Microfluidic Tools for DNA Analysis - DNA Nanotechnology: From Structure to Function - page 113

Fig. 7.1 Flow-through PCR
on a heated chip divided into
three temperature zones [ 8 ]
motion mode by which the PCR reaction solution can be moved repeatedly across
confined zones of different temperatures, meanwhile the cycle number, a key
parameter that always needs to be optimized for a specific PCR reaction, also can
be arbitrarily adjusted [ 9 ]. To replace the inconvenient and bulky syringe pump and
increase the throughput, Sun and coworkers proposed a magnetic actuation method
by which a ferrofluid immiscible with the aqueous PCR reaction solution inside the
channel could propel the PCR samples through different temperature zones [ 10 ].
The design of concentric circular multichannels on one confined region reduced the
overall size of the device while guarantees a high throughput.
To get rid of multiple temperature control, single heating scheme is desirable.
Toward this purpose, a qiandu (right triangular prism)-shaped polydimethylsiloxane
(PDMS) was proposed (Fig. 7.2 a). It could generate a temperature gradient on
its slanted plane when the PDMS block is placed on a single heater with a set
temperature (Fig. 7.2 b). The temperature profile can be accurately regulated by
adjusting the inclination angle of the PDMS during the fabrication process. The low
thermal conductivity of the PDMS allows the formation of a thickness-dependent
temperature gradient. The temperature gradient is suitable for PCR application,
although it is somewhat different from traditional temperatures acquired through
the thermocycler (Fig. 7.2 c).
From these examples, we could find that researchers have already tried to replace
the complicated thermal control for a long time. Apart from above approaches (for
the improvement of hardware), another approach is to change the biochemical basis
of nucleic acid amplifications. So the isothermal amplification techniques, which
use a constant temperature for amplification thereby obviating the need for thermal
cycling, emerged, and the field is growing quickly. To simplify an integrated device
performing isothermal amplifications, some work focused on the development of
heating strategy. Many of them employed the principle of exothermic reactions such
as Mg-Fe alloy and water [ 12 ], calcium oxide and water [ 13 ], or iron, oxygen, and