Paperfuge
ABSTRACT
In a global-health context, commercial centrifuges are expensive, bulky and electricity-powered, and thus constitute a critical bottleneck in the development of decentralized, battery-free point-of-care diagnostic devices. Here, we report an ultralow-cost (20cents), lightweight (2 g), human-powered paper centrifuge (which we name ‘paperfuge’) designed on the basis of a theoretical model inspired by the fundamental mechanics of an ancient whirligig (or buzzer toy; 3,300 BC). The paperfuge achieves speeds of 125,000 r.p.m. (and equivalent centrifugal forces of 30,000 g), with theoretical limits predict-ing 1,000,000 r.p.m. We demonstrate that the paperfuge can separate pure plasma from whole blood in less than 1.5min, and isolate malaria parasites in 15min. We also show that paperfuge-like centrifugal microfluidic devices can be made of polydimethylsiloxane, plastic and 3D-printed polymeric materials. Ultracheap, power-free centrifuges should open up oppor-tunities for point-of-care diagnostics in resource-poor settings and for applications in science education and field ecology.
BIG QUESTION
“What is the best human-powered centrifuge we can design with under $1 in parts?”
Peak force
30,000 g
Blood separation time
<1.5 min
Paper citations
191 publications
What is Paperfuge?
Paperfuge is an ultralow-cost (20 cents), lightweight (2 g), human-powered paper centrifuge designed on the basis of a theoretical model inspired by the fundamental mechanics of an ancient whirligig (or buzzer toy; 3,300 BC). The paperfuge achieves speeds of 125,000 r.p.m. (and equivalent centrifugal forces of 30,000 g), with theoretical limits predicting 1,000,000 r.p.m. We demonstrate that the paperfuge can separate pure plasma from whole blood in less than 1.5 min, and isolate malaria parasites in 15 min. We also show that paperfuge-like centrifugal microfluidic devices can be made of polydimethylsiloxane, plastic and 3D-printed polymeric materials.
(left) Materials used to construct the Paperfuge include two paper discs, wooden handles, string, capillaries, capillary holders and plastic shims. (right) Images of a rotating paperfuge captured with a high-speed camera (frec = 6,000 f.p.s.) and showing a succession of wound (top), unwound (middle) and re-wound (bottom) states, for half a cycle. The insets show the supercoiling of the strings during the wound states. Scale bars are 5 cm.
How quickly can a whirligig toy and Paperfuge spin?
Throughout one cycle, the spinning disc winds and unwinds and reaches rotation speeds ranging from zero to peak rotation speed, depending on the radius of the spinning disc. For example, a disc with a radius of 85mm can peak up to 7,571 r.p.m. whereas a disc of 5mm radius can peak up to 125,000 r.p.m. Centrifuges are characterized by the relative centrifugal force (r.c.f.) they can generate,
Paperfuge, with a radius of 50mm, spins up to 22,065 r.p.m. (or r.c.f. ≈ 10,000 g), sufficient for most sample preparation.
Schematic illustrating the periodic rotation of the paperfuge where the disc starts at zero rotational speed (ϕ̇ =0�̇=0) and then cycles to ϕ̇ max�̇max. e, Plot of ϕ̇ max�̇max and f0 for different hand-powered discs (with Rd of 5, 12.5, 25, 50 and 85 mm, Supplementary Table 3). Scaled images of the disc sizes in relation to a US quarter and a pencil are included for visual comparison.
(left) Schematic illustrating the periodic rotation of the spinning disc.
