Department of Bioengineering, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656, Japan.
Analyst. 2020 Apr 7;145(7):2669-2675. doi: 10.1039/c9an02258a. Epub 2020 Feb 12.
Microfluidics has achieved integration of analytical processes in microspaces and realized miniaturized analyses in fields such as chemistry and biology. We have proposed a general concept of integration and extended this concept to the 10-1000 nm scale exploring ultimate analytical performances (e.g. immunoassay of a single-protein molecule). However, a sampling method is still challenging for nanofluidics despite its importance in analytical chemistry. In this study, we developed a femtoliter (fL) sampling method for volume measurement and sample transport. Traditionally, sampling has been performed using a volumetric pipette and flask. In this research, a nanofluidic device consisting of a femtoliter volumetric pipette and flask was fabricated on glass substrates. Since gravity, which is exploited in bulk fluidic operations, becomes less dominant than surface effects on the nanometer scale, fluidic operation of the femtoliter sampling was designed utilizing surface tension and air pressure control. The working principle of an 11 fL volumetric pipette and a 50 fL flask, which were connected by a nanochannel, was verified. It was found that evaporation of the sample solution by air flow was a significant source of error because of the ultra-small volumes being processed. Thus, the evaporation issue was solved by suppressing the air flow. As a result, the volumetric measurement error was decreased to ±0.06 fL (CV 0.6%), which is sufficiently low for use in nanofluidic analytical applications. This study will present a fundamental technology for the development of novel analytical methods for femtoliter volume samples such as single molecule analyses.
微流控技术实现了分析过程在微空间中的集成，实现了化学和生物学等领域的微型分析。我们提出了一种集成的通用概念，并将这一概念扩展到 10-1000nm 尺度，探索了终极分析性能（例如，单个蛋白质分子的免疫测定）。然而，尽管纳米流体在分析化学中很重要，但它的采样方法仍然具有挑战性。在这项研究中，我们开发了一种用于体积测量和样品输送的纳升级（nL）采样方法。传统上，采样是使用容量移液器和瓶进行的。在这项研究中，在玻璃衬底上制造了由纳升级容量移液器和瓶组成的纳流控装置。由于在纳米尺度上，重力（在体相流体操作中利用的力）比表面效应的影响更小，因此纳升级采样的流体操作利用表面张力和气压控制进行设计。通过纳米通道连接的 11nL 容量移液器和 50nL 瓶的工作原理得到了验证。发现由于处理的体积非常小，样品溶液的蒸发是一个显著的误差源。因此，通过抑制气流解决了蒸发问题。结果，体积测量误差降低到±0.06nL（CV0.6%），足以满足纳流控分析应用的要求。本研究将为纳升级体积样品（如单分子分析）的新型分析方法的发展提供基础技术。
