Dielectrophoresis assisted concentration of micro-particles and their rapid quantitation based on optical means

Abstract

The detection and counting of micro particles having sizes comparable to biological entities can provide a tremendous impetus to rapid diagnostics and clinical applications. MEMS technology has already been used in capture and detection of such micron size entities in miniscule concentrations. For this purpose a concentration step is normally added prior to the detection process. A variety of methodologies are used for quantization of such micron size particles/entities including change in permittivity, medium impedance, magnetic permeability and other means. Although optical studies have been extensively performed prior to this, it has not been used for quantization of the micro particles. We have designed, developed and characterized a MEMS counter which captures micron size fluorescent beads using delectrophoresis (DEP) and monitors their accumulation in a 12 μm x 230 μm size channel and monitors this accumulation as growth of overall fluorescence. The field is generated by a set of finely placed interdigitated microelectrodes. As we apply an alternating voltage at 10 V(pp) for a range of different frequencies we are able to capture the flowing beads and concentrate them by several orders of magnitude. This is also followed by their quantification in terms of growing fluorescence signal. For quantitating the fluorescence values a CCD (charge couple device) module fitted over an inverted fluorescence microscope is used that visualizes the whole capture process and a Labview based image acquisition software simultaneously calculates the signal intensity over these frames and arranges it temporally. Our work will have tremendous utility in developing a rapid bacterial counting procedure and will be a valuable tool in microbiological laboratories.

Dielectrophoresis in microfluidics technology

“…This unique dielectric signature can be utilized to discriminate and identify cells from the other particles or to detect and isolate diseased or damaged cells by means of AC-DEP (DEP force spectra of different cell types can be found elsewhere [118,144]). AC-DEP has been implemented for the separation of cancer cells from blood stream [17,18], the separation of red blood cells and polystyrene particles [19], the separation of human leukocytes [20], the isolation of the malaria-infected cells from the blood [21,22], the separation of the electroporated and non-electroporated cells [23], the separation of the platelets from diluted whole blood [24], the separation of red blood cells and the white blood cells [25], the separation [26][27][28] and sorting [29] of viable and nonviable yeast cells, the separation of healthy and unhealthy oocyte cells [30], the characterization and the sorting stem cells and their differentiated progeny [31], the isolation of rare cells from biological fluids [32], the separation of three distinct bacterial clones of commonly used E. coli MC1061 strain [33], trapping of viable mammalian fibroplast cells [34], trapping of DNA molecules [35], trapping of single cancer and endothelial cells to investigate pairwise cell interactions [36], trapping of bacterial cells for the subsequent electrodisruption or electroporation [37], focusing of polystyrene particles [38], trapping of yeast cells [39], 3-D focusing of polystyrene particles and yeast cells [40], the separation of airborne bacterium, Micrococcus luteus, from a mixture with dust and polystyrene beads [41], trapping and isolation of human stem cell from heterogeneous solution [42], single-cell isolation [43], concentration and counting of polystyrene particles [44], the separation of polystyrene particles, Jurkat cells and HeLa cells …”

Frequency sweep rate dependence on the dielectrophoretic response of polystyrene beads and red blood cells

“…PS bead motion in the electric field was imaged with video microscopy and analyzed using three techniques: intensity profiles, transient response, and particle velocities. Image intensity analysis has been used by other researchers to quantify the pDEP and nDEP behavior of particles representing particle concentration, 31 voltage trapping, 32 cell counting, 33 noncontinuous DEP spectra. 34,35 We also utilize intensity analysis to capture DEP responses.…”

Latest Developments in Micro Total Analysis Systems

“…Ghubade et al have demonstrated dielectrophoresis (DEP) assisted concentration of microparticles (243).…”