Chiral recognition of tryptophan enantiomers using chitosan-capped silver nanoparticles: Scanometry and spectrophotometry approaches.

A new, fast and inexpensive colorimetric sensor was developed for chiral recognition of tryptophan enantiomers using chitosan-capped silver nanoparticles. The function of the sensor was based on scanometry and spectrophotometry of the colored product of a reaction solution containing a mixture of chitosan-capped silver nanoparticles, phosphate buffer and tryptophan enantiomers. The image of the colored solution was taken using the scanometer and the corresponding color values were obtained using Photoshop software which subsequently were used for optimization of the experimental parameters as the analytical signal. Two types of color values system were investigated: RGB (red, green and blue values) and CMYK (cyan, magenta, yellow and black values). The color values indicated that L-tryptophan had better interaction than D-tryptophan with chitosan-capped silver nanoparticles. A linear relationship between the analytical signal and the concentration of L-tryptophan was obtained in the concentration range of 1.3 × 10-5-4.6 × 10-4molL-1. Detection limits, were obtained to be 2.1 × 10-6, 2.4 × 10-6 and 3.8 × 10-6molL-1 for L-tryptophan based on R (red), G (green) and B (blue) values, respectively.