Quinine-Fabricated Surface-Enhanced Raman Spectroscopy Chiral Sensing Platform Enables Simultaneous Enantioselective Discrimination and Identification of Aliphatic Amino Acids

Abstract

Due to low optical activity and structural simplicity, synchronous chiral discrimination and identification of aliphatic amino acids (AAs) are still challenging yet demanding. Herein, we developed a novel surface-enhanced Raman spectroscopy (SERS)-based chiral discrimination-sensing platform for aliphatic AAs, in which l- and d-enantiomers are able to discriminately bind with quinine to generate distinct differences in the SERS vibrational modes. Meanwhile, the plasmonic sub-nanometer gaps supported by the rigid quinine enable the maximization of SERS signal enhancement to reveal feeble signals, allowing for simultaneously acquiring the structural specificity and enantioselectivity of aliphatic amino acid enantiomers in a single SERS spectrum. Different kinds of chiral aliphatic AAs were successfully identified by using this sensing platform, demonstrating its potential and practicality in recognizing chiral aliphatic molecules.

Hydrogen Bonding-Induced Aggregation of Chiral Functionalized AuNS@Ag NPs for Photothermal Enantioanalysis

“…C-AuNS@Ag NPs were handily synthesized via the in situ reduction of Ag + on the surface of AuNSs and simultaneous chiral functionalization. Initially, AuNSs were synthesized using a seed-mediated technique proposed in our previous study and served as the inner core . Subsequently, by utilizing l -ascorbic acid ( l -ASA) as a reductant, Ag + adsorbed on the surface of AuNSs were reduced to Ag 0 and deposited onto AuNSs, resulting in crystal growth and the formation of an Ag coating.…”

“…The stereoisomeric recognition of biomolecules in nature exhibits a noteworthy level of specificity, resulting in two mirror image permutations of enantiomers that elicit quite different biological reactions. , In this context, chiral amino acids play a crucial role in various metabolic processes and serve as indispensable building blocks for proteins and other biomolecules. , In recent years, there has been a shift in emphasis from proteogenic l -amino acids to the emerging biological significance of several d -antipodes. Free d -amino acids have been unveiled to play crucial biological and pathological roles in living organisms. − Although many specific physiological functions are still being investigated, d -amino acids have garnered increasing attention as potential disease markers and for the treatment of neurological disorders, such as schizophrenia, Parkinsonism syndrome, and Alzheimer’s disease. − Additionally, the structural diversity of naturally occurring amino acids has found extensive applications in the chemical industry , and pharmaceutical sciences. − Two types of enantiomers have become inestimable initial ingredient for the stereoselective synthesis of physiological activators and novel functional materials . Consequently, the exploitation of sensitive and accessible analytical techniques to discriminate between enantiomers of amino acids is extraordinarily attractive and challenging.…”

“…Chiral functionalized nanoparticles with Ag-coated Au nanostars (C-AuNS@Ag NPs) were synthesized using a two-step process; the first step involved the synthesis of Au nanostars (AuNSs) through the seed-mediated growth method (please refer to Section 2.1 in the Supporting Information for a detailed preparation procedure). 5 In the second step of the synthesis of C-AuNS@Ag NPs, chiral-ligand-mediated reduction was employed to deposit Ag shells in situ on the AuNS template. Specifically, 40 mL of the prepared AuNSs was poured into a 250 mL volumetric beaker, and 50 mL of ultrapure water was added and stirred for 5 min to homogenize the mixture.…”

Enantioselective and Chemoselective Optical Detection of Chiral Organic Compounds without Resorting to Chromatography

“…The IRM is label‐free, independent of Raman scattering of chiral molecules and it is not susceptible to matrix interferences [103] Au nanostar (AuNS) hydrophobic metasurface (HPMS) and quinine‐functionalized Au nanoparticle (AuNP‐quinine) colloids were prepared and used as SERS platform for enantiospecific sensing of aliphatic amino acids, namely, Glu, Gln, Val, Ala and Ser [104] . It was interpreted that quinine (being the chiral probe) had distinct binding modes for D‐ and L‐enantiomers of Glu, for example, because of the tetrahedral geometry of the quinuclidine skeleton with tertiary nitrogen in it at the vertex.…”

“…[103] (iv) Au nanostar (AuNS) hydrophobic metasurface (HPMS) and quinine-functionalized Au nanoparticle (AuNP-quinine) colloids were prepared and used as SERS platform for enantiospecific sensing of aliphatic amino acids, namely, Glu, Gln, Val, Ala and Ser. [104] It was interpreted that quinine (being the chiral probe) had distinct binding modes for Dand L-enantiomers of Glu, for example, because of the tetrahedral geometry of the quinuclidine skeleton with tertiary nitrogen in it at the vertex. Such a stereoselective binding of quinine with each enantiomer (to the AuNPquinine by H-bond interactions via the À NH 2 and À COOH groups), caused a conformational change (within subnanometer gaps) of the "chiral pocket" in quinine, and led to distinct differences in the SERS vibrational modes in a single SERS spectrum.…”