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  • 1.
    Akpe, Victor
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Photophysical and Chemical Approaches to Cellular Biophysics2008Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The central theme in this thesis is reversibility. Two main attempts has been made to approach reversibility in cellular systems from both chemical and physical points of view. Reversibility of immunolabeling of proteins on the cell surface has been adressed by development of new fluorescent substances optimized for CALI (Chromophore-Assisted Laser Inactivation of protein). Aluminum phthalocyanine (AlPc) is here identified to be a good candidate for a new generation of fluorophores for efficient hydroxyl radical generation. It is shown that cells can be reversibly labeled with antibody-AlPc conjugates. In experiments on living cells the AlPcs were not only active as classic fluorophores but also as photocatalytic substances with destaining properties. Reversibility of cell immobilization is also reported, where cells cultured in microstructures were immobilized and 3D supported using hydrogels. Hydrogel formulation and application was optimized to achieve a system where both viability and ease of use was satisfied. Gel reversibility was actualized with pH and enzyme treatment. The developped method offers the possibility of stop flow culturing cells in controlled and reusable 3D environments.

  • 2.
    Akpe, Victor
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Brismar, Hjalmar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Nyokong, Tebello
    Osadebe, P. O.
    Photophysical and photochemical parameters of octakis (benzylthio) phthalocyaninato zinc, aluminium and tin: Red shift index concept in solvent effect on the ground state absorption of zinc phthalocyanine derivatives2010In: Journal of Molecular Structure, ISSN 0022-2860, E-ISSN 1872-8014, Vol. 984, no 1-3, p. 1-14Article in journal (Refereed)
    Abstract [en]

    This paper addresses the synthesis of octa-substituted benzylthio metallophthalocyanines (OBTMPcs) that contain the central metal ions of Zn2+, Al3+ and Sn4+. The ground state absorption of ZnPc(SR)(8) (OBTZnPc) along with the ZnPc derivatives, well documented in literature were used to study a new concept called the red shift index (RsI). The concept is based on the empirical values of RsI of the different complexes in solvent media. Unequivocally, parameters used in this paper show strong correlations that are consistent with the results obtained. For instance, 12,1 of the complexes tend to increase as the refractive index, n(D), and solvent donor, DN, of solvent increases. Photodegradation (photobleaching) quantum yield, phi(d) measurements of these compounds show that they are highly photostable, phi(d) (0.03-0.33 x 10(-5)). The triplet quantum yield, phi(T) (0.40-0.53) and the triplet lifetime, tau(T) (610-810 mu s) are within the typical range for metallophthalocyanines in DMSO. The photosensitisation efficiency. S-Delta, is relatively high for all the molecules (0.74-0.90). (C) 2010 Elsevier B.V. All rights reserved.

  • 3.
    Akpe, Victor
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Nyokong, Tebello
    Brismar, Hjalmar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Photophysics and photochemistry of zinc, aluminium and tin octakis (benzylthio) phthalocyanines2008Report (Other academic)
  • 4.
    Akpe, Victor
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Ogunsipe, Abimbola
    Madu, Christian
    Brismar, Hjalmar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Red-Shift Index Concept in Solvent Effects of Chromophore-Substituted Metallophthalocyanines: A Look at the Empirical Relationship of the Macroscopic Properties of the Solute-Solvent Interactions2015In: Journal of Solution Chemistry, ISSN 0095-9782, E-ISSN 1572-8927, Vol. 44, no 2, p. 307-326Article in journal (Refereed)
    Abstract [en]

    Solvent effects on the UV/vis spectra of metallopthalocyanines (MPcs) have been interpreted using the red-shift index concept (R (s) I). The concept connects empirically, direct, experimental, easily accessible optical spectral data, which are explained by considering the differential behavior of the solute-solvent interactions at the ground state and excited state using the spectral values of MPcs along with the derived concept, called the associated solvation energy (ASE). R (s) I is formulated from three fundamental parameters, which are: ground state electronic absorption spectrum, polarization red-shift and a scaling factor of MPc (N (dye)) in the respective solvents. The R (s) I is a reflection of the index value of the chromophore substituent of MPc in the solvent; thus, the concept can be used as a solvatochromic parameter to study a wide range of supramolecular and heterocyclic compounds that can be modified at their periphery or 'handles'. Particularly, in this study, the concept has been used to rank MPc candidates by using the statistical mean performance of the solvatochromic parameters, which are red shift index, polarizability efficiency and ASE. We hereby review the solvent effects on the UV/vis spectra of substituted and unsubstituted MPcs.

  • 5.
    Akpe, Victor
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Vernet, Erik
    KTH, School of Biotechnology (BIO), Molecular Biotechnology.
    Gräslund, Torbjörn
    KTH, School of Biotechnology (BIO), Molecular Biotechnology.
    Brismar, Hjalmar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Characterization studies of aluminum phthalocyanine binding to antibodies from SKBR 3 cell line2008Report (Other academic)
  • 6.
    Akpe, Victor
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Vernet, Erik
    KTH, School of Biotechnology (BIO), Protein Technology.
    Madu, Christian
    Obirai, Joseph C.
    Brismar, Hjalmar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Understanding the Photochemical Pathway of In Vitro Target Delivery of Aluminium Phthalocyanine: A Mechanistic Approach Using Radical Reaction Chemistry2014In: ChemPlusChem, ISSN 2192-6506, Vol. 79, no 5, p. 671-679Article in journal (Refereed)
    Abstract [en]

    A classical dye, aluminium phthalocyanine (AlPc), is used to study the photochemical processes involved in the chromophore-assisted laser inactivation technique. Both cell-free and cell-based systems are investigated by novel methods and radical reaction chemistry. Findings on the photochemical pathways in two models representing cell-free and a cell-based systems are reported. In the cell-free system, the unsubstituted, free, fluorescence-active photosensitiser AlPc recovers its fluorescence signal by means of phosphorescence through a reversible photobleaching process. In the cell-based system, photoactivation of substituted AlPc conjugated to an antibody results in the loss of fluorescence signal at the area examined. Reinjection of the AlPc-conjugated antibodies restores the fluorescence signal.

  • 7.
    Li, Li
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Chen, Yun
    Tian, Guangjun
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Akpe, Victor
    KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Xu, Hao
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Gan, Li-Ming
    Skrtic, Stanko
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Brismar, Hjalmar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Fu, Ying
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Reversible Modification of CdSe-CdS/ZnS Quantum Dot Fluorescence by Surrounding Ca2+ Ions2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 19, p. 10424-10433Article in journal (Refereed)
    Abstract [en]

    It has been known for a long time that the fluorescence intensity of colloidal quantum dots (QDs) becomes modified when free ions are added to the QD solution. The consequences of removing free ions from the QD solution, however, have not been closely investigated. In this work we studied fluorescence from 3-mercaptopropionic acid (3-MPA) coated CdSe-CdS/ZnS core-multishell QDs when free Ca2+ ions were added to and subsequently removed from the QD solution. It was found that QD fluorescence intensity was reduced when Ca2+ ions were added to the QD solution, while the wavelength of the QD fluorescence peak remained unchanged. QD fluorescence recovered when the concentration of free Ca2+ ions in the QD solution was reduced by adding Ca2+ chelator (ethylene glycol tetraacetic acid, EGTA). It was further observed that the time of single QD fluorescence at on-state and QD fluorescence lifetimes were also reduced after adding Ca2+ and then recovered when EGTA was added. Theoretical study shows that a free Ca2+ ion can attach stably to the system of [QD + surface ligand], attract the photoexcited electron, and repel the photoexcited hole inside the QD core, leading to the reduction of the radiative recombination between the electron and hole, thereafter decreasing the QD fluorescence intensity, on-state time, and fluorescence lifetimes, as observed experimentally. To the best of our knowledge, this is a first study to show that the changes of QD optical properties are reversible under the influence of Ca2+ ions. We further estimated the equilibrium association constant pK(a) of our QDs with Ca2+, which is much larger than QDs with Mg2+, Na+, and K+, indicating the feasibility of developing a QD-based Ca2+ sensor.

  • 8.
    Liebmann, Thomas
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Rydholm, Susanna
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Akpe, Victor
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Brismar, Hjalmar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Self-assembling Fmoc dipeptide hydrogel for in situ 3D cell culturing2007In: BMC Biotechnology, ISSN 1472-6750, E-ISSN 1472-6750, Vol. 7, no 88Article in journal (Refereed)
    Abstract [en]

    Background: Conventional cell culture studies have been performed on 2D surfaces, resulting in flat, extended cell growth. More relevant studies are desired to better mimic 3D in vivo tissue growth. Such realistic environments should be the aim of any cell growth study, requiring new methods for culturing cells in vitro. Cell biology is also tending toward miniaturization for increased efficiency and specificity. This paper discusses the application of a self-assembling peptide-derived hydrogel for use as a 3D cell culture scaffold at the microscale.

    Results: Phenylalanine derivative hydrogel formation was seen to occur in multiple dispersion media. Cells were immobilized in situ within microchambers designed for cell analysis. Use of the highly biocompatible hydrogel components and simplistic procedures significantly reduced the cytotoxic effects seen with alternate 3D culture materials and microstructure loading methods. Cells were easily immobilized, sustained and removed from microchambers. Differences in growth morphology were seen in the cultured cells, owing to the 3-dimentional character of the gel structure. Degradation improved the removal of hydrogel from the microstructures, permitting reuse of the analysis platforms.

    Conclusion: Self-assembling diphenylalanine derivative hydrogel provided a method to dramatically reduce the typical difficulties of microculture formation. Effective generation of patterned 3D cultures will lead to improved cell study results by better modeling in vivo growth environments and increasing efficiency and specificity of cell studies. Use of simplified growth scaffolds such as peptide-derived hydrogel should be seen as highly advantageous and will likely become more commonplace in cell culture methodology.

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