Ms. Shannon E. Stitzel Profile

Shannon E. Stitzel

at Tufts Univ

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Proceedings Article | 21 February 2002 Paper

Artificial nose employing microsphere sensors for detection of volatile organic compounds

Shannon Stitzel, Keith Albert, Sergei Ignatov, David Walt

Proceedings Volume 4575, (2002) https://doi.org/10.1117/12.456916

KEYWORDS: Sensors, Bacteria, Nose, Chemical elements, Principal component analysis, Environmental sensing, Silica, CCD image sensors, Luminescence, Pollution control

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An artificial nose based on microsphere sensor arrays has been developed for the discrimination of numerous volatile organic compounds. Sensor elements consist of 3-5 micron diameter silica and polymer spheres that have a fluorescent, solvatochromic dye adsorbed to the microsphere surface. These sensors respond to changes in the local polarity of the environment by shifting their excitation and/or emission characteristics, thereby indicating the presence of different volatile compounds. High-density microsphere arrays are fabricated which contain thousands of individual sensor elements and multiple copies of each sensor type. By monitoring the sensors temporal fluorescence responses with a CCD camera, unique patterns are recorded that identify individual analytes or are characteristic of a complex mixture. By summing over the redundant sensor elements within an array, the signal-to-noise ratio can be enhanced. These types of sensor arrays have been used to detect and discriminate between different bacterial strains such as Escherichia coli based on characteristic odors from the live and dead bacteria.

Proceedings Article | 15 December 1999 Paper

Organic vapor detection with fiber optic bead arrays

Shannon Stitzel, Keith Albert, David Walt

Proceedings Volume 3858, (1999) https://doi.org/10.1117/12.372903

KEYWORDS: Sensors, Fiber optics, Luminescence, Fiber optics sensors, Polymers, Bioalcohols, Silica, Optical fibers, Chemical analysis, Land mines

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The need for small, fast responding detection systems is growing and fiber-optic bead arrays offer a different approach to small sensor design. Sensor arrays are fabricated by inserting self-encoded microspheres into microwells etched into the distal face of an imaging fiber. Each imaging fiber is 0.5 - 1 mm in outer diameter and consists of 5,000 - 10,000 individually clad, 3 - 4 micrometers diameter optical fibers bundled together. The bundles are coherent, allowing each microsphere in a well to be addressed as an individual sensor. Microsphere sensors are silica or polymer beads (approximately 3 micrometers in diameter) impregnated with solvatochromic dyes. These dyes alter their fluorescence emission spectra in response to changes in vapor polarity, allowing analytes to be discriminated based on their signature fluorescence response over time. A computational network is trained to recognize these response patterns for each sensor type, allowing for identification of specific organic vapors. Each sensor type is cross- reactive, and has unique fluorescence response patterns to different analytes. The sensor types can be identified based on their unique responses, allowing their position to be registered by observing the identity of the response pattern toward a known standard. Such encoding enables array fabrication to be simplified since sensors can be randomly dispersed throughout the array, instead of specifically patterned within the array. Possible applications for bead array detectors include environmental and industrial monitoring, land mine detection, and medical diagnostics.

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