Laser direct writing of programmable delays for fabrication of paper-based sensors that allow CRP detection

Abstract

Demand for low-cost alternatives to conventional medical diagnostic sensors 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. Research into the development of methodologies that control, and in particular delay the flow of fluids in these devices is an urgently needed requirement that would enable greater functionalities in such paper-based sensors.
In this work, to control fluid-flow, we report the use of a new laser-based direct-write technique that allows programmable fluid delivery in channels within a paper-based device. The technique is based on laser-induced photo-polymerisation, and through adjustment of the laser writing parameters, such as the output power and writing/scanning speed, we can control the porosity of hydrophobic barriers which, when introduced in the fluid paths, produce controllable fluid delay.
Having patterned these barriers at pre-defined locations within fluidic channels, we have achieved flow-delays with a time span ranging from few minutes to an hour and we have also performed a study to understand the influence of the number of barriers and their position on the flow-delay. Finally, we demonstrate the usefulness of such programmable flow delays through a semi-automated paper-sensor that implements a multi-step ELISA for detection of C-reactive protein with a limit-of-detection of 10 ng/mL (Figure 2) - wherein separate flow-arms (with differently programmed delays) were used to sequentially deliver the different reagents through to the detection zone for effecting the multi-step assay.
Since the channels and flow delay barriers can be written via a common laser-writing process, this is a distinct improvement over other methods that require specialist operating environments, or custom-designed equipment. This technique can therefore be used for rapid fabrication of paper-based microfluidic sensors that can perform single or multistep analytical assays.

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Identifiers

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

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

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