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A teardown of the perfect portable medical diagnostic device would make the iPhone seem like rudimentary technology. Like a smartphone, it would combine electronics and software into a seamless user interface for any setting, but it would also, with laboratory-like precision, process human body fluids with fickle mixtures of biological and chemical reagents. It is little wonder that such devices have not yet made it to market.

Nevertheless, recent results from a compact benchtop machine called GeneXpert (see “The Machine That Will Help End TB”) make it easy to grasp how big an impact such a device could have. GeneXpert can diagnose TB drug resistance within a few hours, and it’s simple enough to be used by relatively nontechnical staff in remote clinics situated close to at-risk populations. It now seems likely that this machine will offer early diagnosis for many TB patients in far-flung places, giving them a chance to be treated with effective drugs.

Yet the GeneXpert machine is still confined to laboratory settings, whereas a field-portable system would offer dramatically increased access to medical diagnostics. Startup companies are just beginning to make progress on this approach, with designs that rely on microfluidics, a technology that processes liquids inside submillimeter channels. This technology could also perform more complex tests, such as detecting multiple drug resistance to TB. A breakthrough point-of-care microfluidic device, however, is now 20 years in the making. The basic science has advanced significantly, but there is more to solving this problem, as the very different experiences of GeneXpert and the iPhone show.

Building a portable device that integrates more diverse processes than a smartphone requires focusing from the very beginning on a polished end product. That’s a challenge in an industry not used to creating consumer products, for which a more natural strategy is to bring together a loose team of experts with diverse interests and an ill-defined end goal. On a clinical level, the field impact of GeneXpert highlights the need for careful local specimen collection, trial design and execution, and engagement with financial and political stakeholders. Drawing on such lessons will bring us closer to the goal of running clinical specimens from start to finish in a field setting, using miniaturized microfluidics to give patients the diagnoses they need without delay.