This is the first of two posts on an area of work close to my heart and expertise.  I have so much to say here that I have split it into two posts.  Stay tuned for Chapter 2 in the next few days.

Recently, there has been a growing focus on applying microfluidics for global health challenges.  Microfluidics (exactly what it sounds like) is the science and engineering of fluid flows through channels with dimensions of 0.1 mm or smaller.  For reference, 0.1 mm is the width of a single human hair.  The field began in earnest in the early 1990s, when it was surmised that the same techniques used for making computer chips could be used to fabricate small fluid-handling elements, which could in turn enable chemistry at small length scales.  This has many advantages, including tiny volumes (one billionth of a liter, 10^-9 L, is a typical volume) that save on reagent costs, faster reactions due to reductions in diffusion lengths, and the ability to integrate much functionality on a single substrate.  Many amazing advances have occurred in this field since its inception, but recently the field has been moving in an interesting direction:  backwards.

The first decade of microfluidics witnessed an expansion in the range of technologies and complexity of the systems fabricated, including many by yours truly. The dream was to integrate an entire “lab on a chip” to achieve on a 4”-diameter substrate what took an entire chemistry lab up to that point.  However, the last five or ten years have seen a recognition that one of the best application spaces for microfluidics, that of global health, had an entirely different set of constraints that were not being met by making things more complicated.  Realizing the dream of a portable chemistry lab could enable remote diagnostics at low power, short assay times, and therefore better treatment of neglected and other diseases.  However, even the low power systems required batteries for heating, cooling, or powering detection modules, buffers requiring cold chains were still mandatory, and the systems required trained operators, a rarity in the areas with the most need.  Recently, given the realization of the actual constraints, engineers have sought to make devices that are not just low-power, but no-power, and that perform a diagnostic test within minutes by untrained operators using a minimum of reagents.

Paper microfluidics has been one of the more significant advances.  Just as in home pregnancy tests, a detection of a specific molecule can be made by having biological fluids move through the pores in a piece of paper using capillary action, a result of the type of liquid and the type of paper used. The fluid moves on its own, without the need for pumps, valves, or other complicated technologies.  George Whitesides and colleagues, with funding from the Bill and Melinda Gates Foundation, have developed a suite of paper microfluidic chips for performing a variety of diagnoses in remote regions.  Another fascinating example of this was recently published in Analytical Chemistry, in which the authors devised a rapid blood typing assay using only antibodies and paper, without the need for an indicator dye or particle as is necessary in other tests.  It will be interesting to see where these advances lead in the near future.