Post-growth tailoring of the optical properties of GaAs/AlGaAs quantum well structures

In this paper we describe a method for performing post-growth bandgap engineering in the GaAs/AlGaAs quantum well system. The method used is impurity-free vacancy diffusion. Using both single and multiple quantum well data we show that this allows blue shifts in the optical properties, while retaining both their distinctive excitonic and electrical characteristics. The electrical response is modelled and no comparative degradation of the quantum confined Stark effect is predicted, and this is confirmed experimentally. Possible applications of this technique are mentioned.     

In Memoriam

In memoriam Michael John Richardson.     

Electrochromatography in microchips packed with conventional reversed-phase silica particles

This paper shows the applicability of a disposable and inexpensive microfluidic chip for electrochromatographic separations. The chip, recently developed by us for chip-based LC, was fabricated from PDMS incorporating conventional chromatographic RP silica particles (C18) without the use of frits. Three cephalosporin antibiotics were used to demonstrate the applicability of the chip-based chromatographic packing for electrochromatographic determinations. The used sample injection method utilizes hydrodynamic pressure, thereby, reducing the propensity for sample bias during the injection.     

Apoptosis mechanisms related to the increased sensitivity of Jurkat T-cells vs A431 epidermoid cells to photodynamic therapy with the phthalocyanine Pc 4

To examine the clinical applicability of Pc 4, a promising second-generation photosensitizer, for the photodynamic treatment of lymphocyte-mediated skin diseases, we studied the A431 and Jurkat cell lines, commonly used as surrogates for human keratinocyte-derived carcinomas and lymphocytes, respectively. As revealed by ethyl acetate extraction and absorption spectrophotometry, uptake of Pc 4 into the two cell lines was linear with Pc 4 concentration and similar on a per cell basis but greater in Jurkat cells on a per mass basis. Flow cytometry showed that uptake was linear at low doses; variations in the dose-response for uptake measured by fluorescence supported differential aggregation of Pc 4 in the two cell types. As detected by confocal microscopy, Pc 4 localized to mitochondria and endoplasmic reticulum in both cell lines. Jurkat cells were much more sensitive to the lethal effects of phthalocyanine photodynamic therapy (Pc 4-PDT) than were A431 cells, as measured by a tetrazolium dye reduction assay, and more readily underwent morphological apoptosis. In a search for molecular factors to explain the greater photosensitivity of Jurkat cells, the fate of important Bcl-2 family members was monitored. Jurkat cells were more sensitive to the induction of immediate photodamage to Bcl-2, but the difference was insufficient to account fully for their greater sensitivity. The antiapoptotic protein Mcl-1 was extensively cleaved in a dose- and caspase-dependent manner in Jurkat, but not in A431, cells exposed to Pc 4-PDT. Thus, the greater killing by Pc 4-PDT in Jurkat compared with A431 cells correlated with greater Bcl-2 photodamage and more strongly to the more extensive Mcl-1 degradation. Pc 4-PDT may offer therapeutic advantages in targeting inflammatory cells over normal keratinocytes in the treatment of T-cell-mediated skin diseases, such as cutaneous lymphomas, dermatitis, lichenoid tissue reactions and psoriasis, and it will be instructive to evaluate the role of Bcl-2 family proteins, especially Mcl-1, in the therapeutic response.