Microfluidic paper-based analytical devices (μPADs) are able to perfrom a range of biochemical assays at ultra-low cost. A key feature of μPADs is that they transport fluids without any external manipulation, relying exclusively on capillary action. This capability allows for the execution of complex bioassays with remarkable simplicity. Lately, the integration of electrical components into the μPADs has garnered considerable attention due to the possibility of adding new functionalities and capabilities. However, fabricating electrodes on paper poses immense challenges due to the uneven nature of cellulose materials and high fabrication costs. To this end, Léonard Bezinge in collaboration with the Shih Group at ETH Zurich presented new technique for creating electrofluidic paths on cellulose substrates. They show that such patterns can carry fluidic and electrical currents and be used to develop cutting-edge diagnostic assays. Specifically, the team fabricated electrodes by converting the paper itself into graphenic domains using laser induced pyrolysis. They show that their Laser-Induced Graphene Electronics (LIG-E) not only preserves the microscale structure and microporous nature of cellulose fibers but also retains the wetting and wicking properties attributed to the oxygen-rich surface functional groups. Such an approach enables the independent design of capillary pathways and electronic current overlays. Importantly, the team developed paper-based diagnostic devices using both lateral and vertical flow configurations. In the former, they presented a flow injection analysis device for detecting alkaline phosphatase in serum, with a throughput of more than one assay per minute and calibration-free quantification. In the latter, they realised a HPV16 diagnostic using a CRISPR-based assay. Incredibly, this system exhibited a detection limit of 1 copy per 1 μL-1 for HPV16 and a rapid electrochemical readout.
In the future, it is likely that LIG-E-based diagnostics will be used to a perform a wide range of bioassays in a rapid, quantitative, and low-cost manner.
Written by Rashin Mohammadi
Read the accepted manuscript here