Carbon Nanotube-Based Chemiresistive Sensor Array for Dissolved Gases

Dissolved gases such as oxygen (DO) and ammonia (dNH3) are among the most consequential parameters for water quality assessment. Since the concentrations of DO and dNH3 are interdependent through the nitrogen cycle, simultaneous monitoring can be useful in many applications. For example, in wastewater treatment, aeration baths are used to adjust the rate of ammonia removal by the bioactive sludge. Here, we have developed a sensing array which can monitor dissolved molecular oxygen (DO) and dissolved un-ionized ammonia (dNH3) continuously and simultaneously. This was achieved by functionalizing two sensors made from single- walled carbon nanotube (SWCNT) films with two different molecules; phenyl-capped aniline tetramer (PCAT), and iron phthalocyanine (II) (FePc). It was found that the FePc-doped SWCNT (FePc@SWCNT) sensor demonstrated good sensitivity and selectivity to DO, compared to dNH3. Conversely, we found that the PCAT-doped SWCNT (PCAT@SWCNT) demonstrates greater sensitivity to ammonia. Investigating the effect of different PCAT salts as dopant, we describe the following series of sensor responses to ammonia: Chloride < Crotonate < Fumarate. Additionally, we coated our sensors with PDMS, which is selectively permeable to gases, over ionic species. Finally, using principal component analysis (PCA) and partial least square discriminant analysis, it was possible to discriminate between responses to DO and dNH3, with 100% accuracy. As a result, here, we have developed a compelling proof-of-concept for the use of a single sensing substrate, doped with molecules with distinct mechanisms of interaction with two different analytes, to simultaneously monitor concentrations of two dissolved gases, namely DO and dNH3. This repository contains dataset and code used in chemometric analysis. Dataset contained in dataset folder. Within the array_exp.csv file, "sensor366" represents the current data for a PCAT@SWCNT Fumarate sensor; "sensor353" represents a FePc@SWCNT sensor. The dO meter is a polarographic probe. Times for the ammonia additions and concentrations can be found in the Rmarkdown script. In the root directory, the renv.lock file can be found with required packages. Text outputs from code can also be found in the root directory.