Manipulation of Collective Optical Activity in One-Dimensional Plasmonic Assembly

Abstract

The manipulation of the chirality and corresponding optical activity in the visible-near-infrared (NIR) light region is significant to realize applications in the fields of chemical sensing, enantioselective separation, chiral nanocatalysis, and optical devices. We studied the plasmon-induced circular dichroism (CD) response by one-dimensional (1D) assembly of cysteine (CYS) and gold nanorods (GNRs). Typically, GNRs can form end-to-end assembly through the electrostatic attraction of CYS molecules preferentially attached on the ends of different GNRs. CD responses are observed at both the UV and visible-NIR light region in the 1D assembly, which are assigned to the CYS molecules and the GNRs, respectively. In addition, the wavelength of the CD responses can be manipulated from 550 nm to more than 900 nm through altering the aspect ratios of GNRs in 1D assembly. Anisotropic enhancement of optical activity is discovered, suggesting that the enhancement of the longitudinal localized surface plasmon resonance (LSPR) peak of GNRs in the CD response is much more apparent than that of the transverse LSPR. The CD responses of individual CYS-attached GNRs and CYS-assembled gold nanoparticles (GNPs) substantiate that the form of assembly and the shape of building blocks are significant not only for the intensity but for the line shape of the CD signals.

Giant circular dichroism of a molecule in a region of strong plasmon resonances between two neighboring gold nanocrystals

“…For example, it was a powerful method to differentiate a secondary structure of proteins which can appear in the forms of α-helix, random coil, or β-sheet. Recently the concepts of chirality and CD have been brought to the field of plasmonics [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] . One of the motivations for this development is plasmon-enhanced sensing of chiral molecules.…”

Synthesis and Plasmonic Chiroptical Studies of Sodium Deoxycholate Modified Silver Nanoparticles

“…The CD spectrum of the silver NPs prepared at pH 5.2 exhibits a splitting CD signal with two positive Cotton effects at 390 nm and 543 nm, and a negative Cotton effect at 469 nm (Figure 3a), which is distinct from those of Ag NPs prepared at a pH value higher than the pK a of NaDC. The characteristic splitting of the CD signature of silver NPs prepared at a pH value lower than the pK a of NaDC strongly suggests the existence of plasmonic dipole-dipole interactions between adjacent Ag NPs [33,34]. The absorption of silver NPs prepared at pH 5.2 shows two peaks at 398 and 500 nm (Figure 3b).…”

Plasmonic Circular Dichroism of the Helical Nanosphere Assemblies and the Helical Nanoellipsoid Assemblies

“…9. The large intensity can be attributed to the dramatic enhancement of electric field at the end of nanoellipsoids and the gap of adjacent NPs [13]. The increase of the aspect ratios will reduce the effective volume of the helical structures, and the reduced effective volume of the structure weakens the plasmonic interactions with the incident electromagnetic field and finally leads to the decrease of the CD signals.…”

“…The strong optical activity of the metal NP assemblies derives from the plasmonic interactions between nonchiral NPs arranged in a chiral geometry or the coulomb interactions between the NPs and the linked chiral molecules [5][6][7][8][9][10]. With the advance in both synthetic strategies and theoretical modeling, many chiral metal NP structures have been studied [11][12][13][14][15][16][17][18][19].…”