Raman Spectrum Modification of CdSe/ZnS Quantum Dots at the Bio-conjugation to IgG Antibodies
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Raman Spectrum Modification of CdSe/ZnS Quantum Dots at the Bio-conjugation to IgG Antibodies A. I. Diaz Cano*1, J. Douda1, C. R. Gonzalez Vargas1 and K. Gazarian2 1 UPIITA – Instituto Politécnico Nacional, México D. F. 07738, México. 2 Institute of Biomedical Investigations at UNAM, Mexico D.F. Mexico. ABSTRACT The paper presents the analysis of Raman scattering spectra of non-conjugated and bioconjugated CdSe/ZnS core–shell quantum dots in the range of Raman shifts of 80 - 2000 cm-1. Commercial CdSe/ZnS QDs covered by polymer and characterized by color emission with the maxima at 605 and 655 nm (1.89 and 2.04 eV) were used. Raman scattering spectra were measured at 300K and the excitation by the line 785.0 nm of a solid state LED. The analysis of Raman spectra has shown that the QD bio-conjugation to the immunoglobulin G (IgG) antibodies of the Pseudorabies virus is accompanied by the changes of the intensity of Raman lines related to the CdSe/ZnS core/shell QDs, PEG polymer covered QDs, the Si substrate and/or some organic groups of antibody molecules. The comparison of Raman spectra of CdSe/ZnS QDs with different sizes in non-conjugated and bio-conjugated states gives the opportunity to detect the bio-conjugation without mistake. INTRODUCTION Semiconductor core/shell CdSe/ZnS quantum dots (QDs) with the high intensity of QD photoluminescence (PL) can be used as the bio-luminescent markers varying the PL intensity or the shape of PL spectra when coupled to different biomolecules. It is important to investigate other effects in QDs which can offer the additional information on the structure of bioconjugated QDs. In the past decade semiconductor core/shell quantum dots (QDs) have emerged as a principal candidate in replacing organic fluorophores in biological and medical labeling [1, 2]. The most popular and intensively studied are the core/shell CdSe/ZnS quantum dots. The wide band gap ZnS shell serves as a surface passivating layer and assisting also the electron–hole confinement in the CdSe core [3]. The organic ligand bounded to the surface of QDs plays a significant role in determining their electronic and optical properties [1, 4]. A mixture of trioctylphosphine and trioctylphosphine oxide (TOP/TOPO) is the typical ligand system for most II–VI semiconductors such as CdSe. In recent years, research attention has been attracted to the use of these bio markers for the disease diagnostic using QDs bio-conjugated to specific antibodies (IgG proteins) [1 - 7]. It was shown earlier that the study of QDs optical properties is very significant for understanding the principal characteristics of these biomarkers [4]. Raman scattering study of QDs bio-conjugated with antibodies can be a powerful technique for the proof of actual bio-conjugation [8, 9]. This paper presents the results of Raman scattering study of CdSe/ZnS QDs with and without bioconjugation to the immunoglobulin G (rabbit IgG) antibodies to Pseudorabies virus.
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EXPERIMENTAL DETAILS Commercially available core–shell CdSe/ZnS QDs covered with amine-der
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