Department of Electrical and Computer Engineering, Texas A&M University, College Station, TX, 77843, USA.
Department of Biomedical Engineering, Texas A&M University, College Station, TX, 77843, USA.
Biomed Microdevices. 2022 Jun 30;24(2):23. doi: 10.1007/s10544-022-00621-3.
Dielectric properties of a cell are biophysical properties of high interest for various applications. However, measuring these properties accurately is not easy, which can be exemplified by the large variations in reported dielectric properties of the same cell types. This paper presents a method for measuring the dielectric properties of cells at high frequency, especially lipid-producing microalgae, at single-cell resolution, by integrating an electrorotation-based dielectric property measurement method with a negative dielectrophoretic (nDEP) force-based single-cell trapping method into a single device. In this method, a four-electrode nDEP structure was used to trap a single cell in an elevated position in the center of another four-electrode structure that can apply electrorotational force. By measuring the speed of cell rotation under different applied electrorotation frequencies and fitting the results into a theoretical core-shell cell model, the dielectric properties of cells, including membrane capacitance and cytoplasm conductivity, could be obtained. This system was applied to measure the dielectric properties of lipid-accumulating microalga Chlamydomonas reinhardtii strain Sta6 by applying an electrorotation signal of up to 100 MHz. By utilizing a broad frequency range and expanding the measurement spectra to a high frequency region, increased accuracy in fitting the dielectric parameters to a theoretical model was possible, especially the cytoplasm conductivity. The developed method can be used in various applications, such as screening microalgae based on their lipid production capabilities, separating cells of different dielectric properties, identifying different cell types, as well as conducting basic biophysical analyses of cellular properties.
细胞的介电特性是具有多种应用的高关注度的生物物理特性。然而，准确测量这些特性并不容易，这可以从同一细胞类型的报道介电特性的巨大差异中得到例证。本文提出了一种在高频下测量细胞介电特性的方法，特别是生产脂质的微藻，具有单细胞分辨率，方法是将基于电动旋转的介电特性测量方法与基于负介电泳（nDEP）力的单细胞捕获方法集成到单个装置中。在该方法中，使用四电极 nDEP 结构将单个细胞捕获在另一个四电极结构的中心的升高位置，该结构可以施加电动旋转力。通过测量在不同施加电动旋转频率下细胞旋转的速度并将结果拟合到理论核壳细胞模型中，可以获得细胞的介电特性，包括膜电容和细胞质电导率。该系统应用于测量脂质积累微藻莱茵衣藻 Strain Sta6 的介电特性，施加高达 100MHz 的电动旋转信号。通过利用宽频率范围并将测量光谱扩展到高频区域，可以更准确地将介电参数拟合到理论模型中，特别是细胞质电导率。所开发的方法可用于各种应用，例如根据其脂质生产能力筛选微藻、分离具有不同介电特性的细胞、识别不同的细胞类型以及对细胞特性进行基本的生物物理分析。
