Double core infrared (CdSeTe) / ZnS quantum dots Conjugated to IgG antibodies
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Double core infrared (CdSeTe) / ZnS quantum dots Conjugated to IgG antibodies Tetyana V. Torchynska1, Jose L. Casas Espinola1, Chetzyl Ballardo Rodriguez2, Janna Douda2 and Karlen Gazaryan3 1 ESFM– Instituto Politécnico Nacional, México D. F. 07738, México 2 UPIITA– Instituto Politécnico Nacional, México D. F. 07320, México 3 Instituto de Investigaciones Biomedicas, UNAM, Mexico DF, Mexico
ABSTRACT Double core CdSeTe/ZnS quantum dots (QDs) with emission at 800 nm have been studied by photoluminescence (PL) and Raman scattering methods in the non-conjugated state and after the conjugation to the IgG antibodies. The PL energy shift into the high energy range has been detected in PL spectra of bioconjugated QDs. Raman scattering spectra are studied with the aim to reveal the CdSeTe core compositions, as well as to design the QD energy diagrams. The QD energy diagrams permit to analysis PL spectra and their transformation at the bioconjugation of QDs. It is revealed that the interface in double core QDs has the type II quantum well character that permits to explain the IR optical transition (800nm) in CdSeTe QD core materials with relatively wide band gaps. It is shown that essential PL energy shift is promising for the study of QD bioconjugation with specific antibodies and can be a powerful technique in biology and early medical diagnostics. INTRODUCTION Core/shell quantum dots (QDs) of II-VI group semiconductors (CdSe, CdS, CdSeTe, etc) with the size of 2-8 nm are of great interest owing their bright size-tunable emission, with relatively narrow bandwidth of 30–45 nm [1, 2], and dimensional compatibility with biological macromolecules [3-5]. The QDs have a broad absorption spectrum that allows simultaneous excitation of particles of several sizes with a single excitation wavelength. Additionally, II-VI core/shell QDs are usually characterized by high PL quantum yield (up to 75%) and high resistance to photo- and metabolic degradation. One of the high important scientific areas in biology is the new luminescent markers needed for the better assessment of treatments or the antibody detection at the many types of important human diseases. Core/shell QDs of II-VI semiconductors as the luminescent markers have been investigated intensively during the last decade. QD luminescence intensity depends on concentration of attached bio-molecules, enabling QD application as protein sensors [4, 6]. Note, the full impact of bioconjugation on the optical properties of double core/shell CdSeTe/ZnS QDs and the bioconjugation mechanisms are not yet completely understood. EXPERIMENTAL DETAILS
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Double core/shell CdSeTe/ZnS QDs (Fig.1) commercially available [7] covered by the amine (NH2)-derivatized polyethylene glycol (PEG) polymer were used in a form of colloidal particles diluted in a phosphate buffer saline (PBS) with a 1:200 volumetric ratio. CdSeTe/ZnS QDs are characterized by IR emission with the PL maximum at 800 nm (1.60 eV). At the first the PL and Raman scattering spectra of QDs are studied in nonconjugated states (nam
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