20nm transistor uses sweat to monitor health

A research team at the Nanoelectronic Devices Laboratory at EPFL has created a sensor for scanning of liquids such as perspiration to deliver accurate real time monitoring of a person's level of hydration, stress or fatigue. The innovative 'FinFET' transistor integrates a microfluidic channel through which the fluid to be analysed flows. When the molecules pass, their electrical charge disturbs the sensor, which makes it possible to deduce the fluid's composition.

"The ionic equilibrium in a person's sweat could provide significant information on the state of his health," explained Adrian Ionescu, director of Nanolab. "Our technology detects the presence of elementary charged particles in ultra-small concentrations such as ions and protons, which reflects not only the pH balance of sweat but also more complex hydration of fatigues states. By an adapted functionalisation I can also track different kinds of proteins."

The device does not host only sensors, but also transistors and circuits enabling the amplification of the signals. A layered design isolates the electronic part from the liquid substance.

"Usually it is necessary to use separately a sensor for detection and a circuit for computing and signal amplification," explained Sara Rigante, lead author of the publication. "In our chip, sensors and circuits are in the same device, making it a 'sensing integrated circuit.' This proximity ensures that the signal is not disturbed or altered. We can thereby obtain extremely stable and accurate measurements."

Owing to the size of the transistors at 20nm, it is possible to place a whole network of sensors on one chip, with each sensor locating a different particle.

"We could also detect calcium, sodium or potassium in sweat," said Rigante.

The technology developed at EPFL stands out from its competitors because it is stable, compatible with existing electronics (CMOS), ultra-low power and easy to reproduce in large arrays of sensors. "In the field of biosensors, research around nanotechnology is intense, particularly regarding silicon nanowires and nanotubes.

But these technologies are frequently unstable and therefore unusable for now in industrial applications," said Ionescu. "In the case of our sensor, we started from extremely powerful, advanced technology and adapted it for sensing need in a liquid-gate FinFET configurations. The precision of the electronics is such that it is easy to clone our device in millions with identical characteristics."

In addition, the technology is not energy intensive. "We could feed 10,000 sensors with a single solar cell," claimed Ionescu.

Tests have been carried out by circulating the liquid with a tiny pump. Researchers are now working on a means of sucking the sweat into the microfluidic tube via wicking. This would rid the small analysing 'band-aid' of the need for an attached pump.

- Paul Buckley
??EE Times Europe