Design and integration of an all-in-one biomicrofluidic chip

Abstract

We demonstrate a highly integrated microfluidic chip with the function of DNA amplification. The integrated chip combines giant electrorheological-fluid actuated micromixer and micropump with a microheater array, all formed using soft lithography. Internal functional components are based on polydimethylsiloxane (PDMS) and silvercarbon black-PDMS composites. The system has the advantages of small size with a high degree of integration, high polymerase chain reaction efficiency, digital control and simple fabrication at low cost. This integration approach shows promise for a broad range of applications in chemical synthesis and biological sensinganalysis, as different components can be combined to target desired functionalities, with flexible designs of different microchips easily realizable through soft lithography.

Figure 1

(a) A 3D schematic illustration of a chip’s layered structure. The lower layer contains the GER fluid channels for the micropump and micromixer, as well as the air channels for microvalves and the microheater array. The upper layer contains the microfluidic channels for PCR reagents. (b) The chip with input and output tubes and the temperature sensors. The upper panel shows an image of the fabricated device, placed beside a one dollar Hong Kong coin.

Figure 2

Schematic diagrams showing the three critical steps of the PCR process. (a) Active mixing of the Max Mixer with primer and template in the GER fluid mixer, with the subsequent transport to the reaction loop. (b) With all the valves shut down to form a closed reaction loop, the GER fluid pump continuously circulates the reagents to pass through the three heating zones with the temperatures stabilized at 96, 50, and 72 °C. (c) After completing the desired cycles, the product solution is expelled from the channels by compressed air. The left inset is a snapshot of the expelling process shown schematically in (c).

Figure 3

(a) An image of the mixer when the side channels are not activated. The left panel shows the two reagents, colored green and white, are separated by a sharp interface. Flow baffles deployed at the intersections of the main channel with the side channels are indicated by arrow. On the right is an enlarged image of the fluid at mixer’s outlet, showing no mixing has occurred. The luminosity histogram shows two clearly separated peaks, reflecting the two reagents. (b) An image of the mixer when the side channels are activated with pulsating flows, actuated by the GER fluid. On the right is an enlarged image of the mixed fluid at mixer’s outlet. The homogeneous color indicates that complete mixing has been achieved. This is reflected in the luminosity histogram with a single peak.

Figure 4

(a) Upper panel is an image of the heater array. Lower panel is a process flow diagram illustrating the fabrication procedure of the microheater array using soft lithography. Description of the steps is in the text. (b) Upper panel is an infrared image of the three heating zones. Lower panel is a schematic drawing showing the temperature profile corresponding to the different heating zones. Points are the measured data at respective positions linked by the dashed lines. The red line is the target temperature profile.

Figure 5

(a) Flux of pumped microfluid plotted as a function of the electric field applied on the GER fluid pump. To achieve the desired pumping flux, the required value of the electric field is obtained by using an exponential fit to the data, shown as the solid line. (b) A breakdown of the PCR cycle times at various applied electric field.

Figure 6

(a) UV images of the PCR product at different reaction times. From left to right: the total reaction time is 49, 56, 63, and 73 min as labeled below each strip. To the right is a gene ruler 50-bp DNA ladder (Fermentas, Inc.), with an arrow indicating the 500-bp fragment of the 50-bp DNA ladder, used as the reference. (b) Relationship between the band intensity and total PCR reaction time. Values are normalized with respect to the intensity obtained from the 500-bp fragment of the 50-bp ladder.