Laser-induced photo-polymerisation for creation of paper-based fluidic devices

Abstract

Paper-based microfluidics is a rapidly progressing inter-disciplinary technology driven by the need for low-cost alternatives to conventional point-of-care diagnostic tools. For transport of reagents/analytes, such devices often consist of interconnected hydrophilic fluid-flow channels that are demarcated by hydrophobic barrier walls that extend through the thickness of the paper. Here, we present a laser-based fabrication procedure that uses polymerisation of a photopolymer to produce the required fluidic channels in paper. Experimental results showed that the structures successfully guide the flow of fluids and allow containment of fluids in wells, and hence the technique is suitable for fabrication of paper-based microfluidic devices. The minimum width for the hydrophobic barriers that successfully prevented fluid leakage was ~120 μm and the minimum width for the fluidic channels that can be formed was ~80 μm, the smallest reported so far for paper-based fluidic patterns.

Laser direct-write for fabrication of three-dimensional paper-based devices

“…The basic LDW setup is the same as described in our previous publications for fabrication of 2D microfluidic devices and implementation of flow-control and has been fully optimised via a series of systematic studies. [21][22][23] The results we have achieved and will report in the following sections are therefore based on the same patterning procedure with appropriate adjustment of the patterning conditions such as laser power and scan speed.…”

“…This innovative result presents a solution for not only sealing of paper-based devices by isolating the device between dissimilar outer cladding layers but also, most importantly, permitting 3D pathways to be engineered through judicious assembly of several layers, possibly combined with holes and voids in some layers. In our earlier publications using the same laser-direct write technique, 21,22 we have demonstrated the patterning of varied porous materials such as nitrocellulose membranes, printing paper, fabrics, and we therefore believe that any such material which is porous in nature would be suited for use in the production of the above described multi-layer devices. There are no other requirements that we believe would limit the use of a specific type of material for the creation of multi-layered devices.…”

“…21,22 Through selectively designing and patterning polymerised structures from both sides of the substrate, we could fabricate 3D structures inside a single substrate. Unlike other 3D device fabrication methods, the approach presented here does not require any additional processing equipment or alignment/assembling step and uses the same fabrication approach described earlier for producing a 2D fluidic device.…”

“…[21][22][23] In brief, by controlling the laser patterning conditions, we have shown that we can produce solid hydrophobic structures either partially inside a single layer of paper or all the way through several layers of paper (we have so far demonstrated 3 separate layers). Also, by selectively patterning from both sides of the composite substrate, we have fabricated 3D devices based on both a single layer as well as a multi-layer stacked arrangement.…”

Defining microchannels and valves on a hydrophobic paper by low-cost inkjet printing of aqueous or weak organic solutions

“…As a result, lPADs have emerged as a promising platform for point-of-care analytical applications in clinical diagnostics, [1][2][3] food safety control, 4,5 and environmental testing. 6,7 Various techniques have been used to fabricate lPADs, including photolithography, 8,9 wax printing, [10][11][12] inkjet printing, [13][14][15] laser etching, 16,17 plasma treatment, 18 and use of metal/paper masks. [19][20][21][22][23] Each technique has particular advantages and drawbacks.…”