Poly(dimethylsiloxane) cross-linked carbon paste electrodes for microfluidic electrochemical sensing

Abstract

Recently, the development of electrochemical biosensors as part of microfluidic devices has garnered a great deal of attention because of the small instrument size and portability afforded by the integration of electrochemistry in microfluidic systems. Electrode fabrication, however, has proven to be a major obstacle in the field. Here, an alternative method to create integrated, low cost, robust, patternable carbon paste electrodes (CPEs) for microfluidic devices is presented. The new CPEs are composed of graphite powder and a binder consisting of a mixture of poly(dimethylsiloxane) (PDMS) and mineral oil. The electrodes are made by filling channels molded in previously cross-linked PDMS using a method analogous to screen printing. The optimal binder composition was investigated to obtain electrodes that were physically robust and performed well electrochemically. After studying the basic electrochemistry, the PDMS-oil CPEs were modified with multi-walled carbon nanotubes (MWCNT) and cobalt phthalocyanine (CoPC) for the detection of catecholamines and thiols, respectively, to demonstrate the ease of electrode chemical modification. Significant improvement of analyte signal detection was observed from both types of modified CPEs. A nearly 2-fold improvement in the electrochemical signal for 100 μM dithiothreitol (DTT) was observed when using a CoPC modified electrode (4.0 ± 0.2 nA (n = 3) versus 2.5 ± 0.2 nA (n = 3)). The improvement in signal was even more pronounced when looking at catecholamines, namely dopamine, using MWCNT modified CPEs. In this case, an order of magnitude improvement in limit of detection was observed for dopamine when using the MWCNT modified CPEs (50 nM versus 500 nM). CoPC modified CPEs were successfully used to detect thiols in red blood cell lysate while MWCNT modified CPEs were used to monitor temporal changes in catecholamine release from PC12 cells following stimulation with potassium.

A simple microfluidic electrochemical HPLC detector for quantifying Fenton reactivity from welding fumes

“…2,26 The channels were made by mixing PDMS at a ratio of 10:1 (w/w) of PDMS oligomer: cross linker followed by degassing with a vacuum pump (Vacuubrand, Germany) in a vacuum desiccator. The mixed PDMS was poured on the center of the mold surface slowly to prevent the addition of air bubbles and then baked at 80 °C for 30 min.…”

“…20 For electrochemically active compounds, ECD is useful because of its sensitivity and selectivity. 21-22 ECD can readily detect many molecular targets including phenols, aromatic amines, 21 glutathione, 22 reducing sugars, 23 antioxidants 24,25 and thiols 26 by controlling electrode potential and/or electrode composition. Thus, electrochemistry has been widely demonstrated as a viable detection method for a variety of flow techniques including microfluidic applications.…”

“…Soft lithography coupled with inexpensive electrochemical detectors provides this opportunity. 2,26 These advantages spurred us to create a custom microfluidic-ECD that could be coupled directly to a commercial HPLC-UV system to demonstrate the utility of this analytical method.…”

Silicones for Microfluidic Systems

“…Th ey are fabricated with conventional lithography or sputtering and lift -off techniques. Electrodes can be deposited directly on PDMS molds using molten solder [44,144], metal ion implantation [145], conducting composites (carbon paste fi lling) [146] or singlewalled carbon nanotubes embedded in PDMS surface [147]. Optical components (fi bers, fi lters, photodiodes), important for on-chip detection, can be integrated into a microdevice during the molding step [148] or inserted into formed microchannels [17].…”

Biomimetic Sensors for Rapid Testing of Water Resources

“…Further, we demonstrated that the PDMS: mineral oil CPEs can easily be chemically modified for the detection of biologically relevant molecules. The monitoring of thiols provides an indication of the functioning of numerous critical cellular pathways [19,20]. Traditional carbon paste electrodes can be used to detect thiols, however, they suffer from low peak currents due to poor interactions between the carbon and the thiols.…”