Patrone Paul N, Cooksey Gregory, Kearsley Anthony
National Institute of Standards and Technology.
Phys Rev Appl. 2019;11(3). doi: 10.1103/physrevapplied.11.034025.
Scientists must overcome fundamental measurement problems if microfluidic devices are to become reliable and commercially viable. In particular, microfluidic devices require precise control over operating conditions such as flow-rate, , which is difficult to measure continuously and . Given the small scales involved, state-of-the-art approaches generally require accurate models to infer on the basis of indirect measurements. However, such methods necessarily introduce that dominate at the nL/min scale being targeted by the community. To address these problems, we develop a robust and largely assumption-free scaling method that relates the fluorescence efficiency of fluorophores to through a dosage parameter , which depends on the flow rate and laser power. Notably, we show that this scaling relationship emerges as a universal feature from a class of partial differential equations (PDEs) describing the experimental setup, which consists of an excitation beam and fluorescence detector. . Moreover, the corresponding measurements remain valid down to the scale of 10 nL/min, with some devices potentially capable of reaching 1 nL/min. As an added benefit, the measurement procedure is mathematically simple, requiring a few trivial computations, as opposed to the full solution of a PDE. To support these claims, we discuss and quantify uncertainties associated with our method and present experimental results that confirm its validity.
如果微流控设备要变得可靠并具有商业可行性，科学家们必须克服基本的测量问题。特别是，微流控设备需要精确控制诸如流速等操作条件，而流速很难进行连续测量。考虑到所涉及的微小尺度，目前的先进方法通常需要精确的模型，以便根据间接测量来推断流速。然而，这些方法必然会引入在该领域所针对的纳升/分钟尺度上占主导地位的误差。为了解决这些问题，我们开发了一种强大且基本无需假设的缩放方法，该方法通过一个剂量参数将荧光团的荧光效率与流速联系起来，该剂量参数取决于流速和激光功率。值得注意的是，我们表明这种缩放关系是由描述实验装置（由激发光束和荧光探测器组成）的一类偏微分方程（PDE）中普遍存在的特征。此外，相应的测量在低至10纳升/分钟的尺度下仍然有效，一些设备可能能够达到1纳升/分钟。另外一个好处是，测量过程在数学上很简单，只需要一些简单的计算，而不是求解一个完整的偏微分方程。为了支持这些说法，我们讨论并量化了与我们方法相关的不确定性，并给出了证实其有效性的实验结果。
