A new Electronic Nose using a single, uncoated, high Q surface acoustic wave resonator is described. The commercial expression of this technology, the zNose™, is now providing an on-line quantitative measure of quality for food, beverages, cosmetics, and other manufacturers of aromatic products. The zNose™ can provide a recognizable visual image of specific vapor mixtures (fragrances) containing possibly hundreds of different chemical species in 10 seconds or near real time.
At the same time this new nose is able to speciate and quantify the individual chemicals (hydrocarbons mainly) present in any vapor, odor, or smell.
Because the new acoustic technology is quantitative it is the only electronic nose technology to be validated by the US EPA. An array of sensors simulating the human olfactory response has become known as an zNose™ [Ref. 1]. An eNose™ provides a vectorial image in N-dimensional space (where N equals the number of sensors) of specific vapor mixtures (fragrances) containing possibly hundreds of different chemical species. zNoses™ have only a few sensors, produce responses which are not correlated, multiple sensors respond to the same vapor e.g. overlap, and their sensitivity is very poor. In the chemical sense, an zNose™ using quasi-specific sensor arrays may never be a quantitative measurement instrument.
However, a new approach, based upon fast chromatography and a single high Q acoustic sensor, solves these problems by simulating a virtual sensor array containing hundreds of orthogonal (non-overlapping) sensors. Analysis of any odor is accomplished by serially polling a virtual sensor array or spectrum of retention times. For a zNose™ system, sensor space is defined mathematically by assigning unique retention time slots to each sensor.
The zNose™ is fast (10 seconds), operates over a wide range of vapor concentrations, and has picogram sensitivity. Sending a stream of helium gas and the vapors of interest through a specially coated column causes the vapor's constituent chemicals to split up and travel at different velocities. Emerging from the column at different times, each constituent absorbs and desorbs onto the surface of an acoustic detector, which changes its frequency of vibration depending on how much of the particular chemical is present.
There are many successful applications of this new acoustic technology. Food and beverage, pharmaceutical, and cosmetic companies are using the zNose™ to monitor the quality of their products.
The acoustic sensor can also be used to detect pollutants, explosive materials and other volatile and semi-volatile compounds with part-per- trillion sensitivity.