Review: Microbial analysis in dielectrophoretic microfluidic systems

Abstract

Infections caused by various known and emerging pathogenic microorganisms, including antibiotic-resistant strains, are a major threat to global health and well-being. This highlights the urgent need for detection systems for microbial identification, quantification and characterization towards assessing infections, prescribing therapies and understanding the dynamic cellular modifications. Current state-of-the-art microbial detection systems exhibit a trade-off between sensitivity and assay time, which could be alleviated by selective and label-free microbial capture onto the sensor surface from dilute samples. AC electrokinetic methods, such as dielectrophoresis, enable frequency-selective capture of viable microbial cells and spores due to polarization based on their distinguishing size, shape and sub-cellular compositional characteristics, for downstream coupling to various detection modalities. Following elucidation of the polarization mechanisms that distinguish bacterial cells from each other, as well as from mammalian cells, this review compares the microfluidic platforms for dielectrophoretic manipulation of microbials and their coupling to various detection modalities, including immuno-capture, impedance measurement, Raman spectroscopy and nucleic acid amplification methods, as well as for phenotypic assessment of microbial viability and antibiotic susceptibility. Based on the urgent need within point-of-care diagnostics towards reducing assay times and enhancing capture of the target organism, as well as the emerging interest in isolating intact microbials based on their phenotype and subcellular features, we envision widespread adoption of these label-free and selective electrokinetic techniques.

Electrical measurement of cross-sectional position of particles flowing through a microchannel

“…Schade-Kampmann et al (2008), Haandbaek et al (2014)). The method is also promising for nonspherical particles or cells because, although the latter yield impedance signals depending on their orientation (Jones 1995;Fernandez et al 2017), the transit times and the relative prominence are not significantly affected by particle orientation.…”

Electrokinetically controlled fluid injection into unicellular microalgae

“…The results are consistent with our hypothesis that diffusion is not the dominating flux mechanism within the IP, although further study is needed to confirm that N EP / N EOF is indeed negligible. Salt concentration is another parameter that warrants further study due to its effect on solution conductivity and electrical double layer thickness, which inevitably would affect the transport kinetics and cell viability .…”

Frequency-selective electrokinetic enrichment of biomolecules in physiological media based on electrical double-layer polarization

“…At even higher frequencies wherein permittivity differences dominate the polarization behavior, the small difference in permittivity of the double-layer around the colloid ( ε DL ) versus permittivity of the media ( ε m ) causes weaker levels of nDEP than observed due to the respective conductivity differences in the mid-frequency range. Along similar lines, the net polarization dispersion also depends on colloidal shape 11,28 , due to directional alterations in the depolarization factor: A i , where i = x, y, z ; which is the ratio of the internal electric field induced by charges on the dielectric under external field to its net polarization. Simulations of polarization dispersion (Supporting Information: Fig.…”