Microwave Sensors for the Dielectric Characterization of Biological Cells

正如在相关文献中广泛讨论的那样，微波池表征提供了非破坏性和无标记的明显优势。预计这将为生物医学和生物技术应用开辟新的机会。已经报道了对微流体通道中的细胞悬浮液和单细胞的测量，并且已经记录了健康细胞和死细胞的（电磁）响应的差异。然而，到目前为止，在单细胞水平上仅花费了很少的努力来确定独特的签名，如介电常数。细胞大小及其不均匀性的影响根本没有得到解决。我们的目标是通过开发（小型化）高频传感器和表征方法来缩小这一差距，这些方法可以独立于其大小来确定单细胞的宽带介电特性。应考虑细胞形状不规则、可挤压且可能不均匀。为了实现这些目标，我们提出了两个互补的方法。第一种方法依赖于一个平面传感器，它只探测细胞的一部分，而不探测周围的培养基。为了进行全面检查，应从不同方向/角度探测电池。为此，它将被旋转，这将通过电动旋转的方式电动完成。这将与介电电泳相结合，以产生一种非常灵活的手段来操纵和定位细胞。为此，传感器应为平行板电容器，配有适当偏置的保护电极，这是一种行之有效的方法，可以减轻低频边缘场的负面影响。因此，传感器应照亮整个细胞-或至少是它的重要部分。一个简单的三路单细胞机械陷阱将被集成在这种方法中。在这两种方法中，宽带介电常数应通过基于测量的等效电路模型来提取。为此，应采用我们研究所开发的简单校准程序。对这两种方法的结果进行（统计）比较有望提供有关其意义的线索。这将有助于对不同病理状态的细胞进行分类、解释和理解所获得的结果。该项目阶段的最终目标是找到不同市售细胞系的介电常数足迹，并尽可能区分不同病理状态的细胞，这些细胞可能是健康的、死亡的、癌变的或受电穿孔影响的。在可能的第二个项目阶段，测量和方法将用于研究原电池。

As extensively discussed in the relevant literature, microwave cell characterization offers the distinct advantage of being non-destructive and label-free. This is expected to open-up new opportunities in biomedical and biotechnological applications. Measurements on both cell suspensions and single cells in microfluidic channels have been reported and differences in the (electromagnetic) response of healthy and dead cells have been documented. However, so far only little effort has been spent at single-cell level in determining a unique signature, like the permittivity. The influence of the cell size and of its inhomogeneity has not been addressed at all. We aim at closing this gap by developing (miniaturized) high-frequency sensors and characterization methods with which the broadband dielectric properties of single cells can be determined independently of their size. It shall be taken into account that cells are irregularly shaped, squeezable, and possibly inhomogeneous. To reach these goals we propose two complementary approaches. The first one shall rely on a planar sensor probing only a part of the cell, but not the surrounding culture medium. For a comprehensive examination, the cell shall be probed from different directions/angles. For this, it is to be rotated, which shall be done electrically by means of electrorotation. This will be combined with dielectrophoresis to yield a very flexible means to manipulate and position the cells.In the second approach, the cell shall be probed with a homogeneous field. For this, the sensor shall be a parallel plate capacitor provided with properly biased guard electrodes, a well-proven way to mitigate the negative effect of fringing fields at low frequencies. The sensor shall thus illuminate the whole cell – or at least significant portions of it. A simple three way single cell mechanical trap is to be integrated in this approach.In both approaches, the broadband permittivity shall be extracted by means of measurement-based equivalent circuit models. For this, a simple calibration procedure, which has been developed at our institute, shall be adapted. A (statistical) comparison of the results from the two approaches is expected to provide clues regarding their meaningfulness. This will help classifying, interpreting, and understanding the results obtained with cells of different pathological state.The ultimate objective of this project phase is to find a permittivity footprint for different commercially available cell lines and to differentiate, as far as possible, between different pathological states of cells, which could be healthy, dead, cancerous, or affected by electroporation. In a possible second project phase, the measurements and methods shall be applied to study primary cells.