Laser-direct-write technique for rapid prototyping of multiplexed paper-based diagnostic sensors

Abstract

The demand for low-cost alternatives to conventional point-of-care diagnostic tools has led to significant developments in the field of paper-based diagnostics, and several methods, which include photolithography, inkjet printing, wax printing etc., have been reported for the fabrication of fluidic devices in porous materials such as paper. Here, we present a simple, laser-based direct-write procedure, which relies on light-induced photo-polymerisation of a photopolymer previously impregnated in the porous substrates for fabrication of the user-defined fluidic patterns within such substrates. During the subsequent development step, the un-polymerised photopolymer is washed-out; however, the hydrophobic polymerized structures that remain in the substrate, and extend throughout its thickness define the barrier-walls of the hydrophilic fluidic patterns they demarcate. These structures contain and guide liquids without any leakage, thus validating the feasibility of using this technique in the production of microfluidic devices. Our results show that for cellulose paper, the minimum widths the hydrophobic barrier-walls should have to successfully contain fluids is ~ 120 µm, and similarly, the minimum dimensions a fluidic channel can have to guide fluids is ~ 80 µm, both of which are the smallest values reported so far. These patterns can be produced rapidly via scanning of a low power continuous-wave laser at speeds of the order of one meter per second and we have successfully implemented it in patterning a range of porous materials including nitrocellulose membranes, glass fibre filter and polyvinylidene fluoride. To further validate the applicability of these laser-patterned devices as sensors, we have demonstrated their use for a range of colorimetric assays including the detection of glucose, protein and nitrite, and also an enzyme-linked immunosorbent assay for detection of C-reactive protein. Finally, we have quantified the speed and cost of our laser-based method and believe that it is suited to up-scaling for mass production.

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Identifiers

ORCID for I.N. Katis: orcid.org/0000-0002-2016-557X

ORCID for R.W. Eason: orcid.org/0000-0001-9704-2204

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