Ray, Aarati2022-03-142022-03-142021https://hdl.handle.net/20.500.14540/9065A cost effective and environment friendly synthesis of silver nanoparticles using aqueous extract of Parmelia sulcata has been done. Formation of silver nanoparticles was confirmed by UV-vis spectra as well as color change. XRD study confirmed that the resultant particles are silver nanoparticles having FCC structure with average crystalline size as 7.46 nm. Formed silver nanoparticles were modified by L-cysteine solution. Characterization of L-cys-Ag NPs was done by UV-visible spectrophotometer measuring optical absorbance which increased from 0.1278 to 0.1581. Organophosphorus pesticide namely malathion was detected by mixing it with modified silver nanoparticles. NaCl stimulated color change from brownish yellow to light yellow depending on malathion concentration of 100 ppm, 10 ppm, 1 ppm, 0.1 ppm and 0.01 ppm. With the decrease in malathion concentration, the absorbance at 430 nm gradually increased. Thus this colorimetric sensor allowed a direct quantitative check for the detection of malathion. Keywords: Nanoparticles, Parmelia sulcata Taylor, Organophosphorus pesticide, L-cysteineen-USNanoparticlesParmelia sulcata TaylorOrganophosphorus pesticideL-cysteineThesis