Directly writing barrier-free patterned biosensors and bioassays on paper for low-cost diagnostics

The development of paper-based diagnostics should provide facile fabrication and user-friendliness. A promising solution is to obviate hydrophobic barriers and display intuitive results. Herein, we report a novel "Pen-Writing" technique for providing hydrophobic barrier-free patterned biosensor fabrication and user-friendly bioassay operation. We functionalized the rollerball pen with reagent ink to directly write on-demand patterned paper biosensors of any design. The single-step glucose biosensor and multi-step immunosensor were prepared, and the multi-analyte detection capability was proved. Besides, the reagent ink-based rollerball pen was used to directly write bioassays on paper pre-treated with analytes. To perform continuous, high-throughput fabrication and analysis, we also proposed an automatic platform via combining the reagent ink-based rollerball pen and a desktop pen plotter. Our work provides an easy, affordable and generic solution to prepare customized barrier-free patterned paper biosensors and develop on-site bioassays in low-resource settings.