Table 3.

Key phenotypical findings using single-cell microfluidic impedance cytometry

Cell Phenotype of Interest	Dielectric Property	Sub-cellular Properties
Cell Death: viable, necrotic and apoptotic	Cmem	Loss of viability, e.g. induced by heat-inactivation, causes increased cell membrane permeability with break-down of the membrane integrity, rendering cells non-viable. These result in a decreased Cmem, as the cell loses the ability to function as a perfect insulator at low frequencies. Such phenomena have been observed in literature: heat-treated non-viable MCF7 cells show higher magnitude opacity (i.e. lower Cmem) than viable cells in 1× PBS (ref.160); heat-treated non-viable lymphoma cells show a decrease in absolute impedance phase at 500 kHz in 1× PBS (ref.64); heat-treated non-viable algae cells show a decrease in magnitude opacity (based on 20 MHz / 500 kHz data) in 1× PBS (ref.55); cytotoxic nanomaterials-induced non-viable lymphoma cells show lower impedance phase at 6 MHZ in a 0.25xPBS + sucrose buffer (ref.41); hypertonic stimulus-induced non-viable HUVECs show increased impedance magnitude at low frequency (450 kHz) (ref.119);
	σint & εint	Increased permeability in non-viable cells causes increased ion exchange between the cell interior and medium, together with internal degradation of cell organelles. These result in alterations of the cell interior properties, such as σint & εint, which can be qualitatively observed with changes to impedance at higher frequencies, as reported in literature: heat-treated non-viable yeast cells show a decrease in impedance phase at 10 MHz in 0.5× PBS (ref.72); heat-treated non-viable pollen particles show a decrease in impedance phase at 12 MHz (ref.169); apoptosis causes shedding of smaller-sized apoptotic bodies from cells, identifiable based on their size and greater impedance phase at high frequency (≥10 MHz) in 1× PBS (ref.64);
Immune Cells: cell activation, differentiation and diabetic response	Size & Cmem	Monocytes, lymphocytes and neutrophils are distinguishable based on impedance magnitude and opacity (refs.60,195,196). When processes such as activation or differentiation occur in these cell types, alterations to cell membrane permeability and conformation can result in alterations to Cmem. Various phenomena have been reported in literature: monocyte differentiation into macrophages results in size increase but no impedance magnitude alteration (ref.60); inflammatory stimulus induces an increase in impedance magnitude opacity (i.e. lower Cmem) (ref.60); NETosis neutrophils have higher cell size and magnitude opacity (i.e. lower Cmem) than unstimulated neutrophils (ref.63); diabetic lymphocytes present loss of deformability and higher impedance magnitude at 800 kHz than normal lymphocytes (ref.145); diabetic neutrophils show higher magnitude opacity (i.e. lower Cmem) than monocytes in 1× PBS (ref.60); glucose-stimulated neutrophils show larger size than unstimulated neutrophils at 120 min post-stimulus (ref.63);
Cancer Cells: measuring drug sensitivity & metastasis	Cmem & σcyt	Cancer cells are known for an increased cell membrane roughness and folding, which affects the surface area dependent metric of Cmem, and higher nucleus-to-cytoplasm ratios and cell cycle turnover, which in turn affects estimations of σcyt. Differences in the phenotypes of various cancer cells tied to these specific characteristics have been reported in literature: EpCAM+ CTCs have lower Cmem and higher σcyt than EpCAM- CTCs (ref.162); epithelial-mesenchymal transitions (EMT) on lung tumour cells causes lower Cmem and σcyt (ref.154); lung metastasis adenoid carcinoma cells present a lower Cmem and higher σcyt than non-metastatic adenoid carcinoma cells (ref.163); more tumourigenic pancreatic cancer cells show higher impedance phase at high frequencies (>10 MHz) and lowered σint (ref.71);
Bacteria: detection, viability, germination and antibiotic susceptibility	σint & εint	Gram-negative E. coli and Gram-positive S. aureus are detectable and discriminated using impedance phase at 8 MHz with a buffer of low conductivity (0.085 S/m) (ref.40); Heat-treated C. difficile bacteria show lower impedance phase at 10 MHz than untreated bacteria (ref.153); Germinated vegetative C. difficile bacteria have higher impedance phase at 10 MHz than C. difficile in spore form (ref.153);
Stem Cells: alterations with cell expansion and passage	Size & Cmem	Unexpanded skeletal stem cells are larger than other bone marrow cell populations (ref.161), while the expansion of skeletal stem cells and following passages cause an increase in size and Cmem (assessed by magnitude opacity) (ref.161);