Nanofluidics which integrates analytical systems in 10¹–10³ nm space provides ultra-sensitive analyses at a single-cell and single-molecule level. One of the key technologies for nanofluidics is the ultra-sensitive detection method; however, the ultra-small volume at aL–fL scale makes it challenging. Recently, we have developed a non-fluorescent molecule detection method for nanofluidics called photo-thermal optical diffraction (POD) which utilizes the photo-thermal effect of target molecules and optical diffraction by a single nanochannel. To improve the performance of such diffraction-based detection methods, the design and optimization of optical diffraction are essential. However, it is unknown whether the optical diffraction by a single nanochannel follows general diffraction theory because liquid properties change in the ultra-small space. In this study, we elucidated optical diffraction by a single nanochannel from theoretical calculations and experiments. Our experiments revealed the effect of channel size, channel position, and solvents in the nanochannel, which showed good agreement with proposed theoretical calculations. We also revealed no or little change of refractive index of water in the nanochannel compared with that in the bulk. Finally, we confirmed that the POD signal was proportional to the diffracted light intensity, and the calculated limit of detection of POD was 7.0 × 10^–7 RIU in a detection volume of 0.23 fL. Our theoretical calculations and experimental results can be widely applied to the design and optimization of detection methods using optical diffraction by nanochannels and nanostructures.

将分析系统集成到10 ^{1 –} 10 ^3中的纳米流体 nm空间可在单细胞和单分子水平上提供超灵敏的分析。纳米流体的关键技术之一是超灵敏检测方法。然而，aL–fL规模的超小体积使其具有挑战性。最近，我们开发了一种用于纳米流体的非荧光分子检测方法，称为光热光学衍射（POD），该方法利用目标分子的光热效应和单个纳米通道的光学衍射。为了提高这种基于衍射的检测方法的性能，光学衍射的设计和优化是必不可少的。然而，由于液体性质在超小空间中变化，因此未知单个纳米通道的光学衍射是否遵循一般的衍射理论。在这个研究中，我们从理论计算和实验中阐明了单个纳米通道的光学衍射。我们的实验揭示了通道尺寸，通道位置和纳米通道中溶剂的影响，这与拟议的理论计算显示出良好的一致性。我们还发现，与整体通道相比，纳米通道中水的折射率没有变化或几乎没有变化。最后，我们确认POD信号与衍射光强度成正比，计算出的POD检测限为7.0×10 我们还发现，与整体通道相比，纳米通道中水的折射率没有变化或几乎没有变化。最后，我们确认POD信号与衍射光强度成正比，计算出的POD检测限为7.0×10 我们还发现，与整体通道相比，纳米通道中水的折射率没有变化或几乎没有变化。最后，我们确认POD信号与衍射光强度成正比，计算出的POD检测限为7.0×10^–7 RIU，检测量为0.23 fL。我们的理论计算和实验结果可广泛应用于通过纳米通道和纳米结构进行光学衍射的检测方法的设计和优化。