Paper-Based Electronic Tongue for Rapid and Reusable Quantitative Sensing of Water in Organic Solvents Using Principal Component Analysis

Rapid and quantitative recognition of trace amounts of water in organic solvents is of great importance in industrial operations. Currently the standard methods of determining water content in such cases include the Karl Fischer (KF) titration and fluorescence colorimetry, which are expensive, time consuming, and require skilled operators to perform. Electronic tongues are sensor systems with the ability to analyze and classify complex samples by their chemical composition [1]. Principal Component Analysis (PCA) is a multivariate statistical technique used to reduce the dimensionality of data while retaining as much of the initial variation as possible and is commonly used in electronic tongue applications [1], [2]. In this work, a multifunctional liquid sensing and classification system was developed based on paper comprising pulp fibers adsorbed with multi-walled carbon nanotubes. Papertronics is a field of increasing interest due to the biodegradable nature, flexibility, and light weight of lignocellulosic paper and its ability to be produced at large scale using well-established and cost-effective manufacturing processes [3]. The hygroscopic nature of cellulose fibers causes them to swell radially in response to water molecules, which alters the conductive pathway within the percolated carbon nanotube network present on their surface, leading to a significant change in the paper resistance when wet. Importantly, the swelling behavior strongly depends on the nature of the solvent, which makes it an exceptional material for liquid sensing applications [4]. The electrical response of the sensor was tested and replicated for several liquid solutions of different solvents, concentrations of water in solvents, and ionic strengths of water. Specific features were identified from the response profiles, generating over 800 data points which were implemented in the PCA and used to differentiate between the liquids. The sensing platform can quantify the amount of water in the organic solvent with a sensitivity below 100 ppm and high resolution which makes it competitive with the KF titration. The proposed paper-based electronic tongue demonstrates the ability to rapidly differentiate low concentrations of water in organic solvents, provides an economic alternative to current methods, and enables future discoveries in biosensing and bioelectronics.<br/><br/>[1] “Electronic Tongues–A Review | IEEE Journals & Magazine | IEEE Xplore.” Accessed: Oct. 18, 2023. [Online]. Available: https://ieeexplore.ieee.org/abstract/document/6516019<br/>[2] I. T. Jolliffe, <i>Principal Component Analysis</i>, Second. in Springer Series in Statistics. 2002.<br/>[3] S. M. Goodman <i>et al.</i>, “Scalable manufacturing of fibrous nanocomposites for multifunctional liquid sensing,” <i>Nano Today</i>, vol. 40, p. 101270, Oct. 2021, doi: 10.1016/j.nantod.2021.101270.<br/>[4] A. B. Dichiara, A. Song, S. M. Goodman, D. He, and J. Bai, “Smart papers comprising carbon nanotubes and cellulose microfibers for multifunctional sensing applications,” <i>J. Mater. Chem. A</i>, vol. 5, no. 38, pp. 20161–20169, 2017, doi: 10.1039/C7TA04329E.