Nanooptics and photonics

Effect of conjugation with oligonucleotides on the photoluminescence of the AgInS2/ZnS quantum dots
L. Borkovska1, T. Stara1, A. Rachkov2, J.-L. Doualan3 
1 V. Lashkaryov Institute of Semiconductor Physics of the NAS of Ukraine, 45 Prospect Nauky, 03028 Kyiv, Ukraine. 
E-mail: l_borkovska@ukr.net
2 Institute of Molecular Biology and Genetics of NASU, 150 Zabolotnogo Str., 03680 Kyiv, Ukraine
 3 CIMAP, CEA-CNRS-ENSICAEN, Normandie Université, 6 Blvd Maréchal Juin, Caen, France.

The AgInS2/ZnS core shell quantum dots (QDs) are characterized by high absorption coefficient and intense photoluminescence (PL) in the visible spectral range. These objects also show a reduced toxicity. These cause high perspectives of their application for both in vitro and in vivo bio-imaging. 
Herein, we present the results of the investigations of the influence of conjugation with 80-basic oligonucleotide 80-bcr-abl on the PL of the AgInS2/ZnS QDs stabilized in aqueous media by glutathione. The oligonucleotide reproduces the nucleotide sequence of the mRNA region of the hybrid gene bcr-abl. A protein product of this gene causes the development of pH'-positive forms of leukemia. 
The PL spectra of the QDs in neutral buffer solution showed a wide PL band peaked at about 585 nm. It was characterized by the Stokes shift of ~0.7 eV and ascribed to carrier recombination via the levels of intrinsic defects in the QDs. In the PL excitation spectra, an absorption edge shifted to longer wavelengths as the detection wavelength increased. Simultaneously, the PL relaxation times increased from ~280 ns to 880 ns with the increase of detection wavelength from 510 to 760 nm. These changes were ascribed mainly to variation of QDs in size.
The conjugation influenced the PL characteristics of the QDs. For conjugated QDs the luminescence intensity increased almost twice and the PL band shifted to shorter wavelengths up to 576 nm. Simultaneously, the PL relaxation times increased for all detection wavelengths. This effect is ascribed to passivation of surface defects of the QDs by oligonucleotides and improvement of QD solubility in buffer solution. The effect is supposed to be more pronounced for the QDs of smaller size.