Irena Barbulovic-Nad

Bio-Microarray Fabrication Techniques—A Review

ABSTRACT Microarrays with biomolecules (e.g., DNA and proteins), cells, and tissues immobilized on solid substrates are important tools for biological research, including genomics, proteomics, and cell analysis. In this paper, the current state of microarray fabrication is reviewed. According to spot formation techniques, methods are categorized as “contact printing” and “non-contact printing.” Contact printing is a widely used technology, comprising methods such as contact pin printing and microstamping. These methods have many advantages, including reproducibility of printed spots and facile maintenance, as well as drawbacks, including low-throughput fabrication of arrays. Non-contact printing techniques are newer and more varied, comprising photochemistry-based methods, laser writing, electrospray deposition, and inkjet technologies. These technologies emerged from other applications and have the potential to increase microarray fabrication throughput; however, there are several challenges in applying them to microarray fabrication, including interference from satellite drops and biomolecule denaturization.

DC-dielectrophoretic separation of microparticles using an oil droplet obstacle

A new dielectrophoretic particle separation method is demonstrated and examined in the following experimental study. Current electrodeless dielectrophoretic (DEP) separation techniques utilize insulating solid obstacles in a DC or low-frequency AC field, while this novel method employs an oil droplet acting as an insulating hurdle between two electrodes. When particles move in a non-uniform DC field locally formed by the droplet, they are exposed to a negative DEP force linearly dependent on their volume, which allows the particle separation by size. Since the size of the droplet can be dynamically changed, the electric field gradient, and hence DEP force, becomes easily controllable and adjustable to various separation parameters. By adjusting the droplet size, particles of three different diameter sizes, 1 microm, 5.7 microm and 15.7 microm, were successfully separated in a PDMS microfluidic chip, under applied field strength in the range from 80 V cm-1 to 240 V cm-1. A very effective separation was realized at the low field strength, since the electric field gradient was proved to be a more significant parameter for particle discrimination than the applied voltage. By utilizing low strength fields and adaptable field gradient, this method can also be applied to the separation of biological samples that are generally very sensitive to high electric potential.

Digital microfluidics with impedance sensing for integrated cell culture andanalysis

We report the first digital microfluidic (DMF) system capable of impedance sensing of mammalian cells. The new system was validated in three assays: calibration, proliferation, and serum sensing. In the first assay, three cell lines (HeLa, CHO-K1, and NIH-3T3) were seeded at different densities to determine the relationship between impedance and cell number, which was found to be linear for each type of cell. In the proliferation assay, cells were grown for four days and their proliferation rates were determined by regular impedance measurements. In the serum sensing assay, a dilution series of cell media containing different concentrations of serum was evaluated using impedance measurements to determine the optimum conditions for proliferation. The DMF impedance system is label-free, does not require imaging, and is compatible with long-term cell culture. We propose that this system will be useful for the growing number of scientists who are seeking methods other than fluorescence or cell sorting to analyze adherent cells in situ.

Electrokinetic flow in a free surface-guided microchannel

The purpose of this study is to investigate electro-osmotic flow in a free surface-guided microchannel. Although multiphase microfluidics has attracted interests over the past few years, electro-osmotic flow involving free surfaces has yet to be studied in great detail. Several proposed theoretical models describing this type of electro-osmotic flow need to be verified by experiments. In this work, a surface-guided microchannel was fabricated using an innovative fabrication process. Because the liquid stream was confined by surface properties, solid sidewalls did not exist in this microchannel. Instead, the sidewalls were water-air or water-oil interfaces. Using this microchannel, two systems were investigated: water-air system and water-oil system. The experimental results were compared against three proposed models in order to gain more understandings on this type of electro-osmotic flow. Experimental results show that the liquid velocity near the liquid-fluid interface resembles a pluglike profile for ...