Fabrication of paper-based microfluidic devices via local deposition of photo-polymer followed by UV curing

He, Peijun, Katis, Ioannis, Eason, Robert and Sones, Collin (2017) Fabrication of paper-based microfluidic devices via local deposition of photo-polymer followed by UV curing. 21st International Conference on Miniaturized Systems for Chemistry and Life Sciences, , Savannah, United States. 22 - 26 Oct 2017.

Abstract

Demand for low-cost alternatives to conventional medical diagnostic tools has been the driving force that has spurred significant developments in the diagnostics field. Paper-based fluidic devices, proposed by the Whitesides’ group in 2007 have been regarded as one such alternative [1], and consequently, this field has been progressing rapidly [2].

In our previous works, we have demonstrated the usefulness and versatility of a laser direct-write (LDW) approach in the patterning of fluidic devices in porous materials [3, 4] such as cellulose for the fabrication of diagnostic devices. This lab-based non-lithographic approach with high flexibility has the potential to be up-scaled for mass-production of paper-based devices at affordable costs [4, 5]. A decrease in the total number of fabrication-steps would however not only make this LDW process more efficient as a consequence of reduced fabrication times, but would also make it more cost-effective because of the reduced usage of expensive reagent – translating it into a truly mature technique adoptable for commercial manufacture. To optimise our original technique, we propose the inclusion of a deposition tool that allows localised deposition of the photopolymer at only specific locations on the paper where the fluid containing wall/structures need to be formed within the substrates to create the microfluidic device. This selective photopolymer deposition eliminates the (global) soaking step required to impregnate the photopolymer within the paper, prior to the laser illumination step, and furthermore also makes redundant the subsequent solvent developing step inherent in our original technique.

The LDW setup that allows the implementation of this improvised methodology is described in Figure 1. As shown in the schematic, the photopolymer is locally deposited onto the paper substrate with a deposition nozzle at locations pre-defined by the user’s device design. A laser beam subsequently follows the deposition head and illuminates the deposited patterns thereby inducing photo-polymerisation of the photopolymer. The polymerised patterns define the fluidic walls that serve as demarcation barriers that confine and transport the liquids within the paper device.

Three dispensing conditions were trialled to study the influence of the deposited photopolymer drop-volumes on the creation of impregnable fluid-containing walls. Deposition with droplet volumes of 40, 80 and 100nL at a drop pitch of 0.5mm were tested to define three parallel walls (Figure 2a). The dispensed polymer lines were cured immediately after dispensing with the 405nm laser. The flow properties of the channels were tested by introduction of different liquids (coloured inks in this example) in the adjacent channels (Figure 2b). For all three dispensing conditions, both inks are well-contained and guided in the respective channels without any leakage or cross-contamination. Figure 3, shows an example device, with three channels allowing for sequential delivery of liquids into a common zone, which can be used for either performing a multi-step ELISA or in mixing of different fluids in paper-based devices.

In conclusion, these initial results for an optimised LDW technique indicate its suitability for roll-to-roll manufacture of paper-based microfluidic devices that can be used for a variety of applications.

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Contributors

Author: Ioannis Katis

Author: Robert Eason

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