Browsing by Subject "Breath Sensing"

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    Development of Chemiresistor Based Nanosensors to Detect Volatile Cancer Biomarkers
    (2019-05) Vij, Shitiz; Agarwal, Mangilal; Anwar, Sohel; Towar, Andres
    Researchers have shown links between various hydrocarbons and carbonyl compounds and diseases, such as cancer using exhaled breath analysis through gas chromatography/mass spectroscopy (GC/MS) analysis of volatile organic compounds (VOCs). Trained canines can detect these VOCs and can differentiate a patient suffering from cancer from a healthy control patient. In this project, an attempt has been made to develop highly sensitive sensors for the detection of low concentrations of aldehyde VOCs, such as nonanal, using conductive polymer composites (CPCs) and functionalized gold nanoparticles (f-GNPs). Facile methods have been used to enhance the sensitivity and cross-selectivity of the fabricated sensors towards nonanal. Interdigitated electrodes (IDEs) are fabricated through a photolithography process. Sensors of PEI/carbon black (CB) composite were developed via spin-coating of the material followed by the heat treatment process. Sensors of 1-Mercapto-(triethylene glycol) methyl ether functionalized GNPs are developed via drop-casting of nanomaterial and f-GNP/PEI sensors are fabricated by spin casting PEI film on top of f-GNPs. Fourier Transform Infrared (FTIR) analysis, X-Ray Diffraction (XRD) analysis, contact angle measurement, and Field Emission Scanning Electron Microscopy (FESEM) analysis was conducted to characterize the fabricated devices. The fabricated sensors have been tested with a low concentration of nonanal, nonanone, dodecane, and 1-octanol in dry air. Multiple sensors are fabricated to ensure sensors reproducibility. The sensors have been exposed repeatedly to the targeting VOC toxiv assess the repeatability of the sensors. PEI/CB sensor degradation was studied over a period of 36 days. The fabricated PEI/CB film could detect (1-80 ppm) of nonanal with higher selectivity, than the f-GNPs. The sensor0s sensitivity to nonanal was over fourteen times higher than 2-nonanone, 1-octanol, and dodecane. This shows the high selectivity of the fabricated sensor toward nonanal. In addition, the proposed sensor maintained its sensitivity to nonanal over time showing minimal degradation. The sensor response to nonanal at a relative humidity (RH) of 50% and 85% dropped less than 13% and 32% respectively. The Response of f-GNP sensors to nonanal (400 ppb - 15 ppm), dodecane (5 - 15 ppm), 1-octanol (5 - 15 ppm), and 2-nonanone (5 - 15 ppm) presented a sensitivity (∆R=R0) of 0.217%, 0.08%, 0.192% and 0.182% per ppm of the VOCs respectively. Despite the high sensitivity to the targeting VOCs, the fabricated sensors were damaged in an environment with relative humidity (RH) at 45%. A thin layer of PEI over the film was developed to ensure the sensor could tolerate longtime exposure to water vapor in an environment with RH up to 85% and enhance the sensor selectivity towards nonanal. The f-GNP/PEI sensors with nonanal (400 ppb- 15 ppm), dodecane (100 -200 ppm), 1-octanol (5 - 15 ppm) and 2-nonanone (5 - 15 ppm) presented sensitivity (∆R=R0) of 0.21%, 0.017%, 0.0438% and 0.0035% per ppm of the VOCs respectively.