Facile synthesis of ZnS-CuInS2-alloyed nanocrystals for a color-tunable fluorchrome and photocatalyst

Peptide-functionalized ZCIS QDs as fluorescent nanoprobe for targeted HER2-positive breast cancer cells imaging

In this paper, the synthesis of alloyed CuInZnxS2+x quantum dots (ZCIS QDs), their transfer into aqueous solution via a polymer coating technique, and the use of these nanocrystals to selectively target HER2-positive cells, are reported. By optimizing first the ZnS shell deposition process onto the CuInS2 core, and next the encapsulation of the dots with the amphiphilic poly(maleic anhydride-alt-1-octadecene) (PMAO) polymer, water-dispersible ZCIS QDs were successfully prepared. The nanocrystals with a photoluminescence quantum yield of 35% were purified via centrifugation and ultracentrifugation and high quality nanoparticles with narrow size distributions and surface charges were obtained. After verifying the biocompatibility of PMO-coated ZCIS QDs, we coupled these nanocrystals with the LTVSPWY peptide and demonstrated via MTT assay that both bare and the peptide-linked QDs exhibit low cytotoxicity. The HER2-mediated delivery of the peptide-linked QDs was confirmed by confocal microscopy. This study indicates that as engineered QDs can efficiently be used as fluorescent nanoprobes for selective labelling of HER2-positive SKBR3 cancer cells.

Multinary I-III-VI2 and I2-II-IV-VI4 Semiconductor Nanostructures for Photocatalytic Applications

Semiconductor nanostructures that can effectively serve as light-responsive photocatalysts have been of considerable interest over the past decade. This is because their use in light-induced photocatalysis can potentially address some of the most serious environmental and energy-related concerns facing the world today. One important application is photocatalytic hydrogen production from water under solar radiation. It is regarded as a clean and sustainable approach to hydrogen fuel generation because it makes use of renewable resources (i.e., sunlight and water), does not involve fossil fuel consumption, and does not result in environmental pollution or greenhouse gas emission. Another notable application is the photocatalytic degradation of nonbiodegradable dyes, which offers an effective way of ridding industrial wastewater of toxic organic pollutants prior to its release into the environment. Metal oxide semiconductors (e.g., TiO2) are the most widely studied class of semiconductor photocatalysts. Their nanostructured forms have been reported to efficiently generate hydrogen from water and effectively degrade organic dyes under ultraviolet-light irradiation. However, the wide band gap characteristic of most metal oxides precludes absorption of light in the visible region, which makes up a considerable portion of the solar radiation spectrum. Meanwhile, nanostructures of cadmium chalcogenide semiconductors (e.g., CdS), with their relatively narrow band gap that can be easily adjusted through size control and alloying, have displayed immense potential as visible-light-responsive photocatalysts, but the intrinsic toxicity of cadmium poses potential risks to human health and the environment. In developing new nanostructured semiconductors for light-driven photocatalysis, it is important to choose a semiconducting material that has a high absorption coefficient over a wide spectral range and is safe for use in real-world settings. Among the most promising candidates are the multinary chalcogenide semiconductors (MCSs), which include the ternary I-III-VI2 semiconductors (e.g., AgGaS2, CuInS2, and CuInSe2) and the quaternary I2-II-IV-VI4 semiconductors (e.g., Cu2ZnGeS4, Cu2ZnSnS4, and Ag2ZnSnS4). These inorganic compounds consist of environmentally benign elemental components, exhibit excellent light-harvesting properties, and possess band gap energies that are well-suited for solar photon absorption. Moreover, the band structures of these materials can be conveniently modified through alloying to boost their ability to harvest visible photons. In this Account, we provide a summary of recent research on the use of ternary I-III-VI2 and quaternary I2-II-IV-VI4 semiconductor nanostructures for light-induced photocatalytic applications, with focus on hydrogen production and organic dye degradation. We include a review of the solution-based methods that have been employed to prepare multinary chalcogenide semiconductor nanostructures of varying compositions, sizes, shapes, and crystal structures, which are factors that are known to have significant influence on the photocatalytic activity of semiconductor photocatalysts. The enhancement of photocatalytic performance through creation of hybrid nanoscale architectures is also presented. Lastly, views on the current challenges and future directions are discussed in the concluding section.

A facile method for the synthesis of CuInS2–ZnS quantum dots with tunable photoluminescent properties

CuInS₂/CuInS₂–ZnS quantum dots showed excellent tunable photoluminescent properties, which demonstrate great potential for practical applications due to their non-toxicity and excellent optical properties.

Facile surface engineering of CuInS2/ZnS quantum dots for LED down-converters

Surface engineered CuInS₂ quantum dots with extraodrinary properties in polymer nanocomposites and high stability in sol–gel silica are presented herein.

Synthesis of highly white-fluorescent Cu–Ga–S quantum dots for solid-state lighting devices

Highly efficient, white-emitting Cu–Ga–S quantum dots are synthesized and applied as down-converters for white lighting device fabrication.

Room-temperature and gram-scale synthesis of CsPbX3 (X = Cl, Br, I) perovskite nanocrystals with 50–85% photoluminescence quantum yields

CsPbX₃ perovskite quantum dots with 50–85% photoluminescence quantum yields have been successfully synthesized at room temperature in open air.

Quaternary alloy quantum dots with widely tunable emission – a versatile system to fabricate dual-emission nanocomposites for bio-imaging

Highly luminescent Zn-I-III-VI-based QDs with widely composition-tuned PL emissions have been synthesized for multiscale biomedical optical imaging.

Optimized synthesis of CuInS2/ZnS:Al–TiO2 nanocomposites for 1,3-dichloropropene photodegradation

CuInS₂/ZnS:Al–TiO₂ nanocomposites were optimally prepared by response surface methodology and could be highly efficient for soil fumigant photodegradation.

Temperature-dependent photoluminescence of cadmium-free Cu-Zn-In-S quantum dot thin films as temperature probes

We reported temperature-dependent photoluminescence (PL) studies on Cu-Zn-In-S quantum dot (QD) thin films. In this paper, cadmium-free and luminescent Cu-Zn-In-S quantum dot thin films were in situ formed by thermal decomposition of molecular-based precursors in the open air, without need of the complicated quantum dot synthesis. Molecular-based precursor solutions were prepared by dissolving Cu2O, ZnO, and In(OH)3 in the ethanol solution of butylamine and carbon disulfide. The effects of sintering temperature, sintering time, and the concentration of capping agents on the photoluminescence properties of Cu-Zn-In-S QD thin films have been systematically investigated. It was found that alkali metal ions play an important role in enhancing the PL quantum yield of quantum dot thin films. The as-prepared QD thin films show composition-tunable emission in the range of 535 nm to 677 nm, and the absolute PL quantum yields can reach as high as 22.1%. All of the as-deposited QD thin films show a single-exponential decay to temperature, indicating that these cadmium-free QD thin films have high potential as temperature probes.

Investigation of the size-property relationship in CuInS2 quantum dots

In this work we investigated fundamental properties of CuInS2 quantum dots in dependence of the particle size distribution (PSD). Size-selective precipitation (SSP) with acetone as poor solvent was performed as an adequate post-processing step. Our results provide deep insight into the correlation between particle size and various optical characteristics as bandgap energy, absorption and emission features and the broadness of the emission signal. These structure-property relationships are only achieved due to the unique combination of different analytical techniques. Our study reveals that the removal of 10 wt% of smallest particles from the feed results in an enhancement of the emission signal. This improvement is ascribed to a decreased quenching of the emission in larger particles. Our results reveal the impact of PSDs on the properties and the performance of an ensemble of multicomponent QDs and anticipate the high potential of controlling PSDs by well-developed post-processing.

Small GSH-Capped CuInS2 Quantum Dots: MPA-Assisted Aqueous Phase Transfer and Bioimaging Applications

An efficient ligand exchange strategy for aqueous phase transfer of hydrophobic CuInS2/ZnS quantum dots was developed by employing glutathione (GSH) and mercaptopropionic acid (MPA) as the ligands. The whole process takes less than 20 min and can be scaled up to gram amount. The material characterizations show that the final aqueous soluble samples are solely capped with GSH on the surface. Importantly, these GSH-capped CuInS2/ZnS quantum dots have small size (hydrodynamic diameter <10 nm), moderate fluorescent properties (up to 34%) as well as high stability in aqueous solutions (stable for more than three months in 4 °C without any significant fluorescence quenching). Moreover, this ligand exchange strategy is also versatile for the aqueous phase transfer of other hydrophobic quantum dots, for instance, CuInSe2 and CdSe/ZnS quantum dots. We further demonstrated that GSH-capped quantum dots could be suitable fluorescence markers to penetrate cell membrane and image the cells. In addition, the GSH-capped CuInS2 quantum dots also have potential use in other fields such as photocatalysis and quantum dots sensitized solar cells.

Nanocrystals of Cesium Lead Halide Perovskites (CsPbX₃, X = Cl, Br, and I): Novel Optoelectronic Materials Showing Bright Emission with Wide Color Gamut

Metal halides perovskites, such as hybrid organic-inorganic CH3NH3PbI3, are newcomer optoelectronic materials that have attracted enormous attention as solution-deposited absorbing layers in solar cells with power conversion efficiencies reaching 20%. Herein we demonstrate a new avenue for halide perovskites by designing highly luminescent perovskite-based colloidal quantum dot materials. We have synthesized monodisperse colloidal nanocubes (4-15 nm edge lengths) of fully inorganic cesium lead halide perovskites (CsPbX3, X = Cl, Br, and I or mixed halide systems Cl/Br and Br/I) using inexpensive commercial precursors. Through compositional modulations and quantum size-effects, the bandgap energies and emission spectra are readily tunable over the entire visible spectral region of 410-700 nm. The photoluminescence of CsPbX3 nanocrystals is characterized by narrow emission line-widths of 12-42 nm, wide color gamut covering up to 140% of the NTSC color standard, high quantum yields of up to 90%, and radiative lifetimes in the range of 1-29 ns. The compelling combination of enhanced optical properties and chemical robustness makes CsPbX3 nanocrystals appealing for optoelectronic applications, particularly for blue and green spectral regions (410-530 nm), where typical metal chalcogenide-based quantum dots suffer from photodegradation.

Synthesis and characterization of green Zn-Ag-In-S and red Zn-Cu-In-S quantum dots for ultrahigh color quality of down-converted white LEDs

Eco-friendly green Zn-Ag-In-S (ZAIS) and red Zn-Cu-In-S (ZCIS) core/shell-like alloyed quantum dots (QDs) have been synthesized by a facile hot-injection method with a multiple injection approach. Broad full-width at half-maximum (fwhm) of the photoluminescence (PL) emission and tunability of the green ZAIS and red ZCIS QDs were obtained by adopting a low-temperature core growth and high-temperature multiple alloyed reaction. The alloyed green ZAIS and red ZCIS QDs reached PL quantum yields as high as 0.61 and 0.53; fwhm of the PL peaks were as wide as 81 and 106 nm, respectively. This demonstrates the practical realization of white down-converted light-emitting diodes (DC-LEDs), fully covering the whole visible wavelength range and the cyan gap, using two broad fwhm green ZAIS and red ZCIS QDs. We also characterized the vision and color performance using luminous efficacy (LE), color rendering index (CRI), special CRI for strong red (R9), and color quality scale (CQS) of white DC-LEDs incorporated with green ZAIS and red ZCIS QDs at the correlated color temperature (CCT) range of 2700-10 000 K. The tricolor white DC-LED using broad fwhm green-emitting ZAIS and red-emitting ZCIS core/shell-like alloyed QDs exhibits a moderate LE (31.2 lm/W) and ultrahigh color qualities (CRI = 97, R9 = 97, and CQS = 94) with warm white at a CCT of 3500 K.

Highly bright yellow-green-emitting CuInS₂ colloidal quantum dots with core/shell/shell architecture for white light-emitting diodes

In this study, we report bright yellow-green-emitting CuInS2 (CIS)-based quantum dots (QDs) and two-band white light-emitting diodes (LEDs) using them. To achieve high quantum efficiency (QE) of yellow-green-emitting CIS QDs, core/shell/shell strategy was introduced to high quality CIS cores (QE = 31.7%) synthesized by using metal-oleate precursors and 1-dodecanethiol. The CIS/ZnS/ZnS QDs showed a high QE of 80.0% and a peak wavelength of 559 nm under the excitation of 450 nm, which is well matched with dominant wavelength of blue LEDs. The formation of core/shell/shell structure was confirmed by X-ray diffraction, transmission electron microscopy, and inductively coupled plasma-optical emission spectroscopy analyses. Intense and broad yellow-green emission band of the CIS/ZnS/ZnS is beneficial for bright two-band white light. When the CIS/ZnS/ZnS was coated on the blue LEDs, the fabricated white LED showed bright natural white light (luminous efficacy (η(L)) = 80.3 lm·W(-1), color rendering index (R(a)) = 73, correlated color temperature (T(c)) = 6140 K). The QD-white LED package showed a high light conversion efficiency of 72.6%. In addition, the CIS/ZnS/ZnS-converted white LED showed relatively stable white light against the variation of forward bias currents of 20-150 mA [color coordinates (x, y) = (0.3320-0.3207, 0.2997-0.2867), R(a) = 70-72, T(c) = 5497-6375 K].

Recent progress in magnetic iron oxide-semiconductor composite nanomaterials as promising photocatalysts

Photocatalytic degradation of toxic organic pollutants is a challenging tasks in ecological and environmental protection. Recent research shows that the magnetic iron oxide-semiconductor composite photocatalytic system can effectively break through the bottleneck of single-component semiconductor oxides with low activity under visible light and the challenging recycling of the photocatalyst from the final products. With high reactivity in visible light, magnetic iron oxide-semiconductors can be exploited as an important magnetic recovery photocatalyst (MRP) with a bright future. On this regard, various composite structures, the charge-transfer mechanism and outstanding properties of magnetic iron oxide-semiconductor composite nanomaterials are sketched. The latest synthesis methods and recent progress in the photocatalytic applications of magnetic iron oxide-semiconductor composite nanomaterials are reviewed. The problems and challenges still need to be resolved and development strategies are discussed.

Photocarrier recombination dynamics in ternary chalcogenide CuInS2 quantum dots

Photocarrier recombination dynamics in ternary chalcogenide CuInS₂ quantum dots (CIS QDs) was studied by means of femtosecond transient-absorption (TA) and nanosecond time-resolved photoluminescence (PL) spectroscopy.

Air-exposing microwave-assisted synthesis of CuInS2/ZnS quantum dots for silicon solar cells with enhanced photovoltaic performance

CIS/ZnS QDs were synthesized by microwave irradiation in air. The fabricated QDs/PMMA composite films were first applied to Si solar cells to improve the conversion efficiency by 3.8%.

Highly luminescent, off-stoichiometric CuxInyS2/ZnS quantum dots for near-infrared fluorescence bio-imaging

We synthesized highly luminescent, NIR-emitting copper–indium–sulfur/zinc sulfide (CIS/ZnS) core–shell QDs with a high photoluminescence quantum yield (about 60%) using a heating up method.

One-pot synthesis of colloidal Cdx:CuInS2 quaternary quantum dots used as sensitizers in photovoltaic cells

Cd_x:CuInS₂ quaternary QDs were obtained in a one-pot reaction; these quaternary QDs exhibited enhanced photovoltaic performance compared to pristine CuInS₂ ternary QDs.

Controlled synthesis of ZnxCd1−xS nanorods and their composite with RGO for high-performance visible-light photocatalysis

Zn_0.5Cd_0.5S nanorods with a suitable bandgap and aspect ratio displayed the highest photoresponse to visible light. Zn_0.5Cd_0.5S/RGO nanocomposites with line-to-line interface exhibited enhanced photocatalytic activity.

A near infrared fluorescent/ultrasonic bimodal contrast agent for imaging guided pDNA delivery via ultrasound targeted microbubble destruction

MBs@QDs@PEI/pDNA was prepared to operate as a NIR/Ultrasound bimodal imaging guided platform for targeting delivery of pDNA by UTMD.

The composition effect on the optical properties of aqueous synthesized Cu–In–S and Zn–Cu–In–S quantum dot nanocrystals

The relationship between the optical properties and the compositional variation was investigated in aqueous synthesized Cu–In–S and Zn–Cu–In–S QDs.

Soft template mediated synthesis of Bi–In–Zn–S and its efficient visible-light-driven decomposition of methylene blue

Bi–In–Zn–S nanostructures were successfully synthesized in PEG-PPG-PEG at various temperatures and are used as recyclable photocatalysts for the degradation of methylene blue under visible light (sunlight and 200 W tungsten lamp).

Color Tunable Gd-Zn-Cu-In-S/ZnS Quantum Dots for Dual Modality Magnetic Resonance and Fluorescence Imaging

Inorganic nanoparticles have been introduced into biological systems as useful probes for in vitro diagnosis and in vivo imaging, due to their relatively small size and exceptional physical and chemical properties. A new kind of color tunable Gd-Zn-Cu-In-S/ZnS (GZCIS/ZnS) quantum dots (QDs) with stable crystal structure was successfully synthesized and utilized for magnetic resonance (MR) and fluorescence dual modality imaging. This strategy allows successful fabrication of GZCIS/ZnS QDs by incorporating Gd into ZCIS/ZnS QDs to achieve great MR enhancement without compromising the fluorescence properties of the initial ZCIS/ZnS QDs. The as-prepared GZCIS/ZnS QDs show high T₁ MR contrast as well as "color-tunable" photoluminescence (PL) in the range of 550-725 nm by adjusting the Zn/Cu feeding ratio with high PL quantum yield (QY). The GZCIS/ZnS QDs were transferred into water via a bovine serum albumin (BSA) coating strategy. The resulting Cd-free GZCIS/ZnS QDs reveal negligible cytotoxicity on both HeLa and A549 cells. Both fluorescence and MR imaging studies were successfully performed in vitro and in vivo. The results demonstrated that GZCIS/ZnS QDs could be a dual-modal contrast agent to simultaneously produce strong MR contrast enhancement as well as fluorescence emission for in vivo imaging.

A facile method for the synthesis of quaternary Ag-In-Zn-S alloyed nanorods

Ag-In-Zn-S nanorods with tunable photoluminescence were formed by a convenient synthetic approach, and the nanorods demonstrated a relatively long fluorescence lifetime of 1.248 μs. In addition, Ag-In-Zn-S nanorods of nail shape and rod-particle dimers were successfully produced by adjusting the reaction parameters.

All-solution-processed, multilayered CuInS₂/ZnS colloidal quantum-dot-based electroluminescent device

While significant progress of electroluminescent (EL) quantum dot light-emitting diodes (QD-LEDs) that rely exclusively on Cd-containing II-VI quantum dots (QDs) has been reported over the past two decades with respect to device processing and performance, devices based on non-Cd QDs as an active emissive layer (EML) remain at the early stage of development. In this work, utilizing highly luminescent colloidal CuInS2 (CIS)/ZnS QDs, all-solution-processed multilayered QD-LEDs are fabricated by sequentially spin depositing a hole transport layer of poly(9-vinlycarbazole), an EML of CIS/ZnS QDs, and an electron transport layer of ZnO nanoparticles. Our focus in device fabrication is to vary the thickness of the QD EML, which is one of the primary determinants in EL performance but has not been addressed in earlier reports. The device with an optimal EML thickness exhibits a peak luminance of 1564  cd/m2 and current efficiency of 2.52  cd/A. This record value in efficiency is higher by 3-4 times that of CIS QD-LEDs reported previously.

White lighting device from composite films embedded with hydrophilic Cu(In, Ga)S2/ZnS and hydrophobic InP/ZnS quantum dots

Two types of non-Cd quantum dots (QDs)-In/Ga ratio-varied, green-to-greenish-yellow fluorescence-tuned Cu-In-Ga-S (CIGS) alloy ones, and red-emitting InP ones-are synthesized for use as down-converters in conjunction with a blue light-emitting diode (LED). Among a series of Ga-rich CI1-xGxS/ZnS core/shell QDs (x = 0.7, 0.8, and 0.9), CI0.2G0.8S/ZnS QD is chosen for the hydrophobic-to-hydrophilic surface modification via an in-situ ligand exchange and then embedded in a water-soluble polyvinyl alcohol (PVA). This free-standing composite film is utilized as a down-converter for the fabrication of a remote-type white QD-LED, but the resulting bi-colored device exhibits a cool white light with a limited color rendering index property. To improve white light qualities, another QD-polymer film of hydrophobic red InP/ZnS QD-embedding polyvinylpyrrolidone is sequentially stacked onto the CI0.2G0.8S/ZnS QD-PVA film, producing a unique dual color-emitting, flexible and transparent bilayered composite film. Tri-colored white QD-LED integrated with the bilayered QD film possesses an exceptional color rendering property through reinforcing a red spectral component and balancing a white spectral distribution.

Large-scale synthesis of highly emissive and photostable CuInS2/ZnS nanocrystals through hybrid flow reactor

We report a high-yield, low-cost synthesis route to colloidal CuInS2/ZnS (CIS/ZnS) nanocrystals (NCs) with Cu vacancies in the crystal lattice. Yellow-emitting CIS/ZnS core/shell NCs of high luminescence were facilely synthesized via a stepwise, consecutive hybrid flow reactor approach. It is based on serial combination of a batch-type mixer and a flow-type furnace. In this reactor, the flow rate of the solutions was typically 1 mL/min, 100 times larger than that of conventional microfluidic reactors. This method can produce gram quantities of material with a chemical yield in excess of 90% with minimal solvent waste. This is a noninjection-based approach in 1-dodecanethiol (DDT) with excellent synthetic reproducibility and large-scale capability. The optical features and structure of the obtained CIS/ZnS NCs have been characterized by UV-vis and fluorescence spectroscopies, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDX) and high-resolution transmission electron microscopy (HRTEM). The resulting CIS/ZnS NCs in chloroform exhibit quantum yield (QY) of 61.4% with photoemission peaking at 561 nm and full width at half maximum (FWHM) of 92 nm. The as-synthesized CIS/ZnS NCs were proven to have excellent photostability. The synthesized CIS/ZnS NCs can be a promising fluorescent probe for biological imaging and color converting material for light-emitting diode due to Cd-free constituents.

Ag/Cu co-doped ZnS–In2S3 solid solutions: facile synthesis, theoretical calculations and enhanced photocatalytic activity

ZnS–In₂S₃ nanospheres were prepared by a simple hydrothermal method without using any organic solvents or templates.

Low-cost and gram-scale synthesis of water-soluble Cu-In-S/ZnS core/shell quantum dots in an electric pressure cooker

We report an electric pressure cooker for large-scale synthesis of water-soluble Cu-In-S/ZnS core/shell quantum dots. Low-cost thioglycolic acid and sodium citrate were used as the dual stabilizers. ∼3 grams of quantum dots with a tunable emission from 545 to 610 nm and quantum yield up to 40% were obtained in a batch.

Synthesis and application of colloidal CuInS2 semiconductor nanocrystals

Semiconductor nanocrystals possess size-dependent properties, which make them interesting candidates for a variety of applications, e.g., in solar energy conversion, lighting, display technology, or biolabelling. However, many of the best studied nanocrystalline materials contain toxic heavy metals; this seriously limits their potential for widespread application. One of the possible less toxic alternatives to cadmium- or lead-containing semiconductors is copper indium disulfide (CIS), a direct semiconductor with a bandgap in the bulk of 1.45 eV and a Bohr exciton radius of 4.1 nm. This Review gives an overview of the methods developed during the last years to synthesize CIS nanocrystals and summarizes the possibilities to influence their shape, composition and crystallographic structure. Also the potential of the application of CIS nanocrystals in biolabellling, photocatalysis, solar energy conversion, and light-emitting devices is discussed.

Cadmium and Zinc Alloyed Cu-In-S Nanocrystals and Their Optical Properties

Cadmium (Cd) and zinc (Zn) alloyed copper-indium-sulfide (Cu-In-S or CIS) nanocrystals (NCs) in several nanometers were prepared using thermal decomposition methods, and the effects of Cd and Zn on optical properties, including the tuning of NC photoluminescence (PL) wavelength and quantum yield (QY), were investigated. It was found that incorporation of Cd into CIS enhances the peak QY of NCs whereas zinc alloying diminishes the peak. In contrast with Zn alloying, Cd alloying does not result in a pronounced luminescence blue shift. The further PL decay study suggests that Cd alloying reduces surface or intrinsic defects whereas alloying with Zn increases the overall number of defects.

Adenosine capped QDs based fluorescent sensor for detection of dopamine with high selectivity and sensitivity

Facile detection of dopamine (DA) in biological samples for diagnostics remains a challenge. This paper reported an effective fluorescent sensor based on adenosine capped CdSe/ZnS quantum dots (A-QDs) for highly sensitive detection of DA in human urine samples. In this assay, adenosine serves as a capping ligand or stabilizer for QDs to render high-quality QDs dispersed in water, and as a receptor for DA to attach DA onto the surface of A-QDs. DA molecules can bind to A-QDs via non-covalent bonding, leading to the fluorescence quenching of A-QDs due to electron transfer. The A-QDs based fluorescence probe showed a limit of detection (LOD) of ca. 29.3 nM for DA detection. This facile method exhibited high selectivity and anti-interference in the presence of amino acid, ascorbic acid (AA), uric acid (UA) and glucide with 100-fold higher concentration in PBS solution. Furthermore, it was also successfully used in the detection of DA in the human urine samples with quantitative recoveries (94.80-103.40%).

Simple continuous-flow synthesis of Cu-In-Zn-S/ZnS and Ag-In-Zn-S/ZnS core/shell quantum dots

We present a simple continuous-flow reaction for the synthesis of quaternary Cu-In-Zn-S/ZnS and Ag-In-Zn-S/ZnS core/shell quantum dots (QDs) using inexpensive and low-toxic precursors. The composition and band gap of Cu-In-Zn-S and Ag-In-Zn-S QDs were well controlled by changing the molar ratios of the starting materials. The PL quantum yields of Cu-In-Zn-S/ZnS core/shell quantum dots can reach as high as 40%.

Fluorescent cellulose aerogels containing covalently immobilized (ZnS)x(CuInS2)1-x/ZnS (core/shell) quantum dots

Photoluminiscent (PL) cellulose aerogels of variable shape containing homogeneously dispersed and surface-immobilized alloyed (ZnS)x(CuInS2)1-x/ZnS (core/shell) quantum dots (QD) have been obtained by (1) dissolution of hardwood prehydrolysis kraft pulp in the ionic liquid 1-hexyl-3-methyl-1H-imidazolium chloride, (2) addition of a homogenous dispersion of quantum dots in the same solvent, (3) molding, (4) coagulation of cellulose using ethanol as antisolvent, and (5) scCO2 drying of the resulting composite aerogels. Both compatibilization with the cellulose solvent and covalent attachment of the quantum dots onto the cellulose surface was achieved through replacement of 1-mercaptododecyl ligands typically used in synthesis of (ZnS)x(CuInS2)1-x/ZnS (core-shell) QDs by 1-mercapto-3-(trimethoxysilyl)-propyl ligands. The obtained cellulose-quantum dot hybrid aerogels have apparent densities of 37.9-57.2 mg cm-3. Their BET surface areas range from 296 to 686 m2 g-1 comparable with non-luminiscent cellulose aerogels obtained via the NMMO, TBAF/DMSO or Ca(SCN)2 route. Depending mainly on the ratio of QD core constituents and to a minor extent on the cellulose/QD ratio, the emission wavelength of the novel aerogels can be controlled within a wide range of the visible light spectrum. Whereas higher QD contents lead to bathochromic PL shifts, hypsochromism is observed when increasing the amount of cellulose at constant QD content. Reinforcement of the cellulose aerogels and hence significantly reduced shrinkage during scCO2 drying is a beneficial side effect when using α-mercapto-ω-(trialkoxysilyl) alkyl ligands for QD capping and covalent QD immobilization onto the cellulose surface.

Optimizing the synthesis of red- and near-infrared CuInS2 and AgInS2 semiconductor nanocrystals for bioimaging

This work reports the study of optimization of the reaction parameters on the synthesis of high quality CuInS2 and AgInS2 nanocrystals for bioimaging applications. The concentration of reaction precursors (e.g. Ag, Cu, In and S) plays a key role in determining the emission profile of these ternary quantum dots (QDs). By carefully varying the precursor compositions, the emission of QD can be tuned from red to near infrared (NIR) region. Taking the advantages of NIR emission, which possesses minimal absorption in biological tissues, we have also prepared water-dispersible CuInS2/ZnS and AgInS2/ZnS nanocrystals and demonstrated the high biocompatibility for both deep tissue penetration and tumor targeting. The QDs were stabilized in Pluronic F127 block copolymer micelles, offering us optically and colloidally stable contrast agents for in vitro and in vivo imaging. Two-photon excitation of QD has also been demonstrated, accomplishing a NIR-to-NIR transaction. This study devotes the key steps in promoting the use of ternary QDs as low-toxic, photostable, and cadmium-free semiconductor nanocrystal formulation for multiple imaging applications.

A facile integration of zero- (I-III-VI quantum dots) and one- (single SnO2 nanowire) dimensional nanomaterials: fabrication of a nanocomposite photodetector with ultrahigh gain and wide spectral response

Via the integration of nanocomposites comprising I-III-VI semiconductor quantum dots (QDs) decorated onto a single SnO2 nanowire (NW), we successfully fabricate an ultrahigh-sensitivity and wide spectral-response photodetector. Under the illumination of He-Cd laser (325 nm) with the photon energy larger than the band gap of SnO2 nanowire, remarkably, an ultrahigh photocurrent gain up to 2.5 × 10(5) has been achieved, and an enhancement factor can reach up to 700% (cf. bare SnO2 NW) as light illumination onto the wire with an excitation intensity of 15 W/m(2). Also, a high gain value up to 1.3 × 10(5) is attained with the excited photon energy (488 nm) smaller than the band gap of SnO2 nanowire. Several key factors contribute to ultrahigh photocurrent gain and wide spectral response. First, the decorated quantum dot processes an inherent nature of a large absorption coefficient above its band gap. Furthermore, the single SnO2 nanowire provides an excellent conduction path for the photogenerated carriers as well as bears a large surface-to-volume ratio so that the coupling strength with quantum dots can be greatly enhanced. Most importantly, the spatial separation of photogenerated electrons and holes can be easily achieved due to the charge transfer arising from a type II band alignment between QDs and SnO2 NW. This work thus demonstrates a new approach in which by selectively decorating suitable QDs the photocurrent gain of SnO2 NWs can be greatly enhanced and extended to a wide spectral range of photoresponse previously inaccessible, providing a very useful guideline to create cheap, nontoxic, and highly efficient photodetectors.

Integration of CuInS2-based nanocrystals for high efficiency and high colour rendering white light-emitting diodes

Here we explored the possibility of using CuInS2-based nanocrystals as colour converting materials for light-emitting applications. Using a mixture of red and green emissive CuInS2-based nanocrystals, we successfully fabricated high colour rendering white light-emitting diodes with surface mounted devices and high-power types. The devices exhibit improved luminous efficiency, high colour rendering index and tunable colour temperature. In particular, the low-power surface mounted devices have a luminous efficiency of ~70 lm W(-1), CRI of ~95 and tunable colour temperature of 4600-5600 K, which makes the CuInS2-based nanocrystals promising candidates for commercial applications.