Au–Ag core–shell composite nanoparticles as a selective and sensitive plasmonic chemical probe for <scp>l</scp>-cysteine detection in Lens culinaris (lentils)

The present work reported is a simple and selective method for the colorimetrical detection of L-cysteine in Lens culinaris (or lentils) using Au–Ag core–shell (Au core Ag shell) composite nanoparticles as a chemical probe. The phenomenon is based on the color change of composite nanoparticles from yellowish brown to light blue, followed by a shift of the localized surface plasmon resonance (LSPR) absorption band in the UV-visible region (i.e., 200–800 nm) with the addition of L-cysteine into the solution of bimetallic nanoparticles. The mechanism for the detection of L-cysteine is based on the electrostatic interaction of the metal ion with the thiol group of the amino acid, which causes the red shift of the LSPR band at 685 nm. The size distribution, morphology, composition and optical properties of the Au–Ag core–shell composite nanoparticles were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), energy dispersive X-ray diffraction (EDX), UV-visible spectrophotometer and Fourier transform infrared spectroscopy (FTIR) techniques. An excellent linearity range for the present method was observed in the range of 20–140 μg mL−1 with a limit of detection at 1.95 μg mL−1 and correlation coefficient (R2) of 0.986. A good% recovery of 4.0% showed the selectivity of the method for L-cysteine determination from sample matrices. The advantageous features of the present method are being simple, rapid, low cost and selectivity towards the determination of L-cysteine in lentils.