Sensitive, inline detection of proteins is required for post-chromatographic analyses in proteomics, cell-based assays, and drug discovery workflows. Among the common inline methods, post-column derivatization requires chemical labels, while label-free methods are either expensive (mass spectrometry) or have limited sensitivity at small length scales (UV–Vis). This paper presents a label-free detection technique based on the concept that dissolved proteins can function as surfactants and decrease the dynamic interfacial tension (IFT) of an immiscible (water–oil) interface. Existing methods for measuring IFT, such as axisymmetric drop shape analysis (ADSA), operate in batch mode and are not suitable for continuous detection. Here we show that a microfluidic flow-focusing droplet generator operating at a frequency of > 100 Hz can track IFT changes continuously, with high temporal resolution and small detection volumes. Variations in protein concentration alter the size and shape of the drops/plugs formed, and these changes can be quantified in time using a high-speed camera and in-house image processing software. Moreover, the continuously refreshing interface alleviates issues related to surface aging. Two applications are demonstrated: (1) direct injection of a single protein into a microfluidic chip. (2) post-column detection of protein mixtures separated by high performance size exclusion chromatography (SEC HPLC). Of interest, the dynamic range of protein (bovine serum albumin, BSA) was 50 -10⁴ μg/ml without using HPLC unit. The lowest limit of detection without HPLC unit was ~ 1 μg/ml of thyroglobulin protein in a 1 nl droplet, which equates to 1 fg of total protein. When used as a detector, the aforementioned detection method offered a sensitivity of six orders of magnitude higher than conventional UV–VIS detectors.

蛋白质组学，基于细胞的测定法和药物发现工作流程中的色谱后分析需要对蛋白质进行灵敏的在线检测。在常见的在线方法中，柱后衍生化需要化学标记，而无标记方法要么昂贵（质谱法），要么在小规模（UV-Vis）灵敏度有限。本文提出了一种无标签检测技术，该技术基于以下概念：溶解的蛋白质可以充当表面活性剂并降低不混溶（水-油）界面的动态界面张力（IFT）。现有的测量IFT的方法（例如轴对称液滴形状分析（ADSA））以批处理模式运行，不适用于连续检测。在这里，我们显示了一个微流体流动聚焦液滴发生器，其工作频率> 100 Hz可以以高时间分辨率和较小的检测量连续跟踪IFT变化。蛋白质浓度的变化会改变形成的液滴/塞子的大小和形状，并且可以使用高速相机和内部图像处理软件及时量化这些变化。而且，持续刷新的界面减轻了与表面老化有关的问题。证明了两种应用：（1）将一种蛋白质直接注射到微流控芯片中。（2）柱后检测通过高效尺寸排阻色谱法（SEC HPLC）分离的蛋白质混合物。有趣的是，蛋白质（牛血清白蛋白，BSA）的动态范围是50 -10 这些变化可以使用高速相机和内部图像处理软件及时量化。而且，持续刷新的界面减轻了与表面老化有关的问题。证明了两种应用：（1）将一种蛋白质直接注射到微流控芯片中。（2）柱后检测通过高效尺寸排阻色谱法（SEC HPLC）分离的蛋白质混合物。有趣的是，蛋白质（牛血清白蛋白，BSA）的动态范围是50 -10 这些变化可以使用高速相机和内部图像处理软件及时量化。而且，持续刷新的界面减轻了与表面老化有关的问题。证明了两种应用：（1）将一种蛋白质直接注射到微流控芯片中。（2）柱后检测通过高效尺寸排阻色谱法（SEC HPLC）分离的蛋白质混合物。有趣的是，蛋白质（牛血清白蛋白，BSA）的动态范围是50 -10 （2）柱后检测通过高效尺寸排阻色谱法（SEC HPLC）分离的蛋白质混合物。有趣的是，蛋白质（牛血清白蛋白，BSA）的动态范围是50 -10 （2）柱后检测通过高效尺寸排阻色谱法（SEC HPLC）分离的蛋白质混合物。有趣的是，蛋白质（牛血清白蛋白，BSA）的动态范围是50 -10⁴ 微克/毫升，而无需使用HPLC单元。没有HPLC单元的最低检测限是1 nl液滴中的甲状腺球蛋白蛋白质约为1μg/ ml，相当于1 fg的总蛋白质。当用作检测器时，上述检测方法提供的灵敏度比传统的UV-VIS检测器高六个数量级。