  Small volume fluid handling in single and multiphase microfluidics provides a
promising strategy for efficient bio-chemical assays, low-cost point-of-care
diagnostics and new approaches to scientific discoveries. However multiple
barriers exist towards low-cost field deployment of programmable microfluidics.
Incorporating multiple pumps, mixers and discrete valve based control of
nanoliter fluids and droplets in an integrated, programmable manner without
additional required external components has remained elusive. Combining the
idea of punch card programming with arbitrary fluid control, here we describe a
self-contained, hand-crank powered, multiplex and robust programmable
microfluidic platform. A paper tape encodes information as a series of punched
holes. A mechanical reader/actuator reads these paper tapes and correspondingly
executes a series of operations onto a microfluidic chip coupled to the
platform in a plug-and-play fashion. Enabled by the complexity of codes that
can be represented by a series of holes in punched paper tapes, we demonstrate
independent control of fifteen on-chip pumps with enhanced mixing, on-off
valves and a novel on-demand impact-based droplet generator. We demonstrate
robustness of operation by encoding a string of characters representing the
word "PUNCHCARD MICROFLUIDICS" using the droplet generator. Multiplexing is
demonstrated by implementing an example water quality test utilizing
colorimetric assays for pH, ammonia, nitrite and nitrate content in different
water samples. With its portable and robust design, low cost and ease-of-use,
we envision punch card programmable microfluidics will bring complex control of
microfluidic chips into field-based applications in low-resource settings and
in the hands of children around the world bringing microfluidics and
low-Reynolds number hydrodynamics to everyday classrooms.
