The mechanics of the ancient whirligig (or buzzer toy) have found new life as a hand-powered, ultra-low-cost paper centrifuge.
The 'paperfuge' will open up opportunities for point-of-care diagnostics in resource-poor settings and be broadly applicable across science education and field ecology.
Researchers at Stanford University, led by Manu Prakash, co-inventor of the Foldscope – a microscope that costs US$1 – demonstrated the fundamental mechanics of an ancient whirligig are capable of separating pure plasma from whole blood and can isolate malaria parasites in 15 minutes.
In a report published by scientific journal Nature, the team conducted more than 50 trials and found the paperfuge achieves haematocrit results in 90 seconds (maximum speed of approximately 20,000 rpm and cost US 20 cents) that are comparable to the results obtained using a commercial centrifuge for two minutes (16,000 rpm and cost US$700). (Bhamla, MS et al. Hand-powered ultralow-cost paper centrifuge. Nat. Biomed. Eng. 1, 0009 (2017).
The team also found the paperfuge's other diagnostic applications include plasma separation, quantitative buffy coat analysis (QBC) and integrated centrifugal microfluidic devices for point-of-care (POC) diagnostic testing.
In a global-health context, commercial centrifuges are expensive, bulky and are powered by electricity, thus constituting a critical bottleneck in the development of decentralised, battery-free point-of-care diagnostic devices. They are also the workhorse of any medical diagnostics facility, the first key-step for most diagnostic assays, and generally inaccessible in the field and poorly-resourced conditions. A low-cost, portable, human-powered centrifuge that achieves high speeds is an essential, yet unmet need.
In other news, Physicist Jonathan Coleman of Trinity College Dublin, has shown that the addition of dash of graphene to the stretchy goo known as Silly Putty can transform it into a pressure sensor capable of monitoring a human pulse or even tracking the dainty steps of a small spider.
Dubbing the graphene-spiked Silly Putty, 'G-putty', it is hoped the substance can be developed into a device that continuously monitors blood pressure. It also demonstrates a form of self-repair that may herald smarter graphene composites.
Since graphene was first isolated in 2004, researchers have added these atom-thin sheets of carbon to a panoply of different materials, hoping to create composites that benefit from its superlative strength and electrical conductivity.
But there have been surprisingly few attempts to blend it with 'viscoelastic' materials such as Silly Putty, which behaves as both an elastic solid and a liquid. Leave a lump on top of a hole, for example, and it will slowly ooze through.
Conor Boland, a researcher working in Jonathan Coleman’s nanotechnology lab at Trinity College Dublin, wondered what would happen if he brought the two materials together. “I’d like to be able to say it was carefully planned, but it wasn’t,” Coleman said. “We’ve just got a tradition in my group of using household stuff in our science.” In 2014, the team found that they could make graphene by blitzing graphite in a kitchen blender.
The researchers mixed graphene flakes, roughly 20 atomic layers thick and up to 800 nanometers long, with homemade Silly Putty, a silicone polymer, to produce dark grey G-putty that conducted electricity. Crucially, its electrical resistance changed dramatically when the researchers applied even tiny amounts of pressure. The putty was at least ten times more sensitive than other nanocomposite sensors.
When they wired up a lump of G-putty and held it to a student’s neck, the pulse from his carotid artery was clearly visible in those resistance changes. In fact, the pulse profile was so detailed that they could convert it into an accurate blood-pressure reading. The sensor could also monitor respiration when placed on the student’s chest. And, as a slightly bizarre encore, it recorded the individual steps of a spider weighing just 20 milligrams.
“They did a really extensive demonstration of how versatile it can be,” says Vincenzo Palermo, a materials scientist at the National Research Council of Italy in Bologna. “I think it’s remarkable work, really original.”
Coleman’s team found that the graphene flakes form a conducting network within the putty, and deforming the material breaks that network apart, rapidly increasing its electrical resistance.
G-putty’s low viscosity then allows the graphene flakes to move back into position and reform the network.
“It’s a self-healing phenomenon,” he says.
G-putty could potentially replace conventional continuous physiological monitoring devices, such as blood-pressure monitors that often rely on bulky cuffs around a patient’s arm and offer only a snapshot reading. A cheap, small and non-invasive sensor could provide a simple way to monitor patients at home, in the field and areas of poorly-resourced infrastructure.
However before it can be commercialised, G-putty will have to clear a series of hurdles, including proving that it can be made in large-scale quantities, and real-world testing to assess its long-term performance. For real applications, you need it to work the same way thousands of times. Nature DOI:10.1038/nature.2016.21133