Originally designed for chromatography, electrophoresis, and printing technologies, microfluidics has since found applications in a variety of domains such as engineering, chemistry, environmental, and life sciences. The fundamental reason for this expansion has been the development of miniature components, allowing the handling of liquids at the microscale. For the maturation of microfluidic technologies, the need for affordable, reliable, and quantitative techniques to measure flow rates from 1 nL min⁻¹ to 1 mL min⁻¹ appears as a strong challenge. We review herein the different technologies available and those under development, and discuss their sensing principles and industrial maturity. Given the need of traceability of these measurements, we then focus on the developments of primary standards to measure microfluidic flow rates by metrological institutes. We conclude this review with some perspectives and pending challenges for microfluidic flowmeters.

中文翻译：

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微流体流量计

微流体最初设计用于色谱、电泳和印刷技术，此后已在工程、化学、环境和生命科学等多个领域得到应用。这种扩展的根本原因是微型组件的开发，允许在微尺度上处理液体。随着微流体技术的成熟，需要负担得起、可靠和定量的技术来测量从 1 nL min ^-1到 1 mL min ^-1的流速似乎是一个强大的挑战。我们在此回顾了可用的和正在开发的不同技术，并讨论了它们的传感原理和工业成熟度。鉴于这些测量的可追溯性的需要，我们然后专注于计量机构测量微流体流速的主要标准的发展。我们以微流体流量计的一些观点和悬而未决的挑战来结束这篇综述。