Micro-Photoluminescence Study of Bio-conjugated CdSe/ZnS Nanocrystals
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Micro-Photoluminescence Study of Bio-conjugated CdSe/ZnS Nanocrystals L. Borkovska1, N. Korsunska1, T. Stara1, O. Kolomys1, V. Strelchuk1, T. Kryshtab2, S. Ostapenko3, G. Chornokur3 and C. M. Phelan3 1 V. Lashkaryov Institute of Semiconductor Physics of NASU, pr. Nauky 41, 03028 Kyiv, Ukraine 2 Instituto Politécnico Nacional – ESFM, Av. IPN, Ed. 9, U.P.A.L.M., 07738 Mexico D.F., Mexico 3 H Lee Moffitt Cancer Center and Research Institute, Tampa, Fl-33612, USA E-mail:[email protected]; [email protected] ABSTRACT The effect of bio-conjugation of CdSe/ZnS core-shell quantum dots (QDs) with Interleukin 10 (IL-10) antibodies on the aging of photoluminescence (PL) spectra of the QDs was investigated. The aging occurred upon storage of QDs for about 2 years or thermal annealing at 190 oC for up to 12 hours at atmospheric ambience and consisted in “blue” shifting the PL band position, increasing a PL band half-width and decreasing the PL intensity. The bioconjugation is found to promote PL aging. The aging upon storage is attributed to the oxidation that decreases the QD core dimension, while the aging upon thermal annealing can be due to both oxidation and alloying of CdSe core and ZnS shell. INTRODUCTION To date, one of the most relevant applications of II-VI quantum dots (QDs) is in fluorescence bio-imaging and bio-sensing [1, 2]. In a liquid medium, a bio-conjugation affects mainly the intensity of QD emission and so the dependence of QD photoluminescence (PL) intensity on concentration of attached target molecules is used for QD application as protein sensors [1]. However, other spectroscopic confirmations of successful bio-conjugation (specifically, a spectral shift of emission maximum) can improve the sensitivity of immunofluorescent assays. We have founded earlier that, if a liquid solution of bio-conjugated QDs is dropped on a silicon substrate and then dried at room ambience for several days, a shift of the PL band position to the short-wavelength region (blue shift) occurs [3, 4]. In contrast, a spectral position of the PL band in non-conjugated reference QD samples does not change at the same conditions. The shift in bio-conjugated QDs strongly increased under thermal treatment at elevated temperatures [4, 5] or during long-term storage at room temperature at air ambience [6]. In these cases the changes in color of the QD emission seen by the naked eye can be reached. In this paper, the mechanisms of large blue shifts in bio-conjugated QDs are studied by the micro-PL technique. EXPERIMENTAL DETAILS The CdSe/ZnS core-shell QDs embedded in a silica shell [7] were conjugated to the IL 10 (antihuman IL 10, rat IgG2a) molecule from Serotec using a commercially available QD conjugation kit from Invitrogen Inc. [8]. The bio-conjugation was confirmed with the agarose gel
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electrophoresis technique [3]. A principal PL maximum of the QDs dispersed in a buffer solution was at 585- 590 nm that corresponded to average diameter of core/shell nanocrystals of about 4.4 nm [7]. The samples were produced by deposition of a
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