Microfluidic Tools for DNA Analysis - DNA Nanotechnology: From Structure to Function - page 116

Fig. 7.3 Continuous-flow droplet PCR on a fully automated sampling device. ( a ) Combination of
sequential injection with continuous flow using a two-state loop with two syringe pumps each
connected to a three-way pinch valve. State 1 : Pump 1 sequentially forms samples from the
aspirating tip, while pump 2 pushes continuously the droplets formed in state 2 of the last cycle
to the heating cylinder. State 2 : Pump 1 pushes continuously the droplets formed from state 1 to
the heating cylinder, while pump 2 sequentially forms a new train of droplets. ( b ) Samples and
reagents are aspirated from a microtiter plat containing Ta q polymerase in a common well and
various samples in other individual wells. The droplets are formed by a series of cyclic operations,
including vertical movement in a well and lateral movement between the common well and various
sample wells. The common well oil is surfactant-free perfluorohexane, and the carrier fluid is
perfluorohexane premixed with 0.5 wt % of a fluoroalcohol surfactant. The specific enlargement
of the aspirating tip induces on-flight coalescence of the two primary droplets when they move
through it. ( c ) Capillary wrapped 35 times around a three-zone heating cylinder, endpoint LIF
detection, and output for further storage or analysis (Reprinted with the permission from Ref. [ 20 ].
Copyright 2006 American Chemical Society)
are introduced with another immiscible fluid) have been developed [ 21 , 22 ],
and the water-in-oil droplets have been extensively studied in the past decade.
Alternatively, Yang and coworkers proposed a method for generating agarose-in-
oil droplets on a flow-focusing microfluidic chip [ 23 ]. The size of droplet is tunable
by controlling the channel dimensions, flow rate of aqueous or oil phase, and they
obtained uniform nanoliter droplets, which ensures uniform PCR amplification.
Agarose has a unique thermo-responsive sol-gel switching property (Fig. 7.4 ). It
remains in liquid phase at all PCR temperatures, such that PCR can take place
with high efficiency. The generated droplets were collected into a tube and PCR
amplification was performed off the chip. After the PCR amplification, the solution
phase of the agarose droplet can be switched to the solid-gel phase by simply