Dilution is a standard fluid operation widely employed in the sample preparation process of many bio(chemical) assays. It serves multiple essential functions such as sample mixing with certain reagents at specific dilution ratios, reducing sample matrix effects, bringing target analytes within the linear assay detection range, among many others. Traditionally, sample processing is performed in laboratory settings through manual or automated pipetting. When working in resource-limited settings, however, neither trained personnel nor proper laboratory equipment are available limiting the accessibility to high-quality diagnostic tests. In this work, we present a novel standalone and fully automated microfluidic platform for the stepwise preparation of serial dilutions without the need for any active elements. Stepwise dilution is achieved using the coordinated burst action of hydrophobic burst valves to first isolate a precisely metered volume from an applied sample drop and subsequently merge it with a prefilled diluent liquid. Downstream, expansion chambers are used to mix both reagents into a homogeneous solution. The dilution module was characterized to generate accurate and reproducible (CV < 7%) dilutions for targeted dilution factors of 2, 5 and 10×, respectively. Three dilution modules were coupled in series to generate three-fold logarithmic (log₅ or log₁₀) dilutions, with excellent linearity (R² > 0.99). Its compatibility with whole blood was furthermore illustrated, proving its applicability for automating and downscaling bioassays with complex biological matrices. Finally, autonomous on-chip serial dilution was demonstrated by incorporating the self-powered (i)SIMPLE technology as a passive driving source for liquid manipulation. We believe that the simplicity and modularity of the presented autonomous dilution platform are of interest to many point-of-care applications in which sample dilution and reagent mixing are of importance.

中文翻译：

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彻底改变样品制备：用于连续稀释的新型自主微流控平台

稀释是一种标准流体操作，广泛应用于许多生物（化学）测定的样品制备过程中。它具有多种基本功能，例如以特定稀释比例将样品与某些试剂混合、减少样品基质效应、使目标分析物处于线性测定检测范围内等。传统上，样品处理是在实验室环境中通过手动或自动移液进行的。然而，在资源有限的环境中工作时，既没有经过培训的人员，也没有适当的实验室设备，限制了高质量诊断测试的可及性。在这项工作中，我们提出了一种新颖的独立且全自动的微流体平台，用于逐步制备连续稀释液，而不需要任何活性元件。逐步稀释是通过疏水性爆破阀的协调爆破作用实现的，首先从所施加的样品滴中分离出精确计量的体积，然后将其与预填充的稀释液合并。下游，膨胀室用于将两种试剂混合成均匀溶液。稀释模块的特点是能够分别针对 2、5 和 10× 的目标稀释倍数生成准确且可重复的 (CV < 7%) 稀释液。三个稀释模块串联连接，生成三倍对数（log ₅或 log ₁₀）稀释液，具有出色的线性度（R ² > 0.99）。进一步说明了它与全血的相容性，证明了它对于复杂生物基质的自动化和缩小规模生物测定的适用性。最后，通过将自供电 (i)SIMPLE 技术作为液体操纵的被动驱动源，展示了自主片上连续稀释。我们相信，所提出的自主稀释平台的简单性和模块化对许多现场护理应用很感兴趣，在这些应用中，样品稀释和试剂混合非常重要。