Organic Cation Receptor and Metal Nanocomposite based Chemical Sensors for Environmental Monitoring

Abstract

In recent year, there has been an increase in worldwide concern about the environmental contaminations and its effects on human health caused by noxious and deadly contaminants caused by fast growing urbanization, industrialization and agriculture activities. Analysing the harmful effects of toxic pollutants necessitates the utilization of reliable analytical instruments that can have capacity of rapid screening and low sample handling. Chemical sensors have the potential to play a greater role in the field of environmental monitoring, and recent advancements in technology will make it easier the deployment of chemical devices in field of environment monitoring. Chemical sensors have advances over traditional methods in terms of portability, real time on-site monitoring of analytes. Therefore, the present research work in mainly focused on the synthesis of materials, sensing methods and portable low-cost devices for onsite monitoring of environmentally relevant toxic pollutant. The first chapter introduces the utilizing of chemical sensors in environment surveillance and types of chemical sensors on the basis of output signal produced on interaction with different analytes. Additionally, the utilization of metal nanoparticles and its composite with carbon-based materials have been discussed for the production of electrochemical sensors. In addition, the construction of optical chemical sensors and the different approaches and concepts utilized for the fabrication of colorimetric and fluorometric chemical sensors have been discussed. The two main approaches, namely lock-key single analyte sensing and gustation/olfaction-inspired array-based colorimetric detection, have been examined in depth. Furthermore, the utilizing of nanoparticles and its composites as a nanozyme for colorimetric quantification of analytes has been included. The change in perspective in chemical sensors from single analyte sensing to multiple cross-reactive sensing depend upon machine learning approaches prompted the advancement of sensor array system for segregation of large number of analytes. The different machine learning based approaches have been discussed which were utilized for the processing of multi-dimensional produced by array sensor after interaction with analyte. Finally, a brief outline of literature reports having nanozyme based colorimetric sensors array system for discrimination of analytes has been added along with its working principle. In the second chapter, benzimidazole based organic cation receptors was developed for optical detection of toxic analytes, i.e., zearalenone and fenitrothion in environment samples. In the first part, efficient, user-friendly, selective and sensitive colorimetric quantification of Zearalenone (ZEN) was achieved utilizing azo-dye based organic cation receptor (OCR). Firstly, the organic cation receptor has been impregnated on paper strips and investigated for colorimetric analysis of zearalenone, which gave a sharp color change from whitish to blue after the addition of ZEN. Furthermore, the RGB-based analysis was performed for the detection of ZEN with a limit of detection 0.39 nM, providing significant results as compared to the conventional methodology such as UV−visible absorption spectroscopy with a limit of detection of 0.31 nM, which is less than the WHO’s permissible limit of 50 μg/kg. Further, the interaction of OCR with ZEN has also been corroborated with 1H NMR, cyclic voltammetry, and fluorescence spectroscopy, which confirms its selectivity toward ZEN. The development of colorimetric lateral flow device (CLFD) was developed for portable on-site monitoring of ZEN, which shows promises and alternative recognition methods for ZEN detection in food samples to help a safe worldwide food supply. In part 2, benzimidazolium based cationic receptor R1 was synthesized having amide functionality. The synthesized receptor was then integrated into aggregates by the utilizing of anionic surfactants, which showed aggregation induced emission and results in increase in emission intensity. Moreover, the aggregates were further tested towards pesticide detection and when the receptor R1 was in aggregate form, a substantial boost in fluorescence was seen upon interaction with fenitrothion. The observed change in the chemical shift of the 1H-NMR (proton-nuclear magnetic resonance) signal provided evidence supporting the interaction between the receptor and the analyte via hydrogen bonding. Moreover, the aggregates were also tested in real spiked environment samples which give good detection limit of 22.45 nm. The third chapter deals with the synthesis of cost-effective and efficient CuNi/IL@MWCNTs nanocomposite for electrochemical quantification of imidacloprid (IMD). Firstly, the developed nanocomposite was successfully characterized utilizing numerous techniques like AFM, FESEM, XPS and PXRD and then utilized for specific detection of IMD using cyclic voltammetry based electrochemical approach. The presence of more active sites and synergetic effect of nanocomposite results in higher Rct value and better electron transferability. Moreover, the electrochemical quantification results showed good linearity (0.125–240 μM) and excellent sensitivity (LOD = 11 nM) in food samples. In order to degrade the IMD pesticide, the developed CuNi/IL@MWCNTs has also been successfully tested for catalytic degradation/detoxification of IMD in which nanocomposite act as catalyst. The degradation of IMD in presence of nanocomposite was monitored using UV-visible spectroscopy and LC-MS and showed degradation efficiency of 99.6% in 100 s. Furthermore, after usage, the easy extraction of CuNi/IL@MWCNTs utilizing a magnet makes the catalyst eco-friendlier, cost effective and reproducible. At last, the developed CuNi/IL@MWCNTs nanocomposite wase successfully utilized as bifunctional material for sensitive, selective, cost effective, quick and simple monitoring/degradation of insecticides toxicity in food samples to help a safe world-wide food supply. The perusal of literature revealed the nanozymes, which are artificial nanomaterials having advanced properties in terms of stability, cost of synthesis etc. than natural enzyme are extensively utilized for the development of colorimetric chemical sensor. In fifth chapter, the cost effective, easy to use, colorimetric paper-based sensor was developed based on artificial NiCr2O4 nanozyme for quantification of diethyl-chlorophosphate (DCP). The NiCr2O4 nanozyme were synthesized via hydrothermal approach by taking electroplating sludge waste source for nickel and chromium, which was characterized using different analytical techniques such as PXRD, XPS, TEM, EDX, etc. These characterization techniques revealed successful syntheses of nanozyme and therefore, further utilized to catalysed colourless TMB substrate into bluish-green color in presence of H2O2. Furthermore, the oxTMB was selectively produce yellow color after interaction with DCP. The quantification of DCP has also been achieved using UV–visible spectroscopy as well as the RGB method in solution form. Moreover, in order to fabrication of portable on-site monitoring, NiCr2O4 nanozymes were impregnated on Whatman paper and analysis the change in color via mobile based RGB application. Additionally, we fabricated Portable Colorimetric Kit for on-site quantification of DCP and successfully utilized for environment monitoring by detecting DCP in real environment samples and showed detection as low as 15.4 nM. It is firmly concluded that the fabricated Portable sensor kit is quite simple, affordable, and equipment free, as well as has potential applicability for DCP quantification for environment monitoring. A literature review disclosed an evolutionary shift from single analyte selective sensors to multianalyte cross-reactive arrays in sensing. Consequently, the fourth chapter covers array-based sensing applications for environment monitoring. Herein, a nanozyme based cross-reactive array has been developed utilizing M-NPs@CNTs nanocomposite (M= Ni, Co, Cu) in presence of cationic receptor (MKJ-A), which showed diverse interaction with analytes and composite material. The developed nanocomposites were fully characterized utilizing FESEM, XRD, XPS data. M-NPs@CNTs nanocomposite created the modified peroxidase-like activities of M-NPs@CNTs and composing the sensing principle of colorimetric sensor array. The response of sensor array on interaction with multiple analytes was recorded utilizing UV-visible absorption spectrophotometer. The combination of MDCs sensor array with statistical analysis has been successfully utilized for discrimination of 8 pesticides. Additionally, MDCs sensor array was further tested for recognition and discrimination of mixture of two pesticides having numerous combinations. Furthermore, the MDCs sensor array’s capability to discriminate the pesticides in real water and soil samples has also revealed its practical application. Interactions between multiple nanozymes-based sensors and several pesticides generated complex, high-dimensional datasets that were examined utilizing multivariate statistical methods, such as PCA. The results of the multivariate investigation demonstrated that nanozyme-based array have capability to differentiate numerous analytes. Furthermore, the utility of MDCs sensor for the discrimination of binary mixture of pesticides were also corroborated. Additionally, the MDCs sensor array was utilized for quantification and discrimination of pesticides in real soil and water samples, which demonstrates its practical applicability and provides a cost-effective sensing platform for environment monitoring. In the final chapter, research work was concluded along with the future prospective in field of chemical sensor and chemical sensor devices for onsite quantification of toxic pollutants for environment monitoring.