Laboratory of Microsystems, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.
Laboratory of Microsystems, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.
N Biotechnol. 2015 Sep 25;32(5):433-40. doi: 10.1016/j.nbt.2015.03.008. Epub 2015 Mar 24.
Magnetic micro- and nanoparticles ('magnetic beads') have been used to advantage in many microfluidic devices for sensitive antigen (Ag) detection. Today, assays that use as read-out of the signal the number count of immobilized beads on a surface for quantification of a sample's analyte concentration have been among the most sensitive and have allowed protein detection lower than the fgmL(-1) concentration range. Recently, we have proposed in this category a magnetic bead surface coverage assay (Tekin et al., 2013 [1]), in which 'large' (2.8μm) antibody (Ab)-functionalized magnetic beads captured their Ag from a serum and these Ag-carrying beads were subsequently exposed to a surface pattern of fixed 'small' (1.0μm) Ab-coated magnetic beads. When the system was exposed to a magnetic induction field, the magnet dipole attractive interactions between the two bead types were used as a handle to approach both bead surfaces and assist with Ag-Ab immunocomplex formation, while unspecific binding (in absence of an Ag) of a large bead was reduced by exploiting viscous drag flow. The dose-response curve of this type of assay had two remarkable features: (i) its ability to detect an output signal (i.e. bead number count) for very low Ag concentrations, and (ii) an output signal of the assay that was non-linear with respect to Ag concentration. We explain here the observed dose-response curves and show that the type of interactions and the concept of our assay are in favour of detecting the lowest analyte concentrations (where typically either zero or one Ag is carried per large bead), while higher concentrations are less efficiently detected. We propose a random walk process for the Ag-carrying bead over the magnetic landscape of small beads and this model description explains the enhanced overall capture probability of this assay and its particular non-linear dose response curves.
磁性微球和纳米颗粒（“磁性珠”）已被用于许多微流控设备中，以实现对敏感抗原（Ag）的检测。如今，基于信号数量计数的检测方法（即通过计数固定在表面上的磁珠数量来定量分析物浓度）已经成为最敏感的方法之一，其检测限可以达到 fgmL(-1)浓度范围以下。最近，我们在这个类别中提出了一种磁性珠表面覆盖率检测方法（Tekin 等人，2013 [1]），其中“大”（2.8μm）抗体（Ab）功能化的磁性珠从血清中捕获其 Ag，然后这些携带 Ag 的磁珠暴露于固定的“小”（1.0μm）Ab 包被的磁性珠表面图案上。当系统暴露于磁场时，两种珠类型之间的磁偶极吸引力相互作用被用作接近两个珠表面的手段，并有助于 Ag-Ab 免疫复合物的形成，同时通过利用粘性曳力流来减少大珠的非特异性结合（在不存在 Ag 的情况下）。这种检测方法的剂量-反应曲线有两个显著特点：（i）它能够检测到非常低的 Ag 浓度的输出信号（即珠的数量计数），以及（ii）该检测方法的输出信号与 Ag 浓度呈非线性关系。我们在这里解释了观察到的剂量-反应曲线，并表明所观察到的相互作用类型和我们的检测方法的概念有利于检测最低的分析物浓度（通常每个大珠携带零或一个 Ag），而较高的浓度则检测效率较低。我们提出了一种 Ag 携带珠在小珠的磁性环境中的随机游走过程，这种模型描述解释了该检测方法的增强的整体捕获概率及其特殊的非线性剂量反应曲线。
