Microfluidic impedance cytometry of tumour cells in blood

Abstract

The dielectric properties of tumour cells are known to differ from normal blood cells, and this difference can be exploited for label-free separation of cells. Conventional measurement techniques are slow and cannot identify rare circulating tumour cells (CTCs) in a realistic timeframe. We use high throughput single cell microfluidic impedance cytometry to measure the dielectric properties of the MCF7 tumour cell line (representative of CTCs), both as pure populations and mixed with whole blood. The data show that the MCF7 cells have a large membrane capacitance and size, enabling clear discrimination from all other leukocytes. Impedance analysis is used to follow changes in cell viability when cells are kept in suspension, a process which can be understood from modelling time-dependent changes in the dielectric properties (predominantly membrane conductivity) of the cells. Impedance cytometry is used to enumerate low numbers of MCF7 cells spiked into whole blood. Chemical lysis is commonly used to remove the abundant erythrocytes, and it is shown that this process does not alter the MCF7 cell count or change their dielectric properties. Combining impedance cytometry with magnetic bead based antibody enrichment enables MCF7 cells to be detected down to 100 MCF7 cells in 1 ml whole blood, a log 3.5 enrichment and a mean recovery of 92%. Microfluidic impedance cytometry could be easily integrated within complex cell separation systems for identification and enumeration of specific cell types, providing a fast in-line single cell characterisation method.

Analysis of Parasitic Protozoa at the Single-cell Level using Microfluidic Impedance Cytometry

“…A high reference frequency was selected so that the internal properties of the oocysts could be probed 31, 34 . Impedance magnitude (|Z | ) is plotted on the x -axis and impedance phase (ΦZ) on the y -axis, where each data point represents a single oocyst and its colour reflects the data density.

Figure 4Example impedance scatter plots for four untreated C. parvum samples at a frequency of 18.3 MHz measured in 0.5x PBS of conductivity σ m  = 0.76 S m −1 .

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Spatial concentration distribution analysis of cells in electrode-multilayered microchannel by dielectric property measurement

“…Therefore, the construction of three-dimensional (3D) cellular systems (e.g., Bio Assembler 1 ) became a hot topic to understand the multifaceted properties of cells and focus on those properties, develop the world's fastest measurement and separation techniques with the application of microfluidic systems. 2 In this situation, one of the popular methods is flow cytometry, 3,4 which is a common technology that simultaneously measures and then analyses multiple physical characteristics of single cells, as they flow in a fluid stream through a beam of light. The properties measured include the particle's relative size, relative granularity or internal complexity, and relative fluorescence intensity.…”

Toward Microfluidic Label‐Free Isolation and Enumeration of Circulating Tumor Cells from Blood Samples

“…Che et al introduced Vortex deformability cytometry for mechanical phenotyping, targeting the size as well as the deformability of the cancer cells (28). Alternatives have been introduced for in-flow cancer cell enumeration, using, for example, surface plasmon resonance, photoacoustic, or silicon nanowire array (29)(30)(31), but remain limited in terms of throughput and integration into a fully automated platform. This would enable a completely label-free, fully-integrated isolation and enumeration of the cells, while keeping the cells collected intact for downstream transcriptomic, genomic or proteomic analyses.…”

“…However, such optical imaging required a precise control of the flow, tight dimensions of the imaging area, a very expensive high-speed camera, as well as high-density data storage capabilities, overall limiting its applicability beyond a research prototype (29). Alternatives have been introduced for in-flow cancer cell enumeration, using, for example, surface plasmon resonance, photoacoustic, or silicon nanowire array (29)(30)(31), but remain limited in terms of throughput and integration into a fully automated platform. The use and reliability of impedance cytometry for cancer cell classification has already been demonstrated and can elucidate further biophysical parameters such as cytoplasm content and cell membrane capacitance, thereby extending CTC label-free characterization (29), alongside a possible integration as a module in a complete instrument setup (29,30).…”