Integrating polyaniline : a new electrode material for lab on a chip applications

The creation of disposable, single use devices capable of performing complex tasks is one of the key motivators in Lab on a Chip (LOC) research. Replication techniques allow for low-cost manufacturing of large numbers of plastic devices capable of performing a range of functionalities. Complex tasks, however, often require the integration of electrodes, significantly increasing the costs per device when integrating metal electrodes. This thesis describes the development and application of the conducting polymer, polyaniline (PANI) as a new electrode material within LOC devices. PANI is an inexpensive alternative to metal electrodes that are currently used, most commonly in LOC research. The electrodes were fabricated in thin films of PANI, initially by flash lithography using a studio camera flash and a transparency mask. During flash welding, a conducting polymer circuit was formed from the non-exposed regions. The flash-welding process was enhanced through the use of polymeric substrates, enabling flash welding of PANI films with a thickness ranging from 5 to 14.4 μm, significantly thicker than reported previously. Scanning electron micrographs, light microscope images and conductivity measurements were used to determine the conductive properties and morphology of the PANI electrodes. Raman spectroscopy was used to determine the sharpness of the masked edges. The interface between the flash-welded and masked regions of the PANI films was typically less than 10 μm wide. The conducting regions of the PANI film were shown to be capable of carrying the high voltages of up to 2000 V required for chip electrophoresis, and were stable for up to 30 min under these conditions. The creation of disposable, single use devices capable of performing complex tasks is one of the key motivators in Lab on a Chip (LOC) research. Replication techniques allow for low-cost manufacturing of large numbers of plastic devices capable of performing a range of functionalities. Complex tasks, however, often require the integration of electrodes, significantly increasing the costs per device when integrating metal electrodes. This thesis describes the development and application of the conducting polymer, polyaniline (PANI) as a new electrode material within LOC devices. PANI is an inexpensive alternative to metal electrodes that are currently used, most commonly in LOC research. The electrodes were fabricated in thin films of PANI, initially by flash lithography using a studio camera flash and a transparency mask. During flash welding, a conducting polymer circuit was formed from the non-exposed regions. The flash-welding process was enhanced through the use of polymeric substrates, enabling flash welding of PANI films with a thickness ranging from 5 to 14.4 μm, significantly thicker than reported previously. Scanning electron micrographs, light microscope images and conductivity measurements were used to determine the conductive properties and morphology of the PANI electrodes. Raman spectroscopy was used to determine the sharpness of the masked edges. The interface between the flash-welded and masked regions of the PANI films was typically less than 10 μm wide. The conducting regions of the PANI film were shown to be capable of carrying the high voltages of up to 2000 V required for chip electrophoresis, and were stable for up to 30 min under these conditions. Using a structured layer of dry film photoresist for sealing, a polydimethylsiloxane substrate containing channels and reservoirs was bound to the PANI film to form an integrated microfluidic device. The PANI electrodes were used for the electrophoretic separation of three sugars labelled with 8-When characterising the welding process, only light with a wavelength above 570 nm was found to contribute to the welding process. A 635 nm laser diode was then used successfully for welding by direct writing lithography, for the first time welding PANI nanofibers using a narrow wavelength light-source. The improved accuracy and precision of laser patterning enabled the development of fine electrode patterns that were unachievable through the flash welding process, including those required for Capacitively Coupled Contactless Conductivity Detection, (C4D). This enabled the fabrication of the first fully polymeric LOC device with integrated electrodes employing laser-patterned electrodes to carry the Direct Current (DC) voltages required for fluid handling and electrophoretic separation, as well as the Alternating Current (AC) voltages for C4D. This device was used for the electrophoretic separation of Li+, Na+ and K+ with detection limits down to 25 μM and an efficiency of 22,000 plates/m, which is comparable with the performance of similar electrophoresis - C4D devices with metal electrodes.