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The self-assembled chitosan CdSe quantum dots (QDs) and chitosan CdSe--ZnS core--shell QDs films were prepared using layer-by-layer electrostatic technique. The well-ordered nanostructure and the layer -by-layer deposition of the QDs are revealed by AFM and exciton absorption spectra, respectively.

Second harmonic generation (SHG) is applied widely in frequency conversion, medical imaging, and quantum optics. 4-N,N-dimethylamino-4'-N'-methyl-stilbazolium tosylate (DAST) crystal, which is an outstanding organic nonlinear optical (NLO) material, has attracted considerable attention. To maximize its potential nonlinear properties, new degrees of freedom the controls of the growth interface and temperature were explored to prepare DAST nanoscale-thick films with giant SHG in this work. Results reveal that a phase transition from a triclinic structure to a monoclinic structure in DAST nanoscale-thick films is initially and irreversibly induced at ~120°C. However, the ultrastrong SHG signal which is 4 orders of magnitude larger than those of both an unannealed DAST nanoscale-thick film and an inorganic potassium dihydrogen phosphate crystal can be measured from the DAST nanoscale-thick film deposited on the glass surface and annealed at 200°C. This is attributed to a large second-order nonlinear susceptibility χ(2) of 7.24 nmV-1, high degree of structural ordering, formation of DAST single-crystal micro-platelets, and relaxation of the phase-matched condition in this case. Interestingly, the isotropic giant SHG response can be measured from such a DAST single-crystal nanoscale-thick film, attributed to the synergistic effects of the anisotropic DAST single-crystal micro-platelets with various preferential orientations distributed uniformly on the substrate surface and the interface interactions between DAST and the glass substrate. These findings shed light on the engineering of DAST nanostructures for significantly enhancing the SHG response, and particularly, they also pave an efficient way toward seeking the strongest nonlinear optical performances from DAST and other NLO organic materials for bioimaging and quantum optics. [ABSTRACT FROM AUTHOR]

Nest-like CdS-reduced graphene oxide (CdS-rGO) composites were prepared through a one-pot solvothermal method in which ethylenediamine was used to reduce GO and control the morphology of the CdS, and L-cysteine was used as the sulfur source, reducing agent, and linker between the CdS and rGO. By examining the morphology, structure, and composition of the composites, it could be found that the nest-like CdS particles were decorated on the rGO sheet, and the addition of GO did not influence the crystal structure and shape of the nest-like CdS. Compared with pure CdS, the as-prepared CdS-rGO composites showed enhanced visible light absorption, extended surface area, and facilitated separation of photogenerated charges. Hence, the CdS-rGO composites exhibited improved photocatalytic activity and excellent photostability for the degradation of rhodamine B under visible light irradiation. By combining the good properties of rGO and three-dimensional structured CdS microparticles, the strategy presented in this study is expected to be useful in preparing highly efficient graphene-semiconductor composites for potential applications in various fields. [ABSTRACT FROM AUTHOR]

Abstract??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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]