Date Published: February 19, 2014
Publisher: Public Library of Science
Author(s): Katarina Bengtsson, Sara Nilsson, Nathaniel D. Robinson, Alexei Gruverman.
In nearly all cases, electrophoresis in gels is driven via the electrolysis of water at the electrodes, where the process consumes water and produces electrochemical by-products. We have previously demonstrated that π-conjugated polymers such as poly(3,4-ethylenedioxythiophene) (PEDOT) can be placed between traditional metal electrodes and an electrolyte to mitigate electrolysis in liquid (capillary electroosmosis/electrophoresis) systems. In this report, we extend our previous result to gel electrophoresis, and show that electrodes containing PEDOT can be used with a commercial polyacrylamide gel electrophoresis system with minimal impact to the resulting gel image or the ionic transport measured during a separation.
The quest for increased capacity and cost reduction drives miniaturization (and automation) of chemical analysis methods in life science and chemistry. However, many standard techniques, such as gel electrophoresis (GE) of proteins, DNA fragments, and other large molecules, do not lend themselves to straightforward miniaturization to “lab-on-a-chip” systems. In the specific case of GE, the uniformity of the gel, the resolution of the detection method, and the presence of undesired chemical reactions at the electrodes each impart limitations on how small effective separation devices can be. Advances in gel polymerization technology and the use of difference gel electrophoresis  (DIGE) have reduced the magnitude and consequences of spatial variations in gel properties dramatically, and improved imaging and detection methods have increased the resolution of the resulting gel images. In this paper, we begin to address the third (and less-frequently discussed) challenge – the electrochemical reactions at the electrodes – by performing a preliminary study exploring the potential for using electrochemically-active conjugated polymer electrodes instead of metal electrodes. Such polymer electrodes can eliminate undesired electrochemical products, reduce manufacturing costs, inhibit cross-contamination between gels, and prevent the consumption of the aqueous electrolyte, which is particularly important when reducing the volume of gel used in systems which are not immersed in electrolyte.
We chose the PhastSystem from GE Healthcare Life Sciences, for testing our materials and techniques because it is commercially available, offers relatively easy access to the gels and electrodes (e.g., neither gel nor electrodes are submerged in a liquid buffer) and is currently used in laboratories around the world. However, we performed electronic measurements both in a PhastSystem Separation Unit and with an external measurement system based on a Keithley source-measure unit (SMU). The latter system offered considerably higher measurement resolution. The polyacrylamide (PA) gel (PhastGel 8–25, GE Healthcare) and accompanying agarose PhastGel SDS Buffer Strips (GE Healthcare), which together supply the liquid SDS buffer/electrolyte, were used in both measurement setups. Before any of these measurements, we quickly verified the ability of the PEDOT:PSS electrodes to undergo electrochemical oxidation and reduction in the SDS/TRIS electrolyte used in the PhastSystem.
As described in the methods section, we built a simple electrochemical cell with two thin PEDOT:PSS electrodes on glass microscope slides connected by a SDS Buffer Strip. The PEDOT:PSS electrodes were reversibly and repeatedly oxidized and reduced by switching the polarity of an applied potential of 1 V. This was observed by a color change (electrochromism) between dark (reduced PEDOT) and light (oxidized PEDOT) blue within the electrodes, demonstrating the transport of ions between and into the electrodes, as shown in the video in the supplementary information (Video S1). Note that only the region of PEDOT:PSS contacting (under) the SDS Buffer Strip (the region directly above the silver pads used for contacting the device with the probes from the power source) is available for electrochemistry. The observed color change confirmed the compatibility of the SDS and TRIS buffer with the PEDOT:PSS, particularly that the ions are able to migrate into the partially-hydrated polymer, allowing the PEDOT through the entire thickness of the electrode to switch.
We have demonstrated that PEDOT:PSS electrodes are chemically and electrochemically compatible with SDS-PAGE separations via electrophoresis of a standard benchmark protein mixture. Aside from introducing the polymer electrodes, no change is required in the protocol for performing SDS-PAGE. This result, in conjunction with our previous demonstration of the reduction of water electrolysis when using PEDOT:PSS electrodes , has the potential to pave the way for the development of low-cost, disposable, miniaturized GE systems for accelerated analysis in areas such as proteomics and medical diagnosis (e.g., analysis of proteins associated with tumors in bodily fluids). We hope that this will lead to more advanced and less expensive diagnoses in modern healthcare facilities and in areas of the world where advanced laboratory analyses are not yet readily available.