g-C₃N₄/ Bio–Synthesized Silver Nanoparticle for Fluorometric Bio-Sensing of Acetylcholinesterase and Malathion

Malathion is widely used in agriculture due to their high efficiency as insecticides. They are very toxic hazardous chemicals to both human health and environment even at low concentration. The detection of pesticides (malathion) at the low levels developed by the environmental protection agency (EPA) still remains a challenge. A highly efficient fluorescent biosensor based on g-C₃N₄/AgNPs for AChE and malathion detection is successfully developed by impregnation method. The structural and morphological properties of the nanocomposites were characterized by using powder X-ray diffraction (XRD), fourier- transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The analysis confirmed that there is a strong interfacial interaction between g-C₃N₄ and AgNPs. The fluorescent responses show an increase in intensity upon the additions of AChE which indicates that AChE as enzyme was hydrolyzing the substrate ACh, with the increase in oxidative electron as the preferred route of reaction. The developed OFF-ON sensor immobilizes by Actylcholestrase (AChE) and use as new probe for malathion detection. In the absence of malathion, AChE−g-C₃N₄/AgNCs exhibit high fluorescence intensity. However, the strong interaction of the basic sites to malathion, causes fluorescence quenching via static quenching and Ag form aggregation on the surface of g-C₃N₄. The experimental parameter such as pH of buffer (pH=6), concentration of acetylcholine (1 mM) and malathion (500 μM) were optimized. The sensor was also more sensitive with Stern-Volmer quenching constants (K_SV) of 3.48x10 ³ M ⁻¹. The practical use of this sensor for malathion determination in Khat was also demonstrated. The obtained amount of malathion in Khat is 168.8 μM.