Abstract
We report an observation of rapid (exceeding 2,000 K/s) heating of polydimethylsiloxane (PDMS), one of the most popular microchannel materials, under cyclic loadings at high (~MHz) frequencies. A microheater was developed based on the finding. The heating mechanism utilized vibration damping in PDMS induced by sound waves that were generated and precisely controlled using a conventional surface acoustic wave (SAW) microfluidic system. The refraction of SAW into the PDMS microchip, called the leaky SAW, takes a form of bulk wave and rapidly heats the microchannels in a volumetric manner. The penetration depths were measured to range from 210 μm to 1290 μm, enough to cover most sizes of microchannels. The energy conversion efficiency was SAW frequency-dependent and measured to be the highest at around 30 MHz. Independent actuation of each interdigital transducer (IDT) enabled independent manipulation of SAWs, permitting spatiotemporal control of temperature on the microchip. All the advantages of this microheater facilitated a two-step continuous flow polymerase chain reaction (CFPCR) to achieve the billion-fold amplification of a 134 bp DNA amplicon in less than 3 min.
Highlights
Lab-on-a-chip systems are broadly applicable to sophisticated biophysicochemical processes across a variety of science and engineering fields
We imaged the heating of PDMS caused by the penetration of the leaky surface acoustic waves (SAWs) (Fig. 1b)
We placed a thick slab of PDMS on piezoelectric substrates with interdigital transducers (IDTs) having different finger gap periods
Summary
We imaged the heating of PDMS caused by the penetration of the leaky SAWs (Fig. 1b). We placed a thick slab of PDMS on piezoelectric substrates with IDTs having different finger gap periods. One can activate or deactivate reactions in a microchannel by turning on/off the corresponding heat source pixels, thereby controlling the total number of PCR cycles. These features could be used to optimize the PCR protocols in a continuous flow system just as commercial thermal cyclers do. The ultrafast CFPCR system can be made portable through the use of a palm-sized electronic driver circuit[30] and battery-powered syringe pumps This approach is applicable to heaters, actuators, or sensors for microelectromechanical systems, optofluidics, or paper microfluidics in the fields of food science, biochemical research, and medicine, where there is a need for heating capabilities beyond the limits of current heating technologies
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