ABSTRACT
Plasmonic nanoantennas have considerably stronger polarization-dependent optical properties than their molecular counterparts, inspiring photonic platforms for enhancing molecular dichroism and providing fundamental insight into light-matter interactions. One such insight is that even achiral nanoparticles can yield strong optical activity when they are asymmetrically illuminated from a single oblique angle instead of evenly illuminated. This effect, called extrinsic chirality, results from the overall chirality of the experimental geometry and strongly depends on the orientation of the incident light. Although extrinsic chirality has been well-characterized, an analogous effect involving linear polarization sensitivity has not yet been discussed. In this study, we investigate the differential scattering of rotationally symmetric chiral plasmonic pinwheels when asymmetrically irradiated with linearly polarized light. Despite their high rotational symmetry, we observe substantial linear differential scattering that is maintained over all pinwheel orientations. We demonstrate that this orientation-independent linear differential scattering arises from the broken mirror and rotational symmetries of our overall experimental geometry. Our results underscore the necessity of considering both the rotational symmetry of the nanoantenna and the experimental setup, including illumination direction and angle, when performing plasmon-enhanced chiroptical characterizations. Our results demonstrate spectroscopic signatures of an effect analogous to extrinsic chirality for linear polarizations.
ABSTRACT
The potential of using insect proteins to encapsulate and protect hydrophobic nutraceuticals within biopolymer nano-complexes was examined. Insect proteins were used to form nanoparticles that were uncoated or coated with chitosan. Initially, the nature of the curcumin-mealworm protein interaction was investigated. Curcumin mainly interacted with the hydrophobic core of the insect protein nanoparticles through hydrophobic forces. About one curcumin molecule bound per protein molecule in both the absence and presence of chitosan. The binding constants (K) were 1.1 × 104 M-1 and 0.7 × 104 M-1 for curcumin loaded in the uncoated and coated nanoparticles, respectively. Differential scanning calorimetry showed increased thermal stability of the proteins after interaction with curcumin or chitosan. Encapsulation efficiency of the curcumin within the biopolymer nano-complexes was 30-47% depending on the system. Transmission electron microscopy and dynamic light scattering analysis showed that the biopolymer nano-complexes were spherical and relatively small (d = 143-178 nm). FTIR suggests that curcumin was stabilized more effectively in the coated nano-complexes, due to non-covalent intermolecular interactions. Curcumin release under oral, gastric, and intestinal conditions showed that over 90% of the nutraceutical was released after exposure to model gastrointestinal conditions. The findings demonstrate the potential of using insect proteins for fabricating colloidal delivery systems for water-insoluble nutraceuticals.
