Nonlinear Chiral Metasurfaces Based on Structured van der Waals Materials.

Nonlinear chiral photonics explores the nonlinear response of chiral structures, and it offers a pathway to novel optical functionalities not accessible through linear or achiral systems. Here we present the first application of nanostructured van der Waals materials to nonlinear chiral photonics. We demonstrate the 3 orders of magnitude enhancement of the third-harmonic generation from hBN metasurfaces driven by quasi-bound states in the continuum and accompanied by strong nonlinear circular dichroism at the resonances. This novel platform for chiral metaphotonics can be employed for achieving large circular dichroism combined with high-efficiency harmonic generation in a broad frequency range.

Enhanced interactions of excitonic complexes in free-standing WS2.

Excitonic complexes, bound states of electrons and holes, provide a promising platform in monolayer transition-metal dichalcogenide (TMDC) semiconductors for investigating diverse many-body interaction phenomena. The surrounding dielectric environment has been found to strongly influence the excitonic properties of the TMDC monolayers. While the impact of different dielectric surroundings on two-dimensional semiconductor materials and their strong correlations have been well studied, the effects on exciton formation and its properties resulting from a further reduction in dielectric screening remain elusive. In this study, we examined free-standing tungsten disulfide (WS2) monolayers, where the efficient generation of higher-order correlated excitonic complexes is readily observed. This phenomenon arises from the effective mutual interactions among excitons and internal carriers, attributed to the modulated exciton dynamics generated by the further reduced dielectric screening effect in the freestanding structure. The formation efficiency of excitonic complexes is enhanced and the multiple biexciton species (five particles such as charged biexcitons and acceptor/donor-bound biexcitons) are successfully induced under low excitation intensity and moderate temperature conditions. Our findings offer valuable insights into the influence of the dielectric environment on exciton interactions and enable a productive avenue for exploring fundamental many-body interactions, providing new possibilities for dielectric engineering of atomic thin semiconductors.

Novel reducible linear L-lysine-modified copolymers as efficient nonviral vectors.

The development of biodegradable gene delivery systems with high transfection efficiencies is paramount to the clinical translation of nonviral gene carriers. Therefore, to produce a biocompatible, reducible, effective and non-toxic gene delivery system, we have designed and synthesized novel reducible linear L-lysine modified copolymers (LLCs) as an alternative to high molecular weight poly(L-lysine) (PLL). The molecular weight (MW) of the copolymers was found to be approximately 3.2kDa with a polydispersity index of approximately 1.2. Gel retardation assays showed complete condensation of DNA at N/P ratios greater than 20/1 and exceptional LLC/pDNA polyplex stability during incubation with DNase I. Release of DNA from the polyplexes only occurred in the presence of the reducing agent dithiothreitol (DTT). The particle sizes of LLC/pDNA polyplexes were found to be between 100 and 231 nm with surface charges of 0.8-17 mV respectively. The transfection efficiencies of the polyplexes as determined with a luciferase assay showed that LLC polyplexes produced five times higher transfection efficiencies in HDF cells, three times higher transfection efficiencies in MCF-7 cells, and four times higher transfection efficiencies in MA cells as compared to the optimal PLL control. The LLC/pDNA polyplexes showed significantly lower cytotoxicities as compared to the control in HDF, MCF-7 and MA cells at certain N/P ratios. Therefore, these results suggest that these novel LLCs are efficient, reducible and biocompatible polymers for nonviral gene delivery.