Understanding fluid flows and mass transport in nanospaces is becoming important with recent advances in nanofluidic analytical devices utilizing nanopores and nanochannels. In the present study, we developed a super-resolution and fast particle tracking method utilizing defocusing images with spherical aberration and demonstrated the measurement of nanochannel flow. Since the spherical aberration generates the defocusing nanoparticle image with diffraction rings, the position of fluorescent nanoparticles was determined from the radius of the diffraction ring. Effects of components of an optical system on the diffraction ring of the defocusing image were investigated and optimized to achieve the spatial resolution exceeding the optical diffraction limit. We found that there is an optimal magnitude of spherical aberration to enhance the spatial resolution. Furthermore, we confirmed that nanoparticles with diameters in the order of 10¹ nm, which is much smaller than the light wavelength, do not affect the defocusing images and the spatial resolution because such nanoparticles can be regarded as point light sources. At optimized conditions, we achieved a spatial resolution of 19 nm and a temporal resolution of 160 μs, which are sufficient for the nanochannel flow measurements. We succeeded in the measurement of pressure-driven flow in a nanochannel with a depth of 370 nm using 67 nm fluorescent nanoparticles. The measured nanoparticle velocities exhibited a parabolic flow profile with a slip velocity even at the hydrophilic glass surface but with an average velocity similar to the Hagen–Poiseuille law. The method will accelerate researches in the nanofluidics and other related fields.

中文翻译：

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利用球差测量纳米通道流动的超分辨率散焦纳米粒子图像测速

随着利用纳米孔和纳米通道的纳米流体分析设备的最新进展，了解纳米空间中的流体流动和质量传输变得越来越重要。在本研究中，我们开发了一种利用具有球面像差的散焦图像的超分辨率和快速粒子跟踪方法，并演示了纳米通道流量的测量。由于球差产生带有衍射环的散焦纳米颗粒图像，荧光纳米颗粒的位置由衍射环的半径确定。研究并优化了光学系统组件对散焦图像衍射环的影响，以实现超过光学衍射极限的空间分辨率。我们发现有一个最佳的球面像差幅度来提高空间分辨率。此外，我们证实了直径为 10远小于光波长的¹ nm 不会影响散焦图像和空间分辨率，因为这种纳米粒子可以被视为点光源。在优化条件下，我们实现了 19 nm 的空间分辨率和 160 μs 的时间分辨率，足以进行纳米通道流量测量。我们成功地使用 67 nm 荧光纳米粒子测量了深度为 370 nm 的纳米通道中的压力驱动流。测得的纳米颗粒速度显示出抛物线形流动剖面，即使在亲水玻璃表面处也具有滑移速度，但平均速度类似于哈根-泊肃叶定律。该方法将加速纳米流体学和其他相关领域的研究。