Ultrasmall Nanocrystals Research Articles

Ultra-small gadolinium oxide nanocrystal sensitization of non-small-cell lung cancer cells toward X-ray irradiation by promoting cytostatic autophagy.

BackgroundGadolinium-based nanoparticles (GdNPs) have been used as theranostic sensitizers in clinical radiotherapy studies; however, the biomechanisms underlying the radio-sensitizing effects of GdNPs have yet to be determined. In this study, ultra-small gadolinium oxide nanocrystals (GONs) were employed to investigate their radiosensitizing effects and biological mechanisms in non-small-cell lung cancer (NSCLC) cells under X-ray irradiation.Method and materialsGONs were synthesized using polyol method. Hydroxyl radical production, oxidative stress, and clonogenic survival after X-ray irradiation were used to evaluate the radiosensitizing effects of GONs. DNA double-strand breakage, cell cycle phase, and apoptosis and autophagy incidences were investigated in vitro to determine the radiosensitizing biomechanism of GONs under X-ray irradiation.ResultsGONs induced hydroxyl radical production and oxidative stress in a dose- and concentration-dependent manner in NSCLC cells after X-ray irradiation. The sensitizer enhancement ratios of GONs ranged between 19.3% and 26.3% for the NSCLC cells under investigation with a 10% survival rate compared with that of the cells treated with irradiation alone. Addition of 3-methyladenine to the cell medium decreased the incidence rate of autophagy and increased cell survival, supporting the idea that the GONs promoted cytostatic autophagy in NSCLC cells under X-ray irradiation.ConclusionThis study examined the biological mechanisms underlying the radiosensitizing effects of GONs on NSCLC cells and presented the first evidence for the radiosensitizing effects of GONs via activation of cytostatic autophagy pathway following X-ray irradiation.

Size-dependent stability of ultra-small \u03b1-/\u03b2-phase tin nanocrystals synthesized by microplasma

Nanocrystals sometimes adopt unusual crystal structure configurations in order to maintain structural stability with increasingly large surface-to-volume ratios. The understanding of these transformations is of great scientific interest and represents an opportunity to achieve beneficial materials properties resulting from different crystal arrangements. Here, the phase transformation from α to β phases of tin (Sn) nanocrystals is investigated in nanocrystals with diameters ranging from 6.1 to 1.6 nm. Ultra-small Sn nanocrystals are achieved through our highly non-equilibrium plasma process operated at atmospheric pressures. Larger nanocrystals adopt the β-Sn tetragonal structure, while smaller nanocrystals show stability with the α-Sn diamond cubic structure. Synthesis at other conditions produce nanocrystals with mean diameters within the range 2–3 nm, which exhibit mixed phases. This work represents an important contribution to understand structural stability at the nanoscale and the possibility of achieving phases of relevance for many applications.

Enhanced flux pinning of solution-derived YBa2Cu3O7−x nanocomposite films with novel ultra-small BaMnO3 nanocrystals

The demand for coated conductors with high cost performance has triggered the search for effective artificial pinning centers by the low cost and high-scalability route. In this work, YBa2Cu3O7−x (YBCO) nanocomposite films with BaMnO3 nanosized particles induced by manganese (Mn) addition were prepared by low-fluorine metal-organic deposition. A strategy of rapid heating during the medium-temperature stage was adopted to reduce the size of the BaMnO3 nanoparticles and improve the quality of the YBCO films. An enhanced critical current density and pinning force were found in the high-quality YBCO film embedded with extraordinarily small nanoparticles (average 3 ± 1 nm).

Magnetic microspheres with polydopamine encapsulated ultra-small noble metal nanocrystals as mimetic enzymes for the colorimetric detection of H2O2 and glucose

A novel sandwich-structured magnetic microsphere with ultra-small noble metal nanocrystals as a mimetic enzyme for the colorimetric detection of H2O2 and glucose.

Ultrasmall Co2P2O7 nanocrystals anchored on nitrogen-doped graphene as efficient electrocatalysts for the oxygen reduction reaction

A novel composite electrocatalyst with ultrasmall Co2O2P7 nanocrystals supported on nitrogen-doped graphene has been developed and exhibits remarkable ORR performance.

CuCo2S4 nanocrystals as a nanoplatform for photothermal therapy of arterial inflammation.

Ultrasmall CuCo2S4 nanocrystals (NCs) have been demonstrated as an effective agent in the photothermal therapy (PTT) of tumors, but have not been investigated for treatment of arterial inflammation, which is critical in the initiation and development of atherosclerosis (AS), a leading cause of vascular diseases worldwide. In this study, CuCo2S4 NCs were synthesized and used as an efficient PTT nanoplatform for arterial inflammation. In vitro experiments illustrated an effective ablation of inflammatory macrophages by CuCo2S4 incubation combined with the irradiation with an 808 nm near-infrared (NIR) laser. In vivo experiments in an apolipoprotein E knockout (Apo E-/-) mouse model showed that the local injection with CuCo2S4 followed by irradiation with an 808 nm NIR laser notably ablated infiltrating inflammatory macrophages and effectively reduced arterial inflammation and arterial stenosis. This work provides a new strategy for treatment of AS by exploring bimetal sulfides as effective PTT agents.

Microplasma-synthesized ultra-small NiO nanocrystals, a ubiquitous hole transport material

We report on a one-step hybrid atmospheric pressure plasma-liquid synthesis of ultra-small NiO nanocrystals (2 nm mean diameter), which exhibit strong quantum confinement. We show the versatility of the synthesis process and present the superior material characteristics of the nanocrystals (NCs). The band diagram of the NiO NCs, obtained experimentally, highlights ideal features for their implementation as a hole transport layer in a wide range of photovoltaic (PV) device architectures. As a proof of concept, we demonstrate the NiO NCs as a hole transport layer for three different PV device test architectures, which incorporate silicon quantum dots (Si-QDs), nitrogen-doped carbon quantum dots (N-CQDs) and perovskite as absorber layers. Our results clearly show ideal band alignment which could lead to improved carrier extraction into the metal contacts for all three solar cells. In addition, in the case of perovskite solar cells, the NiO NC hole transport layer acted as a protective layer preventing the degradation of halide perovskites from ambient moisture with a stable performance for >70 days. Our results also show unique characteristics that are highly suitable for future developments in all-inorganic 3rd generation solar cells (e.g. based on quantum dots) where quantum confinement can be used effectively to tune the band diagram to fit the energy level alignment requirements of different solar cell architectures.

Ultrasmall-sized SnS nanosheets vertically aligned on carbon microtubes for sodium-ion capacitors with high energy density

In this work, the porous SnS nanosheets with abundant ultra-small nanocrystals aligned on carbon microtubes are designed to achieve good structural stability, remarkable rate capability and high sodium storage capability.

Revealing a conversion-alloying reaction mechanism behind high capacity and rate capability of SnS/N-doped graphene anode by in situ TEM

Developing an electrode material with improved ionic transport dynamics in a battery has been the focus of research. Here, we report a facile one-step hydrothermal synthesis method to prepare anode material of ultra-small SnS nanocrystals (NCs) anchored on N-doped graphene nanosheets (SnS/N-G), which is expected to significantly the dynamics of lithium transport, enabling an exceptional capacity of 1120.3 mAh g−1 at 0.1 A g−1 after 130 cycles and superior rate capabilities of 446.3 and 340.7 mAh g−1 at 2 and 3 A g−1, respectively. Furthermore, the lithiation/delithiation behaviors of SnS/N-G anode were observed in real time using in situ transmission electron microscopy to reveal the corresponding kinetics. By tracking the full lithiation procedure, in situ electron diffraction and high-resolution TEM imaging found that the original SnS phase was firstly transformed to Sn phase by conversion reaction and then to Li22Sn5 phase by alloying reaction. Notably, a stable and reversible phase transformation was established between Li22Sn5 and Sn phases during subsequent charge-discharge cycles. In the meantime, the volume expansion-induced pulverization of SnS NCs was evidently alleviated by graphene matrix that not only provided a two-dimensional support to buffer the volume change, but also improved the ion migration kinetics, as corroborated by superior rate capability.

Highly efficient inverted planar perovskite solar cells from TiO2 nanoparticles modified interfaces between NiO hole transport layers and conductive glasses

It has been demonstrated that the interfaces in perovskite solar cells (PSCs) have significant influence on photovoltaic performance of PSCs. So interface engineering is very important for achieving high power conversion efficiency (PCE). However, an important interface of fluorine-doped tin oxide conductive glass (FTO)/hole transport layer (HTL) in the inverted planar PSCs is customarily missed. Here, we verify that through modification of the interface between FTO and NiO HTL with ultra-small TiO2 nanocrystals (NCs), the PCE of inverted planar PSCs can be obviously enhanced from the original 15.23% to the highest value of 16.21%. The optical transmittance spectra show that the TiO2 NCs modification has little influence on the transparency of the substrates. The PL and TRPL data reveal clearly enhanced hole-extracting speed owing to the improve coverage and quality of the NiO HTLs on TiO2 NCs-modified FTOs. These features are important reasons for the improved photovoltaic performance of the corresponding devices. This work highlights an effective way for enhancing photovoltaic performance of the inverted planar PSCs through modifying the interfaces between the transparent conductive substrates and the HTLs.

Surfaces/Interfaces Modification for Vacancies Enhancing Lithium Storage Capability of Cu2O Ultrasmall Nanocrystals.

Theoretically, Cu2O delivers a poor Li storage capacity ∼373.9 mA h g-1 based on a so-called conversion reaction (Cu2O + 2Li → 2Cu + Li2O). Herein, we broke through the bottleneck and acquired an impressive lithium storage capability (1122 mA h g-1) tripled more than the theoretical one by an in situ surface/interface engineering process for the first time. The surface/interface modification enabled us to fabricate ultrasmall nanocrystals of Cu2O with Cu vacancies (VCu) of high concentration, somewhat like monovalent anion doping. Except for the conversion reaction-type capacity, VCu enhancing intercalation pesudocapacitance in Cu2O and its reduction product-Cu also contributed a lot to the Li-storage capability. First-principles calculation substantiated that intercalation energy of Li was severely lowered for both Cu vacancy-rich Cu2O and Cu comparing with their stoichiometric counterparts. Another important factor for the enhancement was the surface/interface organic species themselves which could reversibly store Li by redox reactions. The surface/interface modification for vacancies, vacancy inheritance from metal oxide to single metal, and vacancy-enhancing Li-storage capability in metal oxide and single metal all will inspire us a lot in fabricating new-generation advanced electrodes for rechargeable batteries.

Concentration dependent optical transition probabilities in ultra-small upconversion nanocrystals.

Transition probability is of vital importance for luminescence process, whereas the effects of doping concentration have not been explored in the Er3+:NaGdF4. In this work, we investigate the radiative transition probabilities of Er3+ highly doped NaGdF4 sub 10 nm nanocrystals using J-O theory. It is found that the transition probabilities vary with changing Er3+ concentration, especially altering the ratio of Er3+ 2H11/2 to 4S3/2 level, which is highly useful for optical thermometers as they are thermally coupled. To validate the concentration dependent transition probabilities, significant enhancements of upconversion luminescence are achieved by epitaxial growth of the inert shell, and thermal sensing behaviors are investigated using the improved samples.

The ensemble effect of nitrogen doping and ultrasmall SnO2 nanocrystals on graphene sheets for efficient electroreduction of carbon dioxide

The electroreduction of carbon dioxide (CO2) into fuels and other chemicals is an exciting approach to address the urgent climate and energy challenges. However, the unsatisfied efficiency and selectivity for CO2 reduction reaction (CO2RR) with conventional electrocatalysts are the major obstacles. Herein, a facile and effective method is developed to deposit ultrasmall SnO2 nanocrystals on nitrogen-doped graphene via in-situ conversion strategies for highly efficient CO2RR. The comparison studies reveal that the electrocatalytic activity of such electrocatalysts relies on the loading of SnO2 on graphene and the nitrogen doping. The optimal electrocatalyst exhibits a high selectivity for CO2 electroreduction to formate and carbon monoxide at low overpotential (∼ 0.6 V) with a faradaic efficiency of ∼ 89% and a current density of ∼21.3 mA/cm2. Additionally, the optimal electrocatalyst shows an excellent stability for 20 h. The good performance would be contributed to the ensemble effect between the highly dispersed ultrasmall SnO2 nanocrystals and the nitrogen doping on graphene sheets. This work thus provides a rational design strategy for developing efficient CO2 reduction catalysts.

In Situ Dynamic Nanostructuring of the Cu-Ti Catalyst-Support System Promotes Hydrogen Evolution under Alkaline Conditions.

We report an interesting case of in situ dynamic nanostructuring of catalyst and support under hydrogen evolution conditions in basic media. When solution-grown CuO nanoplates on titanium substrates are subjected to hydrogen evolution reaction, besides the reduction of CuO to metallic Cu nanoplates, both catalyst and support simultaneously undergo a nanostructuring process. The process is driven by the dissolution-redeposition of Cu and the alkaline etching of the titanium support. The morphology of the resulting nanocomposite material consists of a porous matrix made of ultrasmall Cu nanocrystals and amorphous TiO x nanoparticles. Interestingly, the nanostructuring of the catalyst can be finely controlled by varying the applied potential. Such a process leads to a 5.4-fold improvement in the catalyst activity, which is attributed not only to its large active surface area (formed upon nanostructuring), but also to an improved water dissociation activity, provided by the in situ formation of TiO x nanoparticles. The final catalyst exhibits -10 mA/cm2 of current density at a small overpotential of -108 mV and a long-term operational stability up to 50 h. Density functional theory calculations show that the co-presence of Cu and TiO2 nanoparticles optimizes the free energy of hydrogen adsorption in the final catalyst. Our work highlights the importance of studying the dynamic evolution of catalysts under operational conditions and choice of proper support that enhances the catalyst activity.

Reduced Magnetic Coupling in Ultrasmall Iron Oxide T1 MRI Contrast Agents

Contrast agents for magnetic resonance imaging (MRI) are essential for evidential visualization of soft tissues pathologies. Contrast-enhanced MRI can be carried out with T1- and T2-weighted sequences that require as contrast agents paramagnetic and superparamagnetic materials, respectively. The T1-weighted imaging is frequently preferred over T2-, as it induces a bright contrast for sharper image analysis and allows more rapid image acquisition. Commonly used and FDA-approved T1 contrast agents, however, were shown to be associated with nephrogenic systematic fibrosis due to Gd3+ release from the injected complexes. Here, ultrasmall iron oxide nanocrystals are produced by scalable flame aerosol technology and investigated as T1 MRI contrast agents by focusing on structure-function relationships and cytocompatibility. The optimized nanocrystals are shown to be a promising cytocompatible alternative to commercial Gd-complexes as they attain comparable relaxivities with no apparent cytotoxicity at clinically relevant concentrations tested in vitro against four different cell types (PC3, HepG2, THP-1, and red blood cells). By using SiO2 as a spacing material, the contrast enhancement could be finely tuned by decreasing the effective magnetic size of iron oxide resulting in significant T1 contrast enhancement due to reduced magnetic coupling.

Iridium nanocrystals encapsulated liposomes as near-infrared light controllable nanozymes for enhanced cancer radiotherapy

Owing to the existence of severe tumor hypoxia and limited X-ray absorption of solid tumors, the therapeutic efficacy of radiotherapy is far from satisfactory. Herein, ultrasmall iridium nanocrystals (IrNCs) with homogeneous size distribution are successfully synthesized. The obtained IrNCs show catalase-like catalytic activity towards hydrogen peroxide (H2O2) with great temperatures/pH stability. As free IrNCs are prone to be toxified by thiol-containing biomolecules, we encapsulate as-prepared IrNCs within stealth liposomal carriers, obtaining Ir@liposome with well-protected catalytic activity in physiological conditions. By utilizing its efficient photothermal conversion ability, such Ir@liposome shows effective near-infrared-(NIR)-responsive catalytic activity towards H2O2 decomposition. As revealed by in vivo photoacoustic imaging, our Ir@liposome exhibits efficient passive tumor accumulation upon intravenous injection, and could efficiently decompose the tumor endogenous H2O2 into O2, particularly upon exposure to the NIR laser. As the results of relieved tumor hypoxia after such treatment and the radiosensitization capability of Ir as a high-Z element, greatly enhanced radio-therapeutic efficacy with Ir@liposome is then achieved. This work thus presents a unique type of NIR light controllable theranostic nanozyme based on noble metal nanocrystals as a nanoscale radiosensitizer with great performance in enhancing cancer radiotherapy.

Nitrogen-doped carbon enhanced mesoporous TiO2 in photocatalytic remediation of organic pollutants

Controllable synthesis of mesoporous photocatalysts is of great interest for the photocatalytic remediation of organic pollutants from wastewater by sunlight. In this work, we have developed a new photocatalyst with nitrogen-doped carbon (NC) and mesoporous TiO2 (mTiO2) interpenetrating hetero-structure by a sol–gel process combined with an in situ carbonization strategy. The synthesized nanospheres possess a uniform particle size (~ 60 nm), high surface area (~ 108 m2/g), and large pore diameter (~ 2.1 nm). Most importantly, the nanospheres consist of ultrasmall TiO2 nanocrystals (~ 8.2 nm), which are uniformly coated by a thin layer of N-doped carbon. Significantly, the resultant NC/mTiO2 composite nanospheres exhibit a broad light absorption in the range of 200–2000 nm (entire wavelength). When serving as a photocatalyst for organic pollutants degradation, high performance was obtained. Accordingly, the resultant NC/mTiO2 composite nanospheres performed in an excellent manner in the photodegradation of methyl orange, and the total removal efficiency was up to 97.7%, much better than that of commercial P25 (19.8%). Furthermore, the nanocomposite also effectively photodegraded other organic pollutants such as methylene blue (dyestuff) and phenol, respectively. Therefore, the resultant NC/mTiO2 nanocomposites have potential applications in environmental cleanup.

Electrochemical solid-state amorphization in the immiscible Cu-Li system

As a typical immiscible binary system, copper (Cu) and lithium (Li) show no alloying and chemical intermixing under normal circumstances. Here we show that, when decreasing Cu nanoparticle sizes into ultrasmall range, the nanoscale size effect can play a subtle yet critical role in mediating the chemical activity of Cu and therefore its miscibility with Li, such that the electrochemical alloying and solid-state amorphization will occur in such an immiscible system. This unusual observation was accomplished by performing in-situ studies of the electrochemical lithiation processes of individual CuO nanowires inside a transmission electron microscopy (TEM). Upon lithiation, CuO nanowires are first electrochemically reduced to form discrete ultrasmall Cu nanocrystals that, unexpectedly, can in turn undergo further electrochemical lithiation to form amorphous CuLix nanoalloys. Real-time TEM imaging unveils that there is a critical grain size (ca. 6 nm), below which the nanocrystalline Cu particles can be continuously lithiated and amorphized. The possibility that the observed solid-state amorphization of Cu-Li might be induced by electron beam irradiation effect can be explicitly ruled out; on the contrary, it was found that electron beam irradiation will lead to the dealloying of as-formed amorphous CuLix nanoalloys.

Assembling Ultrasmall Copper-Doped Ruthenium Oxide Nanocrystals into Hollow Porous Polyhedra: Highly Robust Electrocatalysts for Oxygen Evolution in Acidic Media.

Here, a facile and novel strategy for the preparation of Cu-doped RuO2 hollow porous polyhedra composed of ultrasmall nanocrystals through one-step annealing of a Ru-exchanged Cu-BTC derivative is reported. Owing to the optimized surface configuration and altered electronic structure, the prepared catalyst displays a remarkable oxygen evolution reaction (OER) performance with low overpotential of 188 mV at 10 mA cm-2 in acidic electrolyte, an ultralow Tafel slope of 43.96 mV dec-1 , and excellent stability in durability testing for 10 000 cycles, and continuous testing of 8 h at a current density of 10 mA cm-2 . Density functional theory calculations reveal that the highly unsaturated Ru sites on the high-index facets can be oxidized gradually and reduce the energy barrier of rate-determining steps. On the other hand, the Cu dopants can alter the electronic structures so as to further improve the intrinsic OER activity.

Direct Conversion of Graphene Aerogel into Low-Density Diamond Aerogel Composed of Ultrasmall Nanocrystals

Diamond aerogel, a special kind of carbon aerogel made by sp3 carbon atoms, has been attracting intensive research interest due to its potential applications since it is first synthesized by the conversion of amorphous carbon. Despite of many expectations in diamond aerogel, the study on its synthesis is still not adequate compared with other carbon aerogel. Here we report the synthesis of diamond aerogel by laser heating graphene aerogel (GA) under high pressure in a diamond anvil cell. The results suggest that the density and microstructure of GA, as well as the heating duration obviously affect the diamond aerogel growth. When heating GA with lower laser power, we also observe a transparent carbon phase in experiment, which transforms into graphite and amorphous carbon upon decompression. These results present new insights into our understanding on the transformation from ultralow density carbon to sp3 carbon under high pressure and high temperature. It is possible to tune the microstructures of diamon...