Effects of Bio-conjugation and Annealing on the Photoluminescence and Raman Spectra of CdSe/ZnS Quantum Dots
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Effects of Bio-conjugation and Annealing on the Photoluminescence and Raman Spectra of CdSe/ZnS Quantum Dots L. Borkovska1, N. Korsunska1, T. Stara1, O. Kolomys1, V. Strelchuk1, O. Rachkov 2 and T. Kryshtab3 1 V. Lashkaryov Institute of Semiconductor Physics of NASU, pr. Nauky 41, 03028 Kyiv, Ukraine 2 The Institute of Molecular Biology and Genetics of NASU, Zabolotnogo Str. 150, 03680 Kyiv, Ukraine 3 Instituto Politécnico Nacional – ESFM, Av. IPN, Ed.9 U.P.A.L.M., 07738 Mexico D.F., Mexico E-mail:[email protected]; [email protected] ABSTRACT The effect of thermal annealing at ambient conditions on the photoluminescence (PL) and Raman scattering spectra of non-conjugated and conjugated with S6K2 antibody CdSe/ZnS coreshell quantum dots (QDs) has been studied. In the PL spectra, the annealing is found to produce the blue shift of the PL band spectral position and degradation of the PL intensity. These changes are found to be much more intense in conjugated QDs and are accompanied by the increase of a PL band half-width. In the Raman scattering spectra, the spectral shift and a decrease of the intensity of CdSe LO phonon peak as well as a increase of the intensity and narrowing of the peak ascribed to a mixed interface layer are found. The effect of annealing is supposed to be the result of partial core-shell intermixing that is accompanied by the QD oxidation in bioconjugated QDs. Keywords: Quantum dots; Bio-conjugation; Photoluminescence INTRODUCTION Recently, the application of colloidal II-VI quantum dots (QDs) in fluorescence biosensing and bio-imaging is getting increased attention [1]. We have found earlier that the samples of bio-conjugated CdSe(Te)/ZnS core-shell quantum dots (QDs) dried on a Si substrate can be used for detecting of bio-molecules utilizing the effect of a photoluminescence (PL) spectral shift [2]. We have shown that if a liquid solution of bio-conjugated QDs is deposited on a crystalline Si substrate and then dried, a spectral position of the QD photoluminescence band shifts to shorter wavelengths (a “blue” shift effect) in comparison with the identical nonconjugated QDs [3, 4]. The shift magnitude increased gradually during the sample storage at atmospheric ambience for several days. This effect was observed in CdSe/ZnS and CdSeTe/ZnS core-shell QDs conjugated to different monoclonal antibodies [4]. It has also been found that the process exhibited as the PL spectral shift is facilitated noticeably and the shift magnitude is increased for the samples annealed at above room temperature for hours [3]. For instance, thermal annealing of conjugated QD sample at 190 ºC for 1 hour in air stimulated a blue shift of the PL band of about 15 nm, while thermal annealing at 250 ºC under the same conditions resulted in a blue shift of about 60 nm [3]. Therefore, the thermal annealing can be used as an
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effective processing to change relatively quickly the emission color in conjugated QDs in such a way that this change will be clearly seen by the naked eye. The “blue” shift effect observed in the
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