Tailoring of quantum dot emission efficiency by localized surface plasmon polaritons in self-organized mesoscopic rings.

We report on the tailoring of quantum dot (QD) emission efficiency by localized surface plasmon polaritons in self-organized mesoscopic rings. Ag nanoparticles (NPs) with CdSe QDs embedded in a polymeric matrix are spatially organised in mesoscopic rings and coupled in a tuneable fashion by breath figure formation. The mean distance between NPs and QDs and consequently the intensity of QD photoluminescence, which is enhanced by the coupling of surface plasmons and excitons, are tuned by acting on the NP concentration.

Effect of protons on CdSe and CdSe-ZnS nanocrystals in organic solution.

Core and core-shell quantum dots are covered with a layer of organic ligands which prevents aggregation and eliminates surface defects, thus enhancing the photophysical properties and stability of the material. These ligands are usually Lewis bases and can therefore be affected by the presence of acid in the surrounding environment. We synthesized core CdSe and core-shell CdSe-ZnS quantum dots with various shell thicknesses and different organic ligands, and we investigated the effect of acid and base on their photophysical properties.

Electrochemical properties of CdSe and CdTe quantum dots.

Semiconductor nanocrystal quantum dots (QDs), owing to their unique opto-electronic properties determined by quantum confinement effects, have been the subject of extensive investigations in different areas of science and technology in the past two decades. The electrochemical behaviour of QDs, particularly for CdSe and CdTe nanocrystals, has also been explored, although to a lesser extent compared to the optical properties. Voltammetric measurements can be used to probe the redox levels available for the nanocrystals, which is an invaluable piece of information if these systems are involved in electron transfer processes.

Luminescence quenching in self-assembled adducts of [Ru(dpp)3]2+ complexes and CdTe nanocrystals.

We have investigated chloroform solutions containing tris(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) and CdTe nanocrystal quantum dots (5.6 nm diameter). The electronic levels of these two components are such that the Ru complex can act as an energy donor towards the quantum dot, which can thus behave as an energy acceptor.

Change in conformation with reduction of alpha-helix content causes loss of neutrophil binding activity in fully cytotoxic Shiga toxin 1.

Shiga toxins (Stx) play an important role in the pathogenesis of hemolytic uremic syndrome, a life-threatening renal sequela of human intestinal infection caused by specific Escherichia coli strains. Stx target a restricted subset of human endothelial cells that possess the globotriaosylceramide receptor, like that in renal glomeruli. The toxins, composed of five B chains and a single enzymatic A chain, by removing adenines from ribosomes and DNA, trigger apoptosis and the production of pro-inflammatory cytokines in target cells.

Structural and size effects on the spectroscopic and redox properties of CdSe nanocrystals in solution: the role of defect states.

Two series of CdSe quantum dots (QDs) with different diameters are prepared, according to frequently used protocols of the same synthetic procedure. For each sample the photophysical properties and the potentials for the first reduction and oxidation processes in organic solution are determined. The band gap obtained from electrochemical experiments is compared with that determined from the absorption and luminescence spectra.

A ratiometric luminescent oxygen sensor based on a chemically functionalized quantum dot.

Nanoconjugates composed of CdSe-ZnS core-shell nanocrystals and pyrenyl ligands are shown to exhibit a double photoluminescence. Owing to the different response of the two emission signals towards oxygen, the nanocrystals function as high dynamic range ratiometric luminescent O(2) nanosensors.

Recovery of CdS nanocrystal defects through conjugation with proteins.

The luminescence behavior of CdS nanocrystals in aqueous solution and in the presence of proteins has been deeply investigated. CdS nanocrystals have been prepared in water by thermal decomposition of a single organometallic precursor assisted by thioglycerol, which acts as capping agent. Different experimental conditions have been explored to gain insights into the parameters affecting the nanocrystal growth.

Probing donor-acceptor interactions and co-conformational changes in redox active desymmetrized [2]catenanes.

We describe the synthesis and characterization of a series of desymmetrized donor-acceptor [2]catenanes where different donor and acceptor units are assembled within a confined catenated geometry. Remarkable translational selectivity is maintained in all cases, including two fully desymmetrized [2]catenanes where both donors and acceptors are different, as revealed by X-ray crystallography in the solid state, and by (1)H NMR spectroscopy and electrochemistry in solution. In all desymmetrized [2]catenanes the co-conformation is dominated by the strongest donor and acceptor pairs, whose charge-transfer interactions also determine the visible absorption properties.

Photophysical properties of quinolizinium salts and their interactions with DNA in aqueous solution.

The photophysical properties of three quinolizinium salts (naphto[2,1-b]quinolizinium bromide (Q2), naphto[1,2-b]quinolizinium bromide (Q3), and indolo[2,3-b]quinolizinium tetrafluoroborate (HI)) in fluid media and their interactions with DNA were investigated by steady-state and by nanosecond and femtosecond time-resolved techniques. The main decay pathways of the excited singlet state S(1), fluorescence, intersystem crossing, and internal conversion, were characterized in terms of quantum yields and rate constants. The lowest triplet state of the quinolizinium salts is able to sensitize singlet oxygen in rather high efficiency (phi(Delta) = 0.

Sensing proteins with luminescent silica nanoparticles.

Nanometer sized silica nanoparticles (SiO2-NP) were prepared in water and loaded with two organic compounds, namely perylene and 1,6-diphenyl-1,3,5-hexatriene, which have well-defined and known fluorescence properties. The size of void and dye-doped SiO2-NP were determined by both transmission electron microscopy and atomic force microscopy, which allowed determining the loading effects on the particle size and morphology. Differently loaded nanoparticles were characterized by both steady-state and time-resolved spectrofluorimetric techniques.

Photophysical properties and photobiological behavior of amodiaquine, primaquine and chloroquine.

This article describes the results of a coupled photophysical and photobiological study aimed at understanding the phototoxicity mechanism of the antimalarial drugs amodiaquine (AQ), primaquine (PQ) and chloroquine (CQ). Photophysical experiments were carried out in aqueous solutions by steady-state and time-resolved spectrometric techniques to obtain information on the different decay pathways of the excited states of the drugs and on the transient species formed upon laser irradiation. The results showed that all three drugs possess very low fluorescence quantum yields (10(-2)-10(-4)).

DNA cleavage induced by photoexcited antimalarial drugs: a photophysical and photobiological study.

The interactions and the photosensitizing activity of three antimalarial drugs quinine (Q), mefloquine (MQ) and quinacrine (QC) toward DNA was studied. Evidences obtained by absorption and emission spectroscopy and by linear dichroism measurements indicate that these derivatives bind the macromolecule with a high affinity (binding constants Ka approximately 10(5) M(-1)). The absorption characteristics of the drugs changed markedly by addition of DNA and their fluorescence was quenched with rate constants higher than that of diffusion.

Photophysical and phototoxic properties of the antibacterial fluoroquinolones levofloxacin and moxifloxacin.

Two antibacterial fluoroquinolones, levofloxacin and moxifloxacin, were investigated to evaluate their photophysical properties and to explore the mechanism of their phototoxicity. Photophysical experiments were carried out in aqueous solution by stationary and time-resolved fluorimetry, and by laser flash photolysis, to obtain information on the various decay pathways of the excited states of the drugs and on transient species formed upon irradiation. The results obtained show that levofloxacin is able to photosensitize red blood cell lysis in an oxygen-independent way and induce a high decrease in cell viability after UVA irradiation, although to a lesser degree than the racemic mixture ofloxacin.