Concentration polarization (CP)‐based focusing electrokinetics nanofluidic devices have been developed in order to simultaneously detect and enrich highly diluted analytes on‐a‐chip. However, stabilization of focal points over long time under the application of the electric field remains as a technical bottleneck. If pressure‐assisted preconcentration methods have been proposed to stabilize propagating modes at low inverse Dukhin number , these recent protocols remain laborious for optimizing experimental parameters. In this paper, “electric field E/counter‐pressure P” diagrams have been established during pressure‐assisted electro‐preconcentration of fluorescein as a model molecule. Such E/P diagram allows direct observation of the region for which the optimal counter‐pressure P leads to a stable focusing regime. This region of stable focusing is shown to vary depending of the nanoslit length (100 μm < L_nanoslit < 500 μm) and the nature of the background electrolyte (KCl and NaCl). Longer nanoslits (500 μm) produce stabilization at low counter‐pressure P, whereas NaCl offers a narrower region of stable focusing in the E/P diagram compared to KCl. Finally, the ability of such pressure‐assisted protocol to concentrate negatively charged proteins has been tested with a more applicative protein, i.e., ovalbumin. The corresponding E/P diagram confirms the existence of the stable focusing regime at both low electric field E (≤20 V) and counter‐pressure P (≤0.4 bar). With an enrichment factor as high as 70 after 2 min for ovalbumin at a concentration of 10 μM, such pressure‐assisted nanofluidic electro‐preconcentration protocol appears very promising to concentrate and detect biomolecules.

中文翻译：

---

电预浓缩图可在纳米流体装置中以低反压优化分子富集。

为了同时检测和富集芯片上高度稀释的分析物，已经开发了基于浓度极化（CP）的聚焦电动动力学纳米流体设备。但是，在电场的作用下，长时间保持焦点稳定仍然是技术瓶颈。如果已经提出了压力辅助预浓缩方法来稳定低Dukhin逆数传播模式，这些最新协议在优化实验参数方面仍然很费力。在本文中，在作为模型分子的荧光素的压力辅助电预浓缩过程中，建立了“电场E /反压力P”图。这种E / P图可以直接观察最佳反压P导致稳定聚焦方式的区域。显示的稳定聚焦区域根据纳米缝长度而变化（100μm<L_纳米缝<500μm）和背景电解质（KCl和NaCl）的性质。较长的纳米缝隙（500μm）在较低的反压P下可产生稳定作用，而与KCl相比，NaCl在E / P图中提供了较窄的稳定聚焦区域。最后，这种压力辅助方案浓缩带负电荷的蛋白质的能力已经通过更实用的蛋白质，即卵清蛋白进行了测试。相应的E / P图确认了在低电场E（≤20V）和反压P（≤0.4bar）时都存在稳定的聚焦状态。卵清蛋白浓度为10μM的2分钟后，富集因子高达70，因此这种压力辅助的纳米流体电预浓缩方案非常有可能浓缩和检测生物分子。