Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan.
Research Institute of Electrical Communication, Tohoku University, Sendai 980-8577, Japan.
Sensors (Basel). 2023 Jul 5;23(13):6177. doi: 10.3390/s23136177.
We demonstrate an S-shaped double-spiral microresonator (DSR) for detecting small volumes of analytes, such as liquids or gases, penetrating a microfluidic channel. Optical-ring resonators have been applied as label-free and high-sensitivity biosensors by using an evanescent field for sensing the refractive index of analytes. Enlarging the ring resonator size is a solution for amplifying the interactions between the evanescent field and biomolecules to obtain a higher refractive index sensitivity of the attached analytes. However, it requires a large platform of a hundred square millimeters, and 99% of the cavity area would not involve evanescent field sensing. In this report, we demonstrate the novel design of a Si-based S-shaped double-spiral resonator on a silicon-on-insulator substrate for which the cavity size was 41.6 µm × 88.4 µm. The proposed resonator footprint was reduced by 680 times compared to a microring resonator with the same cavity area. The fabricated resonator exposed more sensitive optical characteristics for refractive index biosensing thanks to the enhanced contact interface by a long cavity length of DSR structures. High quality factors of 1.8 × 10 were demonstrated for 1.2 mm length DSR structures, which were more than two times higher than the quality factors of microring resonators. A bulk sensitivity of 1410 nm/RIU was calculated for detecting 1 µL IPA solutions inside a 200 µm wide microchannel by using the DSR cavity, which had more than a 10-fold higher sensitivity than the sensitivity of the microring resonators. A DSR device was also used for the detection of 100 ppm acetone gas inside a closed bottle.
我们展示了一种 S 型双螺旋微谐振器 (DSR)，用于检测穿透微流道的小体积分析物，例如液体或气体。光学环形谐振器已被用作无标记和高灵敏度生物传感器，通过使用消逝场来感测分析物的折射率。增大环形谐振器的尺寸是放大消逝场与生物分子相互作用的一种解决方案，以获得更高的附着分析物的折射率灵敏度。然而，它需要一个百平方毫米的大平台，并且 99%的腔面积不会涉及消逝场感应。在本报告中，我们展示了一种基于硅的 S 型双螺旋谐振器在绝缘体上硅衬底上的新颖设计，其腔尺寸为 41.6 µm × 88.4 µm。与具有相同腔面积的微环谐振器相比，所提出的谐振器的足迹减少了 680 倍。由于 DSR 结构的长腔长增强了接触界面，因此该谐振器表现出更敏感的光学特性，适用于折射率生物传感。对于 1.2 毫米长的 DSR 结构，展示了 1.8 × 10 的高质量因子，比微环谐振器的质量因子高两倍多。通过使用 DSR 腔检测 200 µm 宽微通道内的 1 µL IPA 溶液，计算出 1410 nm/RIU 的体灵敏度，其灵敏度比微环谐振器的灵敏度高 10 倍以上。DSR 器件还用于检测封闭瓶内的 100 ppm 丙酮气体。
