Plasmon-Coupled Circular Dichroism of Cysteine-Embedded Ag Nanoparticles with Strong Chiral Amplification and Long-Term Stability

Abstract

Plasmonic-coupled circular dichroism (PCCD) represents a versatile method to synthesize chiroplasmonic nanoparticles (NPs), which play irreplaceable roles in various fields such as enantioselective sensing, spectroscopies, and chiral catalysis. Nonetheless, two critical challenges are faced in the development of PCCD-based chiroplasmonic NPs: low chiral amplification and poor stability. To circumvent these restrictions, we herein performed a quantitative study of the enhancement and stability of PCCD by the embedment of chiral molecules in discrete Ag NPs. Our study reveals that the high chiral amplification is attributed to the chiral molecules embedded in NPs, rather than those adsorbed on the surface. The embedment of chiral molecules significantly increases the coupling between chiral molecules and Ag NPs, and thus, a record-high chiral amplification of over 4800 times is achieved. Moreover, the CD signals of the Cys-embedded Ag NPs are almost unchanged after 3 months of storage, also benefiting from the embedment strategy. These results will open up new possibilities for designing new PCCD systems with high chiral amplification and superior stability and lay the groundwork for the applications of PCCD-based chiral NPs.

Rational Design of Plasmonic Nanoparticle‐Molecule Complexes for Chirality Sensing†

“…[ 9,75 ] One typical approach is to construct metallic core‐shell nanostructures with interior nanogaps as hotspots. [ 24,75,95‐96 ] For example, Zheng et al . embedded chiral molecules into interior nanogaps of Au core‐shell NRs and observed enhanced plasmon‐coupled CD signals (Figure 7A).…”

“…More recently, Niu and coworkers also demonstrated the embedment of the chiral molecule at intra‐ particle gaps for both chiral amplification and superior stability. [ 24 ] Despite these pioneering efforts, the embedment strategy still faces challenges in having open access for the detection of chiral molecules, which limits the widespread applications in real‐world.…”

“…[ 15 ] Since then, many studies have been focused on the construction of plasmonic NP‐molecule complexes for chirality sensing. [ 24‐28 ] Fundamentally, how the far field and near field of plasmonic nanostructure interact with a chiral object are extremely important questions but still under progress. To better understand the coupling effect between plasmons and chiral objects in the complexes, we introduce the basic concept of surface plasmon resonance in the next section.…”

Chiro-plasmon responses of x-shaped titanium nitride (TiN) nanoarrays by numerical simulations

“…By combining chiral metamaterials with plasmonic materials, their chiral optical responses, such as circular dichroism (CD) are able to be tuned and regulated, which take advantage of both the unique plasmon properties and chiral metamaterials. Chiral plasmon metamaterials have found broad applications in various fields such as chiral sensing [2][3][4], optical devices [5,6], analytical chemistry [7][8][9], and so on [10][11][12][13][14]. As one of the crucial parameters of chiral optical response, CD is defined as the difference in the absorption of chiral structures illuminated by left-handed and right-handed circularly polarized lights [15], and it is also reported to be estimated by the spectra difference in the scattering, extinction and/or transmittance spectra [16][17][18].…”

Surface Topographical Engineering of Chiral Au Nanocrystals with Chiral Hot Spots for Plasmon-Enhanced Chiral Discrimination

“…A widely recognized phenomenon in plasmonic nanocrystals is the generation of localized enhancements of electromagnetic fields near the surface due to sharp protrusions from surface roughness, commonly known as “hot spots”. , These hot spots associated with surface roughness have been effectively utilized to significantly enhance the sensitivity of sensing measurements, such as surface-enhanced Raman scattering, − localized surface plasmon resonance sensor, − and photocatalysis. , In the case of chiral plasmonic nanocrystals, the chiroptical interaction with incident light can generate localized electromagnetic fields with chiral asymmetry. , Thus, the surface roughness of chiral nanocrystals is anticipated not only to amplify the intensity but also to enhance the chiral asymmetry of the generated localized electromagnetic fields in the vicinity of the surface . Particularly, an ordered surface pattern with chiral edges on the nanocrystals can lead to the amplification of chiral hot spots, which are exploited for the ultrasensitive detection of chiral molecules.…”