Interdigitated Microelectrodes for Bio-sensing Applications
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Abstract
According to the data from Centers for Disease Control and Prevention, Salmonella (S. typhimurium), a common food borne pathogen, is responsible for more than one million illnesses each year in the United States alone. It is one of the top most pathogens contributing to domestically acquired foodborne illnesses resulting in 19,336 hospitalizations and 386 deaths per year. The annual cost, directly and indirectly, associated with food-borne illness, is estimated to be around $77 billion a year. Most food poisoning is caused by the toxins produced by the bacteria or by the bacteria themselves. Once the food is placed in a humid and warm environment, certain bacteria can grow from one to millions in a very short periodic. Identification and detection of this food-borne pathogen is one of the keys to reduce the outbreak caused by this. Most of the conventional methods available for separation and detection of salmonella use specific agar media to separate and count bacterial cells in particular samples. These detection techniques consist of multiple steps and sub-processes which are often time consuming and take 3-4 days for initial results and up to 6-7 days for confirmation. Though these methods provide reliable data, they are not suitable for scenarios where rapid detection is the key.
This work presents the design and simulation of an alternating current-DEP (Dieletrophoresis) field flow fractionation (DEP-FFF) type microfluidic chip which will detach the target cells of S. typhimurium from complex mixed culture solution with high efficiency. For design and simulation of the device, microfluidic channels were created on Silicon wafer and interdigitated electrodes were built in to apply the electric field (and DEP force) on the target cells. In addition to S. typhimurium, other unknown cells (two bacteria) were added to from the mixed solution. The design and simulation process was done by using various modules of finite analysis software - COMSOL Multiphysics. The physical dimensions of the microfluidic chip (length, depth and width) was varied to see the effect of these on cell separation efficiency. For target cells of S. typhimurium the cell separation efficiency was found to be ranging between 80.5% to 95.1%.
Electroporation is one of the most efficient ways to transfect primary cells with minimum adverse effects compared to all other available technologies. As part of this work, electroporation of the cells for DNA transfer was done without damaging the cells. For this purpose, an in situ nanofiber-electroporation chip was developed to deliver DNA into hard-to-transfect cells, especially primary neuronal cells. The in-situ electroporation chip was composed of interdigitated metal electrodes lines and a biocompatible nanofiber membrane on a cover glass substrate. Metal electrodes made of Au were fabricated using liftoff technique on the cover glass substrate in the cleanroom. PCL nanofiber membrane was electropun and was aligned with the electrodes. The chip system provided conducive cell growth environment, and enabled the cells get transfected while the cells adhered during the electroporation. The transferred cells were inspected under the fluorescence microscope after electroporation is done.