Using the Rubik's Cube to directly produce paper analytical devices for quantitative point-of-care aptamer-based assays

In this article, we describe a facile method named as Rubik's Cube stamping (RCS) for equipment-free fabrication of microfluidic paper-based analytical devices (μPADs). RCS is inspired by the worldwide ubiquitous RC toy and requires no specialized electric equipment other than a classical six-faced RC that is assembled with home-made small iron components. It can pattern various rosin microstructures in paper simply by either using different functional faces of the modified RC or applying its internal pivot mechanism to adjust the components' patterning forms on one functional face. Such a versatile stamping method is quite simple and inexpensive, and thus holds potential for producing rosin-patterned μPADs by untrained users in resource-limited environments such as small laboratories and private clinics, or even at home and in the field. Moreover, a set of one-channel devices are fabricated to design a point-of-care aptamer-based assay with near sample-in-answer-out capability that integrates enzymatic reactions for robust yet efficient signal amplification and a personal glucometer for portable, user-friendly, rapid and quantitative readout. Its utility is well demonstrated with the sensitive and specific detection of adenosine as a model target in buffer samples and undiluted human urine within several minutes. With the advantages of low cost, simplicity, portability, rapidity, and aptamer variety, this general point-of-care assay system reported here may find broad applications including home healthcare, field-based environmental monitoring or food analysis and emergency situations.