Microfluidic Tools for DNA Analysis - DNA Nanotechnology: From Structure to Function - page 123

Fig. 7.9 Integrated devices for DNA extraction, amplification, and detection. ( a )LAMPdevice
composed of thermal lysis chamber for DNA extraction, screw valve-controlled channel, and
LAMP reaction channel (Reproduced from Ref. [ 40 ] with permission of The Royal Society of
Chemistry). ( b ) Solid-phase extraction of DNA followed by LAMP amplification: SPE solid-
phase extraction, SI sample inlet, RI reagent inlet, WO waste outlet, LC LAMP chamber, LO
LAMP outlet (Reprinted with the permission from Ref. [ 47 ]. Copyright 2011 American Chemical
Society)
was pumped out of the lysis chamber into the downstream channel when the valve
was unscrewed. The whole process, from cell loading to signal readout, does not
rely on any external instruments besides heating, and accordingly, nonprofessionals
with little training can operate this device. So the instrument-free valve control
is critical to the whole integration and the miniaturization of the microfluidic
devices. As another alternative, researchers developed the centrifuge-less solid-
phase extraction (SPE) that mainly relies on micro-beads [ 41 - 43 ] or micro-pillars
[ 44 - 46 ] having high specific surface area, for on-chip PCR. For the isothermal
amplification, Wu and coworkers incorporated the SPE zone composed of micro-
pillars into the device and performed the loop-mediated isothermal amplification
(LAMP) (Fig. 7.9 b) [ 47 ]. Landers and coworkers developed a fabrication method
for poly(methyl methacrylate) (PMMA) microfluidic devices and chitosan-coating
method for the PMMA pillars for DNA binding [ 46 ]. DNA binding to chitosan is a
pH-dependent process: Charge-charge interactions bind the DNA to the protonated
chitosan at pH 5; neutralization of the charge at pH 9 results in DNA release.
This approach displaced the previous silica-based SPE and hence eliminated PCR-
inhibitory reagents necessary for traditional silica-based purifications, making the
extracted DNA PCR-ready and suggesting facile integration with amplification
devices.
In addition, the complex fluid flow can be controlled by using micro-valves and
pumping [ 48 ], or differential flow resistances resulting from specially designed
channel dimensions [ 43 , 47 ]. Other improvements such as concentrating trace
nucleic acids have been developed by combining magnetic separation [ 49 ].