In this work a sensitive colorimetric method based on the shift in the position of plasmon peak of pvp-stabilized-AgNPs. was used to measure Cysteine and homocysteine in blood plasma. The reaction involves electrostatic interactions between the thiol molecules attached to the surface of the silver nanoparticles. The co-action between particles leads to a decrease in the plasmonic peak at 398 nm and rise of a new peak at 520 nm, resulting a color change from yellow to pink. Effective parameters including nanoparticle concentration, ionic strength, pH of solution and time were studied.
