[Research advances of techniques for quantum dots-based tumor marker detection].

Quantum dots, as a new kind of biological fluorescence material, have properties superior to the traditional organic dyes. In the recent decade, researches about the application of quantum dots in biomedicine have made great progress. Tumor markers have vital importance in the diagnosis and treatment of carcinoma; however, they are not widely used for lack of specificity and sensitivity. Researches about applications of quantum dots in the detection of tumor markers are centralized in three aspects, namely the detection of serum/plasma tumor markers, the detection of tissue and cell tumor markers (such as molecular imaging of cell and tissue), and the detection of tumor in vivo animals. A combination of quantum dots and flow cytometry technique for developing a new technique to detect multiple kinds of tumor markers at the same time with greater sensitivity, specificity, rapidity and convenience may have the potential for clinical use of quantum dots.

A carbon nanotube gas sensor fabricated by dielectrophoresis and its application for NH3 detection.

Multi-walled carbon nanotubes (MWNTs) were successfully manipulated by dielectrophoresis (DEP) to form electrical connection between interdigitated gold electrodes (IDEs) and were demonstrated to serve as gas sensor for NH(3) detection. The MWNTs were suspended in ethanol and deposited on the IDEs under the effect of DEP. After the evaporation of ethanol, the MWNTs remained between the gaps of the IDEs. The electrical conductivity of the DEP-fabricated MWNTs sensor decreased when exposed to NH(3) at room temperature. There is a good linear correlation between the decreasing amplitude of conductance and the NH(3) concentration, and the detection limit of 10 ppm NH(3) could be achieved.

High spatially resolved morphological, structural and spectroscopical studies on copper oxide nanocrystals.

Copper oxide nanocrystals decorated on multi-wall carbon nanotubes have been prepared. Comprehensive morphological, structural and spectroscopical studies have been carried out on the nanometre/atomic scale by the combination of high-resolution transmission electron microscopy and electron energy-loss near-edge structure in electron energy-loss spectroscopy, which has a high spatially resolved capacity advantage over the normally used analytical techniques such as x-ray powder diffraction (XRD) and x-ray photoelectron spectroscopy (XPS). The result reveals that highly crystalline cubic Cu(2)O nanocrystals with highly uniform dispersion, homogeneous size of about 5.3 nm and nearly spherical morphology are synthesized as the predominant phase, while rare individual monoclinic CuO nanocrystals with irregular shape are still present as the minor phase. The analysis based on the survey result and the structural symmetry difference between Cu(2)O and CuO demonstrates that XRD underestimates the presence of the CuO phase with much lower structural symmetry while XPS overestimates the proportion of CuO phase.

New findings in phase transitions of spinel Li1.07Mn1.93O4-delta studied by transmission electron microscopy.

Phase transitions and the related phase identifications at different temperatures for spinel Li(1.07)Mn(1.93)O(4-delta) crystals have been studied by transmission electron microscopy. The preliminary results clearly show the existence of at least two types of low-temperature phase: monoclinic and orthorhombic. Oxygen deficiency may raise the phase-transition temperature for the high-temperature (HT) cubic to low-temperature (LT) tetragonal, monoclinic, or orthorhombic phases. When the oxygen deficiency delta is very close to zero, the transition temperature is below room temperature (RT). Therefore, only the HT cubic spinel is observed at RT. When delta=0.182, the transition temperature is higher than RT, so the structures of the LT phases can be studied at RT. This study reveals the structural relationships between the LT phase and the HT phase. These relationships can be summarized as follows: (1) Two orthogonal cubic [440](Cubic)(*) and [440](Cubic)(*) reciprocal vectors are divided into two parts by {220} and {220} super reflections, respectively. This situation resembles the structures caused by correlated tilting and/or distortion of the octahedra in perovskites. (2) One of the cubic <440>Cubic(*) reciprocal vectors is divided into three parts by weak super-reflections. This situation resembles the modulated structure caused by the charge- and orbital-ordering in the perovskite La(1/3)Ca(2/3)MnO(3) of the space group Pnma. (3) One of the cubic <440>(Cubic)(*) reciprocal vectors, e.g. [440](Cubic)(*), is divided into three parts by stronger super-reflections, at the same time some strong reflections of the cubic spinel, e.g. (111)(Cubic)=(320)(Ortho)/2 disappear, indicating that there is a phase transition containing atomic movement. Items (2) and (3) are new findings in the present work.

Charge density determination in icosahedral AlPdMn quasicrystal using quantitative convergent beam electron diffraction.

Charge density distribution in icosahedral AlPdMn quasicrystal has been studied on a single-crystal specimen by using quantitative convergent beam electron diffraction (QCBED) technique. The QCBED systematic row method was used in the refinement of structure factors. To refine the low-order structure factors, the wave-mechanical formulation of electron diffraction dynamical theory was used in the calculation of electron diffraction intensities for the quasicrystal in fitting the experimental intensity line scan profiles. The shapes of atomic surfaces (occupation domains) were described with symmetry-adapted series of surface harmonics. An iterative procedure was used in determination of structure factors of the quasicrystal. The structure factors of nine strongest symmetry inequivalent reflections according to X-ray diffraction experiment were refined with QCBED technique. The average of refinement results for a given reflection performed on several CBED patterns, which were slightly different in orientation and sample thickness, and on different line scans, was taken as the value of structure factor for the reflection. The obtained structure factors for electrons were transformed into X-ray structure factors with Mott formula. The bonding charge density map for the quasicrystal was constructed with the obtained nine structure factors. Assuming that the atoms are spheres, the gain or loss of electrons for different atoms were calculated. It shows that identical atoms can have different valences at different kinds of positions. The bonding charge is localized along certain directions.

Elastic constants of Si crystal determined by thermal diffuse electron scattering.

The method of determining elastic constants of crystals by measuring thermal diffuse X-ray scattering around some Bragg reflections, is extended to measuring thermal diffuse electron scattering for the first time, in a transmission electron microscope, equipped with a field-emission gun, an [Formula: see text] -type energy filter and a multi-scan charge-coupled device. Quantitative diffuse electron scattering in the vicinity of the [Formula: see text] Bragg reflection was measured on a Si crystal in order to obtain information about elastic constants. Values of the elastic constants ratios C(12)/C(11)=0.4246, C(44)/C(11)=0.4707 obtained by simplex fitting method are consistent with the values C(12)/C(11)=0.3856, C(44)/C(11)=0.4804 determined by other traditional methods. This method may be expected to open a new route to measuring elastic constants of polycrystalline, nanometer-scaled and composite materials.