Nanochemistry and biotechnology 
 Prospects of CdTe quantum dots as fluorescent probes for bioimaging applications
Valakh M.Y1., Dzagan V.M1., Horiunova I.I.,2Borovaya M.N2., Blume Ya.B2., Yemets A.I.2
1. V.E. Lashkaryov Institute of Semiconductor Physics NAS of Ukraine. Pr. Nauki 41, Kyiv- 03028, Ukraine.
E-mail: valakh@nas.gov.ua
2. Institute of Food Biotechnology and Genomics, NAS of Ukraine. Osypovskogo Street, 2a, Kyiv-04123, Ukraine.
E-mail: yemets.alla@nas.gov.ua, marie0589@gmail.com 

One of the fields of modern materials science is the creation of nanoscale materials including semiconductor nanocrystals. Cadmium telluride (CdTe), an important group II–VI semiconductor material with large exciton Bohr radius (7.3 nm) and narrow bulk band gap of 1.5 eV has shown significant potential for LED (energy), FRET (electronics), and biomedical applications due to their size dependent properties. These quantum dots provide excellent photostability, narrow emission and high quantum yield in comparison with organic dyes and therefore explored in live cell bio-imaging [1]. The purpose of this study was to estimate optical properties of CdTe quantum dots produced by colloidal synthesis and to investigate their localization in plant cells by luminescent microscopy. 
CdTe quantum dots were synthesized by colloidal synthesis from Cd and Te precursors in an isothermal quartz reactor. The synthesis process was carried out over a period of 2 to 9 minutes, quantum dots were stabilized by thioglycolic acid. High temperatures (250-300˚C) were needed for obtaining CdTe nanocrystals [2]. The first step of our research was to establish a relationship between the size and optical properties of CdTe quantum dots. Absorbtion spectra were measured by a spectrophotometer Specord UV–VIS Analytik Jena AG (Germany). Luminescent spectra were measured at room temperature using the serial spectrophotometer Cary Eclipse (Varian Inc., Agilent Tech. USA). For bioimaging studies 4-day root seedlings of Arabidopsis thaliana were used. We investigated localization of quantum dots in plant cells by luminescent microscopy. Observations were carried out using a luminescent microscope Axioskop 40 ("Carl Zeiss", Germany). Lens 40X. The images were made using the following filters: FS 02: excitation wavelength – BP 365/12, emission filter LP 397; FS 15: excitation wavelength BP 546/12; emission filter – LP 590: excitation wavelength – 475/40 and separate filter FT 500: excitation wavelength BP – 530/50.
The analysis of obtained spectra revealed a typical properties of CdTe due to the quantum-size effect, namely a shift to the red (long-wave) region with an increasing of synthesis time and, correspondingly, an increasing of a size of quantum dots. Luminescence bands are rather narrow and symmetric. The absorption maxima corresponded to 531, 442 and 582 nm. Luminescent maxima corresponded to 567, 504 and 607 nm. It was shown that optimal size of CdTe quantum dots was 3-5 nm. The next step of the work was devoted to the study of the penetration of luminescent CdTe quantum dots into plant cells. It was established that CdTe quantum dots have an intensive luminescence which makes them an attractive probes for bio-imaging. After 24 h of incubation we observed a localization of CdTe quantum dots in the epidermal cells of the root apex and in the apical meristem cells. Summing up, it was shown that CdTe quantum dots are promising luminescent biomarkers for numerous cell biology applications. Further research will focus on developing a methodology for biological synthesis of CdTe nanoparticles using different biomatrices. 

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