Portable colorimetric sensor array technology (2015)

Humans as a species are generally audio-visual creatures and do not take full advantage of the olfactory sense. Nonetheless, even humans can recognize and differentiate among thousands of different odorants under challenging conditions. Molecular recognition by the olfactory system derives its specifity from a complex pattern of responses generated by cross-reactive olfactory receptors. These receptors are encoded by approximately one thousand genes, which represents roughly 3% of the entire human genome. As a concept, the use of multiple cross-reactive chemical sensors is broadly applicable to any situation in which the sensors can be simultaneously exposed to each of a set of multiple target analytes; such an "artificial nose" has significant potential in all areas of chemical sensor technology.\nThe chemical sensor arrays discussed in this work are based upon cross-reactive colorimetric response: each of many sensor elements in an array is a mixture of dyes or other compounds that changes color upon exposure to an analyte. These arrays typically use strong, poorly-reversible chemical reactions involving a diverse set of color-changing dyes or chromogens; such colorimetric sensor arrays have evolved to be fast, sensitive, portable, and inexpensive. Importantly, the analyte scope of the developed arrays has been shown to be capable of tailoring based on their intended applications, and can be made to be either broad or narrow as desired: in previous works, they have proven to be capable of discriminating among a broad range of analytes including both gaseous and aqueous analytes involving many different types of chemical reactivity, including Lewis and Brønsted acidity/basicity, molecular polarity, redox properties, and chelation.\nOf particular interest is the study of chemicals which are hazardous to human life, by either directly interacting with the human body or indirectly causing a physical effect. This work discusses development of colorimetric sensor arrays for two such cases: aqueous toxins and explosives materials. Both types of analytes are particularly challenging due to their relative lack of chemical reactivity: aqueous toxins derive their toxicity from interaction with specific proteins within the human body, while explosives have high potential energy but are kinetically inert. Targeting these analytes while still maintaining high sensitivity, low noise, and the ability to discriminate among them was the primary focus of these two projects.\nFurther, inexpensive portable technology for the quantitative analysis of these arrays is vitally necessary for their intended use outside of the laboratory. This work discusses development of an automated, truly portable device that fits into a pocket and improves upon previous instrumentation in scan speed, sensitivity, and noise. Since colorimetric sensor arrays are monitored by optical transduction, development of portable scanners involves investigating inexpensive, compact, low-noise optical imagers. Previous works focused on flatbed scanners, which have since shown to have limitations in portability (flatbed scanners will certainly not fit in someone's pocket), scan speed (~15-45 seconds per scan), noise (largely induced by the scanner's moving parts), and processing ability (processed manually). To improve upon this, an optical line imager known as a contact image sensor was used to act as the optical transducer; chemical sensor arrays were printed linearly so as to maintain compatibility with the line imager. The final device included disposable sensor array cartridges, a flow control system, control software, and analysis software for pattern matching.