A Circular Dichroism Probe for L-Cysteine Based on the Self-Assembly of Chiral Complex Nanoparticles

A novel circular dichroism (CD) method to probe 1-cysteine based on the self-assembly of chiral complex nanoparticles from Ag1 and L-cysteine was reported. To speed up the reaction between Ag1 and L-cysteine, the mixture of Ag1 and L-cysteine was ultrasonicated and heated in a water bath. As a result, the time for the reaction to reach equilibrium was reduced from 100 h to 30 mm because of the synergistic effects of temperature and ultrasonication. To confirm that the CD spectra, after treatment of L-cysteine with Ag1, originated from the differential absorption of left- and right-circularly polarized light rather than the effect of light scattering on small particles in solution, L-cysteine was replaced with D-cysteine. The results show that replacement of L-cysteine with D-cysteine produced an opposite CD signal, and demonstrate that the observed behavior did result from the differential absorption of left- and right circularly polarized light.