Tamar Sternfeld

THE OPTICAL NOSE

“Electronic noses” are vapor detection systems that mimic key principles of biological olfaction 1 . The functioning principles of biological, olfactory systems do not rely upon selective interactions with specific analytes, but rather on cross-reactive receptors 2 . The receptors respond to many odors, generating unique response patterns, which serve as “fingerprints” for each odor. Using the principles of biological olfaction, electronic nose systems contain arrays of different types of cross-reactive vapor-sensitive sensors. While it is difficult to discriminate analytes entirely by their responses to a single type of sensor, using an array of sensors yields response patterns that can readily distinguish many different vapors. Ideally, the response mechanisms of the sensors are highly varied and encompass both physical and chemical phenomena 1 . Our electronic nose measures fluorescence intensity responses from an array of polymer sensors over time during exposure to different analyte vapors. The sensors contain solvatochromic dyes that undergo intensity and wavelength shifts depending on changes in microenvironmental polarity. During exposure of the array to vapor-phase analytes, each of the sensor types in the array produces a temporal fluorescence response profile that depends on the sensor-analyte interaction. The combination of different responses from the sensor array to an analyte creates a pattern that characterizes the specific analyte and, therefore, enables identification. Such an array can recognize a variety of volatile organic vapors, and moreover, it can discriminate complex odors that contain multiple components, such as different types of coffees or perfumes. In these complex odors, the electronic nose recognizes the response pattern of the mixture, eliminating the necessity to quantify every single component.

H-1 NMR of C61H26-: the aromatic character of C-60 upon reduction - a view from the bridge of C61H2

The 1H NMR spectrum of the fulleroid C61H26– consists two high field doublets, providing experimental evidence for diamagnetic five-membered rings in C606–.

Optical Microsensor Arrays for Explosives Detection

The electronic nose described in this paper uses a cross-reactive sensor array based on fluorescence sensors. The sensors are fabricated by attaching solvatochromic dyes to different microspheres. The microspheres are then placed into wells chemically etched on the distal end of an optical fibre bundle. The system uses an olfactometer to deliver a pulse of analyte vapour to the sensors. An optical imaging system is employed to monitor fluorescence intensity over time. We use a heterogeneous array that contains different types of sensors, which allows us to classify a large number of analytes and complex odours. The array is formed by randomly distributing microspheres on the end of the fibre array. The position of each microsphere is determined by using a method that compares different sensor responses to their responses to known analytes. The electronic nose has been used to detect explosives and explosivelike vapours at low levels, and was able to detect nitro aromatic compound (NAC) vapour concentrations as low as 5 ppb. In addition, by fabricating a model of a nasal cavity and placing identical sensors at different positions, we demonstrated how the flow environment affects sensor response. By using the information from multiple sensors placed in different spatial positions in the complex flow environment, we demonstrated it is possible to obtain better discrimination between analytes.