Ultrasmall Quantum Dots Research Articles

Surface chemistry regulates the optical properties and cellular interactions of ultrasmall MoS2 quantum dots for biomedical applications.

Molybdenum disulfide quantum dots (MoS2 QDs) have drawn increasing attention owing to their distinct optical properties and potential applications in many fields such as biosensing, photocatalysis and cell imaging. Elucidating the relationship between the surface chemistry of MoS2 QDs and their optical properties as well as biological behaviors is critical for their practical applications, which remain largely unclear. Herein, by adopting a sulfur vacancy modification strategy, a toolbox of MoS2 QDs functionalized with different thiolate ligands was prepared. The effect of surface chemistry on the optical properties of MoS2 QDs was systematically explored by various spectroscopic techniques, revealing the important role of surface ligands in defining their absorption band gap and luminescence quantum yield. Furthermore, cellular experiments showed that the cytotoxicity and intracellular fate (i.e., lysosomal accumulation) of MoS2 QDs are closely related to the properties of surface ligands. Our results underscore the important roles of surface ligands in regulating the properties and biological interactions of these QDs, which will facilitate the future development of MoS2-based materials with precisely controlled functions for biomedical applications.

Nucleation-controlled growth of ultra-small perovskite quantum dots for bright blue light-emitting diodes

Ultra-small blue CsPbBr3QDs with ultrahigh PL QYs are synthesized by using PbBr2clusters as nucleation sites, which then react with Cs-oleate at relatively low temperatures.

Near-infrared Zn-doped Cu2S quantum dots: an ultrasmall theranostic agent for tumor cell imaging and chemodynamic therapy.

Theranostic agents that integrated chemodynamic therapy (CDT) and imaging functions have great potential application in personalized cancer therapy. However, most theranostic agents were fabricated by chemically coupling two or more independent functional units with diagnostic or therapeutic capabilities, and therefore have a large size. To date, one-step synthesis of unmodified ultrasmall quantum dots (QDs) integrating CDT and fluorescence imaging capabilities remains a challenge. Herein, we reported a simple one-step synthesis method of ultrasmall (2.46 nm) Zn-doped Cu2S (Zn:Cu2S) QDs with inherent properties of both high CDT activity and near-infrared fluorescence imaging capability. The fluorescence of Cu2S QDs was significantly enhanced approximately tenfold after Zn doping due to the compensation of defects. In vitro and in vivo experiments demonstrated that the Zn:Cu2S QDs could specifically and significantly inhibit the cancer cell growth (inhibition rate exceeded 65%) without damaging the normal cells. Furthermore, the CDT mechanism study suggested that a Fenton-like reaction occurred after the Zn:Cu2S QDs entered the tumor cells, inducing apoptosis via the mitochondrial signaling pathway, and activating the production of reactive oxygen species (ROS) and autophagy to selectively eliminate tumor cells to achieve CDT. This work proposed a simple one-step synthesis of unmodified ultrasmall QDs with fluorescence imaging and CDT, which provides a promising strategy for QDs to act as multi-functional theranostic agents.

Absorption and emission in the visible range by ultra-small PbS quantum dots in the strong quantum confinement regime with S-terminated surfaces capped with diphenylphosphine

The synthesis and characterization of PbS QDs absorbing and emitting in the visible range is a very challenging task, since it requires the QDs to be within the strong quantum confinement regime (QD size<2.5 nm). It implies not only having “small” QDs, but also stable and monodisperse; characteristics that have been elusive to achieve for many researchers. In the current work, ultra-small PbS QDs (size ~2 nm) were synthesized based on a modification of the Hines method, controlling the reaction time, and adding diphenylphosphine (DPP) which serves as a catalyst and a protective agent in the reaction synthesis. Novel ultra-small PbS QDs with S-terminated surfaces were obtained, which formed at the early stages of the synthesis reaction and are stabilized by the DPP; as it was suggested by the TEM, FTIR and Raman results. The ultra-small PbS QDs display a maximum peak of optical absorption at ~532 nm, with a corresponding optical band gap of 1.82 eV; a maximum peak of emission at ~679 nm, which results in a Stokes shift of 119 nm, smaller than the Stokes shift observed in “larger” PbS QDs. These ultra-small QDs displayed an average size of ~2 nm, with a standard deviation of ~0.3 nm, which was the smallest among the synthesized samples, based on TEM measurements. Finally, the LUMO and HOMO levels were measured by means of cyclic voltammetry and optical absorption spectroscopy. The values of the optical band gap and the energies measured for the LUMO and HOMO levels of these ultra-small PbS QDs were affected by their atomistic surface arrangement and the capping ligand interacting with their surface. Producing variations in their values that doesn’t follow the trends established for quantum confinement effects related to size variation only. Thorough physical and chemical characterization of such ultra-small PbS QDs are crucial in understanding the origin of their optoelectronic properties, which will contribute to better delineate possible future applications.

Solid-state synthesis of ultra-small freestanding amorphous MoP quantum dots for highly efficient photocatalytic H2 production

Cocatalysts can tremendously boost the photocatalytic H2 evolution performance by providing more active sites, accelerating the photogenerated charge separation, and benefiting the proton reduction reaction. To design and develop noble-metal-free cocatalysts with high performance in replace of noble metal Pt is significant for the practical application of solar H2 production. In this work, we have developed a facile solid-state low-temperature phosphorization way to synthesize ultra-small freestanding amorphous MoP quantum dots with an average size of 2.7 nm. Compared with supported MoP heterostructures, the freestanding property and small size enable a compact contact between MoP with CdS, leading to a reduced Schottky barrier and improved photocatalytic activity. The highest photocatalytic performance of MoP/CdS composites is as high as 13.88 mmol h−1 g−1 with an apparent quantum yield (AQY 420 nm) 66.7% and it is 1.44-fold of that of Pt/CdS*. This ultra-high photocatalytic performance is attributed to the small size and amorphous structure of MoP with more exposed active sites and the highly efficient photogenerated charge separation. This low-temperature phosphorization method is expected to be applied to synthesize other freestanding ultra-small metal phosphides quantum dots.

Ultrasmall Ag2Te Quantum Dots with Rapid Clearance for Amplified Computed Tomography Imaging and Augmented Photonic Tumor Hyperthermia.

With the fast development of nanomedicine, the imaging-guided and photo-induced cancer monotherapies can efficiently eliminate tumor lesions, which are strongly dependent on the construction of versatile theranostic nanoplatforms. Among diverse photo-converting nanoplatforms, silver chalcogenide nanoparticles feature high biocompatibility, narrow band gaps, and tunable optical properties, yet Ag2Te-based nanosystems are still at a proof-of-concept stage, and the exploration of Ag2Te-based nanosystems suitable for photonic tumor hyperthermia is challenging. Herein, we report on the construction of versatile ultrasmall Ag2Te quantum dots (QDs) via a facile biomineralization strategy. Especially, these Ag2Te QDs with negligible toxicity and excellent biocompatibility were developed for X-ray computed tomography (CT) imaging-guided photonic tumor hyperthermia by near-infrared (NIR) activation. The fabricated Ag2Te QDs exhibited a high tumor suppression rate (94.3%) on 4T1 breast tumor animal models due to the high photothermal-conversion efficiency (50.5%). Mechanistically, Ag2Te QDs were promising potential CT imaging agents for imaging guidance and monitoring during photonic hyperthermia. Importantly, Ag2Te QDs were rapidly eliminated from the body via feces and urine because of their ultrasmall sizes. This work not only broadens the biomedical applications of silver chalcogenide-based theranostic nanosystems but also provides the paradigm of theranostic nanosystems with a photonic tumor hyperthermia effect and outstanding contrast enhancement of high-performance CT imaging.

Site- and Spatial-Selective Integration of Non-noble Metal Ions into Quantum Dots for Robust Hydrogen Photogeneration

Summary Artificial photosystems consisting of semiconductor quantum dots (QDs) and non-noble metal ions (e.g., Fe2+, Co2+, Ni2+) show intrinsic advantages in efficient and cost-effective hydrogen (H2) evolution. However, well-controlled integration of these metal ions into ultra-small QDs is a major challenge. Here, we present a two-step strategy to realize site- and spatial-selective integration of earth-abundant Fe2+ ions in CdSe QDs; i.e., CdSe QDs are modified with a thin and anisotropic ZnS shell, and partial Zn2+ ions are selectively substituted by Fe2+ via cation exchange. The anisotropic ZnS layer not only passivates CdSe core but also works as an ideal medium to intimately anchor Fe2+. The multifunctional CdSe/Zn1−xFexS QD exhibits extraordinary activity and stability toward H2 photogeneration. Specifically, more than 880 mL (∼39,300 μmol) H2 gas is produced from 6 mL of aqueous solution during a consecutive 172 h (>1 week) experiment, thus achieving a turnover number of >600,000 per QD.

Navigating 2D Monoelemental Materials (Xenes) for Cancer Nanomedicine

Contributing to this issue of Matter, Wei Tao, Tian Xie, and colleagues now demonstrate the killing of two birds (inhibition of tumor recurrence and wound infection) with one stone (germanene-based surgical adjuvant theranostic materials): another breakthrough of two-dimensional monoelemental materials (2D Xenes) as cancer nanomedicine.

Hot-injection synthesis of ultrasmall CuIn3Se5 quantum dots and production of ink-coated films

For the first time, we synthesized ultrasmall colloidal CuIn3Se5 quantum dots (QDs) with an average diameter of 3.5 nm and they were used to obtain nearly continuous ink-coated films by the hot-injection method. Copper chloride, indium chloride, and selenium were used as reagents in oleylamine as the solvent to synthesize CuIn3Se5 QDs without other organometallic precursors. The synthesized CuIn3Se5 QDs had a cubic crystal structure and they exhibited a strong quantum confinement effect according to their optical absorption spectra. The as-deposited and annealed thin films prepared from an ink solution containing these QDs exhibited p-type characteristics, a high band gap, and low surface roughness. The optical constants were determined by interference-free mathematical modeling for the as-deposited and annealed films obtained with the synthesized CuIn3Se5 QDs. Moreover, under 1 sun of simulated radiation, the photocurrent was greatly enhanced (>1000%) for the annealed CuIn3Se5 QD film compared with the as-deposited film. These results suggest that colloidal CuIn3Se5 QD films could potentially be used as an active layer in low-cost highly efficient Cu(In,Ga)Se/CdS thin film solar cells.

Piezopotential-driven simulated electrocatalytic nanosystem of ultrasmall MoC quantum dots encapsulated in ultrathin N-doped graphene vesicles for superhigh H2 production from pure water

A simulated electrocatalytic nanosystem of MoC@NG assembled nanosheet is successfully constructed by a thermolysis procedure and first applied in piezocatalytic H 2 production from pure water. Owing to the unique configuration of MoC quantum dots (QDs) encapsulated in ultrathin N-doped graphene (NG) vesicles (MoC@NG), both the aggregation of MoC QDs and stack of ultrathin NG layers in MoC@NG are suppressed simultaneously. When the integration is subjected in mechanical vibration, ultrathin NG layers can provide piezoelectric potential to trigger hydrogen evolution reaction (HER) on MoC QDs, while MoC QDs could not only collect free electrons to achieve the carriers’ intercomponent separation, but also provide rich and high-activity HER sites with lower overpotential. The rate of piezocatalytic H 2 production from H 2 O is as high as 1.690 μmol h −1 mg −1 , which is the reported highest H 2 evolution rate of piezocatalytic water splitting without any sacrificial agents, even higher than ones in many photocatalytic pure water splitting systems. It is the synergy of piezoelectric ultrathin NG layers and conductive MoC QDs that predominantly contributes to a superhigh piezocatalytic performance. Furthermore, this design concept is expected to break a new ground in piezocatalysis. • MoC@NG is fabricated as a simulated electrocatalytic nanosystem. • MoC@NG has an unique configuration of ultrasmall MoC encapsulated in ultrathin NG. • MoC@NG is first applied in piezocatalytic H 2 evolution from pure H 2 O. • Ultrathin NG layers can provide piezoelectric potential to trigger HER on MoC QDs. • MoC@NG shows the reported highest H 2 evolution rate driven by piezopotential.

Ultrasmall BiOI Quantum Dots with Efficient Renal Clearance for Enhanced Radiotherapy of Cancer.

Emerging strategies involving nanomaterials with high‐atomic‐number elements have been widely developed for radiotherapy in recent years. However, the concern regarding their potential toxicity caused by long‐term body retention still limits their further application. In this regard, rapidly clearable radiosensitizers are highly desired for practical cancer treatment. Thus, in this work, ultrasmall BiOI quantum dots (QDs) with efficient renal clearance characteristic and strong permeability inside solid tumor are designed to address this issue. Additionally, considering that injection methods have great influence on the biodistribution and radiotherapeutic efficacy of radiosensitizers, two common injection methods including intratumoral injection and intravenous injection are evaluated. The results exhibit that intratumoral injection can maximize the accumulation of radiosensitizers within a tumor compared to intravenous injection and further enhance radiotherapeutic efficacy. Furthermore, the radiosensitizing effect of BiOI QDs is revealed, which is not only attributed to the radiation enhancement of high‐Z elements but also is owed to the •OH production via catalyzing overexpressed H2O2 within a tumor by BiOI QDs under X‐ray irradiation. As a result, this work proposes a treatment paradigm to employ ultrasmall radiosensitizers integrated with local intratumoral injection to realize rapid clearance and high‐efficiency radiosensitization for cancer therapy.

Ultrasmall SnS Quantum Dots Anchored onto Nitrogen-Enriched Carbon Nanospheres as an Advanced Anode Material for Sodium-Ion Batteries.

Structural pulverization of metal chalcogenides such as Sn-based compounds is a serious issue for development of high-performance anode materials and results in serious capacity fading during continuous charge and discharge cycles. In this work, we synthesize ultrasmall SnS quantum dots (QDs) anchored onto nitrogen-enriched carbon (NC) nanospheres through facile hydrothermal and carbonization processes to prepare a progressive anode material for sodium-ion batteries. The optimized SnS QDs@NC electrode delivered an initial discharge capacity of 281 mAh g-1 at 100 mA g-1 and exhibited excellent cycling stability with a capacity retention of 75% after 500 cycles at a high current density of 1000 mA g-1. Ex situ XRD, XPS, FE-SEM, TEM measurements, and kinetics study were performed to unveil the sodium storage mechanism of the SnS QDs@NC electrode. A sodium-ion full cell assembled with an SnS QDs@NC anode and a Na3V2(PO4)3 cathode exhibited high capacity and good cycling stability. Such a superior electrochemical performance of SnS QDs@NC can be attributed to the synergistic effects of NC and SnS QDs where NC serves as a conducting matrix to support SnS QDs and helps avoid structural degradation. This work provides a promising strategy to resolve the pulverization issue of alloying and conversion-type anode materials.

Human mesenchymal stem cells encapsulated-coacervated photoluminescent nanodots layered bioactive chitosan/collagen hydrogel matrices to indorse cardiac healing after acute myocardial infarction

Acute Myocardial Infarction (MI) is one of the foremost causes of human death worldwide and it leads to mass death of cardiomyocytes, interchanges of unfavorable biological environment and affecting electrical communications by fibrosis scar formations, and specifically deficiency of blood supply to heart which leads to heart damage and heart failure. Recently, numerous appropriate strategies have been applied to base on solve these problems wound be provide prominent therapeutic potential to cardiac regeneration after acute MI. In the present study, a combined biopolymeric conductive hydrogel was fabricated with conductive ultra-small graphene quantum dots as a soft injectable hydrogel for cardiac regenerations. The resultant hydrogel was combined with human Mesenchymal stem cells (hMSCs) to improved angiogenesis in cardiovascular tissues and decreasing cardiomyocyte necrosis of hydrogel treated acute-infarcted region has been greatly associated with the development of cardiac functions in MI models. The prepared graphene quantum dots and hydrogel groups was physico-chemically analyzed and confirmed the suitability of the materials for cardiac regeneration applications. The in vitro analyzes of hydrogels with hMSCs have established that enhanced cell survival rate, increased expressions of pro-inflammatory factors, pro-angiogenic factors and early cardiogenic markers. The results of in vivo myocardial observations and electrocardiography data demonstrated a favorable outcome of ejection fraction, fibrosis area, vessel density with reduced infarction size, implying that significant development of heart regenerative function after MI. This novel strategy of injectable hydrogel with hMSCs could be appropriate for the effective treatment of cardiac therapies after acute MI.

Ultrasmall aqueous starch-capped CuS quantum dots with tunable localized surface plasmon resonance and composition for the selective and sensitive detection of mercury(ii) ions.

Ultrasmall starch-capped CuS quantum dots (QDs) with controllable size were chemically fabricated in an aqueous medium. The phase of the CuS QDs was confirmed via X-ray diffraction (XRD), whereas the characteristic localized surface plasmon resonance (LSPR) peak in the near-infrared (NIR) region was measured using UV-Vis spectroscopy. Transmission electron microscopy and high bandgap analysis confirmed the formation of ultrasmall CuS QDs in the size range of 4–8 nm. CuS QDs have been used for the selective and sensitive detection of Hg2+ ions through colorimetric and spectroscopic techniques. The selective sensing of Hg2+ ions from various metal ions was detected via a remarkable change in color, damping in LSPR intensity, significant change in the Fourier-transform infrared spectra and X-ray photoelectron spectroscopic measurements. The mechanism of interaction between the CuS QDs and Hg2+ ions has been deeply explored in terms of the role played by the starch and the reorganization of sulfide and disulfide bonds to facilitate the access of Hg2+ ions into the CuS lattice. Finally, an intermediate Cu2−xHgxS nanostructure resulted in the leaching of Cu+ ions into the solution, which were further recovered and reused for the formation of fluorescent Cu2S nanoparticles. Thus, the entire process of synthesis, sensing and reuse paves the way for sustainable nanotechnology.

Daunomycin delivery by ultrasmall graphene quantum dots to DNA duplexes: understanding the dynamics by resonance energy transfer

Daunomycin (DN) is a natural product isolated from Streptomyces and it is widely used as a chemotherapeutic medication because of its antitumour properties. It is an anthracycline antibiotic that inhibits virus multiplication and shows activity against acute leukemia. This drug is either injected into a vein of the subject or typically delivered to cellular nuclei by polymeric or metallic nanoparticles and liposomal or proteinous substrates. The size of these delivering agents becomes a controlling factor affecting the interactions of this drug with nuclear DNA, where it intercalates. The fast-developing area of ultrasmall fluorescent graphene quantum dots (GQDs) provides a new platform for delivering DN, exploiting π-π stacking interactions between the planar anthracenyl moiety of the drug and the crystalline GQDs. The size of the GQDs might allow them to transport the medicine inside nuclei easily so that DN can intercalate between the DNA basal planes. Bringing DN close to the DNA duplex is essential, since the daunosamine residue of the drug binds to the minor groove, easing the intercalation of the anthracenyl moiety. The presented experimental analysis uses a fluorescence resonance energy transfer (FRET) mechanism to provide the details of the dynamics of the delivery of DN by GQDs and its subsequent uptake by the DNA duplex. The process is seen to be governed by differences in the binding constants and the non-interaction of the GQDs with DNA. This research provides vital input into understanding the mechanism of action of DN in greater detail, aiding its applicability in medical science.

In situ confined growth of ultrasmall perovskite quantum dots in metal-organic frameworks and their quantum confinement effect.

The metal halide perovskite quantum dots (APbX3 PeQDs; A = Cs or CH3NH3; X = Cl, Br or I) have emerged as a new type of promising optoelectronic material for light-emitting and photovoltaic applications because of their excellent optical properties. However, the precise control over the size and photoluminescence (PL) emission of APbX3 PeQDs remains a great challenge, which has been one of the main obstacles to the applications of PeQDs. Herein, we report a unique strategy for in situ confined growth of MAPbBr3 (MA = CH3NH3) PeQDs by using porous metal-organic framework (MOF) UiO-66 as a matrix. By introducing Pb(Ac)2 and MABr precursors into the pores of UiO-66 via a stepwise approach, ultrasmall MAPbBr3 PeQDs were in situ grown in the matrix with the size tuned from 6.4 to 3.3 nm by changing the concentration of the Pb(Ac)2 precursor. Accordingly, the PL emission wavelength of the resulting MAPbBr3 PeQDs was blue-shifted from 521 to 486 nm with the size reduction, owing to the strong quantum confinement effect of the PeQDs. Due to the surface passivation effect endowed by the UiO-66 matrix, the ultrasmall MAPbBr3 PeQDs also displayed a high PL quantum yield (PLQY) of 43.3% and a long PL lifetime of 100.3 ns. This study proposes a new strategy to prepare ultrasmall PeQDs and effectively control their sizes and PL emissions, which may open up new avenues for the development of high-performance luminescent PeQDs for diverse applications.

On-Demand Sonochemical Synthesis of Ultrasmall and Magic-Size CdSe Quantum Dots in Single-Phase and Emulsion Systems.

The sonochemical synthesis of CdSe quantum dots (QDs) in a single-liquid bulk phase and in an emulsion-based system is presented. Reactions utilized cadmium oleate and trioctylphosphine selenide precursors and were monitored as a function of sonication time under controlled temperature conditions to isolate the effects of cavitation from those of bulk temperature changes. QD synthesis was found to be slow in the single-phase liquid system (i.e., 1-octadecene) but greatly accelerated in the dispersed system (i.e., emulsions of 1-octadecene in ethylene glycol). It is hypothesized that the emulsion system increases the cavitation efficiency while also delivering acoustic energy in closer proximity to the precursor molecules. The capacity of CdSe production in the emulsion system was found to be 3.8 g/(L h), which is comparable to the typical hot-injection synthesis of CdSe QDs and can likely be further optimized. While the single-phase solvent system was found to produce ultrasmall QDs that exhibit broadband white-light emission, the emulsion system was found to produce well-defined magic-size clusters (MSCs) with photoluminescence quantum yield as high as 34%. Differences in synthesis rate and product properties from the emulsion and single-phase systems were probed by X-ray diffraction, electron microscopy, UV-visible (vis) and photoluminescence spectroscopy, and small-angle X-ray scattering (SAXS). Finally, precise temporal control of the QD synthesis was demonstrated via on-off cycling of the ultrasound waves.

N-Doped Carbon Quantum Dot (NCQD)-Deposited Carbon Capsules for Synergistic Fluorescence Imaging and Photothermal Therapy of Oral Cancer.

Use of nanomaterials blessed with both therapeutic and diagnostic properties is a proficient strategy in the treatment of cancer in its early stage. In this context, our paper reports the synthesis of uniform size N-rich mesoporous carbon nanospheres of size 65-70 nm from pyrrole and aniline precursors using Triton-X as a structure-directing agent. Transmission electron microscopy reveals that these carbons spheres contain void spaces in which ultrasmall nitrogen-doped quantum dots (NCQD) are captured within the matrix. These mesoporous hollow NCQD captured carbon spheres (NCQD-HCS) show fluorescence quantum yield up to 14.6% under λex = 340 nm. Interestingly, samples calcined at >800 °C clearly absorb in the wavelength range 700-1000 nm and shows light-to-heat conversion efficiency up to 52%. In vitro experiments in human oral cancer cells (FaDu) show that NCQD-HCS are internalized by the cells and induce a substantial thermal ablation effect in FaDu cells when exposed under a 980 nm near-infrared laser.

Bright Cool White Emission from Ultrasmall CdSe Quantum Dots

In this work, we employ a post-synthesis ligand treatment of ultrasmall CdSe quantum dots (QDs) with citric acid (CA) to increase the quantum yield (QY) of the as-synthesized CdSe from an average o...

2D Monoelemental Germanene Quantum Dots: Synthesis as Robust Photothermal Agents for Photonic Cancer Nanomedicine.

As a new family member of the emerging two-dimensional (2D) monoelemental materials (Xenes), germanene has shown promising advantages over the prototypical 2D Xenes, such as black phosphorus (BP) and graphene. However, efficient manufacture of novel germanene nanostructures is still a challenge. Herein, a simple top-down approach for the liquid-exfoliation of ultra-small germanene quantum dots (GeQDs) is presented. The prepared GeQDs possess an average lateral size of about 4.5 nm and thickness of about 2.2 nm. The functionalized GeQDs were demonstrated to be robust photothermal agents (PTAs) with outstanding photothermal conversion efficacy (higher than those of graphene and BPQDs), superior stability, and excellent biocompatibility. As a proof-of-principle, 2D GeQDs-based PTAs were used in fluorescence/photoacoustic/photothermal-imaging-guided hyperpyrexia ablation of tumors. This work could expand the application of 2D germanene to the field of photonic cancer nanomedicine.