Simple silanization routes of CdSe and CdTe nanocrystals for biological applications Diogo B. Almeida, Wagner M. Faustino, Gilberto J. Jacob, André A. de Thomaz, Luiz C. Barbosa, Oswaldo L. Alves, Univ. Estadual de Campinas (Brazil); Patricia M. A. Farias, Beate S. Santos, Adriana Fontes, Univ. Federal de Pernambuco (Brazil); Suzete A. O. Gomes, Fundacao Oswaldo Cruz (Brazil); Denise Feder, Univ. Federal Fluminense (Brazil); Italo O. Mazali, Carlos L. Cesar, Univ. Estadual de Campinas (Brazil) ABSTRACT Semiconductor colloidal quantum dots have been, for the past two decades, incorporated in a wide range of applications from catalysis and optical sensors to biolabels. For this reason, simple, cheap and reproducible routes of synthesis are the main goal of many research groups around the world. They seek the production of a very stable and extremely quantum efficient nanocrystal that can afford rough changes in the external environment. Silica capping is becoming a very common tool in the quest for a stable quantum dot, because of its strong and stable structure, this material provides a great insulator to the nanocrystal from the outside. The nanocrystal surface is not chemically favorable to the deposition of the bare silica shell, what demands a bifunctional molecule that provides the linkage between the core and the shell. In this work we present a comparison between several silanization methods of thiol capped CdSe and CdTe quantum dots, showing some simplifications of the routes and an application of the quantum dots produced as fluorescent cell markers in acquisition of confocal microscopy images. KEYWORD LIST Quantum Dots, Silica Shell, Confocal Microscopy, Fluorescent Markers 1 INTRODUCTION The most evident quantum dots (QDs) application in life sciences is the fluorescent tagging of cellular structures. These QDs are produced in a way to link themselves to specifc proteins. For this application, it is desirable a fine control of the emitting wavelength since the ultraviolet until the commercial photomultiplier limit of detection, around 1000 nm. The narrower is the bandwidth emission of the QDs samples, more different cellular structures can be identified with a specific color tag. In this context, the cadmium calcogenides family (CdSe, CdTe, CdS) is particularly adequate to this application. The main reason for substituting the conventional cell markers for functionalized QDs is the fact that they have almost null photobleaching. Many of the conventional organic dyes photobleach in question of seconds or minutes, what makes their manipulation quite complicated and careful because they must be handled in dark environments and the images acquisition must be fast, what turns the task of following cellular process very difficult. Besides the absence of photobleaching, the QDs present other important advantages. One of them is due to the fact that they have a very broad absorption band compared to the conventional dyes, allowing only one excitation source (with a lower wavelength) for the different color emitting QDs. Although cadmium calcogenides can be harmful for live structures, if the atoms are dissociated from the QD, the coating with an inert and resistant material, in our case, silica can prevent this to happen and turn QDs into to a less toxic material than the conventional organic dyes. Some experiments 1,2 show that QDs marked cells can maintain their Nanophotonic Materials V, edited by Zeno Gaburro, Stefano Cabrini, Dmitri Talapin Proc. of SPIE Vol. 7030, 70300I, (2008) · 0277-786X/08/$18 · doi: 10.1117/12.795436 Proc. of SPIE Vol. 7030 70300I-1 2008 SPIE Digital Library -- Subscriber Archive Copy