Core–Shell to Doped Quantum Dots: Evolution of the Local Environment Using XAFS

Internal structure study at an atomic level is a challenging task with far reaching consequences to its material properties, specifically in the field of transition metal doping in quantum dots. Diffusion of transition metal ions in and out of quantum dots forming magnetic clusters has been a major bottleneck in this class of materials. Diffusion of the magnetic ions from the core into the nonmagnetic shell in a core/shell heterostructure architecture to attain uniform doping has been recently introduced and yet to be understood. In this work, we have studied the local structure variation of Fe as a function of CdS matrix thickness and annealing time during the overcoating of Fe₃O₄ core with CdS using X-ray absorption spectroscopy. The data reveals that Fe₃O₄ core initially forms a core/shell structure with CdS followed by alloying at the interface eventually completely diffusing all the way through the CdS matrix to form homogeneously Fe-doped CdS QDs with excellent control over size and size distribution. Study of Fe K-edge shows a complete change of Fe local environment from Fe–O to FeS

Origin of Photoluminescence and XAFS Study of (ZnS)_1–<i>x</i>(AgInS₂)_<i>x</i> Nanocrystals

Donor–Acceptor transition was previously suggested as a mechanism for luminescence in (ZnS)_1–<i>x</i>(AgInS₂)_<i>x</i> nanocrystals. Here we show the participation of delocalized valence/conduction band in the luminescence. Two emission pathways are observed: Path-1 involves transition between a delocalized state and a localized state exhibiting higher energy and shorter lifetime (∼25 ns) and Path-2 (donor–acceptor) involves two localized defect states exhibiting lower emission energy and longer lifetime (>185 ns). Surprisingly, Path-1 dominates (82% for <i>x</i> = 0.33) for nanocrystals with lower <i>x</i>, in sharp difference with prior assignment. Luminescence peak blue shifts systematically by 0.57 eV with decreasing <i>x</i> because of this large contribution from Path-1. X-ray absorption fine structure (XAFS) study of (ZnS)_1–<i>x</i>(AgInS₂)_<i>x</i> nanocrystals shows larger AgS₄ tetrahedra compared with InS₄ tetrahedra with Ag–S and In–S bond lengths 2.52 and 2.45 Å respectively, whereas Zn–S bond length is 2.33 Å along with the absence of second nearest-neighbor Zn–S–metal correlation

Doping Controls Plasmonics, Electrical Conductivity, and Carrier-Mediated Magnetic Coupling in Fe and Sn Codoped In₂O₃ Nanocrystals: Local Structure Is the Key

Multifunctional Fe–Sn codoped In₂O₃ colloidal nanocrystals simultaneously exhibiting localized surface plasmon resonance band, high electrical conductivity, and charge mediated magnetic coupling have been developed. Interactions between Sn and Fe dopant ions have been found critical to control all these properties. Sn doping slowly releases free electrons in the colloidal nanocrystals, after reduction of active complex between Sn⁴⁺ and interstitial O^2–. Unexpectedly, Fe codoping reduces the free electron concentration. Our X-ray absorption fine structure spectroscopy (XAFS) results show that Fe³⁺ and Sn⁴⁺ substitutes In³⁺ in the In₂O₃ lattice for all Fe-doped In₂O₃ NCs and Sn-doped In₂O₃ NCs. Interestingly, for Fe–Sn codoped NCs, a smaller fraction of Fe³⁺ gets reduced to Fe²⁺ by consuming free electrons produced by Sn doping. Therefore, Fe doping can manipulate free electron concentration in Fe–Sn codoped In₂O₃ nanocrystals, controlling both plasmonic band and electrical conductivity. Free electrons, on the other hand, facilitate magnetic coupling between distant Fe³⁺ ions. Such charge mediated magnetic coupling is useful for spin-based applications

Determination of the cytotoxicity of Hsp90 inhibitor, Geldanamycin (GA).

<p>(a)Vero cells were treated with different concentrations of GA (1, 5, 25, 50, 100, 200, 500 µM) for 14 h and the cytotoxicity of the cells were determined by MTT assay. Cellular cytotoxicity was determined in duplicate and each experiment was repeated three times. (b) Cells were observed under microscope (Magnification -10X) for cytotoxicity with increasing concentration of the drug (10, 50, 100, 200 µM) on Vero cells at 14 h. (c) Vero cells treated with (10, 50, 100, 200 µM) of GA were harvested at 24 h, lysed and expression of Hsp90 was analysed in Western blot by probing with Hsp90 antibody. GAPDH served as the loading control. The changes in the band intensity was quantified by normalizing GAPDH and the relative band intensity has been shown as bar diagram in right panel (n = 3;<i>p</i><0.05).</p

Schematic representation of the working model of the cellular signalling molecules in CHIKV infection.

<p>CHIKV infection results in the induction of Hsp90 associated client proteins like Raf1, Akt and various Akt substrates. GA treatment on CHIKV infected cells results in the degradation of Hsp90 associated client proteins which has been explained in the text.</p

Hsp90 inhibitor GA inhibits CHIKV replication.

<p>(a) Vero cells were infected with CHIKV strains, either S 27 or DRDE-06 with MOI 0.01. Effect of GA (10, 50, 100, 200 µM) on (a) uninfected cells (b) in the progression of infection was determined by observing the CPE of the virus infected cells under microscope (Magnification -10X) at 18 and 24 hpi. (c) The mock and CHIKV (S 27 or DRDE-06) infected Vero cells in presence or absence of GA (50 µM) were analyzed for apoptosis by staining with Annexin V and estimating % positive cells for Annexin V. The graph depicts a representative experiment with triplicate values of mean ±SD (*<i>p</i><0.05). (d) The supernatants of the virus infected and GA treated cells were collected at 14 hpi and viral titers were determined by plaque assay. The data represent the mean ±SD of three experiments (*<i>p</i><0.01). (e) GA was added to the virus infected cells at 0, 4, 6, 8 hpi and supernatants were collected at 14 hpi and infectious progeny virus particle titre was determined by plaque assay. All the experiments were repeated three times and data of three independent experiments are represented as mean ±SD (*<i>p</i><0.05). (f) The infected cells (as mentioned in 2e) were harvested and nsP2 protein level was determined by Western blot by probing with nsP2 monoclonal antibody. GAPDH served as the loading control. The fold change in the nsP2 protein level was quantified by normalizing GAPDH and the relative band intensity is shown as bar diagram in the lower panel (n = 3, <i>p</i><0.01).</p

GA reduces nsP2 protein level during CHIKV infection.

<p>Vero cells were infected with either S 27 or DRDE-06 with MOI 0.01 of the virus. (a) Cells were treated with different doses (10 and 50 µM) of GA and the virus infected cells were harvested at 14 hpi and RT- PCR was performed to amplify nsP1, nsP2, nsP3, nsP4, Hsp90AA1 and GAPDH genes.(b) Virus infected cells were treated with 10, 50 and 100 µM doses of GA and harvested at 14 hpi. Western blot analysis was performed with cell lysates and probed with nsP1, nsP2, nsP3, nsP4 and Hsp90 antibody. GAPDH served as the loading control. The band intensities of nsP1-4 were measured for DMSO and 10 µM GA treated samples after normalizing GAPDH and error bars represent the S.D. of the data from three independent experiments (* <i>p</i><0.01). (c) Vero cells were infected with either S 27 or DRDE-06 and treated with 50 µM GA. Cells were harvested at 0, 4, 8 and 12 hpi and probed with nsP2 monoclonal antibody. (d) Vero cells were mock transfected or transfected with 10, 30 and 60 pmol of HSP90AA1 gene siRNA. Hsp90 level was estimated in Western blot by probing with Hsp90 antibody (upper panel). After 24 hrt (30 pmol), cells were super infected with MOI1 of either S 27 or DRDE-06 and harvested at 8 hpi. nsP2 protein level was analysed by Western blot (lower panel). The changes in Hsp90 and nsP2 level were quantified by normalizing GAPDH and the relative band intensity is shown as bar diagram in the right panel (n = 3; <i>p</i><0.05). (e) Vero cells were infected with either S 27 or DRDE-06 (MOI 0.1) virus in presence or absence of GA (50 µM). The cell lysates harvested at 10 and12 hpi for DRDE-06 and S 27 respectively, were co-immunoprecipitated with either polyclonal nsP2 or monoclonal Hsp90 antibodies. Western blot analysis was performed to check the interaction between nsP2 with Hsp90. The extreme right panel represents the negative control where normal mouse IgG was used to pull down the protein complex.</p

Effect of GA on virus replication with different MOIs of CHIKV.

<p>Vero cells were infected with different MOIs (1, 0.1, 0.01) of either S 27 or DRDE-06 virus and treated with 50 µM concentration of GA. (a) The cells were harvested at 8 hpi, lysed and Western blot analysis was performed by probing with nsP2 monoclonal antibody. GAPDH served as the loading control. The reduction in nsP2 level was quantified and the relative band intensity is shown as bar diagram in the right panel (n = 3, <i>p</i><0.05) (b) and (c) The supernatants were collected at 8 hpi and infective progeny virus particle titre was determined by Plaque assay. Data of three independent experiments are represented as mean ±SD (*<i>p</i><0.05).</p

Enhanced activation of Hsp client proteins after CHIKV infection.

<p>Vero cells were infected with either S 27 or DRDE-06 with MOI 0.1 and treated with different doses of GA (10 and 50 µM) and the cells were harvested at 8hpi. Western blot was performed using cell lysates and probed with Hsp90, Raf1, Ras, Akt, pAkt, GSK3β, mTOR, pmTOR, S6K, p70S6K, 4EBP1, p4EBP1 and nsP2 antibodies. GAPDH was used as the loading control.</p

Cluster-Seeded Synthesis of Doped CdSe:Cu₄ Quantum Dots

We report here a method for synthesizing CdSe quantum dots (QDs) containing copper such that each QD is doped with four copper ions. The synthesis is a derivative of the cluster-seed method, whereby organometallic clusters act as nucleation centers for quantum dots. The method is tolerant of the chemical identity of the seed; as such, we have doped four copper ions into CdSe QDs using [Na(H₂O)₃]₂[Cu₄(SPh)₆] as a cluster seed. The controlled doping allows us to monitor the photophysical properties of guest ions with X-ray spectroscopy, specifically XANES and EXAFS at the copper K-edge. These data reveal that copper can capture both electrons and holes from photoexcited CdSe QDs. When the dopant is oxidized, photoluminescence is quenched and the copper ions translocate within the CdSe matrix, which slows the return to an emissive state