3D printed microfluidic devices with electrodes for electrochemical analysis

Abstract

A review with 93 references describing various 3D printing approaches that have been used to create microfluidic devices containing electrodes for electrochemical detection. The use of 3D printing to fabricate microfluidic devices is a rapidly growing area. One significant research area is how to detect analytes in the devices for quantitation purposes. This review article is focused on methods used to integrate electrodes into the devices for electrochemical detection. The review is organized in terms of the methodology for integrating the electrode within the device. This includes (1) external coupling of traditional electrode materials with 3D printed devices; (2) printing conductive electrode materials as part of device printing; and (3) integrating traditional electrodes into the device as part of the print process. Example applications are given and some future directions are also outlined.

Figure 1.

Various 3D printing techniques. A) Stereolithography (SLA) top-down configuration. B) Stereolithography (SLA) bottom-up configuration (more common than bottom-up). Digital light processing (DLP), another variant of SLA, employs a similar setup but utilizes projected UV light from individual pixels rather than a laser to cross-link the resin. C) Dual extrusion-based Fused Deposition modeling (FDM). A good number of commercially available FDM printers utilize only a single extrusion nozzle. D) PolyJet printing, with print heads depositing up to 6 different materials on each layer.

Figure 2.

3D-printed devices with threads for the introduction of tubing and traditional electrode materials. (A – B) CAD rendered design of the device, including threads for fittings with 1) tubing to introduce fluids and 2) house electrode materials. (C) Image of 3D printed device with the Pt-electrodes being screwed into the electrode port, ensuring the alignment of wires with the 500 μm channel of the device. (D – E) Micrographs of the electrodes housed in a flangeless fitting. Au was used as the working electrode and an Ag electrode that was modified with AgCl acting as the reference electrode. Reproduced from Ref. with permission from the Royal Society of Chemistry.

Figure 3.

3D multi-modal device for amperometric detection of nitric oxide (NO) followed by chemiluminescence detection of ATP. (A) CAD rendered design of the device. (B) Micrograph of Au electrode as working electrode before (left) and after (right) modification with Pt-black and Nafion. (C) Image of the assembled device. (D – E) Bar graphs showing average NO and ATP release from healthy RBCs in normoxic and hypoxic conditions. Reproduced from Ref. with permission from the Royal Society of Chemistry.

Figure 4.

3D-printed microfluidic device integrated with biosensors. (A) Picture showing the combination of electrodes in a 27-gauge hypodermic needle. The insert shows different layers of biosensors with 50 μm diameter wire electrodes. (B) The assembled microchip and biosensors system resulting the L-shaped design. (C) Picture of the L-shaped 3D-printed microfluidic device measuring the human tissue metabolite levels in dialysate during the cycling protocol. (D) Graphs showing the data collected from the experimental protocol. (ii – v) Metabolite levels were monitored during four exercise phases of cyclists with the increments of rpm. (vi) Metabolite level during a warming down process. Adapted from ref. with permission.

Figure 5.

3D printed device with flow underneath cell layer and ports to integrate TEER chopstick electrodes. (A) Pictures of the 3D printed device after assembling for the cell culture with flow underneath the cell layer. (B) Image that shows how chopstick electrodes can be accommodated within the device for TEER measurements. (C) TEER measurements of MDCK cells with the introduction of flow (0.2 mL/min) using a peristaltic pump. Adapted from ref. with permission.

Figure 6.

Dual-extrusion FDM printing to fabricate microchip capillary electrophoresis (MCE) device with electrodes above the channel to conduct capacitively coupled contactless conductivity detection (C⁴D). (A) Diagram illustrating the printing process utilizing two extrusion nozzles; one for printing the device and the other for printing the electrodes from conductive filament materials. (B) Image of the MCE-C⁴D device with microchannels and reservoirs filled with a blue dye solution. (C-D) Electropherograms showing a separation of K⁺, Na⁺, and Li⁺ (100 μM, each) obtained with MCE-C⁴D devices (n = 3) with integrated electrodes 3D printed from (C) PLA/carbon black and (D) copper-based filaments. Adapted from reference with permission.

Figure 7.

FDM printing of microfluidic device with conductive electrodes for analyzing carbendazim. (A) Production of electrodes from conductive filaments (carbon black/PLA) and 3D printing of the microfluidic device based on non-conductive PLA filament. (B) Dimensions of the complete microfluidic device, sensors, fluidic paper, and base. (C) Analysis of carbendazim (CBZ) in honey from a portable potentiostat and microfluidic device using a 30 μL sample. (D) Cyclic voltammograms obtained for 1.0 mM CBZ in 0.1 M Britton-Robinson (BR) buffer solution (pH 4.0) at carbon black-PLA electrodes before and after surface treatment; Inset: mechanism of oxidation of CBZ; Scan rate: 50 mV/s. (E) Square wave voltammetry recordings for increasing concentrations of CBZ (0.5 - 40.0 μM) in 0.1 M BR buffer (pH 4.0) Adapted from reference with permission.

Figure 8.

Stacked printing process to embed electrodes during the print process. (A) Step-by-step process of making a 3D printed device with an embedded gold electrode placed in the middle of the channel as well as capillary tubing. Left column contains pictures of various points of the print process, the center column is the cross-sectional CAD rendering of each step, and the right column has text explaining the process. (B) and (C) SEM images of electrode array (5 electrodes, 65 μm in width with 175 μm spacing) and a single gold electrode (65 μm in width) cut from a TEM grid embedded in the middle of the channel. (D) Overlay of single electrode response for bottom or middle placement as well as 5 electrode array response for bottom or middle placement. Adapted from reference with permission.

Figure 9.

3D printed microchip electrophoresis device with amperometric detection. (A) Photograph of 3D printed piece embedded with 100 μm gold wire electrode. (B) Photograph of 3D printed piece with recessive channels printed from positive relief structure on brass mold. (C) The two layers in (A) and (B) are bonded together with a thermal lab press to result in the final device. (D) Insert is a micrograph of the channel/electrode interface, with a 100 μm gold wire electrode aligned at the end of the separation channel. (E) Electropherogram for the separation and detection of dopamine, catechol (200 μM each), and 3,4-dihydroxphenylacetic acid (Dopac, 600 μM) on 100 μm Au electrode. Reproduce from reference with permission.