Probing Bidirectional Plasmon-Plasmon Coupling-Induced Hot Charge Carriers in Dual Plasmonic Au/CuS Nanocrystals.

Heterostructured Au/CuS nanocrystals (NCs) exhibit localized surface plasmon resonance (LSPR) centered at two different wavelengths (551 and 1051 nm) with a slight broadening compared to respective homostructured Au and CuS NC spectra. By applying ultrafast transient absorption spectroscopy we show that a resonant excitation at the respective LSPR maxima of the heterostructured Au/CuS NCs leads to the characteristic hot charge carrier relaxation associated with both LSPRs in both cases. A comparison of the dual plasmonic heterostructure with a colloidal mixture of homostructured Au and CuS NCs shows that the coupled dual plasmonic interaction is only active in the heterostructured Au/CuS NCs. By investigating the charge carrier dynamics of the process, we find that the observed interaction is faster than phononic or thermal processes (< 100 fs). The relaxation of the generated hot charge carriers is faster for heterostructured nanocrystals and indicates that the interaction occurs as an energy transfer (we propose Landau damping or interaction via LSPR beat oscillations as possible mechanisms) or charge carrier transfer between both materials. Our results strengthen the understanding of multiplasmonic interactions in heterostructured Au/CuS NCs and will significantly advance applications where these interactions are essential, such as catalytic reactions.

Copper-Containing Artificial Polyenzymes as a Clickase for Bioorthogonal Chemistry.

Artificial polyenzymes (ArPoly) are tailored combinations of universal protein scaffolds and polymers newly proposed as promising alternatives to natural enzymes to expand the biocatalyst toolbox. The concept of ArPoly has been continuously extended to metal-containing ArPoly to overcome the drawbacks faced by conventional artificial metalloenzymes. Herein, we present a sustainable route to synthesize a novel water-soluble metalloenzyme for copper-catalyzed azide-alkyne cycloadditions in water with remarkable selectivity. In this case, synthetic l-proline monomers were polymerized onto bovine serum albumen in an aqueous medium via copper-mediated "grafting-from" atom-transfer radical polymerization, resulting in protein-polymer-copper conjugates named ArPolyclickase. The copper in ArPolyclickase plays pivotal bifunctional roles, not only as the catalyst for polymerization but also as the coordinated active site for alkyne-azide click catalysis. ArPolyclickase showcases high efficiency, substrate generality, regioselectivity, and ease of product separation for "click chemistry" in water. Notably, ArPolyclickase displays good biocompatibility without imposing copper toxicity on living cells, which offers the prospect for the upcoming bioorthogonal chemistry.

Temperature-Sensitive Localized Surface Plasmon Resonance of α-NiS Nanoparticles.

The presented work shows a synthesis route to obtain nanoparticles of the hexagonal α-NiS phase and core-shell particles where the same material is grown onto previously prepared Au seeds. In the bulk, this nickel sulfide phase is known to exhibit a metal-insulator type phase transition (MIT) at 265 K which drastically alters its electrical conductivity. Since the produced nanoparticles show a localized surface plasmon resonance (LSPR) in the visible range of the electromagnetic spectrum, the development of their optical properties depending on the temperature is investigated. This is the first time an LSPR of colloidal nanoparticles is monitored regarding such a transition. The results of UV-vis absorbance measurements show that the LSPR of the particles can be strongly and reversibly tuned by varying the temperature. It can be switched off by cooling the nanoparticles and switched on again by reheating them above the transition temperature. Additional to the phase transition, the temperature-dependent magnetic susceptibility of α-NiS and Au-NiS nanoparticles suggests the presence of different amounts of uncompensated magnetic moments in these compounds that possibly affect the optical properties and may cause the observed quantitative differences in the LSPR response of these materials.