Development of a Detection Algorithm for Use with Reflectance-Based, Real-Time Chemical Sensing

Abstract

Here, we describe our efforts focused on development of an algorithm for identification of detection events in a real-time sensing application relying on reporting of color values using commercially available color sensing chips. The effort focuses on the identification of event occurrence, rather than target identification, and utilizes approaches suitable to onboard device incorporation to facilitate portable and autonomous use. The described algorithm first excludes electronic noise generated by the sensor system and determines response thresholds. This automatic adjustment provides the potential for use with device variations as well as accommodating differing indicator behaviors. Multiple signal channels (RGB) as well as multiple indicator array elements are combined for reporting of an event with a minimum of false responses. While the method reported was developed for use with paper-supported porphyrin and metalloporphyrin indicators, it should be equally applicable to other colorimetric indicators. Depending on device configurations, receiver operating characteristic (ROC) sensitivities of 1 could be obtained with specificities of 0.87 (threshold 160 ppb, ethanol).

Reflectance-based detection for long term environmental monitoring

“…The device hardware has also been modified to provide improved coverage of the red region of the visible spectrum by the illumination sources [13]. Based on the limited overall gains achieved through modification of algorithm parameters, the current effort evaluated the impact of modifications to the operational parameters of the prototype device.…”

“…We had previously completed a more detailed laboratory study using similar prototype devices [13]. This study provided highly controlled conditions allowing for detailed evaluation of algorithm performance.…”

“…Paper supported porphyrin indicators were prepared using a dip and dry technique [13, 20]. For a 5 × 33 cm swatch, 0.4 mM porphyrin in water (total volume 6 mL) was used.…”

Field Demonstration of a Distributed Microsensor Network for Chemical Detection

“…A significant number of reports describe the development of array-based sensing approaches [ 8 , 9 , 10 , 11 ], including both electrochemical and optical approaches [ 8 , 9 , 12 , 13 , 14 ]. Optical methods range from image capture with post processing to simple color intensity measurements [ 9 , 10 , 15 , 16 , 17 , 18 ].…”

“…It has also been tested against aerosol targets [ 23 ]. For event identification, we have developed a data analysis algorithm that has been used as a standalone program for offline analysis [ 11 , 24 ] and as a component in our instrument control software GUI for real-time analysis during live data feeds. When in the housing, the instrument is 27.4 × 7.6 cm and 7.6 cm tall, weighs 1587 g, and consumes 300 mA of power at 7.5 V ( Figure 1 ).…”