Using dielectrophoretic spectra to identify and separate viable yeast cells

Abstract

Immotile yeast cells were transiently moved in nonuniform sinusoidal electric fields using multiple pairs of micro-parallel cylindrical electrodes equipped with a sequential signal generator (SSG) to analyze cell viability at a clinical scale for the brewery/fermentation industry. Living yeast cells of Saccharomyces cerevisiae during the exponential-stationary phase, with a cell density of 1.15 × 10⁵ cells mL^-1 were suspended in sucrose medium. The conductivity (σ_s) was adjusted to 0.01 S m^-1 with added KCl. Cells exposed in electric field strengths ranging from 32.89 to 40.98 kV m^-1, exhibited positive dielectrophoresis (pDEP) with the lower critical frequencies (LCF) at 85.72 ± 3.59 kHz. The optimized value of LCF was shifted upwards to 780.00 ± 83.67 kHz when σ_swas increased to 0.10 S m^-1. Dielectrophoretic and LCF spectra (translational speed of cells vs. electric field frequencies) of yeast suspensions during positive dielectrophoresis were analyzed in terms of the dielectric properties of the cell membrane and cytoplasm which reflect yeast cell viability and metabolic health status. The dielectrophoretic collection yield of cells using positive dielectrophoresis was reported on the monitor of sequential signal generator software to evaluate the number of living and dead cells through a real-time image processing analyzer. The spectra of both positive dielectrophoresis of the living and dead cells had distinguishable dielectric properties. The conductivity of the yeast cytoplasm (σ_c) of the dead cells was significantly less (≈ ≤ 0.05 S m^-1) than that of the living yeast cells which typically had a cytoplasmic conductivity of ≈ 0.2 S m^-1. This difference between viable and non-viable cells is sufficient for cell separation procedures. KEY POINTS: • Dielectrophoresis can be used to separate viable and non-viable yeast cells, • Cellular dielectric properties can be derived from the analysis of their dielectric spectra, • Cytoplasmic conductivity of viable cells is ≈ 0.2 S m^-1 while that of non-viable cells ≈ ≤ 0.05 S m^-1.

Keywords: Cell dielectric properties; Cytoplasmic conductivity; Dielectrophoresis; Signal generator; Viability; Viable cell separation; Yeast cell.