Paper-based electroanalytical devices for accessible diagnostic testing

Microfluidic paper-based analytical devices (mu PADs) use the passive capillary-driven flow of aqueous solutions through patterned paper channels to transport a sample fluid into distinct detection zones that contain the reagents for a chemical assay. These devices are simple, affordable, portable, and disposable; they are, thus, well suited for diagnostic applications in resource-limited environments. Adding screen-printed electrodes to the detection zones of a mu PAD yields a device capable of performing electrochemical assays (an E mu PAD). Electrochemical detection has the advantage over colorimetric detection that it is not affected by interference from the color of the sample and can be quantified with simple electronics. The accessibility of E mu PADs, however, is limited by the requirement for an external potentiostat to power and interpret the electrochemical measurement. New developments in paper-based electronics may help loosen this requirement. This review discusses the current capabilities and limitations of E mu PADs and paper-based electronics, and sketches the ways in which these technologies can be combined to provide new devices for diagnostic testing.