Department of Applied Chemistry, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656, Japan.
Anal Chem. 2010 Sep 1;82(17):7479-84. doi: 10.1021/ac1017088.
A photothermal detector, named differential interference contrast thermal lens microscope (DIC-TLM), was used to determine the concentration of a nonfluorescent solution in a nanochannel. This method exploits a local change in the refractive index of a solution caused by light absorption. A solution was introduced into a 100-nm scale channel by a pressure-driven nanofluidic control system and its concentration was determined by DIC-TLM. The limit of detection (LOD) was 2.4 microM in a nanochannel that was 21 microm wide and 500 nm deep. The LOD was 3 orders of magnitude smaller than that of conventional method. Moreover, the detection volume was accurately determined to be merely 0.25 fL by using a nanochannel with an optical path length of 500 nm. Based on these results, the number of detected molecules was calculated to be 390. In addition, the concentration of a solution in a nanochannel that was 790 nm wide and 500 nm deep could be determined. Finally, the relationship between sensitivity and channel size was investigated and the sensitivity was found to decrease with decreasing nanochannel size, which indicates that the changes in the refractive indices of water and silica cancel each other out. The DIC-TLM realizes sensitive detection of nonfluorescent species in nanochannels without requiring any special fabrication techniques. Therefore, DIC-TLM is expected to be a highly useful analytical technique in nanofluidics.
一种光热探测器，称为差分干涉对比热透镜显微镜（DIC-TLM），被用于测定纳米通道中无荧光溶液的浓度。该方法利用溶液吸收光引起的局部折射率变化。通过压力驱动的纳流控系统将溶液引入 100nm 尺度的通道中，并通过 DIC-TLM 测定其浓度。在 21μm 宽、500nm 深的纳米通道中，检测限（LOD）为 2.4μM。LOD 比传统方法小 3 个数量级。此外，通过使用光程为 500nm 的纳米通道，精确地将检测体积确定为仅 0.25fL。基于这些结果，计算出检测到的分子数为 390 个。此外，还可以测定 790nm 宽、500nm 深的纳米通道中溶液的浓度。最后，研究了灵敏度与通道尺寸的关系，发现灵敏度随纳米通道尺寸的减小而降低，这表明水和二氧化硅的折射率变化相互抵消。DIC-TLM 无需任何特殊的制造技术即可实现纳米通道中非荧光物质的灵敏检测。因此，DIC-TLM 有望成为纳流控领域中非常有用的分析技术。
