Enhanced optical asymmetry in supramolecular chiroplasmonic assemblies with long-range order

Abstract

Chiral assemblies of plasmonic nanoparticles are known for strong circular dichroism but not for high optical asymmetry, which is limited by the unfavorable combination of electrical and magnetic field components compounded by strong scattering. Here we show that these limitations can be overcome by long-range organization of nanoparticles similar to liquid crystals found in helical assemblies of gold nanorods with human islet amyloid polypeptide. Strong polarization-dependent spectral shift and reduced scattering of energy states with antiparallel orientation of dipoles activated in assembled helices increase optical asymmetry g-factors by more than 4600 times. The liquid crystal-like color variations and nanorods-accelerated fibrillation enable drug screening in complex biological media. Improvement of long-range order also provides structural guidance for the design of materials with high optical asymmetry.

Template-assisted self-assembly of achiral plasmonic nanoparticles into chiral structures

“…27 Kotov and co-workers analyzed by FDTD simulations the impact of the number of nanorods on the absorbance and scattering contributions to the extinction of nanohelices under parallel or averaged orientations. 34 Several of the studies reviewed herein coincide in the observation of an optimal g-factor at a high template loading. 40,45 Naturally, NP dimensions and the interparticle distance within the assembled state are both related to NP loading.…”

“…Similarly, the self-assembly of chiral NPs into periodical structures with long-range registry could benet far-eld optical phenomena and related applications. 34 The surface nanostructuring of PDMS is typically carried out by so lithography methods 72 such as replica molding of premade features, by drop casting and curing of PDMS. Alternatively, regular patterns can be created by the oxidation of previously stretched PDMS surfaces, by means of plasma treatment and subsequent relaxation.…”

“…In contrast, chiral organization could still be observed for smaller nanorods, but with the g-factor decreasing upon reduction of the nanorod size. 34 The interparticle distance in Au nanorod-hIAPP helical assemblies was 5.8 AE 4.4 nm. Such a short spacing between adjacent plasmonic building blocks led to the strong coupling needed for collective chiral resonances to arise.…”

“…At the forefront of chiral geometries, helicoids are the most visually appealing and easily recognized chiral shapes, with high anisotropy and the potential advantage of including periodicity. 34 Helicoidal motifs spontaneously emerge in a wide variety of systems, 35 some of them being potential templates to induce the self-assembly of plasmonic NPs. 36,37 As dictated by the sought interactions with the template of choice, helices, spirals, twisted ribbons and other helicoids might incorporate a large number of NPs.…”

Shining light on chiral inorganic nanomaterials for biological issues

“…Moreover, the induced chirality by such method could reach an anisotropic factor ( g -factor) as high as 10 -1 level. Similarly, helical assemblies based on the cooperative interactions of liquid crystals (LCs) and GNPs in thin films 38 (Figure 2 L) or assembled gold nanorods via DNA linkage 39 , 40 , chiral pyramids made from multiple metal and/or semiconductor NPs 41 (Figure 2 M), chiral nematic-like films with NPs conjugated with cellulose 42 , 43 and chiral photonic crystals fabricated by assembly of colloidal inorganic nanowires 44 (Figure 2 N) are all successfully demonstrated with possibilities for high value of g -factors and tunable chiroptical capabilities in the last decade.…”