Jaleed Khawaja
Jaleed Khawaja
Researcher
Sensors Research Laboratory
University of Warwick
Tel: 02476 528168
Email: J.E.Khawaja@warwick.ac.uk
Electronic Nose, using gold-nanoparticle polymer films in a non-inverting amplifier configuration
On our little planet, we are surrounded by smells of all sorts. Some smells are ?sweet?, some ?flowery?, some ?fruity? while others are pungent or damp or ?not appealing?. These smells are important to us as we identify different substances around us with them. Each flower has a different smell, and so does every fruit. These smells, or odours, are made of mixtures of organic vapours that drift around in our environment. It is these chemical vapours which in perfumes make our environment ?pleasant?, whereas in decaying matter gives off ?unpleasant? odours.
Some of these vapours are dangerous to us in high concentrations, such as toluene or ammonia. The human nose can detect some of these chemicals but only by exposing us to concentrations that are toxic. Other gases can go completely undetected, such as carbon monoxide.
|
|
A general description of the human olfactory system |
Ammonia is highly toxic if inhaled and can trigger asthma. Humans cannot smell it until it reaches 50 parts per million (ppm). Similarly, toluene, which is used in making paints, paint thinners, fingernail polish, lacquers, adhesives, and rubber and in some printing and leather tanning processes, is also harmful for us. It can cause headaches, confusion, and memory loss. Whether or not toluene does this to us depends on the amount we take in and how long we are exposed. Low-to-moderate, day-after-day exposure in our workplace can cause tiredness, confusion, weakness, drunken-type actions, memory loss, nausea, and loss of appetite.
Thus, it is important that we come up with some method of detecting the concentration of these chemical vapours in the air, without exposing ourselves to dangerous concentrations. Working out how the human sense of smell works has been a challenging project for scientists for years. In 2004 Richard Axel and Linda B Buck were awarded the Nobel prize in Physiology for their efforts in trying to understand how our sense of smell works.
The objective of my research is to detect volatile organic compounds using the absorbing quality of a chemical polymer film, which changes its resistance as a chemical vapour passes over it. This chemical film contains nano-scaled particles of gold which help in conducting the signal when a voltage is applied across it. This chemical film acts as chemical sensor.
The problem with chemical sensors used so far, has been that they tend to change their property and quality with time. This is called ageing. The set-up I use tries to minimise the affects of this ageing by using two identical sensors side by side in a non-inverting amplifier configuration. The ?gain? of this configuration is given by
Gain = 1 + R1 / R2
|
|
The Gold non-particle chemical sensors |
where, R1 and R2 are the respective resistances of the two chemical sensors. One of these sensors acts as a reference, i.e. it is isolated from the chemical vapour, whereas the other one is exposed to the chemical vapour. This non-inverting amplifier configuration is put into effect by using an ASIC developed by Jesus Garcia-Guzman as part of his research project. This ?smart? ASIC also has a built in function which takes care of voltage drift which might result in prolonged application of voltage.
|
|
Gold nano-particle chemical sensors combined with the non-inverting amplifier ASIC on Gold plated ceramic packaging. |
The gold nano-particle chemical sensors have been tested with VOCs such as toluene, propan-1-ol, ethanol, and methanol as well as water at 0% relative humidity (rH) and 40% rH.