Synthesis of chiral multi-hole polydopamine nanospheres for spectroscopic and electrochemical discrimination of tryptophan enantiomers

Au nanoparticles (AuNPs) are adsorbed onto the surface of multi-hole polydopamine (mPDA) nanospheres, which are utilized for the covalent bonding of L-cysteine (L-Cys) as the chiral source. The obtained mPDA@AuNPs/L-Cys is applied in the spectroscopic and electrochemical discrimination of tryptophan (Trp) enantiomers. Due to the same rotatory direction of L-Cys and L-Trp, L-Trp is selectively combined with the mPDA@AuNPs/L-Cys, and thus the chiral discrimination of the Trp enantiomers can be successfully achieved. Chiral solid polydopamine (sPDA) nanospheres are also synthesized and used for the chiral discrimination of the Trp enantiomers, while the discrimination ability of the chiral sPDA is significantly lower than that of the chiral mPDA. The improved discrimination ability of the chiral mPDA can be ascribed to its unique multi-hole structure, which is in favour of combining more amount of AuNPs and L-Cys.