PCR-based biosensors

Within the last ten years there have been significant efforts to take PCR out of the laboratory and into the field. This is partially due to an increased demand for rapid and accurate methods of detecting pathogenic bacteria, viruses and other disease-causing agents. Due to its relative accuracy and sensitivity, the polymerase chain reaction (PCR) is well suited to these needs. Miniaturized PCR-based biosensors have been developed utilizing a variety of manufacturing technologies. At least four commercial entities have developed miniaturized PCR-based detection systems with corresponding detection assays targeting DNA from tissue, blood, environmental, or food samples (Herold and Rasooly, 2009. Lab-on-a-Chip Technology. ISBN: 978-1-904455-47-9).

These PCR-based systems are both sensitive and robust, but a variety of contaminants can inhibit successful amplification and diminish their sensitivity. In order to circumvent this problem, DNA is typically extracted and purified from a sample through a variety of lysis protocols and purification techniques. One of the most common methods is chemical lysis followed by DNA purification using silica-based resins. DNA in chaotropic salt containing buffers, such as those containing guanidinium or sodium iodide salts, preferentially binds to silica surfaces, while other macromolecules, such as protein and lipids, remain free in solution. These unwanted components can be removed by various methods, including centrifugation and subsequent alcohol based washing steps. The relatively pure DNA is then eluted in low-ionic strength buffer or water. Simple kits are commercially available based upon particulate matrices with problematic flow rates and no direct integration into chip-based devices (Herold and Rasooly, 2009. Lab-on-a-Chip Technology. ISBN: 978-1-904455-47-9). At least one group has reported the incorporation of silica-based resins into a micro-flow device while others have used microfabricated silica pillar structures for the same purpose.