The mimicry of the underwater mussel adhesion strategy for the development of innovative and versatile dip-coating technologies is exemplified by the introduction of polydopamine (PDA) as a highly adhesive biomaterial for surface functionalization and coating, incorporating the key catechol and amine functionalities of byssal proteins and produced by the oxidative polymerization of dopamine under alkaline conditions.¹ Despite unabated interest and an ever expanding use for various surface functionalization applications, PDA-based technologies suffer from some limitations that have prompted intense studies toward novel mussel-inspired surface chemistry.² They are related to: a) the intrinsic toxicity of the precursor dopamine; b) the use of an alkaline pH; c) the need for high dopamine concentrations (10 mM), and d) difficulties to control film thickness and properties due to the slow kinetics of autoxidation.³ A possible means of bypassing limitations inherent to the autoxidation protocol relies on use of enzymes like tyrosinase, which can be exploited to modulate catecholamine oxidation at pH values around neutrality, and were thus proposed as a practical and convenient ways of obtaining nanometer-thick and uniform films with diverse functionalities.^4,5

Herein, we report the tyrosinase-catalyzed polymerization of tyramine as a mild, versatile and efficient procedure for the development of adhesive PDA-type films (ψ-PDA) that could be obtained at neutral pH (i.e. 6.8) and at much lower substrate concentration (e.g. 1 mM) compared to the standard autoxidative PDA coating protocol (typically 10 mM of dopamine).⁶ ψ-PDA films display structural and physicochemical properties similar to those of PDA films and similar, or even better, antioxidant activity. Finally, the possibility of using tyramine together with confined tyrosinase to achieve site-specific polymerization and/or film deposition is assessed against dopamine. The rationale of the experiments is to prevent the uncontrolled autoxidative deposition of black precipitate, a major drawback of PDA coating technology which may interfere with specific applications. ψ-PDA deposition by tyrosinase-catalyzed tyramine oxidation is thus proposed as a controllable and low-waste technology for selective surface functionalization and coating or for clean eumelanin particle production.

References

[1] Ryu J.H.; Messersnith P.B.; Lee H. ACS Appl. Mater. Interfaces, 2018, 10, 7523-7540.

[2] Lee B.P.; Messersmith P.B.; Israelachvili J.N.; Waite J.H. Annu. Rev. Mater. Res., 41 (2011), 99-132.

[3] Ball V.; Del Frari D.; Toniazzo V.; Runch D. J. Colloid Interface Sci., 386 (2012), 366-372.

[4] Kim J. Y.; Kim, W.I.; Youn W.; Seo J.; Kim B.J.; Lee J.K.; Choi I.S. Nanoscale, 10 (2018), 13351-13355.

[5] Zhong Q.Z.; Richardson J.J.; Li S.; Zhang W.; Ju Y.; Li J.; Pan S.; Chen J.; Caruso F. Angew. Chem. Int. Ed.2019 10.1002/anie.201913509.

[6] Alfieri M.L.; Panzella L.; Youri A.; Napolitano A.; Ball V.; d’Ischia M. Int. J. Mol. Sci. 2020, 21, 4873.

Nanosized coatings of ZrO₂ were deposited on silicon substrates using sol-gel and spin-coating techniques. The precursor solutions were prepared from ZrOCl₂.8H₂O with the addition of different percentage (0.5-5%) of rare earth Gd³⁺ ions as dopant. The thin films were homogeneous, with average thickness of 115 nm and refractive index (n) of 1.83. The X-ray diffraction analysis (XRD) revealed the presence of a varying mixture of monoclinic and tetragonal ZrO₂ polycrystalline phases, depending on the dopant concentration, all of which with nanosized crystallites. Scanning electron microscopy (SEM) as well as atomic force microscopy (AFM) methods were deployed to investigate the surface morphology and roughness of the thin films, respectively. They revealed a smooth, well uniform and crack-free surface with average roughness of 0.5 nm. It was established that the dopant concentration affects the photoluminescence (PL) properties of the samples. The undoped films exhibited broad violet PL emission, while the addition of Gd³⁺ ions resulted in new narrow bands in both UV and visible light regions, characteristic of the rare earth metal. These exact emissions can find useful applications in medical lamps or as red phosphors.

Acknowledgement

Research equipment of distributed research infrastructure INFRAMAT (part of Bulgarian National roadmap for research infrastructures) supported by Bulgarian Ministry of Education and Science under contract D01-284/17.12.2019 was used in this investigation.

The interaction of quantum emitters with photonic antennas created by nanoscale structures may lead to several interesting phenomena with many important potential applications in current and future technology. There are two distinct regimes of light-matter interaction between a quantum emitter and its modified photonic environment, the weak coupling regime and the strong coupling regime, where the quantum emitter has completely different spontaneous emission response. In the weak coupling regime, an initially excited quantum emitter shows an exponential spontaneous emission dynamics (Markovian response), but the spontaneous decay rate can be markedly different from free-space vacuum, and can be either enhanced or suppressed due to the Purcell effect. In the strong coupling regime, there is a coherent exchange of energy between the quantum emitter and its modified nanophotonic environment, which manifest itself in non-exponential spontaneous emission dynamics (non-Markovian response). We investigate the spontaneous emission dynamics of a two-level quantum emitter in proximity to an atomically thin tungsten diselenide (WSe₂) layer at various distances of the emitter from the layer and various free-space decay rates of the emitter. Depending on the distance and the decay rate value, our studies cover the range of weak to strong coupling regime of the light-matter interaction between the quantum emitter and the electromagnetic continuum modified by the WSe₂ layer. We find that the decay dynamics is Markovian under weak coupling conditions, and it becomes strongly non-Markovian, characterized by oscillatory population emitter dynamics, on the top of the overall population decay, as well as population trapping in the emitter. Besides population evolution, we also discuss the non-Markovian spontaneous emission dynamics using a widely used non-Markovianity measure.

Palladium nanoparticles (PdNPs) are one of the most attractive metal nanomaterials because of their excellent physicochemical properties. PdNPs have been studied for many different applications such as Suzuki cross-coupling reactions, hydrogen purification/storage/sensing, CO oxidation, fuel cells, prodrug activation, and antimicrobial therapy. Recently, PdNPs have been explored as photo-absorbers for photothermal therapy and photoacoustic imaging in the treatment of cancer disease. Herein, we reported a scalable, efficient, green, and one-step method to synthesis PdNPs. The chitosan polymer was used as a stabilizer and vitamin C was used as a reducing agent. Interestingly, the reaction temperature can be adjusted to the size of PdNPs. When the reaction temperature was increased from 25^oC to 95^oC, the morphology of resulted PdNPs changed from flower shape to spherical shape and their nanoparticles sizes decreased from 64 nm to 29 nm. The characterization revealed that the obtained PdNPs were relatively uniform in size, shape and stable in aqueous solution.

Lead halide perovskite has attracted great attentions for the applications in perovskite solar cells and LED devices and it also has the great potential in photocatalytic applications due to high extinction coefficients, and long electron-hole diffusion lengths. However, the rapid recombination rate of photogenerated electron-hole pairs still limits the photocatalytic activity. Herein, a novel CsPbBr₃ quantum dots/S doping g-C₃N₄ ultrathin nanosheet 0D/2D heterojunctions photocatalyst are prepared by loading perovskite quantum dots onto ultrathin doped g-C₃N₄. The strategy of S element doping improved the properties of in g-C₃N₄ ultra-thin structure providing more adsorption and reaction sites for photocatalytic activity. And the type II band alignment structure of CsPbBr₃ / g-C₃N₄ heterostructure effectively improved the separation and transmission of photogenerated carriers and inhibit the recombination of photogenerated carriers, thus improving the photocatalytic CO₂ reduction performance. This study provides a facile and effective method for synthesis of halide perovskite based photocatalysts, which holds the potential for further application in environmental and energy field.