Fabrication of Multi-Material Functional Circuits Using Microfluidic Directed Materials Patterning

Traditional circuit board fabrication schemes are not directly applicable to the production of flexible, multi-material circuits. This article reports a technique, microfluidic directed material patterning, which combines soft microfluidic stamps and low-temperature solution-phase deposition to generate multi-material circuits on flexible, non-planar polymeric supports. Specifically, metallic and semiconductive traces are combined on commodity plastic films to yield functional photosensitive circuits that can be used in the spectrophotometric detection and concentration measurement of microdroplets on 3D "e-plates." The photoresistive material cadmium sulfide is used in these circuits because it is suitable for visible light detection and it can be deposited directly from aqueous solutions following established bath deposition procedures. This method can produce colorimetric devices capable of quantifying micromolar concentrations of Allura Red in microdroplets of Kool-Aid. This technique presents the opportunity for producing single-use or low-use disposable/recyclable devices for flexible 3D sensors and detectors following a convenient, low-waste fabrication scheme. The general capabilities of this approach, in terms of substrate geometry and device layout (e.g., the number, area, and pattern of photoresistive elements), can be applied to the design and manufacture of more intricate, multiplexed devices supportive of advanced and/or specialized functions that go beyond those reported in this initial demonstration. Soft microfluidic reactors together with solution-phase deposition procedures are used to fabricate multi-material photodetection circuits on flexible, 3D polymer films. Spectrophotometric droplet detection using "e-plates" fabricated following this method is demonstrated. The versatility of this approach enables the manufacture of low-cost, specialized flexible sensors using a convenient, single-tool processing scheme. image