Symmetry-Guided Engineering of Polarization by 2D Moiré Metasurfaces.

Cylindrical vector (CV) beams exhibit spatially varying polarization important in optical communication, super-resolution microscopy, and high-throughput information processing. Compared to radially or azimuthally polarized CV beams that are cylindrically symmetric, hybrid-electric (HE) beams offer increased optical tunability because of their polygonally symmetric polarizations. However, efforts to generate and isolate HE beams have relied on bulky optical assemblies or devices with complex and stringent fabrication requirements. Here, we report a moiré-based metasurface approach to engineer HE polarization states with high degrees of rotational symmetry. Importantly, polarization symmetries can be tailored based only on the reciprocal lattice of the metasurface and not the real-space patterns. Our modular method outlines important design principles for shaping light at the nanoscale.

Spiky Gold Nanoparticles, a Nanoscale Approach to Enhanced Ex Vivo T-Cell Activation.

While existing synthetic technologies for ex vivo T-cell activation face challenges like suboptimal expansion rates and low effectiveness, artificial antigen-presenting cells (aAPCs) hold great promise for enhanced T-cell based therapies. In particular, gold nanoparticles (AuNPs), known for their biocompatibility, ease of synthesis, and versatile surface chemistry, are strong candidates for use as nanoscale aAPCs. In this study, we developed spiky AuNPs with branched geometries to present activating ligands to primary human T-cells. The special structure of spiky AuNPs enhances biomolecule loading capacity and significantly improves T-cell activation through multivalent binding of costimulatory ligands and receptors. Our spiky AuNPs outperform existing systems including Dynabeads and soluble activators by promoting greater polyclonal expansion of T-cells, boosting sustained cytokine production, and generating highly functional T-cells with reduced exhaustion. In addition, spiky AuNPs effectively activate and expand CD19 CAR-T cells while demonstrating increased in vitro cytotoxicity against target cells using fewer effector cells than Dynabeads. This study underscores the potential of spiky AuNPs as a powerful tool, bringing new opportunities to adoptive cell therapy applications.

Room-temperature strong coupling between CdSe nanoplatelets and a metal-DBR Fabry-Pérot cavity.

The generation of exciton-polaritons through strong light-matter interactions represents an emerging platform for exploring quantum phenomena. A significant challenge in colloidal nanocrystal-based polaritonic systems is the ability to operate at room temperature with high fidelity. Here, we demonstrate the generation of room-temperature exciton-polaritons through the coupling of CdSe nanoplatelets (NPLs) with a Fabry-Pérot optical cavity, leading to a Rabi splitting of 74.6 meV. Quantum-classical calculations accurately predict the complex dynamics between the many dark state excitons and the optically allowed polariton states, including the experimentally observed lower polariton photoluminescence emission, and the concentration of photoluminescence intensities at higher in-plane momenta as the cavity becomes more negatively detuned. The Rabi splitting measured at 5 K is similar to that at 300 K, validating the feasibility of the temperature-independent operation of this polaritonic system. Overall, these results show that CdSe NPLs are an excellent material to facilitate the development of room-temperature quantum technologies.

Electrochemical Control of Strong Coupling of CdSe Exciton-Polaritons in Plasmonic Cavities.

This work reports in situ (active) electrochemical control over the coupling strength between semiconducting nanoplatelets and a plasmonic cavity. We found that by applying a reductive bias to an Al nanoparticle lattice working electrode the number of CdSe nanoplatelet emitters that can couple to the cavity is decreased. Strong coupling can be reversibly recovered by discharging the lattice at oxidative potentials relative to the conduction band edge reduction potential of the emitters. By correlating the number of electrons added or removed with the measured coupling strength, we identified that loss and recovery of strong coupling are likely hindered by side processes that trap and/or inhibit electrons from populating the nanoplatelet conduction band. These findings demonstrate tunable, external control of strong coupling and offer prospects to tune selectivity in chemical reactions.

Room-Temperature Polariton Lasing from CdSe Core-Only Nanoplatelets.

This paper reports how CdSe core-only nanoplatelets (NPLs) coupled with plasmonic Al nanoparticle lattices can exhibit exciton-polariton lasing. By improving a procedure to synthesize monodisperse 4-monolayer CdSe NPLs, we could resolve polariton decay dynamics and pathways. Experiment and theory confirmed that the system is in the strong coupling regime based on anticrossings in the dispersion diagrams and magnitude of the Rabi-splitting values. Notably, polariton lasing is observed only for cavity lattice periodicities that exhibit specific dispersive characteristics that enable polariton accumulation. The threshold of polariton lasing is 25-fold lower than the reported photon lasing values from CdSe NPLs in similar cavity designs. This open-cavity platform offers a simple approach to control exciton polaritons anticipated to benefit quantum information processing, optoelectronics, and chemical reactions.

Reducing Effective System Dimensionality with Long-Range Collective Dipole-Dipole Interactions.

Dimensionality plays a crucial role in long-range dipole-dipole interactions (DDIs). We demonstrate that a resonant nanophotonic structure modifies the apparent dimensionality in an interacting ensemble of emitters, as revealed by population decay dynamics. Our measurements on a dense ensemble of interacting quantum emitters in a resonant nanophotonic structure with long-range DDIs reveal an effective dimensionality reduction to d[over ¯]=2.20(12), despite the emitters being distributed in 3D. This contrasts with the homogeneous environment, where the apparent dimension is d[over ¯]=3.00. Our work presents a promising avenue to manipulate dimensionality in an ensemble of interacting emitters.

Liquid lasing from solutions of ligand-engineered semiconductor nanocrystals.

Semiconductor nanocrystals (NCs) can function as efficient gain materials with chemical versatility because of their surface ligands. Because the properties of NCs in solution are sensitive to ligand-environment interactions, local chemical changes can result in changes in the optical response. However, amplification of the optical response is technically challenging because of colloidal instability at NC concentrations needed for sufficient gain to overcome losses. This paper demonstrates liquid lasing from plasmonic lattice cavities integrated with ligand-engineered CdZnS/ZnS NCs dispersed in toluene and water. By taking advantage of calcium ion-induced aggregation of NCs in aqueous solutions, we show how lasing threshold can be used as a transduction signal for ion detection. Our work highlights how NC solutions and plasmonic lattices with open cavity architectures can serve as a biosensing platform for lab-on-chip devices.

Nanoparticle Anisotropy Increases Targeting Interactions on Live-Cell Membranes.

This paper describes how branch lengths of anisotropic nanoparticles can affect interactions between grafted ligands and cell-membrane receptors. Using live-cell, single-particle tracking, we found that DNA aptamer-gold nanostar nanoconstructs with longer branches showed improved binding efficacy to human epidermal growth factor receptor 2 (HER2) on cancer cell membranes. Inhibiting nanoconstruct-HER2 binding promoted nonspecific interactions, which increased the rotational speed of long-branched nanoconstructs but did not affect that of short-branched constructs. Bivariate analysis of the rotational and translational dynamics showed that longer branch lengths increased the ratio of targeting to nontargeting interactions. We also found that longer branches increased the nanoconstruct-cell interaction times before internalization and decreased intracellular trafficking velocities. Differences in binding efficacy revealed by single-particle dynamics can be attributed to the distinct protein corona distributions on short- and long-branched nanoconstructs, as validated by transmission electron microscopy. Minimal protein adsorption at the high positive curvature tips of long-branched nanoconstructs facilitated binding of DNA aptamer ligands to HER2. Our study reveals the significance of nanoparticle branch length in regulating local chemical environment and interactions with live cells at the single-particle level.

Ligand Separation on Nanoconstructs Affects Targeting Selectivity to Protein Dimers on Cell Membranes.

This work demonstrates that targeting ligand density on nanoparticles can affect interactions between the nanoconstructs and cell membrane receptors. We discovered that when the separation between covalently grafted DNA aptamers on gold nanostars was comparable to the distance between binding sites on a receptor dimer (matched density; MD), nanoconstructs exhibited a higher selectivity for binding to the dimeric form of the protein. Single-particle dynamics of MD nanoconstructs showed slower rotational rates and larger translational footprints on cancer cells expressing more dimeric forms of receptors (dimer+) compared with cells having more monomeric forms (dimer-). In contrast, nanoconstructs with either increased (nonmatched density; NDlow) or decreased ligand spacing (NDhigh) had minimal changes in dynamics on either dimer+ or dimer- cells. Real-time, single-particle analyses can reveal the importance of nanoconstruct ligand density for the selective targeting of membrane receptors in live cells.