Si Xiao

Immunofluorescence detection with quantum dot bioconjugates for hepatoma in vivo

The use of highly specific and highly sensitive immunofluorescent probes is a promising approach for biomedical imaging in living tissue. We focus on immunofluorescence with quantum dot bioconjugates for hepatoma detection in vivo. We synthesized specific immunofluorescent probes by linking quantum dots to AFP (alpha-fetoprotein) antibody for specific binding AFP-an important marker for hepatocellular carcinoma cell lines. In in vivo studies, the characteristic quantum dot (QD) fluorescent property is exhibited by the QDs-Anti-AFP probes in tumor and they demonstrate active tumor targeting and spectroscopic hepatoma imaging with an integrated fluorescence imaging system. We investigate the inhomogeneous distribution of the QDs-Anti-AFP probes in tumor by using a site-by-site measurement method to test their ability for distribution studies of cancer cells. These results demonstrate the practicality of QD bioconjugates as attractive fluorescent probes for biomedical detection.

Surface functionalization of ZnO nanotetrapods with photoactive and electroactive organic monolayers.

Two strategies have been explored for organic functionalizations of ZnO nanotetrapods via anchoring groups of carboxylate and phosphonate. With these methods, oleyl chains were assembled on the surfaces of the ZnO nanotetrapods, significantly enhancing their solubility in nonpolar solvents, such as chloroform and toluene. The surface functionalization strategies have been extended to electroactive and photoactive molecules such as protoporphyrin and C(60) on the ZnO nanotetrapods. The surface-modified ZnO nanotetrapods were characterized comprehensively, revealing a uniform, covalently linked monolayer assembled on the surface. This work opens a broad perspective for the application of the organically functionalized nanotetrapods in optoelectronics and biomedicine.

Controlled Synthesis and Upconverted Avalanche Luminescence of Cerium(III) and Neodymium(III) Orthovanadate Nanocrystals with High Uniformity of Size and Shape

We report on controlled synthesis of uniform LnVO4 (Ln = Ce and Nd) nanocrystals (NCs) with square-plate and H-shaped morphologies in nanosized reverse microemulsion reactors, via a facile solvo/hydrothermal strategy. The NCs were thoroughly characterized by X-ray diffraction, transmission electron microscopy (TEM), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDS), infrared absorption spectroscopy, and photoluminescence. Possible mechanisms of the rare-earth orthovanadate NC growth and size and shape evolution are proposed. A unique upconverted avalanche luminescence property pertaining to the NCs has been discovered, systematically studied, and mechanistically discussed. Our work combines synthetic and optical studies of the NCs and lays a foundation for reinventing their applications in optoelectronics among others.

Fluorescence Analysis with Quantum Dot Probes for Hepatoma Under One- and Two-Photon Excitation

A new class of fluorescent probe produced by conjugating semiconductor quantum dots (QDs) with protein molecule is proposed as an alternative to conventional organic labels. However the fluorescence characteristics of the QD bioconjugates are not clear while they are excitied with one- or two-photon laser pulse. We synthesized specific immunofluorescent probes by linking QDs to alpha fetoprotein (AFP) antibody for specific binding alpha-fetoprotein -an important marker for hepatocellular carcinoma cell lines, and archived specific fluorescence detection with the QDs-Anti-AFP in nude mice. Then, we have analyzed the fluorescence characteristics of QDs-Anti-AFP and original QDs both under one- and two-photon excitations. The results demonstrated that QDs-Anti-AFP’s fluorescent spectral and lifetime haven’t varied much from that of original QDs. Moreover, QDs-Anti-AFP have exhibited higher fluorescence efficiency than QDs under two-photon examination.

The Influence of Surface Trapping and Dark States on the Fluorescence Emission Efficiency and Lifetime of CdSe and CdSe/ZnS Quantum Dots

To investigate the influence of surface trapping and dark states on CdSe and CdSe/ZnS quantum dots (QDs), we studied the absorption, fluorescence intensity and lifetime by using one-and two-photon excitation, respectively. Experimental results show that both one- and two-photon fluorescence emission efficiencies of the QDs enhance greatly and the lifetime increase after capping CdSe with ZnS due to the effective surface passivation. The lifetime of one-photon fluorescence of CdSe and CdSe/ZnS QDs increase with increasing emission wavelength in a supralinear way, which is attributed to the energy transfer of dark excitons. On the contrary, the lifetime of two-photon fluorescence of bare and core-shell QDs decrease with increasing emission wavelength, and this indicates that the surface trapping is the dominant decay mechanism in this case.

Photochromism and two-photon luminescence of Ag-TiO 2 granular composite films activated by near infrared ps/fs pulses

We reported photochromism and largely enhanced visible two-photon luminescence (TPL) of Ag-TiO(2) granular composite films by using ps/fs laser at the wavelength of 800 nm. Three types of photochromism spectra were observed when the Ag atom fraction are less than, comparable to and larger than the percolation threshold. The strong surface-plasmon-resonance enhanced visible TPL emissions near Ag(2)O transition band from the photoactivated Ag-TiO(2) samples were also observed. Furthermore, we found that the TPL intensity saturatedly increased while the absorbance at 800 nm exponentially decreased with the same rate as the increasing of photoactivation time, which means that both photochromism and TPL of Ag-TiO(2) composite films are originated from the photo-oxidation of Ag to Ag(+). These observations exhibit the multifunctional features of Ag nanoparticle materials.

CHARGE TRANSFER FROM MONOLAYERED CdSe/ZnS QUANTUM DOTS TO C60

The interaction between C60 and quantum dots (QDs) has attracted much attention recently due to its potential applications in solar cells, for example, as a promising renewable energy source. In this paper, monolayer self-assembled CdSe/ZnS core/shell QDs films were prepared and drop-coated with different amounts of C60. A significant photoluminescence quenching and an emission lifetime reduction were observed in the QDs-C60 composite films, and the quenching efficiency was increased with the increasing of the C60 content. Together with the reduced emission lifetime, the results here provide direct evidence for the charge transfer process in the QDs-C60 system.

Monodisperse nanocrystals of LnV0 4 (Ln = Ce, Nd): Controlled synthesis and upconverted avalanche luminescence

LnVO4 (Ln=Ce and Nd) nanocrystals (NCs) with square plate, H-shaped, and rod-like morphologies have been synthesized in nanosized reverse micelle reactors, via a facile solvo/hydrothermal strategy. We have also identified a unique upconverted avalanche luminescence properly pertaining to the NCs, and undertaken a systematic mechanistic study.