Engineering a monolithic 3D paper-based analytical device (μPAD) by stereolithography 3D printing and sequential digital masks for efficient 3D mixing and dopamine detection

Stereolithography 3D printing and digital masks in sequence are used herein to manufacture 3D µPAD in a monolithic layer of paper within 1 s. Multiple experiments were systematically conducted to further understand the fundamentals and limitation of this manufacturing process, and a novel 3D mixer and a fluorescent chemosensor assay used to determine dopamine concentration at high-alkaline pH conditions were successfully demonstrated. Experiment results showed: (1) the 3D mixer is superior than conventional 2D mixer regarding mixing performance and repeatability, (2) dopamine detection and pH indicator can be realized with fewer operation steps and shorter processing time, (3) a truly 3D µPAD, including multilayer microchannels within a monolithic paper substrate, can be created with fewer reagent loss and higher transportation efficiency, (4) a smallest microchannel, 100 µm wide microchannel, can be successfully created on µPAD. These results clearly proved that this proposed 3D µPAD is not only a novel format of µPAD, but it can also simplify the operation steps for an analytical assay while improving the mixing phenomenon via 3D mixer and using minimum sample volume.