Beyond wax printing: The future of paper analytical device fabrication

Many microfluidic "lab on paper" devices have been demonstrated for point-of-use applications, but scalable fabrication methods are necessary for these devices to make it past the proof-of-concept stage and become viable commercial products. Commercially available wax printers such as the Xerox ColorQube presented a near-ideal compromise between cost, ease of prototyping, and throughput, but in 2016, these printers were discontinued, and now, alternative methods are needed. In this review, we survey current paper analytical device (PAD) fabrication methods through the lens of scalability, focusing on the tradeoffs between resolution, ease of prototyping, cost, and throughput. Categories discussed include handmade, semi-automated, batch, laboratory-based, printer-based, and roll-to-roll fabrication methods. Hand-, batch-, semi-automated, and laboratory-based fabrication methods suffer from low throughput and high hands-on labor requirements. Roll-to-roll methods are high throughput but costly, while printer-based methods offer a compromise between cost and throughput. By highlighting the comparative merits of existing methods, we hope to offer insight into what makes a method "scalable" or "manufacturable."