Low Cost Optoelectronic Sensors for Gas Monitoring in Diverse Environment

Gas sensors are used extensively in monitoring of the environment. Many volatile organic compound gases found in the environment severely impact the health of an individual. Volatile organic compounds are also present in food odors (i.e. fruits, coffee, poultry) and we believe sensing them using gas sensors may provide an effective indicator of food freshness. For these sensors to be used en masse, they need to be affordable, sensitive, user-friendly, easy to fabricate, and ecofriendly. Thus the objective is design, fabricate, test and validate low-cost optoelectronic sensor arrays for some targeted application in medical diagnostics and food quality monitoring.;Towards this goal, cellulosic paper is among the most promising substrates, since it is inexpensive, flexible, lightweight, portable and biodegradable. Several paper-based gas sensor platforms functionalized with different gas sensitive elements (e.g. chemo-responsive dyes, conductive nanomaterials) have been presented for gas detection in diverse environments. In one work, a paper-based microfluidic platform functionalized with an array of chemo-responsive dyes is built. Selective sensing of dissolved ammonia and carbon dioxide is achieved with ppm level sensitivity. In another work, a disposable food sensor is made on paper substrate with colorimetric microbeads arrays arranged as a geometric barcode to monitor the food spoilage. The sensor is fabricated through a stamping process, which is easy and highly reproducible. This barcode sensor can distinguish hourly change of food freshness at room temperature. Another paper based optoelectronic platform with combined optical and electrical chemi-resistive sensor arrays is used for sensing and discriminating several volatile gases and mixtures. By combining the optical and electrical approaches, a unique optoelectronic signature is generated for each gas analyte and its mixtures. Using support vector machine (SVM) based machine learning approach enables accurate classification of these gases from the combined use of both optical and electrical sensor responses.;Another part of work includes a couple of sensor platforms with dye-contained colorimetric microbeads as the core sensing element. These works include an optical fiber sensor functionalized with colorimetric beads for the detection of gastric gas at ppm level; a microfluidic sensing platform incorporating colorimetric beads for detection of ammonia concentration in saliva with sub-ppm sensitivity; the colorimetric beads embedded hydrogel fiber used to monitor the pH of the skin for wound healing.;In summary, several optoelectronic sensor platforms have been developed, which combine the advantages of clean room free fabrication, low-cost paper-based substrate material with highly sensitive sensing materials such as chemoresponsive dyes. These as-fabricated cost-effective and highly reproducible sensor platforms have been used to realize gas sensing in diverse environments.