ChemistrySelect Research Article doi.org/10.1002/slct.202403774 www.chemistryselect.org Synthesis of Multifunctional Chemosensors for Naked Eye Detection of Cu 2+ and Hg 2+ ; Application in Paper Strips, Water, and Food Sample Annasaheb Dhawale [a] and Darshak R. Trivedi* [a] Three chemosensors ISA-1, ISA-2, and ISA-3 were synthesized for the detection of Cu 2+ and Hg 2+ ions in a 50% H 2 O-DMF solution. ISA-1 is specifically designed for the detection of Cu 2+ ions, while ISA-2 can detect both Cu 2 + and Hg 2 + ions. Upon interaction with Cu 2 + , ISA-1 undergoes a naked-eye colorimetric transition from pink to blue. ISA-2 exhibits a similar pink-to-blue color change in the presence of Cu 2+ ion, however, colorless when exposed to Hg 2+ ion. The detection limits for Cu 2+ using ISA-1 and ISA-2 are 0.574 ppm and 0.0074 ppm, respectively, both of which are sig- nificantly lower than the WHO guideline of ≤1.5 ppm for Cu 2+ in drinking water. These chemosensors have also been successfully integrated into paper strips and logic gate systems and applied for the analysis of water and food samples. 1. Introduction Dating back to the age of metals between 8000 and 5000 B.C., Copper and Mercury have been a pivotal element in human civilization, utilized for a myriad of applications ranging from the crafting of utensils and weaponry to the facilitation of technological advancements in modern industries. [ 1 ] How- ever, with industrialization came the inadvertent generation of copper-laden waste, exacerbating its environmental presence. Consequently, what was once a valuable resource has now become a significant contributor to water and environmental toxicity. [ 2 ] Functionally, copper assumes critical roles in biological sys- tems, particularly in enzymatic processes crucial for energy maintenance and metabolic activities. [ 3 ] While copper is an essential element for human health, maintaining a balanced level is crucial. Both copper deficiency and excess can lead to various disorders. [ 4] For instance, imbalances have been impli- cated in neurodegenerative diseases like Alzheimer’s, as well as genetic conditions such as Menkes and Wilson diseases. [ 5 ] Fur- thermore, excessive copper intake can be toxic to animals and plants. Recognizing the potential detrimental effects of copper at high concentrations, regulatory agencies like the World Health Organization (WHO) and the United States Environmental Pro- tection Agency (USEPA) have established maximum permissible limits for copper and mercury in drinking water, these limits are set at 1.3 ppm and 0.006 ppm, respectively. [ 6,7 ] Moreover, cop- per’s pervasiveness in water sources beyond permissible limits, [a] A. Dhawale, D. R. Trivedi Supramolecular Chemistry Laboratory, National Institute of Technology Karnataka (NITK), Surathkal, Shrinivasnagar, Manglore 575025, India E-mail: darshakrtrivedi@nitk.edu.in Supporting information for this article is available on the WWW under https://doi.org/10.1002/10.1002/slct.202403774 as stipulated by regulatory bodies like the USEPA and WHO, necessitates vigilant monitoring and detection strategies. Mercury, another elemental stalwart, boasts a rich historical narrative, tracing its usage back to antiquity for various purposes, including artisanal endeavors and medicinal applications. [ 8] However, its notoriety stems from its profound toxicity and environmental repercussions, its adverse effects on health and ecosystems prompted a reevaluation of mercury’s utility. [ 9] The daily intake is less than 0.01 milligrams in humans and does not prove hazardous in this minute amount. However, in much higher doses it is toxic. [ 10] The seriousness of mercury poisoning was felt by the world when the Minamata Incident happened in 1956, wherein deaths were reported due to the consump- tion of fish infected with methylmercury (CH 3 Hg). The USEPA and WHO have recommended a permissible limit of 2 ppb and 6 μg/L respectively of Hg 2+ concentration in drinking water. [ 10] There is an immense need for the detection of copper and mer- cury in various places, especially in the water supplies that are meant for domestic consumption and industrial discharge. The modern-day methods such as AFM, ICP-MS, ICP-AES, FAAS, etc. are capable of detection of Cu 2+ and Hg 2+ but they suffer from several infirmities; in particular high cost of instrumentation, non-portable equipment, complicated and difficult to handle machinery and so forth. [ 11 ] Supramolecular self-assembly-based chemosensors are a winsome alternative pertaining to their immense selectivity, sen- sitivity, low cost, and primarily ready-to-use on-field detection of analyte proclivities. [ 12 ] Out of these, colorimetric chemosen- sors are the most widely used pertaining to their naked-eye detection of the target analytes present in the sample. [ 13 ] Fur- thermore, they do not involve the employment of any expensive instrumentation and are usually conveyable, thereby making it an excellent substitute for the traditional methods of analyte detection. These chemosensor molecules’ function is based upon the “supramolecular assembly” approach. [ 14] They bind with the analyte ions utilizing the host-guest chemistry that involves the ChemistrySelect 2024, 9, e202403774 (1 of 13) © 2024 Wiley-VCH GmbH