Nose-on-a-chip Aims To Mimic The Real Thing

An ambitious project is underway to build the world’s smallest electronic nose.

If the project succeeds, it is expected that the technology would have many potential applications in areas such as environmental monitoring, healthcare and food safety.

The aim is to combine the odour sensors together with the signal processing components on to a single silicon chip, around a square centimetre in size. The instrument would require very little power and could be held comfortably in the palm of the hand.

The project is being carried out by scientists and engineers from the universities of Leicester, Warwick and Edinburgh, with funding from the Swindon based Engineering and Physical Sciences Research Council.

Electronic noses have been around for some years, and are used in the food, beverage and perfumery industries. However, the machines are large, have limited sensitivity and need to be re-calibrated frequently.

“We are hoping we can improve on existing systems by following biology much more closely,” says Dr Tim Pearce of the University of Leicester, who is co-ordinating the research. “The information processing of our system is very much inspired by how the olfactory system works in nature.”

In common with most existing electronic noses, the sensing part of the device will consist of arrays of electrically conductive polymers. However, the new system intends to process and interpret the signals in a way much more akin to biology.

“When sufficient numbers of odour molecules interact with an olfactory receptor neuron in the real nose, an action potential is induced – a spike of voltage that is sent down a nerve fibre to be processed by the olfactory pathway of the brain,” says Dr Pearce. “We will design our system to do a similar thing. When the mixture of odour molecules meets our sensor array, a volley of spikes will be generated. If there is a high concentration of odour molecules, trains of spikes will be generated and their frequency will be proportional to the concentration of the molecule.”

This ‘neuromorphic’ approach introduces a time factor into the system – the number of spikes per second – unlike the signals in conventional electronic noses, which usually ignore time information. This gives the signal processor another layer of information, which could be useful, for example, when trying to distinguish between complex mixtures of odour molecules.

At Warwick University Professor Julian Gardner is assembling novel mechanisms for channelling the odours on to the sensor arrays. Professor Gardner says, “We are taking recent developments in the fields of nanotechnology and polymer physics to design novel microsystems that are able to mimic our nasal passages and olfactory sensors. Combining such technologies with biologically-inspired signal processing methods developed at Leicester and Edinburgh should lead to a new generation of so-called micro-noses or a nose-on-a-chip.”

At Edinburgh Dr Alister Hamilton’s team is devising ways to integrate the whole system on to a single silicon chip. “We are designing analogue circuits that interface to the sensor array developed at Warwick, and sending the signals into some analogue circuits that mimic the mammalian olfactory system,” says Dr Hamilton. “We’re using parallel analogue computation strategies that are derived from biology rather than implementing a conventional digital processor. By concentrating on very low power consumption analogue circuits we hope to produce a system with long battery life.”