The production of paper-based colorimetric sensors

The global industrial revolution is accelerating the spread of heavy metals into the environment. Consumption of plant-based foods, drinking unsafe water, and polluted air with heavy metals have long-term effects on human health. The presence of heavy metals and their removal from nature are considered permanent pollutants to the environment. It is essential to develop low-cost, portable biosensor systems that allow detection in the field to prevent their spread and measure the level of pollution. In this thesis, gold and silver nanoparticles with citrate coating were synthesized using heat and no heat-based techniques to investigate their colorimetric sensor potential. These nanoparticles were evaluated against various heavy metals, and the responding metals were observed. Gold and silver nanoparticles are great candidates for colorimetric sensors compared to other particles due to their localized surface plasmon resonance (LSPR) properties. Citrate-coated silver nanoparticles of spherical shape with a core size of 7 nm, were synthesized with and without heating. The silver nanoparticles were colorimetrically tested with different ions and showed high specificity against Cr3+ ions, yet their sensitivity differed based on the method used for synthesis. The paper was selected to obtain environmentally friendly and cheap sensors to create a portable system that can be used in the field. The particles were printed on the paper using an inkjet printer with a piezoelectric printhead. The sensor system was applied to drinking and seawater samples. Measurements were made by adding 20 µM Cr3+ ion into 1 ml of real samples. Pre-addition and postaddition values were calculated and recovery values in percentages were found. The percentage was 106.3184 ± 2.378161 for drinking water and 90.97246 ± 1.453167 for seawater. The study presents a effect of temperature on the dispersion kinetics of nanoparticles, their appearance, and their interaction with metal ions.