Gravity-Driven Microfluidics for Low-Cost Diagnostics

Researchers at Duke University have developed a gravity-powered microfluidic device that is intended for use as a diagnostic technology in low-resource areas. Microfluidics have enormous potential for point-of-care diagnostics, but the inclusion of tiny pumps and other sophisticated electronic components dramatically increases the complexity and cost of such devices. In an effort to develop a low-cost alternative, these researchers have turned to gravity as a way to shuttle drops around the tiny channels within a device, using spots of dried reagents to influence the assay, and different areas that are covered with specialized surface coatings to influence the path of the drops and their speed. The researchers hope that the technology could unlock point-of-care diagnostics for those living in the most remote and low-resource areas.

Microfluidics are a game changer, allowing for complex biomedical diagnostic assays, that previously would have required expensive and bulky lab equipment, to occur on a tiny chip. Some of the people poised to gain most from this revolution in miniaturization live in low-resource areas, with no easy access to hospitals and clinics. However, unless such technologies are also low cost, they may still lie beyond the reach of many such people.

With this in mind, these researchers have created a low-cost microfluidic system that relies on gravity instead of pumps, and which the researchers claim could be created very simply, even by carving channels in a block of wood. “The elegance in this approach is all in its simplicity — you can use whatever tools you happen to have to make it work,” said Hamed Vahabi, one of the developers of the new technology. “You could theoretically even just use a handsaw and cut the channels needed for the test into a piece of wood.”

Such technologies involve shuttling droplets around small channels, including biological samples and reagents that make the assay possible. Some use capillary action to move droplets, but this is rarely enough to make the assay work, requiring tiny electrical pumps as a supplement which drastically increases the cost of the technology.

“Most microfluidic devices need more than just capillary forces to operate,” said Ashutosh Chilkoti, another researcher involved in the study. “This approach is much simpler and also allows very complex fluid paths to be deigned and operated, which is not easy or cheap to do with microfluidics.”

Instead, these researchers used specialised surface coatings to increase the ‘slipperiness’ or ‘stickiness’ of specific channels, increasing the speed and tendency of droplets to traverse the routes that they had designed. A specialized rig that the device is placed in turns it at 90 degrees to initiate the gravity powered droplet race, and a simple LED and light detector can read the signals produced by the assay.

“We came up with many different elements to control the motion, interaction, timing and sequence of multiple droplets in the device,” said Vahabi. “All of these phenomena are well-known in the field, but nobody thought of using them to control the motion of droplets in a systematic way before.”

See a video demonstrating the technology below: