Photoluminescence transformation of core/shell CdSe/ZnS quantum dots at the conjugation to biomolecules
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Photoluminescence transformation of core/shell CdSe/ZnS quantum dots at the conjugation to biomolecules T. V. Torchynska1, I. Ch. Ballardo Rodríguez2 and Ye. Shcherbyna3 1
ESFM – Instituto Politécnico Nacional, México D. F. 07738, México, UPIITA- Instituto Politécnico Nacional, México D. F. 07738, México, 3 National Technical University –“KPI”, Kiev, 03056, Ukraine 2
Abstract The paper presents the results of PL spectrum analysis of CdSe/ZnS QDs covered by PEG polymer with and without bioconjugation to bio-molecules – the Osteopontin antibodies. Commercial CdSe/ZnS QDs used in the study are characterized by the color emission with the maximum at 640 nm (1.96 eV) at 300K. It is shown that PL spectra of nonconjugated QDs can be presented as a superposition of PL bands related to exciton emission in the CdSe core (1.96 eV) and some high energy PL bands (in the spectral range 2.37 – 3.00 eV). The comparative study of PL spectrum at high (300K) and low (10K) temperatures has testified that high energy PL bands deal with electronhole emission via interface states at the CdSe/ZnS/polymer interfaces. It is revealed that the QD bioconjugation to the anti Osteopontin antibody is accompanied by the change dramatically in PL spectra. Main features of PL spectrum transformstions deal with decreasing the PL intensity of interface related PL bands and the rise of intensity of CdSe core related PL bands. The explanation of mentioned effects has been proposed on the base of re-charging of interface related states at the bioconjugation process.
1 Introduction Semiconductor crystallites, known as nanocrystals or quantum dots (QDs), can essentially improve the using of fluorescent markers in biology and medicine [1]. The ability to cover the QDs with biomolecules is a critical step in producing efficient bio-luminescent markers. The most popular QDs are core/shell CdSe/ZnS QDs due to their specific and unique optical properties. The emission of CdSe/ZnS QDs is characterized by high photoluminescence quantum yields and can be changed with the variation of CdSe core size due to the quantum confinement effect [2]. The overcoating of CdSe QDs with higher band gap ZnS material has increased the PL quantum yield due to passivating nonradiative surface recombination states (such as dangling bonds) as well as due to increasing the potential barrier at the QD surface [3]. As result the core/shell CdSe/ZnS QDs have been widely used in optoelectronic and biological applications [4]. QDs being conjugated to biomolecules serve as luminescence tags in antigen-antibody biochemical reactions and can be used in early cancer diagnostics [1]. The confirmation of QD bioconjugation using the detection of essential transformation of PL spectra is highly important. This paper presents the results of PL analysis of CdSe/ZnS core/shell QDs nonconjugated and bioconjugated to bio-molecules – the anti Osteopontin antibodies.
2 Experimental details Commercially available core-shell CdSe/ZnS QDs, covered with PEG polymer, are used in a form of colloidal
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