Plasmonic Chiral Metamaterials with Sub-10 nm Nanogaps

Abstract

Sub-10 nm nanogaps are enantioselectively fabricated between two nanocrescents based on nanoskiving and show tailored circular dichroism (CD) activity. The mirror symmetry of the nanostructure is broken by subsequent deposition with different azimuthal angles. Strong plasmonic coupling is excited in the gaps and at the tips, leading to the CD activity. The dissymmetry g-factor of the chiral nanogaps with 5 nm gap-width is −0.055, which is 2.5 times stronger than that of the 10 nm gap-width. Moreover, the surface-enhanced Raman scattering (SERS) performance of L/D-cysteine absorbed on chiral nanogaps manifests as the emergence of enantiospecific Raman peaks and the appearance of distinct changes in SERS intensities, which affirms that chiral nanogaps can recognize specific cysteine enantiomers via standard Raman spectroscopy in the absence of circularly polarized light source and a chiral label molecule. The sub-10 nm chiral nanogaps with tailored chiroptical responses show great potential in a class of chiral applications, such as chiral sensing, polarization converters, labelfree chiral recognition, and asymmetric catalysis.

High-Throughput Fabrication of Triangular Nanogap Arrays for Surface-Enhanced Raman Spectroscopy

“…Under near-resonant illumination conditions, periodic arrays of metallic nanogaps can generate tremendous electromagnetic field enhancements due to extreme localization of the incident light, which in turn can cause nearby molecules to display a range of surface-enhanced optical properties such as increased absorption, Raman scattering, second-harmonic generation, and chiroptical behavior. ,− To test the performance of the TNG arrays as SERS substrates, a 10 –4 M solution of the widely used Raman probe methylene blue (MB) was drop-cast onto the three ( N = 1, 2 and 5) Au/Au TNG arrays, and Raman spectra were recorded under equivalent conditions at a probe wavelength of 785 nm (see Experimental Section). The spectra are shown in Figure a, together with a spectrum for a thin gold film of thickness 30 nm obtained under equivalent conditions.…”

DNA-mediated dynamic plasmonic nanostructures: assembly, actuation, optical properties, and biological applications

“…127,165 Moreover, the surface plasmon resonances can cause chiral plasmonic system to show a strong characteristic CD response in the visible region. 24,30,137,166 By exploiting the programmability and scalability of DNA selfassembly, colloidal nanoparticles have been assembled into various LH or RH plasmonic structures. 30,[167][168][169][170][171] Organizing anisotropic nanoparticles such as AuNRs into asymmetric nanoassemblies, enhanced chirality can be generated compared to isotropic NP nanostructures due to the high dissymmetry factor and strong plasmon antenna effect.…”

“…[15][16][17] When excited in a sub-wavelength structure, these oscillations allow for the confinement and manipulation of light at the nanoscale, which will have profound implications for the assembly of plasmonic structures to enable novel phenomena and properties, such as distance-dependent spectral shift, chirality, surface-enhanced Raman scattering (SERS), and surface enhanced fluorescence (SEF). [18][19][20][21][22][23][24] Over the past twenty years, DNA nanotechnology has provided novel and unprecedented research directions in the construction, assembly and application of plasmonic nanomaterials, and has become even more fantastic in mutual collaboration. Meanwhile, DNA is an ideal construction material due to its excellent sequence specificity and programmability, which also makes DNA nanostructures extremely rich in versatility.…”

“…15–17 When excited in a sub-wavelength structure, these oscillations allow for the confinement and manipulation of light at the nanoscale, which will have profound implications for the assembly of plasmonic structures to enable novel phenomena and properties, such as distance-dependent spectral shift, chirality, surface-enhanced Raman scattering (SERS), and surface enhanced fluorescence (SEF). 18–24…”

Nanoscience and Nanotechnology at Jilin University: A Virtual Issue

“…Recently, Zhang's group successfully made plasmonic asymmetric sub-10 nm nanogaps between two nanocrescents using colloidal lithography. 13 The chiral-nanogap-based metamaterials show tailored circular dichroism activity and can be used to detect chiral molecular enantiomers, which hold great promise for applications such as chiral sensing, polarization converters, label-free chiral recognition, and asymmetric catalysis. Prof. Kun Liu achieved significant enhancement of chiroptical activity using L-/D-glutathione oligomers to induce the chiral self-assembly of gold nanorods, in comparison to that by glutathione unimers.…”