Changhua Zhou

Inorganic Sn–X complex ligands capped CuInS2 nanocrystals with high electron mobility

We report a facile method for the synthesis of size-controlled triangular CuInS2 (CIS) semiconductor nanocrystals (NCs) in the organic phase, and then, molecular metal chalcogenide complexes capped CIS NCs can be synthesized by exchanging original organic compounds with (NH4)4Sn2S6 inorganic ligands in environmentally benign solvent. The properties of CIS NCs (coated by both organic and inorganic ligands) were characterized by UV–Vis spectroscopy, fourier transform infrared, transmission electron microscopy, X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, and dynamic light scattering. CuInS2 NCs (before and after ligand exchange) films were spin coated on cleaned ITO glass substrates, and the charge transport properties were detected by current-voltage characteristic. We observed that the ligands on the surface of CIS NCs have been exchanged successfully, and the electrical transparency of (NH4)4Sn2S6-CIS NCs films was obviously increased than CIS NCs with organic capping ligands.

Phosphine-free synthesis of Zn1−xCdxSe/ZnSe/ZnSexS1−x/ZnS core/multishell structures with bright and stable blue–green photoluminescence

Highly photoluminescent (PL) Zn1−xCdxSe/ZnSe/ZnSexS1−x/ZnS core/multishell nanocrystals were successfully synthesized by a phosphine-free method. Alloyed ZnSexS1−x was chosen as the shell material to epitaxially grow on pre-synthesized Zn1−xCdxSe nanocrystals. By decreasing the molar ratio between Se and S in ZnSexS1−x, the shell composition gradually changed from ZnSe to ZnS. The PL emissions of these core/multishell nanocrystals can be tuned from 450 to 530 nm. The PL quantum yields (QYs) of as-synthesized nanocrystals reached 50 to 75% with full width at half maximum (FWHM) between 28 and 45 nm. By an organic–aqueous phase transfer method, such core/multishell nanocrystals can be transferred into water successfully using an amphiphilic oligomer (polymaleic acid n-hexadecanol ester) as a surface coating agent. It was found that the shell thicknesses of the as-synthesized core/multishell nanocrystals dramatically affected the phase transfer efficiency. Stability tests showed that the water-soluble Zn1−xCdxSe/ZnSe/ZnSexS1−x/ZnS core/multishell nanocrystals with 10 monolayers of shells had very high PL QY and stability in various physiological conditions.

Targeting of embryonic stem cells by peptide-conjugated quantum dots.

Background Targeting stem cells holds great potential for studying the embryonic stem cell and development of stem cell-based regenerative medicine. Previous studies demonstrated that nanoparticles can serve as a robust platform for gene delivery, non-invasive cell imaging, and manipulation of stem cell differentiation. However specific targeting of embryonic stem cells by peptide-linked nanoparticles has not been reported. Methodology/Principal Findings Here, we developed a method for screening peptides that specifically recognize rhesus macaque embryonic stem cells by phage display and used the peptides to facilitate quantum dot targeting of embryonic stem cells. Through a phage display screen, we found phages that displayed an APWHLSSQYSRT peptide showed high affinity and specificity to undifferentiated primate embryonic stem cells in an enzyme-linked immunoabsorbent assay. These results were subsequently confirmed by immunofluoresence microscopy. Additionally, this binding could be completed by the chemically synthesized APWHLSSQYSRT peptide, indicating that the binding capability was specific and conferred by the peptide sequence. Through the ligation of the peptide to CdSe-ZnS core-shell nanocrystals, we were able to, for the first time, target embryonic stem cells through peptide-conjugated quantum dots. Conclusions/Significance These data demonstrate that our established method of screening for embryonic stem cell specific binding peptides by phage display is feasible. Moreover, the peptide-conjugated quantum dots may be applicable for embryonic stem cell study and utilization.

Synthesis of size-tunable photoluminescent aqueous CdSe/ZnS microspheres via a phase transfer method with amphiphilic oligomer and their application for detection of HCG antigen

High quality water-soluble photoluminescent (PL) microspheres consisting of CdSe/ZnS quantum dots (QDs) and amphiphilic oligomers (polymaleic acid n-hexadecanol ester) were prepared by a versatile phase transfer method in an emulsion system. Controlled synthesis of different sizes of PL microspheres can be conducted by simply changing the initial oligomer concentration and/or the water/chloroform volume ratio. When the oligomer/QDs molar ratio exceeded 200 : 1, only oligomer-coated monodisperse CdSe/ZnS QDs without any aggregation were obtained. If the molar ratio ranged from 20 : 1 to 120 : 1, size-tunable PL microspheres could be obtained with a size range from 151 to 50 nm. Both of them exhibited high stability in aqueous solution under a wide range of pH, different salt concentrations, and thermal treatment at 100 °C. FTIR spectroscopy, transmission electron microscopy, dynamic light scattering, and fluorescence microscopy were used to characterize the PL microspheres and oligomer-coated monodisperse QDs. It is demonstrated that the stability of PL microspheres indeed depended on their dimensions. Larger PL microspheres could provide more hydrophobic protection for their interior QDs than smaller PL microspheres. A biosensor system (lateral flow immunoassay system, LFIA) for the detection of human chorionic gonadotrophin (HCG) antigen was developed by using CdSe/ZnS PL microspheres as fluorescence labels and a nitrocellulose filter membrane for lateral flow. The result showed that the PL microspheres were excellent fluorescence labels to detect HCG antigen in this LFIA system. The sensitivity of HCG antigen detection can reach 0.5 IU L−1, which is almost 20 times higher than traditional LFIAs using tinctorial labels.

Multiplexed detection of influenza A virus subtype H5 and H9 via quantum dot-based immunoassay

Abstract A quantum dot-based lateral flow immunoassay system (QD-LFIAS) was developed to simultaneously detect both influenza A virus subtypes H5 and H9. Water-soluble carboxyl-functionalized quantum dots (QDs) were used as fluorescent tags. The QDs were conjugated to specific influenza A virus subtype H5 and H9 antibodies via an amide bond. When influenza A virus subtype H5 or H9 was added to the QD-LFIAS, the QD-labeled antibodies specifically bound to the H5 or H9 subtype viruses and were then captured by the coating antibodies at test line 1 or 2 to form a sandwich complex. This complex produced a bright fluorescent band in response to 365nm ultraviolet excitation. The intensity of fluorescence can be detected using an inexpensive, low-maintenance instrument, and the virus concentration directly correlates with the fluorescence intensity. The detection limit of the QD-LFIAS for influenza A virus subtype H5 was 0.016 HAU, and the detection limit of the QD-LFIAS for influenza A virus subtype H9 was 0.25 HAU. The specificity and reproducibility were good. The simple analysis step and objective results that can be obtained within 15min indicate that this QD-LFIAS is a highly efficient test that can be used to monitor and prevent both Influenza A virus subtypes H5 and H9.

Facile synthesis of high-quality CuInZnxS2+x core/shell nanocrystals and their application for detection of C-reactive protein

Highly photoluminescent (PL) CuInZnxS1+x nanocrystals (NCs) and CuInZnxS1+x/ZnS core/shell NCs were successfully synthesized by a facile colloidal method. First, a facile and reliable non-injection method for the synthesis of photoluminescent CuInZnxS2+x NCs was developed with inexpensive reagents. The relative PL quantum yields (QYs) of CuInZnxS2+x NCs could reach up to 30%, with tunable emissions in the range 580–780 nm. Then, CuInZnxS2+x/ZnS core/shell NCs were synthesized and showed greatly improved optical properties, the PL QY of the CuInZnxS2+x/ZnS NCs can reach up to 60%. Even in the near-infrared region, the PL QY still can achieve up to 45% due to the successful controlled red shift of PL during the ZnS shell growth process. More importantly, such core/shell NCs can be transferred into water successfully using amphiphilic oligomer (polymaleic acid n-hexadecanol ester) as a surface coating agent by an organic-aqueous phase transfer method and the PL QYs can be well controlled over 40%. Furthermore, a biosensor system (lateral flow immunoassays system, LFIA) for the detection of C-reactive protein (CRP) was developed by using this water-soluble CuInZnxS2+x/ZnS core/shell NCs as fluorescent label and a nitrocellulose filter membrane for lateral flow. The results showed that such CuInZnxS2+x/ZnS core/shell NCs were excellent fluorescent labels to detect CRP. The detection sensitivity for CRP could reach 1 ng mL−1.

Controlled synthesis of different types iron oxides nanocrystals in paraffin oil

Monodisperse Fe3O4 and FeO nanocrystals (NCs) with different sizes (from 10 nm to 50 nm) and different shapes (cube, sphere, and ellipsoid) were synthesized by simply adjusting reaction temperature or molar ratio of Fe/oleic acid (OA) during the decomposition of FeO(OH) in noncoordinating solvent. The concentration of OA affected the nucleation and growth of NCs by improving the chemical reaction driving force during the syntheses of different types of iron oxide NCs. It has been found that the reaction temperature influenced the reaction activity between FeO(OH) and OA. The structure of Fe oleate complexes was studied using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM) were used for structural and chemical characterization of as-prepared iron oxide NCs.

Controlled synthesis of monodisperse manganese oxide nanocrystals

Monodisperse manganese oxide nanocrystals (NCs) have been successfully synthesized through the decomposition of Mn(acac)2 in nonpolar solvent. By simply adjusting the nucleation temperature, NCs with Mn3O4 or MnO structures were synthesized in sizes ranging from 5 to 25 nm. To obtain monodisperse NCs, the growth temperature was set at 30 °C lower than the nucleation temperature by injecting paraffin oil. It has been demonstrated that every ligand (including oleic acid, oleylamine, and dodecanol) played an important role during the synthesis process. The structure and shape properties of manganese oxide NCs synthesized with different ligands have been studied and characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and transmission electron microscopy (TEM).

Facile preparation of metal telluride nanocrystals using di-n-octylphosphine oxide (DOPO) as an air-stable and less toxic alternative to the common tri-alkylphosphines

In this paper, we have developed a “green” method for the synthesis of metal telluride nanocrystals. In this method, di-n-octylphosphine oxide (DOPO) has been used to disperse Te and form Te–DOPO precursor. This new Te precursor was found to be highly reactive and suitable for the synthesis of metal telluride nanocrystals in various monodispersity, size, and shape. Dot-/tetrapod-shaped CdTe, dot-shaped ZnTe, dot-/cubic-shaped PbTe, dot-/rod-shaped Ag2Te, cubic-shaped Cu2−xTe, ternary alloyed CuInTe2, and quaternary alloyed Cu2ZnSnTe4 semiconductor nanocrystals all have been well-controlled synthesized. The photoluminescence emission of as-synthesized CdTe nanocrystals covered a wide range (570–735 nm) and the quality of as-synthesized metal telluride nanocrystals were reached or exceed the level compared with the traditional method using phosphine–Te precursor. The possible dissolving molecular mechanism of Te in DOPO in this synthesis was specially studied and illustrated that intramolecular proton transfer from the phosphorus (formation of DOPO–Te complex) was essential in the synthesis of metal telluride nanocrystals. This method provided a greener and less expensive route to large-scale synthesis of all kinds of high quality metal telluride nanocrystals.

Synthesis of silica protected photoluminescence QDs and their applications for transparent fluorescent films with enhanced photochemical stability

In this paper, we have demonstrated a novel and simple way to prepare transparent composite fluorescent films by using poly (acrylic acid) co-polymer as a matrix and silica coated photoluminescence (PL) quantum dots (QDs) as light-emitting materials. The strategies include preparing aqueous amphiphilic oligomer (polymaleic acid n-hexadecanol ester, PMAH) modified QDs, encapsulating the aqueous QDs in silica with a modified Stöber method and fabricating the QD-PMAH-SiO(2)-polymer composite fluorescent films with a spin-coating method. The obtained light-emitting thin films were transparent under room light and showed bright red, green and deep-blue light under the irradiation of UV light. The PL intensity of the composite films increased incrementally with the number of layers and the concentration of QD-PMAH-SiO(2) within each film. A white light emitting film was also fabricated by combining the silica coated red, green and deep-blue QDs in a proper ratio. Moreover, the photochemical stability of the QD-PMAH-SiO(2) in composite film was enhanced significantly compared with PMAH coated QDs, because of a thicker and compact passivating silica layer formed on the surfaces of the PL QDs.