Investigations of sensors based on new molecular architectonics: synthesis, fabrication, and application
Prof. Praveen Ramamurthy
16th February, 2024 (Friday), 02:00 PM (India Standard Time)
Rapid industrialization and expansion of urban landscapes in large cities generate maximum polluting ingredients to the surrounding environment. While organic pollutants occur naturally, the rise in anthropogenic and geogenic activities has contributed to an increase in inorganic pollutants in groundwater resources. These toxic by-products should be detected and remedied from the start of the polluting source itself before it reaches out to the ecosystem. Monitoring these inorganic pollutants is imperative to avoid their adverse impacts on ecological and human health. Thus far, variegated detection systems have been reported; however, restricted selectivity, specificity and uncompetitive lower limit of detection impede their extensive deployment. Additionally, sophisticated, and advanced instruments available for the identification of heavy-metal toxins require skilled technicians for appropriate interpretation. Although the traditional colourimetric and/or fluorimetric methods of detecting these analytes are common, there is an underlying hindrance in the detection limit, and ease of usage. Contextually, solid-state sensors are a better alternative as they operate on low power, provide a better detection limit and have higher reliability. To this extent, my thesis focuses on the design and testing of solid-state sensors to detect analytes such as nitrates, fluorides, and the mutagenic carcinogenic heavy metal hexavalent chromium. Metal-oxide-based solid-state sensors have often exhibited a lack of selectivity and specificity. Hence, the work presented here explores a low-cost alternative viz., bandgap engineered organic conjugated molecular sensors. Biomimetic-based molecular architecturing of a thiourea-based carbon nanocomposite has been developed to selectively detect nitrate ions in water with a detection limit of 10 ppm. The device architecture is that of a chemiresistor. The notorious inorganic contaminant, nitrate, has a high interference from fluoride ion. Consequently, a selective fluoride sensor has also been reported, which shows a limited response to nitrate ions. A statistical dimensional-reduction method called ‘Principal Component Analysis’ (PCA) has been employed to achieve pattern recognition by minimising the loss of data. Furthermore, fluorimetric and solid-state sensing methods have been established to detect mutagenic hexavalent chromium. The fluorimetric titration method has shown a detection limit of 9µM and this was further improved by fabricating a carbon-nanocomposite-based thick-film chemiresistive sensor, with a limit of detection of 1 ppm. The solid-state sensor reported for this purpose employs a ‘doctor-blading’ technique to achieve enhanced response, in addition to high reliability and repeatability. We have then developed a lesser-explored phenolphthalein-structured Schiff base molecular library for the objective study of colourimetric and fluorimetric detection of iron and hexavalent chromium, respectively. Molecular simulations have been carried out for the ground state geometrical optimizations; bandgap is determined through TDDFT calculations using Gaussian software.