Realization of a salt bridge-free microfluidic reference electrode

Abstract

We report on the design of a microfluidic electrochemical cell with a true Ag/AgCl reference electrode that does not rely on a physical barrier or salt bridge, but instead takes advantage of slow diffusion times in micro-channels. The device concept is demonstrated in PDMS using the Ir(+IV)/Ir(+III) redox couple as an example. A scaling analysis provides limits of operation for the device.

Microfluidic Microdialysis: Spatiotemporal Control over Solution Microenvironments Using Integrated Hydrogel Membrane Microwindows

“…This ability to sculpt electric fields naturally suggests novel capabilities for a variety of experiments, including electrophoretic separations [74], local electrophoretic delivery [75], microfluidic salt bridges (e.g., for maintaining separate reference and working electrode solutions [76]), and localized or selective electroporation of cells, organisms, or vesicles [77]. While electrically permeable gels could also be made with contact lithography for these applications (and have been, in some cases [78][79][80][81]), HMMs enable closer electrode spacing, allowing higher currents and smaller dimensions to be obtained.…”

Rapid bench-top fabrication of poly(dimethylsiloxane)/polystyrene microfluidic devices incorporating high-surface-area sensing electrodes

“…To seal the tubing in place, optical adhesive 88 (Norland Products, Inc., Cranbury, NJ) was applied on the non-bonding face of the PS and cured for 20 min in an UV illumination chamber. Two electrode designs were prepared; one to characterize electro-active surface area (device 1) and the other, based on a design previously described by Dydek et al, 3 was used for electrochemical sensing (device 2). All electrodes in device 1, as well as the working and counter electrodes in device 2, were made from 50 nm-thick gold films, while the reference electrodes in device 2 were made from 50 nm-thick platinum films.…”

“…In particular, the encapsulation of electrodes within microfluidic channels enables the on-chip use of electrochemical sensing techniques that provide highly sensitive detection of label-free analytes over a wide range of concentrations. [1][2][3] To date, most microelectrodes integrated into LoC devices have been mostly fabricated using techniques inherited from the semiconductor industry (e.g., photolithography, thin film deposition, etching, and anodic bonding). 4 Despite the success of these techniques in producing fully assembled devices, they typically entail the use of one or more costly and time-consuming processes that require access to clean-room facilities.…”

Dual-patterned immunofiltration (DIF) device for the rapid efficient negative selection of heterogeneous circulating tumor cells

“…After the fabrication of two layers with uniquely engraved patterns, both layers were treated with O 2 plasma and accurately aligned above the microscope, by adding few drops of 80% ethanol between the layers, for the maintenance of the hydrophilic characteristics during assembly. 19 Finally, the assembled layers were heated to 110 °C for 30 min above the hot plate to evaporate the remaining ethanol and to ensure the strong covalent bonding between the layers. Aside from the DIF device, we also prepared a one-side patterned device and a non-patterned device with the same procedure, as a control group.…”

“…The single patterned device was also formed in the same dimensions, except for having channels between the rings instead of the bridges, resulting in a similar structure to the conventional micropost-based cell filtration devices. [24][25][26] Cells were modeled with diameter of 8 μm and approximately 200 of them were entered in each structure with an inlet pressure of 10 Pa. Fig.…”