Microwave Sensors for the Dielectric Characterization of Biological Cells

正如在相关文献中广泛讨论的那样，微波电池的表征提供了非破坏性和无标签的独特优势。预计这将在生物医学和生物技术应用方面开辟新的机会。已经报道了对微流体通道中的细胞悬浮液和单个细胞的测量，并记录了健康细胞和死亡细胞(电磁)反应的差异。然而，到目前为止，在单细胞水平上只花了很少的努力来确定一个独特的特征，比如介电常数。细胞大小及其不均质性的影响根本没有被提及。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，利用这些传感器和表征方法，可以独立于单个电池的大小来确定其宽带介电性能。应考虑到细胞形状不规则、可挤压，并且可能是不均匀的。为了实现这些目标，我们提出了两种互补的方法。第一种方法将依靠平面传感器，只探测细胞的一部分，而不探测周围的培养液。为进行全面检查，应从不同方向/角度对细胞进行探测。为了做到这一点，它将被旋转，这将通过电旋转的方式完成。这将与介电泳法结合在一起，产生一种非常灵活的方法来操纵和定位细胞。在第二种方法中，细胞应该用均匀的电场进行探测。为此，传感器应该是一个平行板电容器，配有适当偏置的保护电极，这是一种经过充分验证的方法，可以在低频下减轻边缘场的负面影响。因此，传感器应照亮整个电池--或至少照亮电池的重要部分。在该方法中集成了一个简单的三向单室机械陷阱，两种方法都通过基于测量的等效电路模型来提取宽带介电常数。为此，应采用我们研究所开发的一种简单的校准程序。对这两种方法的结果进行(统计)比较，可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所获得的结果进行分类、解释和理解。该项目阶段的最终目标是为不同的商业可用细胞系找到介电足迹，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。在可能的第二项目阶段，应将测量和方法应用于研究原代细胞。

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.