Rapid and selective concentration of bacteria, viruses, and proteins using alternating current signal superimposition on two coplanar electrodes

Abstract

Dielectrophoresis (DEP) is usually effective close to the electrode surface. Several techniques have been developed to overcome its drawbacks and to enhance dielectrophoretic particle capture. Here we present a simple technique of superimposing alternating current DEP (high-frequency signals) and electroosmosis (EO; low-frequency signals) between two coplanar electrodes (gap: 25 μm) using a lab-made voltage adder for rapid and selective concentration of bacteria, viruses, and proteins, where we controlled the voltages and frequencies of DEP and EO separately. This signal superimposition technique enhanced bacterial capture (Escherichia coli K-12 against 1-μm-diameter polystyrene beads) more selectively (>99%) and rapidly (~30 s) at lower DEP (5 Vpp) and EO (1.2 Vpp) potentials than those used in the conventional DEP capture studies. Nanometer-sized MS2 viruses and troponin I antibody proteins were also concentrated using the superimposed signals, and significantly more MS2 and cTnI-Ab were captured using the superimposed signals than the DEP (10 Vpp) or EO (2 Vpp) signals alone (p < 0.035) between the two coplanar electrodes and at a short exposure time (1 min). This technique has several advantages, such as simplicity and low cost of electrode fabrication, rapid and large collection without electrolysis.

AC electrokinetic immobilization of organic dye molecules

“…Thus, AC electrophoresis might not only contribute to migration of charged molecules towards electrode surfaces; even more important, the concept of AC electrophoresis provides an explanation for the permanent character of the immobilization of molecules. The hypothesis of migrating molecules by AC electrophoresis is further supported by our observation of gas bubbles at the electrodes at frequencies below 5 kHz [24,42] caused by water electrolysis, which has often been mentioned in the literature [22,28,[43][44][45]. Another interesting result was reported by Ying et al for the accumulation of DNA fragments and nucleotide triphosphate at the tip of a nanopipette, conducted at a frequency of 0.5 Hz [46].…”

Analysis of microorganisms with nonlinear electrokinetic microsystems

“…The use of DEP was preferred as it is a simpler and cost‐effective method of depositing the material as opposed to the traditional method of chemical vapor deposition [41]. The uses for the technology are similar to other bioparticles: separation [42], enrichment [79], and analysis [43] of viral particles. Shown in Fig.…”

“…Shown in Fig. 3B is the device with two coplanar Iridium tin oxide (ITO) electrodes used to dielectrophoretically trap MS2 and cTnI‐Ab viruses with a combination of AC EO and DEP [42]. The group expressed the challenges in imaging the viral particles leading to an increase in exposure time for the image.…”

“…The group theorized that such superimposition would increase the capture rate of the molecules and particles of interest, and so it did. They also used their technology to try to concentrate viral particles to determine whether a better result could be achieved by combining EK forces, and in a similar fashion to the first test, their suspicions were proved correct [42]. The big achievement of this group is not necessarily the success of their experiments but the critiques and limits of EK technologies.…”

High-Sensitivity in Dielectrophoresis Separations

“…Similar techniques have been recently applied, taking advantage of multi-frequency signals (amplitude, frequency, or phase modulated) on a single electrode array to generate dissimilar DEP actuation forces on particles of interest to separate polystyrene microspheres based on size [32], algae cells based on lipid content [33], and MCF7 cancer cells from diluted blood [34]. Planar multifield configurations have also been extended to concentrate viruses, proteins, and bacteria [35].…”