Water-soluble quantum dots for biomedical applications

Semiconductor nanocrystals are 1-10nm inorganic particles with unique size-dependent optical and electrical properties due to quantum confinement (so they are also called quantum dots). Quantum dots are new types of fluorescent materials for biological labeling with high quantum efficiency, long-term photostability, narrow emission, and continuous absorption spectra. Here, we discuss the recent development in making water-soluble quantum dots and related cytotoxicity for biomedical applications.     

Large Voltage Generation of Flexible Thermoelectric Nanocrystal Thin Films by Finger Contact

This paper demonstrates that thermal energy radiated from a human finger can be converted efficiently into electricity by a nanocrystal (NC) thin film that substantially suppresses thermal conduction, but still allows electric conduction. The converting efficiencies of the chalcogenide NC thin films with dimensions 40 µm × 20 µm × 20 nm, prepared on flexible substrates by a solution process, are maximized by adjusting the NC size. A Seebeck coefficient of S = 1829 µV K^?1, and a dimensionless thermoelectric figure‐of‐merit, ZT = 0.68 are achieved at ambient temperature for p‐ and n‐type NC thin films, respectively. A thermoelectric array consisting of p‐ and n‐type NC thin films generates a voltage of 645 mV for a temperature gradient of 10 K. Furthermore, the donut‐shaped pn array can generate a voltage of 170 mV from the heat supplied by an individual's finger.     

Highly Efficient Flexible Hybrid Nanocrystal‐Cu(In,Ga)Se2 (CIGS) Solar Cells

A novel scheme for hybridizing inkjet‐printed thin film Cu(In,Ga)Se₂ (CIGS) solar cells with self‐assembled clusters of nanocrystal quantum dots (NQDs), which provides a 10.9% relative enhancement of the photon conversion efficiency (PCE), is demonstrated. A non‐uniform layer of NQD aggregates is deposited between the transparent conductive oxide and a CdS/CIGS p‐n junction using low cost pulsed‐spray deposition. Hybridization significantly improves the external quantum efficiency of the hybrid devices in the absorption range of the NQDs and in the red to near‐IR parts of the spectrum. The low wavelength response enhancement is found to be induced by luminescent down‐shifting (LDS) from the NQD layer, while the increase at longer wavelengths is attributed to internal scattering from NQD aggregates. LDS is demonstrated using time‐resolved spectroscopy, and the morphology of the NQD layer is investigated in fluorescence microscopy and cross‐sectional transmission electron microscopy. The influence of the NQD dose on the PCE of the hybrid devices is investigated and an optimum value is obtained. The low costs and limited material consumptions associated with pulsed‐spray deposition make these flexible hybrid devices promising candidates to help push thin‐film photovoltaic technology towards grid parity.     

Preparation of Gold Nanoparticles and their Applications in Anisotropic Nanoparticle Synthesis and Bioimaging

In this review, we highlight our recent achievements in using colloidal gold nanoparticles as building blocks for fabrication of anisotropic and multicomponent nanoparticles (e.g., nanoshells, semiconductor nanocrystals, and gold nanorods). The tunable optical properties of these nanoparticles are well suited for various biomedical and biophotonic applications.     

Li4Ti5O12 Nanocrystals Synthesized by Carbon Templating from Solution Precursors Yield High Performance Thin Film Li‐Ion Battery Electrodes

Nanocrystals of Li₄Ti₅O₁₂ (LTO) have been prepared by processing an ethanol‐toluene solution of LiOEt and Ti(OiPr)₄ using a carbon black template. The mechanism of crystal growth has been tracked by SEM and TEM microscopies. The resulting nanocrystals grown using the carbon template (C‐LTO) show less aggregation than materials prepared from solution without the template (S‐LTO), which is reflected in higher surface area (27 m²/g) and concomitantly smaller particle size (58 nm) for C‐LTO compared to 20 m²/g and 201 nm for S‐LTO. Electrochemically, thin‐film electrodes composed of C‐LTO demonstrate reversible cycling, storing ～160 mAh/g at both 1 C (175 mA/g) and 10 C current. Important is that resistance to charge transfer between the C‐LTO nanocrystals and added conducting carbon is 3 times smaller than that for S‐LTO. Accordingly, C‐LTO shows excellent rate capability, maintaining an energy‐storage capacity >150 mAh/g even at 100 C current. These characteristics solidify C‐LTO a suitable replacement for carbon as a Li‐ion battery anode.     

Upconverted photoluminescence in Ho3+ and Yb3+ codoped Gd2O3 nanocrystals with and without Li+ ions

The upconversion photoluminescence of Ho³⁺ ion sensitized by Yb³⁺ ion in Ho³⁺/Yb³⁺codoped Gd₂O₃ nanocrystals with and without Li⁺ is investigated in this paper. Strong fluorescence in the green (534–570 nm) and red (635–674 nm) regions of the spectrum has been observed, arising from the ⁵F₄/⁵S₂ → ⁵I₈ and ⁵F₅ → ⁵I₈ transitions of Ho³⁺ ion, respectively. Yb³⁺ ion is considered to be a better sensitizer for catching enough pumping energy and transferring considerable energy to Ho³⁺ in the Ho³⁺/Yb³⁺system. The upconversion intensity emitted by Ho³⁺ is greatly enhanced when Li⁺ is added to the Ho³⁺/Yb³⁺ codoped Gd₂O₃ nanocrystals.     

Nanocrystal technology, drug delivery and clinical applications

Nanotechnology will affect our lives tremendously over the next decade in very different fields, including medicine and pharmacy. Transfer of materials into the nanodimension changes their physical properties which were used in pharmaceutics to develop a new innovative formulation principle for poorly soluble drugs: the drug nanocrystals. The drug nanocrystals do not belong to the future; the first products are already on the market. The industrially relevant production technologies, pearl milling and high pressure homogenization, are reviewed. The physics behind the drug nanocrystals and changes of their physical properties are discussed. The marketed products are presented and the special physical effects ofnanocrystals explained which are utilized in each market product. Examples of products in the development pipelines (clinical phases) are presented and the benefits for in vivo administration of drug nanocrystals are summarized in an overview.     

Quantum dots targeted to the assigned organelle in living cells

Fluorescent nanocrystal quantum dots (QDs) have the potential to be applied to bioimaging since QDs emit higher and far longer fluorescence than conventional organic probes. Here we show that QDs conjugated with signal peptide obey the order to transport the assigned organelle in living cells. We designed the supermolecule of luminescent QDs conjugated with nuclear- and mitochondria-targeting ligands. When QDs with nuclear-localizing signal peptides were added to the culture media, we can visualize the movements of the QDs being delivered into the nuclear compartment of the cells with 15 min incubation. In addition, mitochondrial signal peptide can also transport QDs to the mitochondria in living cells. In conclusion, these techniques have the possibility that QDs can reveal the transduction of proteins and peptides into specific subcellular compartments as a powerful tool for studying intracellular analysis in vitro and even in vivo.     

Quantitative characterization of quantum dot‐labeled lambda phage for Escherichia coli detection

We characterize CdSe/ZnS quantum dot (QD) binding to genetically modified bacteriophage as a model for bacterial detection. Interactions among QDs, lambda (λ) phage, and Escherichia coli are examined by several cross‐validated methods. Flow and image‐based cytometry clarify fluorescent labeling of bacteria, with image‐based cytometry additionally reporting the number of decorated phage bound to cells. Transmission electron microscopy, image‐based cytometry, and electrospray differential mobility analysis allow quantization of QDs attached to each phage (4–17 QDs) and show that λ phage used in this study exhibits enhanced QD binding to the capsid by nearly a factor of four compared to bacteriophage T7. Additionally, the characterization methodology presented can be applied to the quantitative characterization of other fluorescent nanocrystal‐biological conjugates. Biotechnol. Bioeng. 2009;104: 1059–1067. Published 2009 Wiley Periodicals, Inc.     

Sol–gel synthesis,characterization and luminescence properties of SrMgAl2SiO7:Eu2+ as a novel nanocrystalline phosphor

In this research, a new SrMgAl₂SiO₇:Eu²⁺ phosphor was synthesized via the sol–gel method. The phase‐forming processes were studied by thermogravimetric–differential thermal analysis and X‐ray diffraction technique. Scanning electron microscopy showed that there is uniform morphology and microstructure owing to the sol–gel route. Spectrophotometry and colorimetry analyses illustrated that, under short ultraviolet excitation, the main emission peak occurred at 421 nm and also a relatively pure blue color was observed that was ascribed to the 4f⁶5d¹(²D) → 4f⁷(⁸S_7/2) transition of Eu²⁺ with color coordination of x = 0.187, y = 0.077. Finally, it was found that the color and phase purity of the synthesized powder increased as calcinations time increased. Copyright © 2010 John Wiley & Sons, Ltd.