Decreasing microfluidic evaporation loss using the HMDL method: open systems for nucleic acid amplification and analysis

Abstract

Evaporation is of great importance when dealing with microfluidic devices with open air/liquid interfaces due to the large surface-to-volume ratio. For devices utilizing a thermal reaction (TR) reservoir to perform a series of biological and chemical reactions, excessive heatinduced microfluidic evaporation can quickly lead to reaction reservoir dry out and failure of the overall device. In this study, we present a simple, novel method to decrease heat-induced fluid evaporation within microfluidic systems, which is termed as heat-mediated diffusion-limited (HMDL) method. This method does not need complicated thermal isolation to reduce the interfacial temperature, or external pure water to be added continuously to the TR chamber to compensate for evaporation loss. The principle of the HMDL method is to make use of the evaporated reaction content to increase the vapor concentration in the diffusion channel. The experimental results have shown that the relative evaporation loss (V loss /V ini ) based on the HMDL method is not only dependent on the HMDL and TR region's temperatures (T HMDL and T TR ), but also on the HMDL and TR's channel geometries. Using the U-shaped uniform channel with a diameter of 200 lm, the V loss /V ini within 60 min is low to 5% (T HMDL = 105°C, T TR = 95°C). The HMDL method can be used to design open microfluidic systems for nucleic acid amplification and analysis such as isothermal amplification and PCR thermocycling amplification, and a PCR process has been demonstrated by amplifying a 135-bp fragment from Listeria monocytogenes genomic DNA.

Fast identification of foodborne pathogenic viruses using continuous-flow reverse transcription-PCR with fluorescence detection

“…In addition, the LOD of the RVs RNA concentration was estimated to be 6.4 9 10 4 copies ll -1 . However, the common drawbacks, such as adsorption of the reagents to the channel surface (Zhang et al 2006), being prone to evaporation of the sample solution and formation of gas bubbles (Zhang and Xing 2010a), the requirement of precise temperature control are also the challenging issues to be solved for increasingly popularity of microfluidic RT-PCR in the future. Despite these obstacles, we believe that the microfluidic RT-PCR and on-line fluorescence detection described here holds great potential for the rapid detection of RNA-based viruses in a convenient platform.…”

Single-Molecule DNA Amplification and Analysis Using Microfluidics

“…Microreactors etched on chips using a variety of fabrication techniques ,, have been well applied to amplify single DNA molecules. These reactors are formed on chips in two different formats: single chamber and multiple chamber (Table ).…”

A disposable, integrated loop-mediated isothermal amplification cassette with thermally actuated valves

“…Although it is quite possible that we could have obtained a lower detection limit, we did not attempt to carry out experiments with smaller numbers of target particles since our sample dilution method could not provide us with a sufficiently accurate estimate of the number of target molecules in the reaction mix at very low target concentrations. We are aware, however, of reports on single-molecule DNA amplification and detection (Zhang and Xing 2010). To verify the real-time measurements, we subjected the LAMP products to gel electrophoresis.…”

“…It is desirable to seal the reaction chamber to reduce the introduction of contaminants and to prevent evaporation as the nucleic acid amplification process takes place at an elevated temperature. Although valveless technologies have been developed to reduce evaporation (Zhang and Xing 2010), valves are still predominantly used for sealing in microfluidics (Chen et al 2007;Wang et al 2006;Das et al 2007;Oh and Ahn 2006). Diverse, ingenious actuation mechanisms for microfluidic valves have been developed such as piezoelectric (Li et al 2004;Shao et al 2004), magnetic (Bae et al 2002;Gaspar et al 2008), thermal (Kim et al 2004;Chen et al 2008), pneumatic (Lagally et al 2004;Lien et al 2009), and hydraulic (Oh et al 2005).…”