Paper microzones as a route to greener analytical chemistry

Actuators, detectors and controllers associated with most current microfluidic chips continue to be bulky and costly. The ability of paper (and other porous materials) to wick fluids circumvents the need for a pump, making such devices portable, low-cost, and ideal for use in low-resource settings. Such devices are known as "paper microfluidic devices" and when combined with smartphones as recording devices, represent an ultimate achievement in green analytical chemistry. The carbon footprint of such an approach to chemical analysis is almost negligible. In this paper, recent developments in the field of paper microfluidic devices are described with an emphasis on the simplest variant of paper microfluidics: microzones on paper. The role of smartphones as an inexpensive and green counterpart to paper microzones with a similarly low environmental impact level and simplicity of operation is also described.