Abstract
Biological populations of cells show considerable cell-to-cell variability. Study of single cells and analysis of cell heterogeneity are considered to be critical in understanding biological processes such as stem cell differentiation and cancer development. Recent advances in lab-on-a-chip techniques have allowed single-cell capture in microfluidic channels with the possibility of precise environmental control and high throughput of experiments with minimal usage of samples and reagents. In recent years, label-free techniques such as electrical impedance spectroscopy have emerged as a non-invasive approach to studying cell properties. In this study, we have designed and fabricated a microfluidic device that combines hydrodynamic trapping of single cells in pre-defined locations with the capability of running electrical impedance measurements within the same device. We have measured mouse embryonic stem cells (mESCs) at different states during differentiation (t=0h, 24h and 48h) and quantitatively analysed the changes in electrical parameters of cells during differentiation. A marked increase in the magnitude of the cell impedance is found during cell differentiation, which can be attributed to an increase in cell size. The analysis of the measurements shows that the nucleus-to-cytoplasm ratio decreases during this process. The degree of cell heterogeneity is observed to be the highest when the cells are at the transition state (24h), compare with cells at undifferentiated (0h) and fully differentiated (48h) states. The device enables highly efficient single cell trapping and provides sensitive, label-free electrical impedance measurements of individual cells, enabling the possibility of quantitatively analysing their physical state as well as studying the associated heterogeneity of a cell population.
Highlights
Biological populations of cells show considerable cell-to-cell variability
Fixed mouse embryonic stem cells were used in this experiment
A microfluidic device with integrated coplanar electrodes has been demonstrated for trapping and impedance sensing of individual cells
Summary
Biological populations of cells show considerable cell-to-cell variability. Study of single cells and analysis of cell heterogeneity are considered to be critical in understanding biological processes such as stem cell differentiation and cancer development. The device enables highly efficient single cell trapping and provides sensitive, label-free electrical impedance measurements of individual cells, enabling the possibility of quantitatively analysing their physical state as well as studying the associated heterogeneity of a cell population. Recent advances in micro-/nanofabrication and lab-on-a-chip techniques have allowed single-cell impedance spectroscopy, i.e., single-cell impedance flow cytometry (Gawad et al, 2001; Holmes et al, 2009; Malleo et al, 2010; Sun and Morgan, 2010), opening up the possibility of studying single cells and cell-to-cell heterogeneity These studies have allowed the distinction of different cell type subpopulations within a mixed sample (Gawad et al, 2001; Holmes et al, 2009), and simplified analysis such that it is possible to extract parameters that describe the cell such as cell size, membrane capacitance and cytoplasm conductivity (Asami 2002; Gawad et al, 2004). An example of coupling cell capture with impedance analysis has been illustrated by Malleo et al, who have demonstrated impedance study of HeLa cells in response to chemical disruption in a microfluidic device containing multiple trapping sites (Malleo et al, 2010)
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