Strategies for enhancing the speed and integration of microchip genetic amplification.

In this work, we explore the use of methods that allow a significant acceleration of genetic analysis within microchips fabricated from low thermal conductivity materials such as glass or polymers. Although these materials are highly suitable for integrating a number of genetic analysis techniques onto lab-on-a-chip devices, their low thermal conductivity limits the rate at which heat can be transferred and hence lowers the speed of thermal cycling. However, short thermal cycling times are the key to bringing PCR to clinical point-of-care applications. Although shrinking the PCR reaction chamber volume can increase the speed of thermal cycling, this strategy is not always suitable, particularly when dealing with clinical samples with low analyte concentrations. In the present work, we combine two alternate strategies for decreasing the time required to perform PCR: implementing a heat sink and optimizing the PCR protocol. First, the heat sink substantially reduces the thermal resistance opposing heat dissipation into the ambient environment, and eliminates the parasitic thermal capacitance of the regions in the microchip that do not require heating. The low thermal conductivity of glass is used to our advantage to design the heat-sink placement to achieve fast thermal transitions while maintaining low power consumption. Second, we explore the application of two-stage PCR to provide a further reduction in the time required to perform genetic amplification by merging the annealing and extension stages of the commonly used three-stage PCR approach. In combination, we reduce the time required to perform thermal cycling by roughly a factor of 3 while improving the temperature control.

Electrically controlled microvalves to integrate microchip polymerase chain reaction and capillary electrophoresis.

Microvalves are key in realizing portable miniaturized diagnostic platforms. We present a scalable microvalve that integrates well with standard lab on a chip (LOC) implementations, yet which requires essentially no external infrastructure for its operation. This electrically controlled, phase-change microvalve is used to integrate genetic amplification and analysis via capillary electrophoresis--the basis of many diagnostics. The microvalve is actuated using a polymer (polyethylene glycol, PEG) that exhibits a large volumetric change between its solid and liquid phases. Both the phase change of the PEG and the genetic amplification via polymerase chain reaction (PCR) are thermally controlled using thin film resistive elements that are patterned using standard microfabrication methods. By contrast with many other valve technologies, these microvalves and their control interface scale down in size readily. The novelty here lies in the use of fully integrated microvalves that require only electrical connections to realize a portable and inexpensive genetic analysis platform.

Dynamic temperature measurement in microfluidic devices using thermochromic liquid crystals.

Thermochromic liquid crystals (TLCs) are used to explore the temperature transients during thermal cycling for microchip-based polymerase chain reaction (PCR). By analyzing the reflected spectra of the TLCs over time, temperature vs. time trajectories were extracted and overshoots/undershoots were estimated. To our knowledge, this is the first report of TLC-based dynamic temperature measurements in a microfluidic device for all PCR temperature stages.

An inexpensive and portable microchip-based platform for integrated RT-PCR and capillary electrophoresis.

We present an inexpensive, portable and integrated microfluidic instrument that is optimized to perform genetic amplification and analysis on a single sample. Biochemical reactions and analytical separations for genetic analysis are performed within tri-layered glass-PDMS microchips. The microchip itself consists of integrated pneumatically-actuated valves and pumps for fluid handling, a thin-film resistive element that acts simultaneously as a heater and a temperature sensor, and channels for capillary electrophoresis (CE). The platform is comprised of high voltage circuitry, an optical assembly consisting of a laser diode and a charged coupled device (CCD) camera, circuitry for thermal control, and mini-pumps to generate vacuum/pressure to operate the on-chip diaphragm-based pumps and valves. Using this microchip and instrument, we demonstrate an integration of reverse transcription (RT), polymerase chain reaction (PCR), and capillary electrophoresis (CE). The novelty of this system lies in the cost-effective integration of microfluidics, optics, and electronics to realize a fully portable and inexpensive system (on the order of $1000 in component costs) for performing both genetic amplification and analysis - the basis of many medical diagnostics. We believe that this combination of portability, cost-effectiveness and performance will enable more accessible healthcare.