Department of Science, Hongik University , 94 Wausan-ro, Mapo-gu, Seoul, Republic of Korea.
Neuroscience Institute, Gil Hospital , Incheon 405-760, South Korea.
ACS Appl Mater Interfaces. 2017 Sep 20;9(37):31478-31487. doi: 10.1021/acsami.7b09252. Epub 2017 Sep 7.
We demonstrated modulation of the waveguide mode mismatch via liquid cladding of the controllable refractive index for label-free quantitative detection of concentration of chemical or biological substances. A multimode optical fiber with its core exposed was used as the sensor head with the suitable chemical modification of its surface. Injected analyte liquid itself formed the liquid cladding for the waveguide. We found that modulation of the concentration of analyte injected enables a degree of the waveguide mode mismatch to be controlled, resulting in sensitive change in optical power transmission, which was utilized for its real-time quantitative assay. We applied the device to quantitating concentration of glycerol and bovine serum albumin (BSA) solutions. We obtained experimentally the limit of detection (LOD) of glycerol concentration, 0.001% (volume ratio), corresponding to the resolvable index resolution of ∼1.02 × 10 RIU (refractive index unit). The presented sensors also exhibited reasonably good reproducibility. In BSA detection, the sensor device response was sensitive to change in the refractive indices not only of liquid bulk but also of layers just above the sensing surface with higher sensitivity, providing the LOD experimentally as ∼3.7 ng/mL (mass coverage of ∼30 pg/mm). A theoretical model was also presented to invoke both mode mismatch modulation and evanescent field absorption for understanding of the transmission change, offering a theoretical background for designing the sensor head structure for a given analyte. Interestingly, the device sensing length played little role in the important sensor characteristics such as sensitivity, unlike most of the waveguide-based sensors. This unraveled the possibility of realizing a highly simple structured label-free sensor for point-of-care testing in a real-time manner via an optical waveguide with liquid cladding. This required neither metal nor dielectric coating but still produced sensitivity comparable to those of other types of label-free sensors such as plasmonic fiber ones.
我们通过可控制折射率的液体包层来调制波导模式失配，从而实现了对化学或生物物质浓度的无标记定量检测。我们使用暴露芯的多模光纤作为传感器头，并对其表面进行适当的化学修饰。注入的分析物液体本身形成了波导的液体包层。我们发现，注入的分析物浓度的调制可以控制波导模式失配的程度，从而导致光功率传输发生敏感变化，可用于实时定量分析。我们将该器件应用于定量检测甘油和牛血清白蛋白 (BSA) 溶液的浓度。我们通过实验获得了甘油浓度的检测限 (LOD)，为 0.001%（体积比），对应于可分辨的折射率分辨率约为 1.02×10 RIU（折射率单位）。所提出的传感器还表现出相当好的重现性。在 BSA 检测中，传感器装置的响应对液体本体和传感表面上方的层的折射率变化都很敏感，具有更高的灵敏度，实验上的 LOD 约为 3.7ng/mL（质量覆盖度约为 30pg/mm）。我们还提出了一个理论模型，同时考虑了模式失配调制和消逝场吸收，以理解传输变化，为设计给定分析物的传感器头结构提供了理论背景。有趣的是，与大多数基于波导的传感器不同，该装置的传感长度在诸如灵敏度等重要传感器特性方面几乎没有作用。这为通过具有液体包层的光波导以实时方式实现用于即时护理测试的高度简单结构的无标记传感器开辟了可能性。这既不需要金属也不需要介电涂层，但仍能产生与等离子体光纤等其他类型的无标记传感器相当的灵敏度。
