Synthesis of double perovskite and quadruple perovskite nanocrystals through post-synthetic transformation reactions

Lead-free halide perovskite nanocrystals (NCs) represent a group of emerging materials which hold promise for various optical and optoelectronic applications. Exploring facile synthetic methods for such materials has been of great interest to not only fundamental research but also technological implementations. Herein, we report a fundamentally new method to access lead-free Bi-based double perovskite (DP) and quadruple perovskite (or layered double perovskite, LDP) NCs based on a post-synthetic transformation reaction of Cs₃BiX₆ (X = Cl, Br) zero-dimensional (0D) perovskite NCs under mild conditions. The produced NCs show good particle uniformity, high crystallinity, and comparable optical properties to the directly synthesized NCs. The relatively slow kinetics and stop-on-demand feature of the transformation reaction allow real-time composition–structure–property investigations of the reaction, thus elucidating a cation-alloyed intermediate-assisted transformation mechanism. Our study presented here demonstrates for the first time that post-synthetic transformation of 0D perovskite NCs can serve as a new route towards the synthesis of high-quality lead-free perovskite NCs, and provides valuable insights into the crystal structures, excitonic properties and their relationships of perovskite NCs.

Lead-free perovskite nanocrystals are synthesized by post-synthetic transformation reactions. The post-synthetic transformations show the structural flexibility of zero-dimensional perovskite nanocrystal materials.     

Facilely prepared aggregation-induced emission (AIE) nanocrystals with deep-red emission for super-resolution imaging

Organic nanocrystals (NCs) with high brightness are highly desirable for biological imaging. However, the preparation of NCs by a facile and fast method is still challenging. Herein, an aggregation-induced emission (AIE) luminogen of 4,4′-(5,6-difluorobenzo[c][1,2,5]thiadiazole-4,7-diyl)bis(N,N-bis(4-methoxyphenyl)aniline) (DTPA-BT-F) in the deep-red region is designed with intensive crystalline features to obtain NCs by kinetically controlled nanoprecipitation. The prepared AIE NCs with high brightness and good photo-stability are then applied in super-resolution imaging via stimulated emission depletion (STED) nanoscopy. As observed, the nanostructures in lysosomes of both fixed and live cells are well visualized with superior lateral resolutions under STED nanoscopy (full width at half maximum values, 107 and 108 nm) in contrast to that in confocal imaging (548 and 740 nm). More importantly, dynamic monitoring and long-term tracking of lysosomal movements in live HeLa cells, such as lysosomal contact, can also be carried out by using DTPA-BT-F NCs at a superior resolution. To the best of our knowledge, this is the first case of AIE NCs prepared by nanoprecipitation for STED nanoscopy, thus providing a new strategy to develop high performance imaging agents for super-resolution imaging.

AIE nanocrystals with high brightness in the deep-red region were facilely prepared by kinetically controlled nanoprecipitation. These nanocrystals were then applied in super-resolution cellular imaging via STED nanoscopy.     

In-vitro cytotoxicity evaluation of surface design luminescent lanthanide core/shell nanocrystals

Lanthanide nanocrystals (NCs) are the most promising luminescent materials for bioapplications, but their use is hindered by difficulties in obtaining biocompatible and photoluminescence lanthanide NCs. To solve this problem, a simple and versatile strategy was developed for improving the luminescence efficiency with the hydrophilicity of the lanthanide NCs. In this study, the effects of shell formation on structural, morphological, and optical properties (optical absorption, band-gap energy, excitation, emission, and luminescent decay time) were evaluated. To improve the luminescence efficiency and aqueous dispersion, luminescent core-NCs were encapsulated with inert NaGdF₄ and amorphous silica layers. These surface coating layers significantly improved the luminescence efficiency and dispersion of the core/shell NCs in which the silica surface provides a negatively charged surface to the NCs at physiological pH. Optical properties of these NCs strongly depend on the external change of NCs, demonstrating the impact of coating in improving the luminescence efficiency. The outcomes can be ascribed to the development of surface chemical bonds between core/shell and noncrystalline SiO₂ shell via GdOSi bridges, activating the ‘dormant’ Ce³⁺ and Tb³⁺ ions on the surface of NCs. An intensive emission and good hydrophilic property from the active functional groups in solutions show a great potential for applications such as multi-analyte fluorescent biolabeling, optical biosensing, staining, display, and other optical technologies. The core/shell/SiO₂ NCs showed higher nontoxicity and biocompatibility with respect to the core NCs because of biocompatible silica surface modification, facilitating entry into the living cells. Therefore, this developed synthesis approach might advance the field of biomolecule-based nanotechnology in near future.     

Snapshots of key intermediates unveiling the growth from silver ions to Ag70 nanoclusters

Nanoclusters (NCs) are considered as initial states of condensed matter, and unveiling their formation mechanism is of great importance for directional synthesis of nanomaterials. Here, we initiate the reaction of Ag(i) ions under weak reducing conditions. The prolonged reaction period provides a unique opportunity for revealing the five stages of the growth mechanism of 20-electron superatomic Ag₇₀ NCs by a time-dependent mass technique, that is, aggregate (I) → reduction (II) → decomposition and recombination (III) → fusion (IV) → surface recombination and motif enrichment (V), which is different from the formation process applicable to the gold clusters. More importantly, the key intermediates, Ag₁₄ without free electrons (0e) in the first (stage I) and Ag₂₄ (4e) in the second (stage II), were crystallized and structurally resolved, and the later transformation rate towards Ag₇₀ was further controlled by modulating solvents for easy identification of more intermediates. In a word, we establish a reasonable path of gradual expansion in size and electrons from Ag(i) ions to medium-sized 20e Ag₇₀. This work provides new insights into the formation and evolution of silver NCs, and unveils the corresponding optical properties along with the process.

The bottom-up synthesis of “medium-sized” Ag₇₀ (20e) was controlled and tracked, and then revealed. The crystallized key intermediates of Ag₁₄ (0e) and Ag₂₄ (4e) present the growth snapshots of silver nanoclusters.     

Growth of Au nanoparticles on phosphorylated zein protein particles for use as biomimetic catalysts for cascade reactions at the oil–water interface

Chemo-enzymatic cascade processes are invaluable due to their ability to rapidly construct high-value products from available feedstock chemicals in a one-pot relay manner. However, they have proven to be challenging because of the mutual inactivation of both catalysts. A conceptually novel strategy based on Pickering interfacial catalysis (PIC) is proposed here to address this challenge. This study aimed to construct a protein-stabilized Pickering system for biphasic cascade catalysis, enabled by phosphorylated zein nanoparticles (ZCPOPs) immobilized in gold nanoparticles (Au NCs). Ultra-small Au NCs, 1–2 nm in diameter, were integrated into ZCPOPs at room temperature. Then, the as-synthesized ZCPOPs–Au NCs were used to stabilize the oil-in-water (o/w) Pickering emulsion. Besides their excellent catalytic activity and recycling ability in a variety of oil phases, ZCPOPs–Au NCs possess unpredictable catalytic activity and exhibit mimicking properties of horseradish peroxidase. Particularly, the cascade reaction is well achieved using a metal catalyst and a biocatalyst at the oil–water interface. The result showed that such a combination of chemo- and biocatalysis improved the catalytic yield more than two times compared with that of sole metal catalysis. This study opened a new avenue to design nanomaterials using the combination of chemo- and biocatalysis in a Pickering emulsion system for multistep syntheses.

A robust chemo- and biocatalytic cascade PIC with a recovery catalyst and a separation product was developed. The results groundbreakingly highlighted the preliminary applications of artificial enzymes and bio-enzymes in a one-pot cascade PIC.     

Highly Luminescent Heterostructured Copper‐Doped Zinc Sulfide Nanocrystals for Application in Cancer Cell Labeling

The structural characteristics of the seed‐mediated synthesis of heterostructured CuS–ZnS nanocrystals (NCs) and Cu‐doped ZnS (ZnS:Cu) NCs synthesized by two different protocols are compared and analyzed. At high Cu dopant concentrations, segregated subclusters of ZnS and CuS are observed. The photoluminescence quantum yield of ZnS:Cu NCs is about 50–80 %; a value much higher than that of ZnS NCs (6 %). Finally, these NCs are coated with a thin silica shell by using (3‐mercaptopropyl)triethoxysilane in a reverse microemulsion to make them water soluble. Cytotoxicity experiments show that these silica‐coated NCs have greatly reduced toxicity on both cancerous HeLa and noncancerous Chinese hamster ovary cells. The labeling of cancerous HeLa cells is also demonstrated.     

Increasing protein stability by engineering the n → π* interaction at the β-turn

Abundant n → π* interactions between adjacent backbone carbonyl groups, identified by statistical analysis of protein structures, are predicted to play an important role in dictating the structure of proteins. However, experimentally testing the prediction in proteins has been challenging due to the weak nature of this interaction. By amplifying the strength of the n → π* interaction via amino acid substitution and thioamide incorporation at a solvent exposed β-turn within the GB1 proteins and Pin 1 WW domain, we demonstrate that an n → π* interaction increases the structural stability of proteins by restricting the ϕ torsion angle. Our results also suggest that amino acid side-chain identity and its rotameric conformation play an important and decisive role in dictating the strength of an n → π* interaction.

Amino acid residues adopt a right-handed α-helical conformation with increasing strength of the n → π* interaction. We also demonstrate a direct consequence of n → π* interactions on enhancing the structural stability of proteins.     

Aggregation-free and high stability core–shell polymer nanoparticles with high fullerene loading capacity,variable fullerene type,and compatibility towards biological conditions

Fullerenes have unique structural and electronic properties that make them attractive candidates for diagnostic, therapeutic, and theranostic applications. However, their poor water solubility remains a limiting factor in realizing their full biomedical potential. Here, we present an approach based on a combination of supramolecular and covalent chemistry to access well-defined fullerene-containing polymer nanoparticles with a core–shell structure. In this approach, solvophobic forces and aromatic interactions first come into play to afford a micellar structure with a poly(ethylene glycol) shell and a corannulene-based fullerene-rich core. Covalent stabilization of the supramolecular assembly then affords core-crosslinked polymer nanoparticles. The shell makes these nanoparticles biocompatible and allows them to be dried to a solid and redispersed in water without inducing interparticle aggregation. The core allows a high content of different fullerene types to be encapsulated. Finally, covalent stabilization endows nanostructures with stability against changing environmental conditions.

A polymer nanoparticle approach to biorelevant and robust fullerene nanoparticles is presented.     

Synthesis and characterization of high-quality ZnS, ZnS:Mn2+, and ZnS:Mn2+/ZnS (core/shell) luminescent nanocrystals

High-quality ZnS, ZnS:Mn2+, and ZnS:Mn2+/ZnS (core/shell) nanocrystals (NCs) were synthesized via a high-boiling solvent process and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectra. The monodisperse ZnS NCs (size = 8 nm), which self-assembled into several micrometer-sized domains, were achieved by adopting poly(ethylene glycol) (PEG) in the reaction process (without using a size-selection process). The obtained ZnS:Mn2+ and ZnS:Mn2+/ZnS core/shell NCs are highly crystalline and quasimonodisperse with an average particle size of 6.1 and 8.4 nm, respectively. All of the as-formed NCs can be well dispersed in hexane to form stable and clear colloidal solutions, which show strong visible emission (blue for ZnS and red-orange for ZnS:Mn2+ and ZnS:Mn2+/ZnS) under UV excitation. The growth of a ZnS shell on ZnS:Mn2+ NCs, that is, the formation of ZnS:Mn2+/ZnS core/shell NCs, resulted in a 30% enhancement in the PL intensity with respect to that of bare ZnS:Mn2+ NCs due to the elimination of the surface defects.     

Shaping non-noble metal nanocrystals via colloidal chemistry

Non-noble metal nanocrystals with well-defined shapes have been attracting increasingly more attention in the last decade as potential alternatives to noble metals, by virtue of their earth abundance combined with intriguing physical and chemical properties relevant for both fundamental studies and technological applications. Nevertheless, their synthesis is still primitive when compared to noble metals. In this contribution, we focus on third row transition metals Mn, Fe, Co, Ni and Cu that are recently gaining interest because of their catalytic properties. Along with providing an overview on the state-of-the-art, we discuss current synthetic strategies and challenges. Finally, we propose future directions to advance the synthetic development of shape-controlled non-noble metal nanocrystals in the upcoming years.

This minireview describes the state-of-the-art of shape-controlled nanocrystals of third raw transition metals and discusses future directions to advance their synthetic development, which is important for many applications.     

Self-trapped exciton emission and piezochromism in conventional 3D lead bromide perovskite nanocrystals under high pressure

Developing single-component materials with bright-white emission is required for energy-saving applications. Self-trapped exciton (STE) emission is regarded as a robust way to generate intrinsic white light in halide perovskites. However, STE emission usually occurs in low-dimensional perovskites whereby a lower level of structural connectivity reduces the conductivity. Enabling conventional three-dimensional (3D) perovskites to produce STEs to elicit competitive white emission is challenging. Here, we first achieved STEs-related emission of white light with outstanding chromaticity coordinates of (0.330, 0.325) in typical 3D perovskites, Mn-doped CsPbBr₃ nanocrystals (NCs), through pressure processing. Remarkable piezochromism from red to blue was also realized in compressed Mn-doped CsPbBr₃ NCs. Doping engineering by size-mismatched Mn dopants could give rise to the formation of localized carriers. Hence, high pressure could further induce octahedra distortion to accommodate the STEs, which has never occurred in pure 3D perovskites. Our study not only offers deep insights into the photophysical nature of perovskites, it also provides a promising strategy towards high-quality, stable white-light emission.

We first achieved self-trapped exciton emission with outstanding white-light chromaticity coordinates of (0.330, 0.325) in conventional 3D halide perovskite nanocrystals through pressure engineering.     

Total synthesis,isolation, surfactant properties,and biological evaluation of ananatosides and related macrodilactone-containing rhamnolipids

Rhamnolipids are a specific class of microbial surfactants, which hold great biotechnological and therapeutic potential. However, their exploitation at the industrial level is hampered because they are mainly produced by the opportunistic pathogen Pseudomonas aeruginosa. The non-human pathogenic bacterium Pantoea ananatis is an alternative producer of rhamnolipid-like metabolites containing glucose instead of rhamnose residues. Herein, we present the isolation, structural characterization, and total synthesis of ananatoside A, a 15-membered macrodilactone-containing glucolipid, and ananatoside B, its open-chain congener, from organic extracts of P. ananatis. Ananatoside A was synthesized through three alternative pathways involving either an intramolecular glycosylation, a chemical macrolactonization or a direct enzymatic transformation from ananatoside B. A series of diasteroisomerically pure (1→2), (1→3), and (1→4)-macrolactonized rhamnolipids were also synthesized through intramolecular glycosylation and their anomeric configurations as well as ring conformations were solved using molecular modeling in tandem with NMR studies. We show that ananatoside B is a more potent surfactant than its macrolide counterpart. We present evidence that macrolactonization of rhamnolipids enhances their cytotoxic and hemolytic potential, pointing towards a mechanism involving the formation of pores into the lipidic cell membrane. Lastly, we demonstrate that ananatoside A and ananatoside B as well as synthetic macrolactonized rhamnolipids can be perceived by the plant immune system, and that this sensing is more pronounced for a macrolide featuring a rhamnose moiety in its native ¹C₄ conformation. Altogether our results suggest that macrolactonization of glycolipids can dramatically interfere with their surfactant properties and biological activity.

We show that macrolactonization of gluco- and rhamnolipids dramatically interfere with their surfactant properties and biological activity.     

Engineering multifunctional metal/protein hybrid nanomaterials as tools for therapeutic intervention and high-sensitivity detection

Protein-based hybrid nanomaterials have recently emerged as promising platforms to fabricate tailored multifunctional biologics for biotechnological and biomedical applications. This work shows a simple, modular, and versatile strategy to design custom protein hybrid nanomaterials. This approach combines for the first time the engineering of a therapeutic protein module with the engineering of a nanomaterial-stabilizing module within the same molecule, resulting in a multifunctional hybrid nanocomposite unachievable through conventional material synthesis methodologies. As the first proof of concept, a multifunctional system was designed ad hoc for the therapeutic intervention and monitoring of myocardial fibrosis. This hybrid nanomaterial combines a designed Hsp90 inhibitory domain and a metal nanocluster stabilizing module resulting in a biologic drug labelled with a metal nanocluster. The engineered nanomaterial actively reduced myocardial fibrosis and heart hypertrophy in an animal model of cardiac remodeling. In addition to the therapeutic effect, the metal nanocluster allowed for in vitro, ex vivo, and in vivo detection and imaging of the fibrotic disease under study. This study evidences the potential of combining protein engineering and protein-directed nanomaterial engineering approaches to design custom nanomaterials as theranostic tools, opening up unexplored routes to date for the next generation of advanced nanomaterials in medicine.

Engineering protein-based hybrids by combining protein engineering and nanotechnology: a protein-nanocluster hybrid for theranostic use in myocardial fibrosis shows the potential to create tailored multifunctional biologics for biomedicine.     

Revitalizing silver nanocrystals as a redox catalyst by modifying their surface with an isocyanide-based compound

Silver is an excellent catalyst for oxidation reactions such as ethylene epoxidation, but it shows limited activity toward reduction reactions. Here we report a strategy to revitalize Ag nanocrystals as a redox catalyst for the production of an aromatic azo compound by modifying their surface with an isocyanide-based compound. We also leverage in situ fingerprint spectroscopy to acquire molecular insights into the reaction mechanism by probing the vibrational modes of all chemical species at the catalytic surface with surface-enhanced Raman spectroscopy. We establish that binding of isocyanide to Ag nanocrystals makes it possible for Ag to extract the oxygen atoms from the nitro-groups of nitroaromatics and then use these atoms to oxidize isocyanide to isocyanate. Concurrently, the coupling between two adjacent deoxygenated nitroaromatic molecules leads to the formation of an aromatic azo compound.

Ag nanocrystals can serve as a redox catalyst for the production of an aromatic azo compound when their surface is modified with an isocyanide-based molecule.     

Hybrid approach to the synthesis of highly luminescent CdTe/ZnS and CdHgTe/ZnS nanocrystals

We report the synthesis of highly luminescent CdTe/ZnS and CdHgTe/ZnS core/shell semiconductor nanocrystals (NCs). A hybrid of two synthesis routes leads to novel nanocrystal compositions and small core/shell sizes (4-5 nm) that emit in the far-red and near-infrared regions. These particles exhibit higher resistance to oxidation and photobleaching, have high quantum yields, and could be used for biological labeling and imaging.     

Metal–ligand bond strength determines the fate of organic ligands on the catalyst surface during the electrochemical CO2 reduction reaction

Colloidally synthesised nanocrystals (NCs) are increasingly utilised as catalysts to drive both thermal and electrocatalytic reactions. Their well-defined size and shape, controlled by organic ligands, are ideal to identify the parameters relevant to the activity, selectivity and stability in catalysis. However, the impact of the native surface ligands during catalysis still remains poorly understood, as does their fate. CuNCs are among the state-of-the-art catalysts for the electrochemical CO₂ reduction reaction (CO₂RR). In this work, we study CuNCs that are capped by different organic ligands to investigate their impact on the catalytic properties. We show that the latter desorb from the surface at a cathodic potential that depends on their binding strength with the metal surface, rather than their own electroreduction potentials. By monitoring the evolving surface chemistry in situ, we find that weakly bound ligands desorb very rapidly while strongly bound ligands impact the catalytic performance. This work provides a criterion to select labile ligands versus ligands that will persist on the surface, thus offering opportunity for interface design.

The metal–ligand binding strength is a key parameter in determining the role and fate of the surface ligands on nanoparticle catalysts during the electrochemical CO₂ reduction reaction.     

Self-focusing by Ostwald ripening: a strategy for layer-by-layer epitaxial growth on upconverting nanocrystals

We demonstrate a novel epitaxial layer-by-layer growth on upconverting NaYF(4) nanocrystals (NCs) utilizing Ostwald ripening dynamics tunable both in thickness and composition. Injection of small sacrificial NCs (SNCs) as shell precursors into larger core NCs results in the rapid dissolution of the SNCs and their deposition onto the larger core NCs to yield core-shell structured NCs. Exploiting this NC size dependent dissolution/growth, the shell thickness can be controlled either by manipulating the number of SNCs injected or by successive injection of SNCs. In either of these approaches, the NCs self-focus from an initial bimodal distribution to a unimodal distribution (σ <5%) of core-shell NCs. The successive injection approach facilitates layer-by-layer epitaxial growth without the need for tedious multiple reactions for generating tunable shell thickness, and does not require any control over the injection rate of the SNCs, as is the case for shell growth by precursor injection.     

Trace mild acid-catalysed Z → E isomerization of norbornene-fused stilbene derivatives: intelligent chiral molecular photoswitches with controllable self-recovery

Stilbene derivatives have long been known to undergo “acid-catalyzed” Z → E isomerization, where a strong mineral acid at high concentration is practically necessary. Such severe reaction conditions often cause undesired by-reactions and limit their potential application. Herein, we present a trace mild acid-catalyzed Z → E isomerization found with stilbene derivatives fused with a norbornene moiety. By-reactions, such as the migration of the C C double bond and electrophilic addition reactions, were completely inhibited because of the ring strain caused by the fused norbornene component. Direct photolysis of the E isomers at selected wavelengths led to the E → Z photoisomerization of these stilbene derivatives and thus constituted a unique class of molecular switches orthogonally controllable by light and acid. The catalytic amount of acid could be readily removed, and the Z → E isomerization could be controlled by turning on/off the irradiation of a photoacid, which allowed repeated isomerization in a non-invasive manner. Moreover, the Z isomer produced by photoisomerization could spontaneously self-recover to the E isomer in the presence of a catalytic amount of acid. The kinetics of Z → E isomerization were adjustable by manipulating catalytic factors and, therefore, unprecedented molecular photoswitches with adjustable self-recovery were realized.

Quantitative Z → E isomerization was catalyzed by trace mild acids to offer molecular switches orthogonally controllable by acid and light.     

胶体半导体纳米晶的能带宽调控新方法

由于量子限域效应,半导体纳米晶的能带宽随粒子大小而改变。单纯依靠改变纳米晶大小来调控能带宽将引起许多技术和应用上的不便。本文对胶体半导体纳米晶的能带宽调控新概念和新的合成途径,包括近年来发展起来的通过采用合金纳米晶、反转Type－I及Type－II核/壳结构等进行了综述,并对各种途径的优缺点进行了描述。     

Synthesis and green up-conversion fluorescence of colloidal La0.78Yb0.20Er0.02F3/SiO2 core/shell nanocrystals

Water-soluble PVP-stabilized hexagonal-phase La_0.78Yb_0.20Er_0.02F₃ nanocrystals (NCs) were synthesized by hydrothermal method. The NCs were coated with a very thin silica shell, and amino groups were introduced to the surface of silica shells by copolymerization of 3-aminopropyl(triethoxy)silane. The core/shell NCs can be dispersed in ethanol and water to form stable colloidal solution. The transmission electron microscopy (TEM), selected area electron diffraction (SAED), powder X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR) were used to characterize the core/shell materials. In addition, the green up-conversion fluorescence mechanism of La_0.78Yb_0.20Er_0.02F₃/SiO₂ NCs was studied with a 980-nm diode laser as excitation source. The water solubility, small core/shell particles size, and well colloidal stability mean the green up-conversion fluorescence NCs have potential applications in bioassay.