Enantiospecific molecular fingerprinting using potential-modulated surface-enhanced Raman scattering to achieve label-free chiral differentiation

Abstract

Chiral differentiation is critical in diverse fields ranging from pharmaceutics to chiral synthesis. While surface-enhanced Raman scattering (SERS) offers molecule-specific vibrational information with high detection sensitivity, current strategies rely on indirect detection using additional selectors and cannot exploit SERS' key advantages for univocal and generic chiral differentiation. Here, we achieve direct, label-free SERS sensing of biologically important enantiomers by synergizing asymmetric nanoporous gold (NPG) nanoparticles with electrochemical-SERS to generate enantiospecific molecular fingerprints. Experimental and in silico studies reveal that chiral recognition is two pronged. First, the numerous surface atomic defects in NPG provide the necessary localized asymmetric environment to induce enantiospecific molecular adsorptions and interaction affinities. Concurrently, the applied potential drives and orients the enantiomers close to the NPG surface for maximal analyte-surface interactions. Notably, our strategy is versatile and can be readily extended to detect various enantiomers. Furthermore, we can achieve multiplex quantification of enantiomeric ratios with excellent predictive performance. Our combinatorial approach thus offers an important paradigm shift from current approaches to achieve label-free chiral SERS sensing of various enantiomers.