Emission variation in CdSe/ZnS quantum dots conjugated to Papilloma virus antibodies
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Emission variation in CdSe/ZnS quantum dots conjugated to Papilloma virus antibodies Juan A. Jaramillo Gómez1, Tetyana V. Torchynska2, Jose L. Casas Espinola2 and Janna Douda1 1
UPIITA – Instituto Politécnico Nacional, México D. F. 07340, México
2
ESFM – Instituto Politécnico Nacional, México D. F. 07738, México
ABSTRACT The paper presents a comparative study of the photoluminescence (PL) and Raman scattering spectra of core-shell CdSe/ZnS quantum dots (QDs) in nonconjugated states and after the conjugation to the anti-human papilloma virus (HPV), HPV 16-E7, antibodies. All optical measurements are performed on the dried droplets of the original solution of nonconjugated and bioconjugated QDs located on the Si substrate. CdSe/ZnS QDs with emission at 655 nm have been used. PL spectra of nonconjugated QDs are characterized by one Gaussian shape PL band related to the exciton emission in the CdSe core. PL spectra of bioconjugated QDs have changed essentially: the core PL band shifts into the high energy spectral range (“blue” sift) and becomes asymmetric. A set of physical reasons has been proposed for the “blue” shift explanation of the core PL band in bioconjugated QDs. The variation of PL spectra versus excitation light intensities has been studied to analyses the exciton emission via excited states in QDs. Finally the PL spectrum transformation for the core emission in bioconjugated QDs has been attributed to the electronic quantum confined effects stimulated by the electric charges of bioconjugated antibodies. INTRODUCTION Semiconductor nanocrystals of the II-VI group (CdSe, CdS, CdSeTe..etc), known as quantum dots (QDs), have been investigated for the different applications including the light emitting diodes, solar cells, optical amplifier media, biology and medicine [1-6]. The integration of nanotechnology with biology and medicine is expected to produce the major advances in the fluorescence resonance energy transfer (FRET) [5-7], in gene technology [8], cell tracking [5,6] and imaging [9-11]etc. The conjugation of biomolecules with core/shell QDs has been achieved using functional groups (linkers) on the QD surface [12,13], and/or with the help of electrostatic interaction between the QDs and biomolecules [14]. However the full impact of bioconjugation process on the QD optical properties and bioconjugation mechanisms are not yet completely understood. This paper presents the study of PL of CdSe/ZnS QDs covered by the amine (NH2)derivatized polyethylene glycol polymer in non-conjugated states and after the conjugation to biomolecules – anti-human papilloma virus (HPV), HPV 16-E7, antibodies. EXPERIMENTAL DETAILS
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Core-shell QDs commercially available [15] 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. CdSe/ZnS QDs with emission at 655 nm (1.90 eV) have been investigated. All optical measurements are performed on the dried droplets of the original solution of
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