posted on 2007-02-15, 00:00authored byMichael G. Roper, Christopher J. Easley, Lindsay A. Legendre, Joseph A. C. Humphrey, James P. Landers
A completely noncontact temperature system is described
for amplification of DNA via the polymerase chain reaction
(PCR) in glass microfluidic chips. An infrared (IR)-sensitive pyrometer was calibrated against a thermocouple
inserted into a 550-nL PCR chamber and used to monitor
the temperature of the glass surface above the PCR
chamber during heating and cooling induced by a tungsten lamp and convective air source, respectively. A time
lag of less than 1 s was observed between maximum
heating rates of the solution and surface, indicating that
thermal equilibrium was attained rapidly. Moreover, the
time lag was corroborated using a one-dimensional heat-transfer model, which provided insight into the characteristics of the device and environment that caused the
time lag. This knowledge will, in turn, allow for future
tailoring of the devices to specific applications. To alleviate
the need for calibrating the pyrometer with a thermocouple, the on-chip calibration of pyrometer was accomplished by sensing the boiling of two solutions, water
and an azeotrope, and comparing the pyrometer output
voltage against the known boiling points of these solutions.
The “boiling point calibration” was successful as indicated
by the subsequent chip-based IR-PCR amplification of a
211-bp fragment of the B. anthracis genome in a
chamber reduced beyond the dimensions of a thermocouple. To improve the heating rates, a parabolic gold
mirror was positioned above the microfluidic chip, which
expedited PCR amplification to 18.8 min for a 30-cycle,
three-temperature protocol.