A Comparative Study of the Band-Edge Exciton Fine Structure in Zinc Blende and Wurtzite CdSe Nanocrystals.

In this paper, we studied the role of the crystal structure in spheroidal CdSe nanocrystals on the band-edge exciton fine structure. Ensembles of zinc blende and wurtzite CdSe nanocrystals are investigated experimentally by two optical techniques: fluorescence line narrowing (FLN) and time-resolved photoluminescence. We argue that the zero-phonon line evaluated by the FLN technique gives the ensemble-averaged energy splitting between the lowest bright and dark exciton states, while the activation energy from the temperature-dependent photoluminescence decay is smaller and corresponds to the energy of an acoustic phonon. The energy splittings between the bright and dark exciton states determined using the FLN technique are found to be the same for zinc blende and wurtzite CdSe nanocrystals. Within the effective mass approximation, we develop a theoretical model considering the following factors: (i) influence of the nanocrystal shape on the bright-dark exciton splitting and the oscillator strength of the bright exciton, and (ii) shape dispersion in the ensemble of the nanocrystals. We show that these two factors result in similar calculated zero-phonon lines in zinc blende and wurtzite CdSe nanocrystals. The account of the nanocrystals shape dispersion allows us to evaluate the linewidth of the zero-phonon line.

Electron Spin Coherence in CdSe Nanocrystals in a Glass Matrix.

The coherent spin dynamics of electrons in CdSe nanocrystals embedded in a glass matrix with diameters from 3.3 up to 6.1 nm are investigated by time-resolved Faraday ellipticity at room and cryogenic temperatures. Only one Larmor precession frequency is detected, which corresponds to the larger of the two precession frequencies and thus g-factor values found in the typical signal from solution-grown colloidal CdSe nanocrystals. We identify this frequency accordingly as associated with the spin precession of resident electrons localized in the nanocrystals in the vicinity of the surface. We provide a detailed theoretical analysis of the exciton level spin structure in the magnetic field and model the spin dynamics in CdSe nanocrystals of different symmetries. This allows us to exclude the exciton as the origin of the experimentally observed oscillating signal. At a cryogenic temperature of 6 K, an additional nonoscillating component emerges in the spin dynamics. We consider several possible origins of this signal and conclude that it is related to the hole spin polarization.

Exciton Binding Energy in CdSe Nanoplatelets Measured by One- and Two-Photon Absorption.

Colloidal semiconductor nanoplatelets exhibit strong quantum confinement for electrons and holes as well as excitons in one dimension, while their in-plane motion is free. Because of the large dielectric contrast between the semiconductor and its ligand environment, the Coulomb interaction between electrons and holes is strongly enhanced. By means of one- and two-photon photoluminescence excitation spectroscopy, we measure the energies of the 1S and 1P exciton states in CdSe nanoplatelets with thicknesses varied from 3 up to 7 monolayers. By comparison with calculations, performed in the effective mass approximation with account of the dielectric enhancement, we evaluate exciton binding energies of 195-315 meV, which is about 20 times greater than that in bulk CdSe. Our calculations of the effective Coulomb potential for very thin nanoplatelets are close to the Rytova-Keldysh model, and the exciton binding energies are comparable with the values reported for monolayer-thick transition metal dichalcogenides.

Polarized emission of CdSe nanocrystals in magnetic field: the role of phonon-assisted recombination of the dark exciton.

The recombination dynamics and spin polarization of excitons in CdSe nanocrystals synthesized in a glass matrix are investigated using polarized photoluminescence in high magnetic fields up to 30 Tesla. The dynamics are accelerated by increasing temperature and magnetic field, confirming the dark exciton nature of low-temperature photoluminescence (PL). The circularly polarized PL in magnetic fields reveals several unusual appearances: (i) a spectral dependence of the polarization degree, (ii) its low saturation value, and (iii) a stronger intensity of the Zeeman component which is higher in energy. The latter feature is the most surprising being in contradiction with the thermal population of the exciton spin sublevels. The same contradiction was previously observed in the ensemble of wet-chemically synthesized CdSe nanocrystals but was not understood. We present a theory which explains all the observed features and shows that the inverted ordering of the circularly polarized PL maxima from the ensemble of nanocrystals is a result of competition between the zero phonon (ZPL) and one optical phonon-assisted (1PL) emission of the dark excitons. The essential aspects of the theoretical model are different polarization properties of the dark exciton emission via ZPL and 1PL recombination channels and the inhomogeneous broadening of the PL spectrum from the ensemble of nanocrystals exceeding the optical phonon energy.

Surface spin magnetism controls the polarized exciton emission from CdSe nanoplatelets.

The surface of nominally diamagnetic colloidal CdSe nanoplatelets can demonstrate paramagnetic behaviour owing to the uncompensated spins of dangling bonds, as we reveal here by optical spectroscopy in high magnetic fields up to 15 T using the exciton spin as a probe of the surface magnetism. The strongly nonlinear magnetic field dependence of the circular polarization of the exciton emission is determined by the magnetization of the dangling-bond spins (DBSs), the exciton spin polarization as well as the spin-dependent recombination of dark excitons. The sign of the exciton-DBS exchange interaction depends on the nanoplatelet growth conditions.

Dual-Emitting Dot-in-Bulk CdSe/CdS Nanocrystals with Highly Emissive Core- and Shell-Based Trions Sharing the Same Resident Electron.

Colloidal CdSe nanocrystals (NCs) overcoated with an ultrathick CdS shell, also known as dot-in-bulk (DiB) structures, can support two types of excitons, one of which is core-localized and the other, shell-localized. In the case of weak "sub-single-exciton" pumping, emission alternates between the core- and shell-related channels, which leads to two-color light. This property makes these structures uniquely suited for a variety of photonic applications as well as ideal model systems for realizing complex excitonic quasi-particles that do not occur in conventional core/shell NCs. Here, we show that the DiB design can enable an unusual regime in which the same long-lived resident electron can endow trionlike characteristics to either of the two excitons of the DiB NC (core- or shell-based). These two spectrally distinct trion states are apparent in the measured photoluminescence (PL) and spin dynamics of core and shell excitons conducted over a wide range of temperatures and applied magnetic fields. Low-temperature PL measurements indicate that core- and shell-based trions are characterized by a nearly ideal (∼100%) emission quantum yield, suggesting the strong suppression of Auger recombination for both types of excitations. Polarization-resolved PL experiments in magnetic fields of up to 60 T reveal that the core- and the shell-localized trions exhibit remarkably similar spin dynamics, which in both cases are controlled by spin-flip processes involving a heavy hole.

Long-Lived Negative Photocharging in Colloidal CdSe Quantum Dots Revealed by Coherent Electron Spin Precession.

Photoinduced charging in CdSe colloidal quantum dots (QDs) is investigated by time-resolved pump-probe spectroscopy that is sensitive to electron spin polarization. This technique monitors the coherent spin dynamics of optically oriented electrons precessing around an external magnetic field. By addition of 1-octanethiol to the CdSe QD solution in toluene, an extremely long-lived negative photocharging is detected that lives up to 1 month in an N2 atmosphere and hours in an air atmosphere at room temperature. 1-Octanethiol not only acts as a hole acceptor but also results in a reduction of the oxygen-induced photo-oxidation in CdSe QDs, allowing air-stable negative photocharging. Two types of negative photocharging states with different spin precession frequencies and very different lifetimes are identified. These findings have important implications for understanding the photophysical processes in colloidal nanostructures.

Origin of Two Larmor Frequencies in the Coherent Spin Dynamics of Colloidal CdSe Quantum Dots Revealed by Controlled Charging.

Coherent spin dynamics in colloidal CdSe quantum dots (QDs) typically show two spin components with different Larmor frequencies, whose origin is an open question. We exploit the photocharging approach to identify their origin and find that surface states play a key role in the appearance of the spin signals. By controlling the photocharging with electron or hole acceptors, we show that the specific spin component can be enhanced by the choice of acceptor type. In core/shell CdSe/ZnS QDs, the spin signals are significantly weaker. Our results exclude the neutral exciton as the spin origin and suggest that both Larmor frequencies are related to the coherent spin precession of electrons in photocharged QDs. The lower frequency is due to the electron confined in the middle of the QD, and the higher frequency to the electron additionally localized in the vicinity of the surface.

Characteristics of Notch2(+) pancreatic cancer stem-like cells and the relationship with centroacinar cells.

Notch2, a surface marker in cell lines, is used to isolate, identify and localise pancreatic cancer stem-like cells and is a target for therapy of these cells. Sphere formation was induced in Panc-1 and Bxpc-3 pancreatic cancer cell lines, and Notch2(+) cells were separated from Bxpc-3 and Panc-1 cell lines by magnetic activated cell sorting (MACS). Expression of stem cell-related markers, OCT4, Nanog and PDX1, were measured by immunofluorescent (IF) staining. Expression of Notch2 was also determined immunohistochemically in pancreatic tissues. Notch2(+) cells were transplanted in subcutaneous of mice. AQP1 and AQP5 were also measured by IF in Bxpc-3 cells. The Notch signal pathway inhibitor, Compound E (CE), was used to treat Notch2(+) Bxpc-3 cells, and their vitalities were subsequently measured by the CCK-8 method. Positive expression of OCT4, Nanog and PDX1 was observed in Notch2(+) cells. Notch2(+) cells at centroacinar cell (CAC) and terminal ductal locations expressed AQP1 and AQP5. They were strongly tumourigenic in mice, and CE inhibited proliferation of Notch2(+) Bxpc-3 cells to some degree. OCT4 and Nanog can be used as markers of self-renewal in pancreatic cancer stem cells. Notch2(+) cells in human pancreatic cancer Bxpc-3 and Panc-1 cell lines had the properties of cancer stem cells. The results suggest that Notch2(+) pancreatic cancer stem-like cells had a close relationship with CAC.

The expression of stem cell-related indicators as a prognostic factor in human lung adenocarcinoma.

INTRODUCTION: The purpose of the present study was to detect the presence of BASC-like stem cell-related indicators, such as clara cell secretory protein (CCSP), Octamer-4 (OCT4) and Bmi-1, and evaluate their implications in the prognosis of patients with lung adenocarcinoma. METHODS: Specimens of 134 cases of lung adenocarcinoma were collected after radical surgery from January 1999 to June 2004. RESULTS: One hundred and twenty-six cases showed cells that were positive for CCSP, 99 cases positive for OCT4, 91 cases simultaneous expression of CCSP and OCT4 and 74 cases positive for Bmi-1. Bmi-1 was significantly higher in patients at stage III compared to patients at stages I and II. The pattern of survival curves showed that Bmi-1 was a significant prognostic factor of poor overall survival in lung adenocarcinoma patients (P = 0.0000), and the patients with OCT4(+) expression showed a greater increase in mortality than OCT4(-) patients (P = 0.0103). The results of univariate and multivariate Cox analysis revealed that the pathological stages of tumor node metastases (P = 0.037), OCT4 (P = 0.046) and Bmi-1 expression (P = 0.001) were independent prognostic factors. CONCLUSIONS: OCT4 and Bmi-1 may be good biomarkers to predict the prognosis of patients with completely resected lung adenocarcinoma.

[Lung adenocarcinoma stem cell phenotypes and their correlation with patient prognosis].

OBJECTIVE: To detect the cancer stem cells and to evaluate their prognostic implication in patients with lung adenocarcinoma. METHODS: Three phenotypic markers of cancer stem cells (SP-C, CCSP and OCT4) in lung adenocarcinoma were detected by immunofluorecence staining. The correlation among the clinicopathological parameters and phenotypes of cancer stem cells as well as survival were analyzed by Cox proportional hazard method. RESULTS: Of the 57 cases, cancer stem cells were detected in 52, including OCT4(+) bronchioloalveolar stem cell (BASC) phenotype (SP-C(+) CCSP(+) OCT4(+)) in 40 cases and OCT4(-) BASC phenotype (SP-C(+) CCSP(+) OCT4(-)) in 12 cases. Statistical analysis revealed that the phenotype of cancer stem cells was related with the cellular differentiation, i.e. the OCT4(+) BASC phenotype occurred more frequently in the well-differentiated tumors, while the OCT4(-) BASC phenotype usually presented in most of the poorly-differentiated ones. Cox analysis showed that the OCT4(+) BASC phenotype was one of prognostic factors. CONCLUSION: The lung adenocarcinoma stem cells have phenotypic features of bronchioalveolar stem cells (SP-C(+) CCSP(+)). The expression of self-renewal regulatory gene OCT4 in these cells indicates an aggressive nature and unfavorable prognosis.

[Analysis of EGFR mutations in 176 cases of non-small cell lung cancer].

OBJECTIVE: To analyze the incidence and profile of mutations in epidermal growth factor receptor (EGFR) in Chinese patients with non-small cell lung cancer (NSCLC). METHODS: A total of 176 cases of NSCLC tissue was enrolled in this study, among which 123 normal lung samples were also included. The tissue DNA was extracted and the EGFR gene in exon 19 to 21 was subjected for PCR amplification and direct sequencing. RESULTS: The EGFR gene in exon 19-21 was of wild type in all normal lung tissues detected. Mutations were found in 57 cases of 176 lung cancer samples, with an incidence of 32. 4%. Mutations were mainly detected in the exon 19 (37/57 cases, 64. 9% ) and exon 21 (18/57 cases, 31. 6% ) , while that in the exon 20 was rare (2/57 cases, 3. 5% ). There were 7 types of EGFR mutation in the exon 19, resulting in the deletion of codon 746 to 753. A missense mutation was detected in exon 20, dealing with codon 789 to 793. The mutation in exon 21 belonged to the single missense substitution in codon 858. The EGFR mutations were more frequent in female patients than male ones, in adenocarcinoma and adenosquamous cell carcinoma versus cancer of other histologies. CONCLUSION: EGFR mutation is a tumor-specific somatic abnormality. Some one third of Chinese NSCLC tumors harbor EGFR mutations, especially in exons 19 and 21. These mutations are more frequently detected in female, adenocarcinoma and adenosquamous cell carcinoma.

[Efficient generation and functional characteristics of dendritic cells from malignant pleural effusion in patients with lung cancer].

OBJECTIVE: To clarify whether functionally competent dendritic cells (DC) can be generated from malignant pleural effusion in patients with lung cancer. METHODS: Malignant effusion-associated monocytes were separated by adherence from malignant effusion-associated mononuclear cells and cultured in medium with granulocyte macrophage colony-stimulating factor (GM-CSF) plus interleukin 4 (IL-4). TNF-alpha was added for the last 24 h before culture termination. Cultured DC were identified by (1) using microscopy, scanning electron microscopy, and immunocytochemistry for the morphological features; (2) phenotypic markers; and (3) functional characteristics including a high stimulatory capacity to activate proliferation of lymphocyte in an allogeneic mixed leukocyte reaction and the ability to produce high levels of IFN-gamma. RESULTS: Cultured DC had the typical morphological features. The phenotype of DCs generated from effusion showed higher expression of CD(86) (84.6 +/- 6.1)%, HLA-DR (81.1 +/- 13.0)%, CD(40) (42.0 +/- 21.7)%, CD(1a) (20.0 +/- 9.5)% and lower expression of CD(14) (4.8 +/- 3.5)% than the control group. There was a significant difference in the stimulatory activity in allogeneic lymphocyte proliferation and the ability to produce high levels of IFN-gamma between DC derived from the malignant effusion and the control group. CONCLUSION: These findings suggest that DC can be generated from malignant pleural effusion, which might be a useful source of DC for immunotherapy.

[Implication of micrometastatic cancer cells in the peripheral blood on prognosis of non-small cell lung cancer].

OBJECTIVE: To evaluate the relationship of micrometastatic cancer cells in the blood and prognosis of patients with non-small cell lung cancer (NSCLC). METHODS: Blood samples were collected from peripheral vein perioperatively and from the pulmonary vein intraoperatively in NSCLC patients. Cancer cells were detected by flow cytometry, as described previously. The patients were followed up and analyzed statistically. RESULTS: Cancer cells in blood samples were detected in 20 of 58 patients (34.5%). Patients under 57 years of age or with stage III/IV lesions had higher positive findings than those over 57 years or with stage I/II lesions (P = 0.000 and 0.006, respectively). On the basis of 40 month follow-up data, the 2- and 3-year survival rates of patients with positive and negative results were 30.0% vs 20.0%, and 52.6% vs 50.0%, respectively. There was significant difference between the overall survival curves which favored patients with negative findings (P = 0.0291 and 0.0092, respectively). CONCLUSION: This study indicates that cancer cells can be detected in the blood perioperatively from NSCLC patients which means poor prognosis.

[Vascular endothelial growth factor inhibits dendritic cells from patients with non-small cell lung carcinoma].

OBJECTIVE: To detect the effect of vascular endothelial growth factor (VEGF) on dendritic cells (DC) in patients with non-small cell lung cancer (NSCLC). METHODS: The measurement of DC in the peripheral blood was performed by a novel flow cytometric assay in 85 patients with NSCLC and 14 healthy volunteers. Enzyme-linked immunosorbent assay (ELISA) was used to measure the concentration of VEGF(165) in the plasma. CD(14)(+) peripheral blood mononuclear cells (PBMC) were cultured to obtain DC in vitro with cytokines. VEGF(165) was added to evaluate its effect on DC differentiation and survival. The phenotypes and apoptosis of cultured cells were detected by flow cytometry. RESULTS: In comparison with healthy volunteers, the level of VEGF(165) was significantly increased (P < 0.05), while that of DC was significantly decreased (P < 0.01) in patients with NSCLC. No significant correlation was noted between the concentration of VEGF(165) and age, gender, differentiation and histological types in patients with NSCLC, neither was found in the level of DC (P > 0.05). The concentration of VEGF(165) was closely associated with TNM stage and distal metastasis (P < 0.05), while no correlation was found between the concentration of VEGF(165) and lymph node metastasis (P > 0.05). Significant correlations were noted between the level of DC in patients with NSCLC and TNM stage, lymph node metastasis and distal metastasis (P < 0.05). There was a negative correlation between the concentration of VEGF(165) and the level of DC (P < 0.05). Patients with abnormally elevated VEGF(165) showed significantly fewer DC. Cells cultured in vitro in the presence of VEGF(165) exhibited higher expression of CD(+)(14)(P = 0.000) and increased ratio of apoptic cells (P < 0.01), but decreased expression of CD(40), CD(86) and HLA-DR (P < 0.01), as compared to cells cultured without VEGF(165). CONCLUSIONS: The level of DC and the concentration of VEGF in the peripheral blood can reflect the malignancy of NSCLC. NSCLC can over-express VEGF to inhibit DC differentiation and maturation to evade host immune surveillance.

Can tumor uptake Tc-99m MDP ?

Abstract. To explore the mechanism of technetium-99m-methylene diphosphonate (MDP) uptake within tumor through analyze a distribution of Tc-99m MDP in mice bearing tumor cell lines. Methods: The uptake of Tc-99m MDP was analyzed in seven human tumor cell lines ( SPC-A1 adenocarcinoma of lung cancer, Bcap-37 Breast cancer, T-24 Bladder cancer, SKOV3 Ovary carcinoma, Hela-229 Cervical carcinoma, SCI-OS Osteosarcoma, SCI-375 Melanoma) and mouse Lewis lung cancer cell line. They were transplanted into athymic mice, SCID nude mice and C57BL/6 mice, respectively. Approximately 10(6) cells of each cell line were injected subcutaneously into a right chest of mouse. After 4&5 weeks, the Tc-99m MDP scintigraphy were determined 6 hours after tail vein injection of 74MBq in 0.05ml every mouse. Result: Biodistribution and tumor uptake MDP was different in the various cell types investigated. According to the RegionRatio program of Siemens Power Macintosh 9500 Computer System, region of interests (RIOs) placed on a small part of the tumor and horizontal copied to left background (T/B) and thoracic spine (T/N) of mice in Tc-99m MDP imaging. The average cpm/pixel ratios were calculated by standardized uptake measure (SUM) and determined the tumor-positive value (T/B) greater than or equal to 1.2. T/B of cell lines were sorted from higher to lower as follows: SCI-OS, Lewis, SKOV3, SCI-375, T-24, SPC-A1, Bcap-37, Hela-229. T/N: SCI-OS, SKOV3, T-24, SCI-375, Lewis, SPC-A1, Bcap-37, Hela-229. The biodistribution data of 99Tcm-MDP in SPC-A1 tumor-bearing BALB/c nude mice were given as ID/g and represent the meansñSD (n=13) in 30 hours after injection of Tc-99m MDP. ID/g of major tissue were sorted from higher to lower as follows: thoracic spine, lumbar, ribs, kidneys, the center of tumor, the ulcer of tumor, the surrounding of tumor, lymph node, blood, lungs, heart, liver. Conclusions: Most of tumor can uptake Tc-99m MDP including human adenocarcinoma. The uptake rate in the center tissue of tumor is higher than other part of tumor. The uptake rate of tumor is higher than non-skeletal tissue unless kidneys. It maybe connected with necrosis or calcification of tumor. Calcium and phosphorus ions were seen frequently in larger tumor. Not only it was caused by fibrous scar and/or surrounding tissues of granuloma but also intra-tumor coagulation and liquefaction necrosis