1. Field of the Invention
This invention relates to compositions and methods for in-system priming of microfluidic devices. More specifically, aspects of the present invention relate to compositions and methods for in-system priming of microfluidic devices utilizing a priming solution comprising adding and/or increasing concentrations of surfactant in a buffer solution.
2. Discussion of Related Art
The detection of nucleic acids is central to medicine, forensic science, industrial processing, crop and animal breeding, and many other fields. The ability to detect disease conditions (e.g., cancer), infectious organisms (e.g., HIV), genetic lineage, genetic markers, and the like, is ubiquitous technology for disease diagnosis and prognosis, marker assisted selection, correct identification of crime scene features, the ability to propagate industrial organisms and many other techniques. Determination of the integrity of a nucleic acid of interest can be relevant to the pathology of an infection or cancer. One of the most powerful and basic technologies to detect small quantities of nucleic acids is to replicate some or all of a nucleic acid sequence many times, and then analyze the amplification products. Polymerase chain reaction (PCR) is perhaps the most well-known of a number of different amplification techniques.
PCR is a powerful technique for amplifying short sections of deoxyribonucleic acid (DNA). With PCR, one can quickly produce millions of copies of DNA starting from a single template DNA molecule. PCR includes a three-phase temperature cycle of denaturation of DNA into single strands, annealing of primers to the denatured strands, and extension of the primers by a thermostable DNA polymerase enzyme. This cycle is repeated so that there are enough copies to be detected and analyzed. In principle, each cycle of PCR could double the number of copies. In practice, the multiplication achieved after each cycle is always less than 2. Furthermore, as PCR cycling continues, the buildup of amplified DNA products eventually ceases as the concentrations of required reactants diminish. For general details concerning PCR, see Sambrook and Russell, Molecular Cloning—A Laboratory Manual (3rd Ed.), Vols. 1-3, Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y. (2000); Current Protocols in Molecular Biology, F. M. Ausubel et al., eds., Current Protocols, a joint venture between Greene Publishing Associates, Inc. and John Wiley & Sons, Inc., (supplemented through 2005) and PCR Protocols A Guide to Methods and Applications, M. A. Innis et al., eds., Academic Press Inc. San Diego, Calif. (1990).
Real-time PCR refers to a growing set of techniques in which one measures the buildup of amplified DNA products as the reaction progresses, typically once per PCR cycle. Monitoring the accumulation of products over time allows one to determine the efficiency of the reaction, as well as to estimate the initial concentration of DNA template molecules. For general details concerning real-time PCR see Real-Time PCR: An Essential Guide, K. Edwards et al., eds., Horizon Bioscience, Norwich, U.K. (2004).
More recently, a number of high throughput approaches to performing PCR and other amplification reactions have been developed, e.g., involving amplification reactions in microfluidic devices, as well as methods for detecting and analyzing amplified nucleic acids in or on the devices. Microfluidic systems are systems that have at least one microfluidic channel (a.k.a., microchannel) through which a fluid may flow, which microfluidic channel has at least one internal cross-sectional dimension, (e.g., depth, width, length, diameter) that is typically less than about 1000 micrometers. Thermal cycling of the sample for amplification is usually accomplished in one of two methods. In the first method, the sample solution is loaded into the device and the temperature is cycled in time, much like a conventional PCR instrument. In the second method, the sample solution is pumped continuously through spatially varying temperature zones. See, for example, Lagally et al. (Analytical Chemistry 73:565-570 (2001)), Kopp et al. (Science 280:1046-1048 (1998)), Park et al. (Analytical Chemistry 75:6029-6033 (2003)), Hahn et al. (WO 2005/075683), Enzelberger et al. (U.S. Pat. No. 6,960,437) and Knapp et al. (U.S. Patent Application Publication No. 2005/0042639).
Microfluidic devices, such as microfluidic chips, are generally primed for sample analysis to prevent, for example, air bubbles from being present in mixtures that are used to fill channels, and wells, within a microfluidic chip. The presence of air bubbles in mixtures in a chip may adversely affect the testing of chemical or biological samples using the microfluidic chip. For example, air bubbles may cause the flow of liquid within the chip to be uncontrollable. Air bubbles may also, in some systems, cause reduced thermal control. The priming of a microfluidic chip, if performed inaccurately or incorrectly, may cause an analysis performed using the microfluidic chip to be erroneous and, hence, unreliable. As it is often not known at the time a test is made whether the microfluidic chip has been primed correctly, it is important to make certain that priming procedures are accurate and precise in order to reduce the likelihood of inaccurate test results.