Year/Course: 2012-2013, Lent 2013

Contact: Tanya Hutter & Professor Stephen Elliott, Chemistry
Mentor: Michael Katz & Marc Bax

Porous silicon is inexpensive to manufacture and can be used to produce small, simple optical sensors for a wide range of gases and other materials. The silicon can be used in its bare state, or functionalised with the appropriate chemical markers, depending on the gases being detected.

The porous silicon can be manufactured with controlled porosity, and can have up to four separate sections on a single chip, allowing several vapours to be detected simultaneously from a single measurement. Their first challenge was to develop a sensor for ammonia gas which was not affected by the surrounding humidity (current sensors are notoriously sensitive to humidity). They did this by sensing the ammonia and water vapour separately but simultaneously in a multiplex chip, and then using the water vapour reading to correct the ammonia reading.

poroussilicon

Many other gases can be detected using the same method, from inorganic gases such as CO and CO2, to volatile organic compounds such as ethanol, fuel, and industrial solvents (many of which are toxic). Due to the small size of the nanopores in the silicon, many vapours will spontaneously condense inside the silicon, filling the pores as a liquid. This means that the sensor is sensitive to low concentrations.

Existing sensors tend to be very sensitive and reliable, but are on a lab-scale of size and cost. The advantage of our technique is the ability to produce sensors that are low-cost and portable, and also potentially small enough to fit into devices such as mobile phones.

The challenge for the i-Team is to investigate the different markets and applications for gas sensors, and identify the applications that best fit the unique characteristics of the sensors, focusing in particular on the applications which do not require the silicon to be functionalised with biomarkers.