Chiral Plasmonic Shells: High-Performance Metamaterials for Sensitive Chiral Biomolecule Detection

Abstract

Low-cost and large-area chiral metamaterials (CMs) are highly desirable for practical applications in chiral biosensors, nanophotonic chiral emitters, and beyond. A promising fabrication method takes advantage of self-assembled colloidal particles, onto which metal patches with defined orientation are created using glancing angle deposition (GLAD). However, using this method to make uniform and well-defined CMs over macroscopic areas is challenging. Here, we fabricate a uniform large-area colloidal particle array by interface-mediated self-assembly and precisely control the structural handedness of chiral plasmonic shells (CPSs) using GLAD. Strong chiroptical signals arise from twisted currents at the main, corner, and edge of CPSs, allowing a balance between strong chiroptical and high transmittance properties. Our shell-like chiral geometry shows excellent sensor performance in detecting chiral molecules due to the formation of uniform superchiral fields. Systematic investigations optimize the interplay between peak and null point resonances in different CPSs and result in a record consistency chiral sensor parameter U, i.e., 3.77 for null points and 0.0867 for peaks, which are about 54 and 1.257 times larger than the highest value (0.068) of previously reported CMs. The geometrical chirality, surface plasmonic resonance, chiral surface lattice resonance, and chiral sensor performance evidence the chiroptical effect and the excellent chiral sensor performance.

Probing Interactions between Chiral Plasmonic Nanoparticles and Biomolecules

“…A first possibility involves the assembly of discrete chiral nanoparticles onto pre‐patterned substrates [31] . Alternatively, achiral nanoparticles can be adsorbed onto substrates, and subsequently prompted to form chiral structures via capillary forces, [74] specific interactions with ligands, [75,76] or further treatment using techniques like glancing angle deposition [77,78] …”

“…[31] Alternatively, achiral nanoparticles can be adsorbed onto substrates, and subsequently prompted to form chiral structures via capillary forces, [74] specific interactions with ligands, [75,76] or further treatment using techniques like glancing angle deposition. [77,78] A beautiful example in this direction is the recent work by Nam and co-workers, comprising arrays of discrete chiral nanoparticles (Au helicoids) on a PDMS substrate pre-patterned with a lattice of nanowells. [31] The helicoids were inserted into the wells by first allowing the particles to self-assemble at a water-hexane interface, followed by dip-coating of the substrate.…”

“…A different approach, which was undertaken by Hou and coworkers, comprises functionalization of a monolayer of achiral particles on a substrate by glancing angle deposition, so that chiral elements are present in the final structure. [78] The authors used this method to fabricate an array of nanoparticles with chiral plasmonic shells, which generated strong, localized, optically chiral near fields (Figure 3b-i). The material was able to distinguish between l-and d-tryptophan amino acids on the surface, which have different effective refractive indices (k) amplified by the field.…”

“…b) Detection of enantiomers by using a periodic array of nanospheres coated with a chiral metal component, by glancing angle deposition: i) Representative SEM images; ii) the CD peak (λ peak ) and zero-crossing point (λ null ) shift in a different direction, depending on the amino acid enantiomer used. Reproduced with permission from ref [78]…”

Chiral ZnO-CuO Nanorod Arrays for Circularly Polarized Photodetection

“…These materials could be chiral molecules, chiral polymers, or crystals with structures of chiral space groups, e.g., chiral perovskites. − The other is to build the chiral layer from intrinsically achiral structured materials by constructing the chiral shape, pattern, morphology, or assembly in the feature size from nanometer to micrometer scales. − The latter breaks the material limitations that principally any materials, organic or inorganic, conductor, semiconductor, or even insulator can be effective candidates. It brings about opportunities of converting achiral photodetective materials into chiral counterparts by various methods such as CPL irradiation, , templating, , grazing angle deposition, − laser direct writing, electron beam lithography, , chiral molecule induced nanocrystal synthesis, , or film growth. − Among the chiral candidates, inorganic semiconducting materials may have a tunable band structure, higher carrier mobility, and good stability, making them suitable for building high-performance CPL photodetectors. , …”