Yolk−shell structured Au@Ag@mSiO2 as probe for sensing of cysteine enantiomers and Cu2+ based on circular dichroism
A yolk−shell structured Au@Ag@mSiO2 probe was fabricated by coating a layer of mesoporous silica on the surface of Au@Ag core-shell nanosphere, followed by partially removing the Ag shell. Mirror symmetrical chiral signals at ~258 nm in the UV region were observed for the probe upon coupling with cysteine enantiomers on the surface of Au@Ag. The intensity of the CD signal of the probe is enhanced with increasing L/D-Cys concentration, allowing the quantitatively determination of the cysteine enantiomers. The developed method exhibits an excellent linear relationship between the CD signal and L-Cys concentration ranging from 10 μM to 90 μM with a limit of detection of 8.5 μM. In the presence of Cu2+, the CD signal of probe was weakened due to the oxidation of L-cysteine to L-cystine catalyzed by Cu2+. Based on this phenomenon, a new strategy for detection of Cu2+ can be established. Under optimized condition, the CD signal decreases linearly with the log of the concentration of Cu2+ in the range from 1 to 250 nM with a detection limit of 0.1 nM.