计，利用两微环光谱叠加的"游标卡尺"效应来进一步提升传感灵敏度。本项目从理论上探索增强波导模场与生物分子相互作用的物理机制，并利用电子束光刻和硅干法刻蚀技术制作生物传感器。以DNA分子检测为例，验证生物传感的高灵敏度和低检测极限。本项目的研究将从理论机理上突破现有硅基光波导生物传感器的灵敏度局限，可望将灵敏度提升2个数量级，并为制作高度集成、超灵敏生物传感芯片提供实验指导。

集成光学微腔具有很高的谐振品质因子和极小的体积，可在微纳米尺度上增强光与物质的相互作用，在生物化学传感方面具有广阔应用前景。然而，传统的集成光学微腔传感器仅依靠光谱的漂移来测量环境折射率改变，只能用于单一被探测物的实折射率传感，无法用于多种被探测物的同时检测，极大的限制了集成微腔传感器在复杂传感中的应用。为解决上述瓶颈问题，本课题提出一种基于硅基亚波长光栅结构微环的复折射率传感器。通过微环回音廊谐振模与亚波长波导法布里-珀罗谐振模之间的干涉，产生非对称的Fano谐振谱线。利用Fano谱线的峰值波长漂移来检测折射率实部改变，同时利用Fano谱线的斜率来测量折射率虚部改变，从而实现对多种混合物质的复折射率传感。该新型传感器利用亚波长光栅波导的结构特点，显著增强了光与物质的相互作用，同时利用Fano谱线的陡峭特点，大大提高了复折射率传感灵敏度。对葡萄糖溶液的传感结果表明，该传感器对折射率实部的传感灵敏度为366nm/RIU，而对折射率虚部的传感灵敏度则高达9700/RIU。该传感器可利用标准CMOS工艺批量制作，可望进一步实现阵列化，从而能够同时探测多种目标物质或分子。