Physico-Chemical nanomaterials science

The effect of electrolytic aggregation of Au nanoparticles on optical characteristics of AgInS2/ZnS QDs modified with oligonucleotides
Nesterenko Y.O.1, Rachkov O.E.1, Kozoriz K.O.2, Borkovska L.V.2,  
1 Institute of Molecular Biology and Genetics of NASU, 150 Zabolotnogo Str., 03680 Kyiv, Ukraine
E-mail: anen.cheshir@gmail.com
2 V. Lashkaryov Institute of Semiconductor Physics of the NAS of Ukraine, 45 Prospect Nauky, 03028 Kyiv, Ukraine. 

The interaction of exciton in semiconductor nanocrystal, the so-called quantum dot (QD), with plasmon of metal nanoparticle (NP) is widely used in optical sensors for detection of biological and chemical substances in the solutions. Here, we present the results of investigations of the influence of electrolytic aggregation of gold nanoparticles (Au-NPs) on optical characteristics of the AgInS2/ZnS QDs modified with oligonucleotides. The QDs were stabilized with mercaptoacetic acid and glutathione, and the Au-NPs were processed with lipoic acid and mercaptohexanol. The QDs and Au-NPs were modified, respectively with 19-bases (MP-SH) and 26-bases (SH-DP) thiolated oligonucleotides. The nanoobjects were placed in buffer solutions SSC of different multiplicity (0.1×, 0.25×, 0.5×SSC). 
The photoluminescence (PL) spectra of QD modified with oligonucleotides (MP-QDs) show a wide band in the yellow-red spectral region caused by radiative recombination of carriers via the levels of defects in the QDs. The adding of Au-NPs modified with oligonucleotides (Au-DP) resulted in the decrease of PL intensity. This was accompanied by the changes in optical absorption. Specifically, the increase in absorption recorded at 620 nm and 690 nm took place. The effect enhanced as the multiplicity of buffer solution increased and was ascribed to formation of aggregates of Au-NPs and QDs. In fact, formation of aggregates of Au-NPs caused the change of frequency of surface plasmon resonance (SPR) which manifested in the appearance of absorption “shoulder” at about 620 nm.
The process of aggregate formation depended on type of QD’s stabilizing ligand. In particular, for the solutions of Au-DP and glutathione stabilized MP-QDs stored for 24 hours a precipitation on the bottom of the tube was observed and accompanied with complete quenching of the PL intensity.
The effect should be taken into account when the sensor system for detection of specific sequences of nucleic acids in solutions is developed.