Concentration-dependent tri-mode morphological evolution of silver nanotriangles for homocysteine enantiomer determination

Enantioselective quantification of biomolecules is a precondition for a comprehensive understanding of their functions. Current methods for enantiomer detection typically rely on the separation pretreatments or chiral reagents. Herein the determination of homocysteine (Hcy) enantiomers is accomplished through the tri-mode morphological evolution of Ag nanotriangles (AgNTs). It is found that different concentrations of Hcy induce morphological evolution of AgNTs in three modes: etching, protection, and cracking, because Hcy preferentially binds to different facets of AgNTs at specific concentrations. Experimental and computational results reveal that at the low concentrations, the thiol group (–SH) of Hcy perturbs the {110} crystal facet, resulting in the etching of AgNTs from the tips. At the medium concentrations, the hydroxyl group of Hcy covers all facets, protecting AgNTs against other etchants. As the concentration increases, –SH of Hcy intensely disturbs the {111} crystal facet, leading to the cracking of AgNTs into small nanoparticles. This morphological evolution enables selective detection of Hcy within two broad linear ranges, distinguishing Hcy from cysteine in the cracking process. Notably, L-Hcy exhibits a significantly faster rate of AgNTs cracking compared to D-Hcy. Accordingly, enantiomeric excess of Hcy is directly determined with the pure nanomaterials in the absence of separation pretreatments or chiral reagents. Overall, this work highlights the impacts of chiral biomolecules on morphology of nanomaterials, providing an alternative perspective of designing nanosensors for enantioselective quantification.