Phase-changing sacrificial layers in microfluidic devices: adding another dimension to separations

Abstract

The use of polymers in microchip fabrication affords new opportunities for the development of powerful, miniaturized separation techniques. One method in particular, the use of phase-changing sacrificial layers, allows for simplified designs and many additional features to the now standard fabrication of microchips. With the possibility of adding a third dimension to the design of separation devices, various means of enhancing analysis now become possible. The application of phase-changing sacrificial layers in microchip analysis systems is discussed, both in terms of current uses and future possibilities.

Figure 1. Schematic overview of using phase changing sacrificial layers for solvent bonding microfluidic devices

(A) A PDMS layer (crosshatched) is placed on top of an imprinted PMMA chip. (B) The polymer chip is heated and the channels are filled with liquid sacrificial material (gray with white vertical lines). (C) After the sacrificial layer is cooled and solidified (gray with horizontal white lines) the PDMS covering is removed and solvent (black) is added to the top of the PMMA chip. (D) A covering plate is placed on top of the imprinted chip and bonded. (E) The bonded chip is heated and the wax is removed from the channels in the completed device. Reprinted with permission from ref. ; copyright 2005, American Chemical Society (ACS).

Figure 2. The integration of a semipermiable membrane with an open mirofluidic channel using phase changing sacrificial layers

(A) A PMMA piece with an opening is placed on top of a protected channel. (B) A monomer solution in placed in the PMMA well. (C) The mixture is photopolymerized. (D) The device is heated and the wax is removed. Reprinted with permission from ref. ; copyright 2006, ACS.

Figure 3. Key features of a multichannel separation device with a crossover channel

(A) Optical image of channels embossed in PMMA at the crossover interface. (B) Optical micrograph of channels filled with a sacrificial material. (C) Photograph of a completed multilayer device. (D) Channels filled with colored solution to show fluidic independence. Reprinted with permission from ref. ; copyright 2008, ACS.

Figure 4. Potential multilayer microdevice designs enabled by sacrificial fabrication methods

(A) A layout with four standard microchip capillary electrophoresis systems. (B) A crossover channel format that reduces reservoir numbers and makes better use of space. (C) Three pieces of a device that illustrates how crossover channels can be individually addressable and available for functionalizaton before assembly into a more complex microfluidic network. (D) A three-dimensional illustration of the formation of an electrospray nozzle on a chip to facilitate coupling to a mass spectrometer. (E) Integration of an electromagnet in a microfluidic device near a separation channel, using phase changing sacrificial materials and a thin polymer film.