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Manu Prakash, a bio-engineer at Stanford University, designs cheap tools that can make a big difference in the poorest parts of the world.

At the Ted (Technology, Entertainment and Design) conference in Vancouver, he showed off his latest gizmo - a cardboard centrifuge that can spot malarial parasites in blood.

Toy-inspired, it costs 20 cents (15p).

He also launched a citizen science project to identify disease-carrying mosquitoes by their sound.

The "abuzz" project asks people to record the sound of mosquitoes' wings beating, on the microphones of their mobile phones, which are available even on the most basic models.

Acquiring acoustic data on wing beat sounds - the frequency of which varies from species to species - together with the time and location of the human-mosquito encounter creates a "powerful tool" for identifying where disease-carrying mosquitoes may be.

Prof Prakash has a passion for getting low-cost scientific tools with a practical use into the poorest communities.

"There are one billion people who live with no infrastructure, electricity or healthcare," he told the Ted audience.

"Frugal science is about building solutions for these communities."

Prof Prakash - who has also designed a paper microscope that costs less than a dollar (80p) - came up with the idea of Paperfuge during a field trip in Uganda.

He spotted a $1,000 centrifuge - a medical tool used to separate liquids such as blood - being used in a remote clinic as a doorstop.

"They had no electricity so it was useless to them," said Prof Prakash.

On returning to his Stanford lab, he was inspired to create a cheaper option, by toys - first a yoyo and then a whirlygig - also known as a button on a string - that is made using a spherical object suspended on threads that are then pulled to make it spin.

"Could we use the physics of these objects to build centrifuges?" he asked.

Prof Prakash and his colleague Saad Bhamla recruited three undergraduate engineering students from Massachusetts Institute of Technology (MIT) and Stanford to build a mathematical model of how the device worked.

The team created a computer simulation to capture design variables such as disc size, string elasticity and pulling force.

They also borrowed equations from the physics of supercoiling DNA strands, and eventually created a prototype that spun at up to 125,000 revolutions per minute.

"There are some beautiful mathematics hidden inside this object," Prof Prakash said.

Using the device to spin blood in a capillary coated with orange dye for 15 minutes separates malarial parasites from red blood cells, enabling them to be spotted under a microscope.

And in 2014, Prof Prakash launched Foldscope, a paper microscope that costs under a dollar.

Foldscope has now sold 50,000 units in 130 countries.

Used by amateurs and children as well as scientists, the projects it has inspired are being shared on a citizen science .

Prof Prakash plans to ship one million more microscopes this year.