Bioactive surface design based on conducting polymers and applications to biosensors

Erdem, Rengin
Quantum dots are fluorescent semiconductor nanocrystals that have unique optical properties such as high quantum yield and photostability. These nanoparticles are superior to organic dyes and fluorescent proteins in many aspects and therefore show great potential for both in vivo and in vitro imaging and drug delivery applications. However, cytototoxicity is still one of the major problems associated with their biological applications. The aim of this study is in vitro characterization and assessment of biological application potential of a novel silver sulfide quantum dot coated with mercaptopropionic acid (2-MPA). In vitro studies reported in this work were conducted on a mouse fibroblast cell line (NIH/3T3) treated with Ag2S/2-MPA quantum dots in 10-600 μg/mL concentration range for 24 h. Various fluorescence spectroscopy and microscopy methods were used to determine metabolic activity, proliferation rate and apoptotic fraction of QD-treated cells as well as QD internalization efficiency and intracellular localization. Metabolic activity and proliferation rate of the QD treated cells were measured with XTT and CyQUANT® cell proliferation assays, respectively. Intracellular localization and qualitative uptake studies were conducted using confocal laser scanning microscopy. Apoptosis studies were performed with Annexin V assay. Finally, we also conducted a quantitative uptake assay to determine internalization efficiency of the silver sulfide particles. Correlated metabolic activity and proliferation assay results indicate that Ag2S/2-MPA quantum dots are highly cytocompatible with no significant toxicity up to 600 μg/mL treatment. Optimal cell imaging concentration was determined as 200 μg/mL. Particles displayed a punctuated cytoplasmic distribution indicating to endosomal entrapment. In vitro characterization studies reported in this study indicate that Ag2S/2-MPA quantum dots have great biological application potential due to their excellent spectral and cytocompatibility properties. Near-infrared emission of silver sulfide quantum dots provides a major advantage in imaging since signal interference from the cells (autofluorescence) which is a typical problem in microscopic studies is minimum in this part of the emission spectrum. The results of this study are presented in an article which was accepted by Journal of Materials Chemistry. DOI: 10.1039/C2JM31959D.


Exciton related nonlinear optical properties of a spherical quantum dot
Aksahin, E.; Unal, V. Ustoglu; Tomak, Mehmet (2015-11-01)
The nonlinear optical properties of an exciton in a spherical quantum dot (QD) is studied analytically. The nonlinear optical coefficients are calculated within the density matrix formalism. The electronic problem is solved within the effective mass approximation. The contributions from the competing effects of the confinement, the Coulomb interaction, and the applied electric field are calculated and compared with each other. We have made no assumptions about the strength of the confinement. We concentrate...
Interacting electrons in a 2D quantum dot
Akman, N; Tomak, Mehmet (1999-04-01)
The exact numerical diagonalization of the Hamiltonian of a 2D circular quantum dot is performed for 2, 3, and 4 electrons. The results an compared with those of the perturbation theory. Our numerical results agree reasonably well for small values of the dimensionless coupling constant lambda = a/a(B) where a is the dot radius and a(B) is the effective Bohr radius. Exact diagonalization results are compared with the classical predictions, and they are found to be almost coincident for large lambda values.
Thermal characterisation of quantum cascade lasers with Fabry Perot modes
Gundogdu, Sinan; Pisheh, Hadi Sedaghat; Demir, Abdullah; Guenoven, Mete; AYDINLI, ATİLLA; Sirtori, Carlo (2018-04-26)
Quantum cascade lasers are coherent light sources that rely on intrersubband transition in periodic semiconductor quantum well structures. They operate at frequencies from mid-infrared to terahertz. In cases of long wavelength and typical low thermal conductivity of the active region, temperature rise in the active region during operation is a major concern. Thermal conductivity of QCL epi-layers differ significantly from the values of bulk semiconductors and measurement of the thermal conductivity of epi-l...
Spin–orbit effects on the nonlinear optical properties of a quantum dot in simultaneous electric and magnetic fields
Aytekin, O.; Turgut, Sadi; Tomak, Mehmet (Elsevier BV, 2014-11)
We report on the nonlinear optical properties of a quantum dot including the Rashba spin-orbit interaction (RSOI) with external electric and magnetic fields. The effect of dot size is considered. We do not make any assumptions about the strength of the confinement. We use the numerical diagonalization of the Hamiltonian to determine the electronic structure. The confining potential is taken to be of the Woods-Saxon type. We find the effect of RSOI on nonlinear optical coefficients.
Nonlinear optical properties of a Poschl-Teller quantum well under electric and magnetic fields
AYTEKİN, ÖZLEM; Turgut, Sadi; Tomak, Mehmet (2012-04-01)
The nonlinear optical properties of a Poschl-Teller Quantum well (PTQW) under electric and magnetic fields are studied. The salient feature of this potential is its flexibility. It can be made asymmetrical by a proper choice of its two parameters. Optical rectification, second and third-harmonic generation susceptibilities are calculated using the density matrix formalism. We study the effects of quantum confinement, electric and magnetic fields on all of these optical coefficients.
Citation Formats
R. Erdem, “Bioactive surface design based on conducting polymers and applications to biosensors,” M.S. - Master of Science, Middle East Technical University, 2012.