Separation and Detection of Escherichia coli and Saccharomyces cerevisiae Using a Microfluidic Device Integrated with an Optical Fibre

This paper describes the development of an integrated system using a dry film resistant (DFR) microfluidic channel consisting of pulsed field dielectrophoretic field-flow-fractionation (DEP-FFF) separation and optical detection. The prototype chip employs the pulse DEP-FFF concept to separate the cells (Escherichia coli and Saccharomyces cerevisiae) from a continuous flow, and the rate of release of the cells was measured. The separation experiments were conducted by changing the pulsing time over a pulsing time range of 2⁻24 s and a flow rate range of 1.2⁻9.6 μ L min - 1 . The frequency and voltage were set to a constant value of 1 M Hz and 14 V pk-pk, respectively. After cell sorting, the particles pass the optical fibre, and the incident light is scattered (or absorbed), thus, reducing the intensity of the transmitted light. The change in light level is measured by a spectrophotometer and recorded as an absorbance spectrum. The results revealed that, generally, the flow rate and pulsing time influenced the separation of E. coli and S. cerevisiae. It was found that E. coli had the highest rate of release, followed by S. cerevisiae. In this investigation, the developed integrated chip-in-a lab has enabled two microorganisms of different cell dielectric properties and particle size to be separated and subsequently detected using unique optical properties. Optimum separation between these two microorganisms could be obtained using a longer pulsing time of 12 s and a faster flow rate of 9.6 μ L min - 1 at a constant frequency, voltage, and a low conductivity.

Dielectrophoretic Microfluidic Device for in Vitro Fertilization

The aim of this work was to create a microfluidic platform that uses in vitro fertilization (IVF) and avoids unnecessary damage to oocytes due to the dielectrophoretic force manipulation of the sperms and oocytes that occurs in a traditional IVF operation. The device from this research can serve also to decrease medium volumes, as well as the cost of cell culture under evaporation, and to prevent unnecessary risk in intracytoplasmic sperm injection (ICSI). To decrease the impact and destruction of the oocyte and the sperm, we adopted a positive dielectrophoretic force to manipulate both the sperms and the oocyte. The mouse oocytes were trapped with a positive dielectrophoretic (p-DEP) force by using Indium Tin Oxide (ITO)-glass electrodes; the ITO-glass electrode chip was fabricated by wet etching the ITO-glass. The polydimethylsiloxane (PDMS) flow-focusing microfluidic device was used to generate microdroplets of micrometer size to contain the zygotes. The volume of the microdroplets was controlled by adjusting the flow rates of both inlets for oil and the DEP buffer. As a result, the rate of fertilization was increased by about 5% beyond that of the DEP treatment in traditional IVF, and more than 20% developed to the blastocyst stage with a low sperm-oocyte ratio.

Double Sided-Design of Electrodes Driving Tunable Dielectrophoretic Miniature Lens

We demonstrate the design methodology, geometrical analysis, device fabrication, and testing of a double-sided design (DSD) of tunable-focus dielectrophoretic liquid miniature lenses. This design is intended to reduce the driving voltage for tuning the lens, utilizing a double-sided electrode design that enhances the electric field magnitude. Fabricated devices were tested and measurements on a goniometer showed changes of up to 14° in the contact angle when the dielectrophoretic force was applied under 25 V_rms. Correspondingly, the back focal length of the liquid lens changed from 67.1 mm to 14.4 mm when the driving voltage was increased from zero to 25 V_rms. The driving voltage was significantly lower than those previously reported with similar device dimensions using single-sided electrode designs. This design allows for a range of both positive and negative menisci dependent on the volume of the lens liquid initially dispensed.

Design and fabrication of an electrohydrodynamically actuated microlens with areal density modulated electrodes

In this paper, we introduce an electrode design for electrohydrodynamically actuated liquid microlenses. The effective electrode areal density radially increases which results in centering of the liquid tunable microlens with a planar device structure. A model was developed to demonstrate the centering mechanism of the liquid microlens. 3D electrostatic simulation was conducted and validity of the idea was examined. A simple fabrication process that uses readily available SU-8 as the insulator was developed and surface modified, hydrophobic SU-8 layer was used to construct the microlens. Focal length of the microlens was measured to vary from 10.1 mm to 5.8 mm as the voltage varied from zero to 100 V.