Microchip-based electrochemical detection using a 3-D printed wall-jet electrode device.

Three dimensional (3-D) printing technology has evolved dramatically in the last few years, offering the capability of printing objects with a variety of materials. Printing microfluidic devices using this technology offers various advantages such as ease and uniformity of fabrication, file sharing between laboratories, and increased device-to-device reproducibility. One unique aspect of this technology, when used with electrochemical detection, is the ability to produce a microfluidic device as one unit while also allowing the reuse of the device and electrode for multiple analyses. Here we present an alternate electrode configuration for microfluidic devices, a wall-jet electrode (WJE) approach, created by 3-D printing. Using microchip-based flow injection analysis, we compared the WJE design with the conventionally used thin-layer electrode (TLE) design. It was found that the optimized WJE system enhances analytical performance (as compared to the TLE design), with improvements in sensitivity and the limit of detection. Experiments were conducted using two working electrodes - 500 µm platinum and 1 mm glassy carbon. Using the 500 µm platinum electrode the calibration sensitivity was 16 times higher for the WJE device (as compared to the TLE design). In addition, use of the 1 mm glassy carbon electrode led to limit of detection of 500 nM for catechol, as compared to 6 µM for the TLE device. Finally, to demonstrate the versatility and applicability of the 3-D printed WJE approach, the device was used as an inexpensive electrochemical detector for HPLC. The number of theoretical plates was comparable to the use of commercially available UV and MS detectors, with the WJE device being inexpensive to utilize. These results show that 3-D-printing can be a powerful tool to fabricate reusable and integrated microfluidic detectors in configurations that are not easily achieved with more traditional lithographic methods.

Use of 3D Printing and Modular Microfluidics to Integrate Cell Culture, Injections and Electrochemical Analysis.

Fabrication of microchip-based devices using 3-D printing technology offers a unique platform to create separate modules that can be put together when desired for analysis. A 3-D printed module approach offers various advantages such as file sharing and the ability to easily replace, customize, and modify the individual modules. Here, we describe the use of a modular approach to electrochemically detect the ATP-mediated release of nitric oxide (NO) from endothelial cells. Nitric oxide plays a significant role in the vasodilation process; however, detection of NO is challenging due to its short half-life. To enable this analysis, we use three distinct 3-D printed modules: cell culture, sample injection and detection modules. The detection module follows a pillar-based Wall-Jet Electrode design, where the analyte impinges normal to the electrode surface, offering enhanced sensitivity for the analyte. To further enhance the sensitivity and selectivity for NO detection the working electrode (100 µm gold) is modified by the addition of a 27 µm gold pillar and platinum-black coated with Nafion. The use of the pillar electrode leads to three-dimensional structure protruding into the channel enhancing the sensitivity by 12.4 times in comparison to the flat electrode (resulting LOD for NO = 210 nM). The next module, the 3-D printed sample injection module, follows a simple 4-Port injection rotor design made of two separate components that when assembled can introduce a specific volume of analyte. This module not only serves as a cheaper alternative to the commercially available 4-Port injection valves, but also demonstrates the ability of volume customization and reduced dead-volume issues with the use of capillary-free connections. Comparison between the 3-D printed and a commercial 4-Port injection valve showed similar sensitivities and reproducibility for NO analysis. Lastly, the cell culture module contains electrospun polystyrene fibers with immobilized endothelial cells, resulting in 3-D scaffold for cell culture. With the incorporation of all 3 modules, we can make reproducible ATP injections (via the 3-D printed sample injection module) that can stimulate NO release from endothelial cells cultured on a fibrous insert in the cell culture module which can then be quantitated by the pillar WJE module (0.19 ± 0.03 nM/cell, n = 27, 3 inserts analyzed each day, on 9 different days). The modular approach demonstrates the facile creation of custom and modifiable fluidic components that can be assembled as needed.

3D-printed Microfluidic Devices: Fabrication, Advantages and Limitations-a Mini Review.

A mini-review with 79 references. In this review, the most recent trends in 3D-printed microfluidic devices are discussed. In addition, a focus is given to the fabrication aspects of these devices, with the supplemental information containing detailed instructions for designing a variety of structures including: a microfluidic channel, threads to accommodate commercial fluidic fittings, a flow splitter; a well plate, a mold for PDMS channel casting; and how to combine multiple designs into a single device. The advantages and limitations of 3D-printed microfluidic devices are thoroughly discussed, as are some future directions for the field.