CsPbBr3 QD/AlOx Inorganic Nanocomposites with Exceptional Stability in Water,Light, and Heat

Herein, the assembly of CsPbBr₃ QD/AlO_x inorganic nanocomposites, by using atomic layer deposition (ALD) for the growth of the amorphous alumina matrix (AlO_x ), is described as a novel protection scheme for such QDs. The nucleation and growth of AlO_x on the QD surface was thoroughly investigated by miscellaneous techniques, which highlighted the importance of the interaction between the ALD precursors and the QD surface to uniformly coat the QDs while preserving the optoelectronic properties. These nanocomposites show exceptional stability towards exposure to air (for at least 45 days), irradiation under simulated solar spectrum conditions (for at least 8 h), and heat (up to 200 °C in air), and finally upon immersion in water. This method was extended to the assembly of CsPbBr_x I_3−x QD/AlO_x and CsPbI₃ QD/AlO_x nanocomposites, which were more stable than the pristine QD films.     

Optimizing the Atomic Layer Deposition of Alumina on Perovskite Nanocrystal Films by Using O2 As a Molecular Probe

Encapsulation methods have shown to be effective in imparting improved stability to metal-halide perovskite nanocrystals (NCs). Atomic layer deposition (ALD) of metal oxides is one of the promising approaches for such encapsulation, yet better control on the process parameters are required to achieve viable lifetimes for several optoelectronic and photocatalytic applications. Herein, we optimize the ALD process of amorphous aluminum oxide (AlO_x) as an encapsulating layer for CsPbBr₃ NC thin films by using oxygen (O₂) as a molecular diffusion probe to assess the uniformity of the deposited AlO_x layer. When O₂ reaches the NC surface, it extracts the photogenerated electrons, thus quenching the PL of the CsPbBr₃ NCs. As the quality of the ALD layer improves, less quenching is expected. We compare three different ALD deposition modes. We find that the low temperature/high temperature and the exposure modes improve the quality of the alumina as a gas barrier when compared with the low temperature mode. We attribute this result to a better diffusion of the ALD precursor throughout the NC film. We propose the low temperature/high temperature as the most suitable mode for future implementation of multilayered coatings.     

Quantifying the Thermodynamics of Ligand Binding to CsPbBr3 Quantum Dots

Cesium lead halide perovskites are an emerging class of quantum dots (QDs) that have shown promise in a variety of applications; however, their properties are highly dependent on their surface chemistry. To this point, the thermodynamics of ligand binding remain unstudied. Herein, ¹H NMR methods were used to quantify the thermodynamics of ligand exchange on CsPbBr₃ QDs. Both oleic acid and oleylamine native ligands dynamically interact with the CsPbBr₃ QD surface, having individual surface densities of 1.2–1.7 nm^?2. 10‐Undecenoic acid undergoes an exergonic exchange equilibrium with bound oleate (K_eq=1.97) at 25 °C while 10‐undecenylphosphonic acid undergoes irreversible ligand exchange. Undec‐10‐en‐1‐amine exergonically exchanges with oleylamine (K_eq=2.52) at 25 °C. Exchange occurs with carboxylic acids, phosphonic acids, and amines on CsPbBr₃ QDs without etching of the nanocrystal surface; increases in the steady‐state PL intensities correlate with more strongly bound conjugate base ligands.     

Photoluminescence Quenching in Self‐Assembled CsPbBr3 Quantum Dots on Few‐Layer Black Phosphorus Sheets

An ordered self‐assembly of CsPbBr₃ quantum dots (QDs) was generated on the surface of few‐layer black phosphorus (FLBP). Strong quenching of the QD fluorescence was observed, and analyzed by time‐resolved photoluminescence (TR‐PL) studies, DFT calculations, and photoconductivity measurements. Charge transfer by type I band alignment is suggested to be the cause of the observed effects.     

Interface effects and relaxation processes in nanocomposites based on CdSe/ZnS semiconductor quantum dots and porphyrin molecules

Controllable self-assembly and properties of nanocomposites based on CdSe/ZnS semiconductor quantum dots (QDs) and tetrapyridylporphyrin molecules (H₂P) as well as the dynamics of relaxation processes in these systems were studied for solutions and single nanoobjects in the temperature range of 77–295 K. It was proved that the formation of surface states of different nature is crucial to nonradiative relaxation of exciton excitation in QDs. The efficiency of QD→Н₂Р energy transfer was shown to be at most 10–15%. Regularities of photoluminescence (PL) quenching for QDs in nanocomposites in solutions of different polarity correlate with the dependences of PL blinking for single QDs. A scheme was proposed of excited states and main relaxation channels of exciton excitation energy in semiconductor QDs and QD–Н₂Р nanocomposites.     

Highly Luminescent and Ultrastable CsPbBr3 Perovskite Quantum Dots Incorporated into a Silica/Alumina Monolith

We successfully prepared QDs incorporated into a silica/alumina monolith (QDs‐SAM) by a simple sol–gel reaction of an Al–Si single precursor with CsPbBr₃ QDs blended in toluene solution, without adding water and catalyst. The resultant transparent monolith exhibits high photoluminescence quantum yields (PLQY) up to 90 %, and good photostability under strong illumination of blue light for 300 h. We show that the preliminary ligand exchange of didodecyl dimethyl ammonium bromide (DDAB) was very important to protect CsPbBr₃ QDs from surface damages during the sol–gel reaction, which not only allowed us to maintain the original optical properties of CsPbBr₃ QDs but also prevented the aggregation of QDs and made the monolith transparent. The CsPbBr₃ QDs‐SAM in powder form was easily mixed into the resins and applied as color‐converting layer with curing on blue light‐emitting diodes (LED). The material showed a high luminous efficacy of 80 lm W⁻¹ and a narrow emission with a full width at half maximum (FWHM) of 25 nm.     

Amino‐Assisted Anchoring of CsPbBr3 Perovskite Quantum Dots on Porous g‐C3N4 for Enhanced Photocatalytic CO2 Reduction

Halide perovskite quantum dots (QDs) have great potential in photocatalytic applications if their low charge transportation efficiency and chemical instability can be overcome. To circumvent these obstacles, we anchored CsPbBr₃ QDs (CPB) on NH_x‐rich porous g‐C₃N₄ nanosheets (PCN) to construct the composite photocatalysts via N?Br chemical bonding. The 20 CPB‐PCN (20 wt % of QDs) photocatalyst exhibits good stability and an outstanding yield of 149 μmol h^?1 g^?1 in acetonitrile/water for photocatalytic reduction of CO₂ to CO under visible light irradiation, which is around 15 times higher than that of CsPbBr₃ QDs. This study opens up new possibilities of using halide perovskite QDs for photocatalytic application.     

High‐Performance CsPb1−xSnxBr3 Perovskite Quantum Dots for Light‐Emitting Diodes

All inorganic CsPbBr₃ perovskite quantum dots (QDs) are potential emitters for electroluminescent displays. We have developed a facile hot‐injection method to partially replace the toxic Pb²⁺ with highly stable Sn⁴⁺. Meanwhile, the absolute photoluminescence quantum yield of CsPb_1−x Sn_x Br₃ increased from 45 % to 83 % with Sn^IV substitution. The transient absorption (TA) exciton dynamics in undoped CsPbBr₃ and CsPb_0.67Sn_0.33Br₃ QDs at various excitation fluences were determined by femtosecond transient absorption, time‐resolved photoluminescence, and single‐dot spectroscopy, providing clear evidence for the suppression of trion generation by Sn doping. These highly luminescent CsPb_0.67Sn_0.33Br₃ QDs emit at 517 nm. A device based on these QDs exhibited a luminance of 12 500 cd m⁻², a current efficiency of 11.63 cd A⁻¹, an external quantum efficiency of 4.13 %, a power efficiency of 6.76 lm w⁻¹, and a low turn‐on voltage of 3.6 V, which are the best values among reported tin‐based perovskite quantum‐dot LEDs.     

Ligand-Assisted Coupling Manipulation for Efficient and Stable FAPbI3 Colloidal Quantum Dot Solar Cells

For emerging perovskite quantum dots (QDs), understanding the surface features and their impact on the materials and devices is becoming increasingly urgent. In this family, hybrid FAPbI₃ QDs (FA: formamidium) exhibit higher ambient stability, near-infrared absorption and sufficient carrier lifetime. However, hybrid QDs suffer from difficulty in modulating surface ligand, which is essential for constructing conductive QD arrays for photovoltaics. Herein, assisted by an ionic liquid formamidine thiocyanate, we report a facile surface reconfiguration methodology to modulate surface and manipulate electronic coupling of FAPbI₃ QDs, which is exploited to enhance charge transport for fabricating high-quality QD arrays and photovoltaic devices. Finally, a record-high efficiency approaching 15 % is achieved for FAPbI₃ QD solar cells, and they retain over 80 % of the initial efficiency after aging in ambient environment (20–30 % humidity, 25 °C) for over 600 h.     

Capillary electrophoretic studies on quantum dots and histidine appended peptides self‐assembly

Herein, we designed four peptides appended with different numbers of histidine (His_n‐peptide). We launched a systematic investigation on quantum dots (QDs) and His_n‐peptide self‐assembly in solution using fluorescence coupled CE (CE‐FL). The results indicated that CE‐FL was a powerful method to probe how ligands interaction on the surface of nanoparticles. The self‐assembly of QDs and peptide was determined by the numbers of histidine. We also observed that longer polyhistidine tags (n ≤ 6) could improve the self‐assembly efficiency. Furthermore, the formation and separation of QD‐peptide assembly were also studied by CE‐FL inside a capillary. The total time for the mixing, self‐assembly, separation, and detection was less than 10 min. Our method greatly expands the application of CE‐FL in QDs‐based biolabeling and bioanalysis.     

Formation of Surface Traps on Quantum Dots by Bidentate Chelation and Their Application in Low‐Potential Electrochemiluminescent Biosensing

Bidentate chelation, meso‐2,3‐dimercaptosuccinic acid (DMSA), was used as a stabilizer for the synthesis of CdTe quantum dots (QDs). The bidentate chelate QDs, characterized with FT‐IR, PL, and UV/Vis spectroscopy; element analysis; and high‐resolution transmission electron microscope, exhibited surface traps due to the large surface/volume ratio of QD particle and the steric hindrance of the DMSA molecule. The unpassivated surface of the QDs produced a narrower band gap than the core and electrochemiluminescent (ECL) emission at relatively low cathodic potential. In air‐saturated pH 7.0 buffer, the QDs immobilized on electrode surface showed an intense ECL emission peak at ?0.85 V (vs. Ag/AgCl). H₂O₂ produced from electrochemical reduction of dissolved oxygen was demonstrated to be the co‐reactant, which avoided the need of strong oxidant as the co‐reactant and produced a sensitive analytical method for peroxidase‐related analytes. Using hydroquinone/horseradish peroxidase/H₂O₂ as a model system, a new, reagentless, phenolic, ECL biosensor for hydroquinone was constructed, based on the quenching effect of ECL emission of QDs by consumption of co‐reactant H₂O₂. The biosensor showed a linear range of 0.2–10 μM with acceptable stability and reproducibility. This work opens new avenues in the search for new ECL emitters with excellent analytical performance and makes QDs a more attractive alternative in biosensing.     

Facile synthesis of fluorescent quantum dot‐polymer nanocomposites via frontal polymerization

We report an available approach for quickly fabricating CdS QD‐polymer nanocomposites via frontal polymerization (FP). First, we synthesized (3‐mercaptopropyl)‐1‐trimethoxysilane (MPS)‐capped CdS quantum dots (QDs). With these MPS‐capped CdS QDs containing mercapto groups, MPS‐capped CdS QDs can be easily incorporated into a poly(N‐methylolacrylamide) (PNMA) matrix via FP. A variety of features for preparing QD‐polymer nanocomposites, such as initiator concentration and CdS concentration, were thoroughly investigated. The fluorescence properties of QD‐polymer nanocomposites prepared via FP are comparatively investigated on the basis of ultraviolet–visible (UV–vis) spectra and photoluminescence (PL) spectra. Results show that the PL intensity of QD‐polymer nanocomposites prepared via the FP method is superior to that obtained by the traditional batch polymerization (BP) method. In addition, by measuring the changes of PL intensity of the samples immersed in different concentrations of copper acetate solution, we found the QD‐polymer nanocomposites can be ultrasensitive to copper ions. This FP process can be exploited as a facile and rapid way for synthesis QD‐polymer nanocomposites on a large scale, avoiding the fluorescence quenching of nanocrystals during incorporation nanocrystals into polymer matrices. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2170–2177, 2010     

Controlled self-assembly of hydrophobic quantum dots through silanization

We demonstrate the formation of one-, two-, and three-dimensional nanocomposites through the self-assembly of silanized CdSe/ZnS quantum dots (QDs) by using a controlled sol-gel process. The self-assembly behavior of the QDs was created when partially hydrolyzed silicon alkoxide monomers replaced hydrophobic ligands on the QDs. We examined systematically self-assembly conditions such as solvent components and QD sizes in order to elucidate the formation mechanism of various QD nanocomposites. The QD nanocomposites were assembled in water phase or on the interface of water and oil phase in emulsions. The partially hydrolyzed silicon alkoxides act as intermolecules to assemble the QDs. The QD nanocomposites with well-defined solid or hollow spherical, fiber-like, sheet-like, and pearl-like morphologies were prepared by adjusting the experimental conditions. The high photoluminescence efficiency of the prepared QD nanocomposites suggests partially hydrolyzed silicon alkoxides reduced the surface deterioration of QDs during self-assembly. These techniques are applicable to other hydrophobic QDs for fabricating complex QD nanocomposites.     

A Novel Magneto-fluorescent Nano-bioprobe for Cancer Cell Targeting,Imaging and Collection

Silica-coated magnetic polystyrene nanospheres (MPN) containing CdTe/CdS quantum dots (QDs) and Fe₃O₄ nanoparticles were prepared, and novel anti-EGFR antibodies were conjugated onto these magneto-fluorescent nanocomposites (MPN–QDs–SiO₂) for cancer cell targeting, imaging and collection. Transmission electron microscopy (TEM), scanning electron microscopy (SEM) images and energy-dispersive x-ray spectrometry (EDS) data showed that the MPN had been successfully coated with QDs and a silica shell, and the nanocomposites obtained with negative charged surfaces were well dispersed. The bioconjugates could be used for specifically labeling and separating cancer cells (MDA-MB-435S, SMMC-7721), but did not recognize and separate the K562 cells because the human epidermal growth factor receptor (EGFR) was not expressed on the surface. Because the anti-EGFR antibody, which we have developed, could specifically recognize certain cancer cells that highly expressed EGFR on their surface, these nanoscale bioconjugates, synchronously exhibiting fluorescence and magnetism, may be used in novel bioprobes for labeling and collecting rare cancer cells, which may be beneficial for early cancer diagnosis.     

In-vivo fluorescence imaging technique using colloid solution of multiple quantum dots/silica/poly(ethylene glycol) nanoparticles

This paper describes a method for producing silica particles containing multiple quantum dots (QD/SiO₂), a method for surface-modifying the particles with poly(ethylene glycol) (QD/SiO₂/PEG), and an in vivo fluorescence imaging technique using colloid solution of the QD/SiO₂/PEG particles. The QDs used were ZnS-coated CdSe_xTe_1?x nanoparticles surface-modified with carboxyl groups, and had an average size of 10.3 ± 2.1 nm. The QD/SiO₂ particles were fabricated by performing sol–gel reaction of tetraethyl orthosilicate using NaOH as a catalyst in the presence of the QDs. The produced particles formed core–shell structure composed of multiple QDs and silica shell, and had an average size of 50.2 ± 17.9 nm. Surface-modification of the QD/SiO₂ particles with PEG, or PEGylation of the particle surface, was performed by using methoxy polyethylene glycol silane. Fluorescence of QD colloid solution was not quenched even through the silica-coating and the PEGylation. Tissues of a mouse could be imaged by injecting the concentrated colloid solution into it and measuring fluorescence intensity emitted from the tissues.     

Atomic Layer Deposition of Iron Sulfide and Its Application as a Catalyst in the Hydrogenation of Azobenzenes

The atomic layer deposition (ALD) of iron sulfide (FeS_x ) is reported for the first time. The deposition process employs bis(N ,N′ ‐di‐tert‐butylacetamidinato)iron(II) and H₂S as the reactants and produces fairly pure, smooth, and well‐crystallized FeS_x thin films following an ideal self‐limiting ALD growth behavior. The FeS_x films can be uniformly and conformally deposited into deep narrow trenches with aspect ratios as high as 10:1, which highlights the broad applicability of this ALD process for engineering the surface of complex 3D nanostructures in general. Highly uniform nanoscale FeS_x coatings on porous γ‐Al₂O₃ powder were also prepared. This compound shows excellent catalytic activity and selectivity in the hydrogenation of azo compounds under mild reaction conditions, demonstrating the promise of ALD FeS_x as a catalyst for organic reactions.     

Flexibly regulated electrochemiluminescence of all-inorganic perovskite CsPbBr3 quantum dots through electron bridge to across interfaces between polar and non-polar solvents

All-inorganic perovskite quantum dots (QDs) have attracted great interests due to its outstanding properties. But their poor stability in polar solvents seriously hampered wide applications in analytical chemistry. In this work, strong, stable and flexibly regulated the electrochemiluminescence (ECL) emission form CsPbBr₃ QDs was successfully obtained and applied in the analysis of polar solvents through the unique structure of closed bipolar electrode (BPE). To demonstrate the feasibility, it was successfully used in the detection of tetracycline (Tc) aqueous solution. CsPbBr₃ QDs was immersed into organic solution in anode microcell of closed BPE while Tc aqueous solution was added into cathode microcell. The two microcells were physically separated and would not interfere with each other. But the bio-recognition event between aptamer and Tc in cathode microcell would induce the ECL signal change in anode microcell through the electrons conducted by BPE as the bridge. The ECL emission can be flexibly regulated by environmental factors of both polar and non-polar solvents and the interface status of the BPE. Compared with traditional methods to overcome the intrinsic instability in polar medium, the reported method does not need any further surface modifications, has no limitations on the targets and can provide wide development space for further deep research, which may open a new direction for the ECL sensing of CsPbBr₃ QDs.     

Assembly kinetics of nanocrystals via peptide hybridization

The assembly kinetics of colloidal semiconductor quantum dots (QDs) on solid inorganic surfaces is of fundamental importance for implementation of their solid-state devices. Herein an inorganic binding peptide, silica binding QBP1, was utilized for the self-assembly of nanocrystal quantum dots on silica surface as a smart molecular linker. The QD binding kinetics was studied comparatively in three different cases: first, QD adsorption with no functionalization of substrate or QD surface; second, QD adsorption on QBP1-modified surface; and, finally, adsorption of QBP1-functionalized QD on silica surface. The surface modification of QDs with QBP1 enabled 79.3-fold enhancement in QD binding affinity, while modification of a silica surface with QBP1 led to only 3.3-fold enhancement. The fluorescence microscopy images also supported a coherent assembly with correspondingly increased binding affinity. Decoration of QDs with inorganic peptides was shown to increase the amount of surface-bound QDs dramatically compared to the conventional methods. These results offer new opportunities for the assembly of QDs on solid surfaces for future device applications.     

Aptamer based lysozyme assay using fluorescent CuInS<Subscript>2</Subscript> quantum dots and graphene oxide,and its application to inhibitor screening

We report on a widely applicable approach for protein detection by using triple-helix DNA mediated CuInS₂ quantum dot (QD) and graphene oxide (GO) nanocomposite. The CuInS₂ QDs were coated with mercaptopropionic acid and then covalently linked to a hairpin aptamer against lysozyme (HLA). Single-stranded DNA (triple helix-forming oligonucleotide; THFO) readily absorbs on the surface of GO via π-stacking interaction, and this results in the formation of THFO-GO. If HLA-CuInS₂ QDs are added to the THFO-GO system, the fluorescence of HLA-CuInS₂ QDs (at excitation/emission wavelengths of 590/665 nm) is quenched. Lysozyme has a higher affinity for HLA than THFO. Therefore, in the presence of lysozyme, it will bind to the HLA-CuInS₂ QD and displace the THFO-GO. This results in the restoration of fluorescence that is related to the concentration of lysozyme. The fluorescence of the QDs is turned on. The calibration plot is linear in the 0.01 to 1.8 ng·mL￣¹ concentration range, with a 3 pg·mL￣¹ detection limit (at a signal-to-noise ratio of 3). The method was also applied to study the inhibition of lysozyme by Ivy _Ec . In our perception, this method has a wide scope in that it may become applicable to any protein for which an appropriate aptamer is available.

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Graphical abstract A novel convenient and universal fluorescence nanoprobe for sensitive and selective detection of lysozyme and inhibitor screening was established using triple-helix DNA mediated CuInS₂ QDs and GO nanocomposites

     

Seed-mediated synthesis, properties and application of γ-Fe2O3-CdSe magnetic quantum dots

Seed-mediated growth of fluorescent CdSe quantum dots (QDs) around γ-Fe₂O₃ magnetic cores was performed at high temperature (300 °C) in the presence of organic surfactants. Bi-functional magnetic quantum dots (MQDs) with tunable emission properties were successfully prepared. The as-synthesized MQDs were characterized by high-resolution transmission electron microscopy (HRTEM) and dynamic light scattering (DLS), which confirmed the assembly of heterodimers. When a longer growth period was employed, a homogeneous dispersion of QDs around a magnetic nanoparticle was obtained. The magnetic properties of these nanocomposites were examined. The MQDs were superparamagnetic with a saturation magnetization of 0.40 emu/g and a coercivity of 138 Oe at 5 K. To demonstrate their potential application in bio-labeling, these MQDs were coated with a thin silica shell, and functionalized with a polyethylene glycol (PEG) derivative. The functionalized MQDs were effectively used for the labeling of live cell membranes of 4T1 mouse breast cancer cells and HepG2 human liver cancer cells.