Print–Pause–Print Fabrication of Tailored Electrochemical Microfluidic Devices

Abstract

Three-dimensional (3D) printing technology has emerged as a powerful technology for the fabrication of low-cost microfluidics. Nevertheless, the fabrication of microfluidic devices integrating high-performance electrochemical sensors in practical applications is still an open challenge. Although automatic fabrication of the microfluidic device and the electrodes can be successfully carried out using a one-step multimaterial fused filament fabrication (FFF) approach, the as-printed electrochemical performance of these electrodes is not good enough for chemical (bio)sensing and their surface modification is challenging because after closing the channel there is no physical access to the electrode. Thus, here a pause–print–pause (PPP) microfabrication approach was implemented. The fabrication was paused before printing the microfluidics, and the filament-based electrodes were directly modified on the printing bed via stencil printing, drop casting, and electrodeposition. To exemplify this versatile workflow, the design of a microfluidic glucose sensor was proposed. To this end, first, the working and counter electrodes were stencil printed with graphite ink while the reference electrode was stencil printed with Ag|AgCl ink. Then, Prussian blue was formed on the working electrode either by drop casting or by electrodeposition, and glucose oxidase was drop cast on top. At this point, the microfabrication process was resumed, and the microfluidics were printed on top of the modified electrodes to complete the construction of hybrid electrochemical fluidic fused filament fabricated devices (h-eF 4 Ds). This print–pause–print approach is not limited to ink-based electrodes or glucose oxidase, and we envisage these results will pave the way for the effective integration of electrodes in microfluidic devices in a simple and clean-room-free approach, allowing the development of highly customized eF 4 Ds for a plethora of analytes with high significance.

Spark-Discharge-Activated 3D-Printed Electrochemical Sensors

“…The different activation strategies aim to eliminate the thermoplastic material from the surface of the electrode, uncovering the conductive carbon material. Chemical treatment either dissolves completely the polymer by immersing electrodes in organic solvents , or saponificates the polymer chains in alkaline media. , Other popular methods include electrochemical treatments, ,, surface sanding, laser scribing, or oxygen plasma . Some of these approaches are not effective on their own and require to be combined to obtain a suitable response .…”

“…Despite being conductive, as-printed electrodes are not suitable for most electrochemical applications; hence, their surface needs to be activated. Conductive filament activation is a hot topic these days, and there are plenty of strategies proposed for this end at different stages of the fabrication: pre-, 10 mid-, 11 and postprinting. Postprinting methods are the most extended because they can be performed on-demand.…”

“…Chemical treatment either dissolves completely the polymer by immersing electrodes in organic solvents 12 , 13 or saponificates the polymer chains in alkaline media. 10 , 14 Other popular methods include electrochemical treatments, 11 , 15 , 16 surface sanding, 17 laser scribing, 18 or oxygen plasma. 19 Some of these approaches are not effective on their own and require to be combined to obtain a suitable response.…”