Chiral Nanostructured Bimetallic Au–Ag Films for Enantiomeric Discrimination

Abstract

circular dichroism, [3] electronic circular dichroism [4] and Raman optical activity, [5] has been used in both quantitative analysis and absolute configuration study of the enantiomers. However, the feasibility of enantiomeric discrimination by chiral chromatography strongly depends on molecular polarity and mass of enantiomers, which narrows applicable conditions and molecules for each chiral column. Chiral spectroscopy is impossible to be used for enantioselective discrimination of racemates or chiral molecules with inherently weak optical response suffering from poor resolution and low sensitivity. [6] Recently, we developed new strategies, PM-ChA [7] and SERS-ChA [8] of chiral nanostructured Au films (CNAFs) to enantiomers, which demonstrated enantiomeric determination, based on the selective generation of photomagnetic fields (PMFs) and selective enhancement of Raman scattering of enantiomeric molecules on CNAFs, respectively. These methods are available for all the enantiomers regardless of their sizes, polarities, or chromophores, which overcome the drawbacks of chromatography and spectroscopy.Silver (Ag) nanomaterials show strong SPR effects and excellent electrical conductivity, making them promising for plasmonic sensing systems and optoelectronic devices. [9] Therefore, doping with Ag should allow modulating the SPR and increasing conductivity of composite nanomaterials, which is expected to generate stronger local electromagnetic fields and further enhance the SERS intensities. This strategy provides the possibility for simultaneous enhancement of the PM-ChA and SERS-ChA effects of chiral noble metal nanomaterials. However, multi-metal compounding by the wet chemical deposition method sometimes suffers from difficulty in finding a reductant with appropriate reducing potential for simultaneous codeposition of metal ions in the precursor solution.Electrodeposition is a universal, efficient, and low-consumption technique for the preparation of Ag containing composite nanomaterials comparing with the other methods, [10] because deposition occurs in a very limited range on the electrode surface and the electrodeposition method allows precisely controlled reduction potential and duration time for Ag material preparation. [11] In addition, reduction reaction rates of different metal ions can be adjusted by changing the reduction potential, which makes them uniformly deposited Herein, the chiral nanostructured bimetallic Au-Ag films (CNAAFs) with both photomagnetic-chiral anisotropy to enantiomers (PM-ChA C-E ) and surface-enhanced Raman scattering-chiral anisotropy to enantiomers (SERS-ChA C-E ) for efficient enantiomeric discrimination are reported. The CNAAFs are synthesized by electrodeposition on n-type Si (n-Si) substrates with the assistance of N-acetyl-L/D-cysteine (S/R-NAC) as symmetry-breaking agents, which are consisted of polycrystalline Boerdijk-Coxeter-Bernal (BCB) tetrahelical structured Au-Ag alloy nanowires grown on n-Si substrates perpendicularly. The anisotropic factors of PM-ChA C-E ...

Spin Selectivity-Based Enantiomeric Discrimination by Chiral Nanostructured Au Films

“…Therefore, based on the chirality-induced spin selectivity theory, − the mechanism of SERS-ChA C–E can be deduced (Figure b). (i) Anisotropic photomagnetic fields were generated by antipodal CNAFs owing to chirality-induced spin selectivity of CNAFs under laser irradiation, resulting in effective spin polarization in chiral structures. , The strength of spin selectivity depends on the length of the path through which the electron passes due to the selectivity of the chiral potential for electrons . (ii) The selective SPC between CNAFs and enantiomers results in the selective enhancement of the magnetic fields of CNAFs .…”

“…Chirality is known as the geometric asymmetry of a large group of molecules with a non-superposable mirror image, either left- or right-handedness. , Due to the homochirality in biosystems that are very sensitive to the chiral orientation of compounds, enantiomeric discrimination is of vital importance in both pharmaceutical fields and investigating life activities. , For enantiomeric discrimination, chiral response, which depends on the handedness matching and mismatching between the enantiomers and chiral structures, is often employed. − …”

Multicomponent chiral plasmonic hybrid nanomaterials: recent advances in synthesis and applications

“…More recently, more chiral hybrid plasmonic materials have been designed and used as excellent substrates for significantly amplifying the molecular vibrational signal, particularly for SERS. 79,130…”

“…4c ). 79 SEM and TEM images revealed that the films grew perpendicular to the substrate, forming polycrystalline Boerdijk–Coxeter–Bernal (BCB) four-fold helical structures composed of AuAg alloy. CD diffuse reflectance spectra indicated chiroptical signals at 545 nm for the entire substrate, exhibiting mirror-image symmetry influenced by the chirality of the molecules.…”

Gold-Nanoparticle-Based Chiral Plasmonic Nanostructures and Their Biomedical Applications

“…With the rapid development of chiral plasmonic nanostructures/superstructures, further study of their chirality-related optical properties become possible, such as chiral-field-steered emissions and surface-enhanced Raman scattering (SERS) [ 74 , 75 ], photothermal chirality [ 76 , 77 ], and chiral photoluminescence (PL) from chiral structures themselves [ 78 , 79 ] to name a few ( Figure 3 ). Using the combination of chiral plasmonic antenna and monolayer transition metal dichalcogenides, Lu et al demonstrated the huge modulation of the valley-polarized PL of monolayer MoS 2 located in a nanogap of two AuNRs in a chiral configuration ( Figure 3 a) [ 78 ].…”