Photonic crystals in biology

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400 450 500 550 600 Poster Session, Tuesday, June 15 Theme A1 - B702 Surface Modification of Colloidal Oil Soluble CdS x Se 1-x Quantum Dots with Thiolated Organic Surfactants 1 Caner Ünlü and Serdar Özçelik 1 *, 1 Izmir Institute of Technology, Faculty of Science, Department of Chemistry, Urla-Izmir 35430 Abstract-This is the first demonstration about synthesis and ligand exchange of colloidal alloyed quantum dots by the two phase method. We first synthesized CdS x Se 1-x quantum dots by a modified two phase synthesis method in toluene by using trioctylphosphineoxide (TOPO) as surfactant and then exchanged surface chemistry of the quantum dots with different organic surfactants consisting of thiol groups, such as 3 – Mercaptopropionic acid (3 – MPA) , N – Acetyl L – Cysteine (NAC) and Cysteamine. Quantum dot s passed to aqueous medium from oil medium with a loss in quantum yields. Fluorescence spectra of the surface exchanged quantum dots shifted towards red around 10 nm. Bawendi et.al. developed a simple method to synthesize monodisperse semiconductor colloidal nanoparticles. [1] They become popular because of their unique optical properties such as high quantum yield, larger extinction coefficient and photostability, etc. Usually quantum dots were successfully synthesized in oil media, such as toluene, heptane, hexane, etc. But these quantum dots dispersible in oil medium are not preferred for use in biological applications. However, Alivisatos et.al showed that quantum dots can also be prepared in water and therefore can be used as fluorescent labeling agent in cells. This utilization extends the applications of quantum dots to biomedical fields [2]. For biological applications, quantum dots must be water dispersible. There are several methods to make quantum dots water dispersible. The most studied method is the ligand exchange method. Basically, quantum dots with high quantum yields prepared in oil based solvents, and then the hydrophobic surfactants exchanged with hydrophilic ones. Water dispersible quantum dots surface chemistries are designed to provide reactive groups such as amine (–NH2), carboxy l (– COOH) or mercapto (–SH) groups for direct conjugation to biomolecules. In this study, we reported synthesis of colloidal CdS x Se 1-x alloyed quantum dots in toluene and surface modification of them with different thiolated organic surfactants, 3 – MPA, NAC and cysteamine. P P O O CdSSe O O P P NAC H 3 C N + O COOH were achieved with some degree of loss in the yield (Figure 2). The quantum yield of water dispersible CdS x Se 1-x dropped from %60 to %10. Also, fluorescence spectra of water dispersible CdS x Se 1-x quantum dots shifted to red about 10 nm when it is compared to the TOPO capped spectra of quantum dots (Figure 3). This project is supported by DPT and TUBITAK (Grant No: 108T446) a) b) Figure 2. a) Luminescence image of TOPO, 3 – MPA and NAC capped quantum dots with the same size. b) Luminescence image of 3 – MPA capped CdS x Se 1-x quantum dots with different size Normalized Intensity Wavelength (nm) Normalized Intensity 450 500 550 600 650 Wavelength (nm) Figure 3. Change in fluorescence spectrum of quantum dots after ligand exchange procedure. Red lines correspond to TOPO capped CdS x Se 1-x quantum dots while black lines correspond to 3 – MPA capped CdS x Se 1-x quantum dots. *Corresponding author: 0Tserdarozcelik@iyte.edu.tr [1] Murray, C. B., Noms, D. J., and Bawendi, M. G. ,1993. Journal of American Chemical Society 115: 8706-8715 [2] Bruchez, Jr M., Moronne, M., Gin, P., Weiss, S., Alivisatos, AP., 1998. Science. 281:2013-2016 HOOC O N + H 3 C S S CdSSe S CH 3 S N + O COOH HOOC N + O CH 3 Figure 1. Illustration of Surface Modification of TOPO capped CdS x Se 1-x quantum dots with NAC Highly luminescent and monodisperse TOPO capped colloidal CdSxSe 1-x alloyed quantum dots were synthesized by a modified two phase method at mild conditions in toluene. Oil dispersible CdS x Se 1-x collo ids possessed quantum yields around 60 %. Surfaces of the oil dispersible CdS x Se 1-x quantum dots were modified by a new method developed by us. As a result, 3 – MPA, NAC and cysteamine capped alloyed CdS x Se 1-x quantum dots 6th Nanoscience and Nanotechnology Conference, zmir, 2010 236
Poster Session, Tuesday, June 15 Theme A1 - B702 Synthesis and compos itional tunable spectral properties of CdSe x Te 1-x ternary alloys Seda Özdemir 1 , Gü lçin Ünal 1 ,Serdar Özçelik 1 * 1 Abstract-We synthesized ternary CdSe xTe 1-x colloidal nanocrystals and showed that the spectral properties of the alloy were tuned by the composition of the alloy. The photoluminescence spectra spans from 450 to 650 nm . The PL quantum efficiency reached up to 22%. XRD analysis proved that crystal structure of the alloy is zinc-blend. The size of the nanocrystal is 5.0 nm. The level of cytotoxicity was found to be 2.5 μg/ml for PC3 and MCF7 cells. Colloidal semiconductor nanocrystals are important class of nanoscale materials because of inexpensive synthesis and continuous tunability of their physical, specifically optical, properties. Understanding relationship among chemical composition and physical properties of ternary alloyed nanocrystals is crucial for the advancement of new technological applications. Controlling spectroscopic properties of alloyed nanocrystals by the ratio of alloying elements may yield significant improvement in performance [1,2]. The goal of this study was to produce and characterize water-dispersible lu minescent alloyed CdSe x Te 1-x semiconductor nanocrystals, which may be suitable for bioimaging. We synthesized CdSe x Te 1-x colloidal nanocrystals utilizing wet-chemistry techniques at low temperature (100 o C) and in one-step. The characteristic PL wavelengths of synthesized nanocrystals by varying the alloy composition showed emission in a range from 450 to 650 nm (Figure 1). Alloyed ternary nanocrystals have %17 photoluminescence quantum yield. After coating the nanocrystals with CdS shell the photoluminescence quantum yield of the alloys increased up to % 22. Figure 2. XRD signals of the alloys increasing amount of Te causing the shift. Alloyed nanocrystals contain toxic element such as Cd. MTT assay was used to determine the level of cytotoxicity of CdSe x Te 1-x nanocrystals. The lethal concentration for Confocal microscopy indicates that the nanocrystals were accumulated in the cytoplasm of the cells. Figure 3. MTT assay for MCF7 cells. This study was supported by TUBITAK (Grant no 108T446) and DPT. Corresponding author: serdarozcelik@iyte.edu.tr [1] Gu, Z., Zou, L., Fang, Z., Zhu, W., Zhong, X., 2008, One pot synthesis of highly luminescent CdTe/CdS core/shell nanocrystals in aqueous phase, Nanotechnology 19, 135604. [2] Thakar, R., Chen, Y., Snee, P.T., 2007, Efficient emission from core/(doped)shell nanoparticles: Applications for chemical sensing, Nano Letters, Vol. 7, No. 11, 3429-3432. Figure 1. Normalized emission spectrum of CdSe x Te 1-x nanocrystals and photographs of the alloys under visible and UV light illumination. The crystal structure of the alloy was found to be zinc blende. XRD signal shifts to lower angles by increasing the amount of Te in the alloy (Fig. 2). 6th Nanoscience and Nanotechnology Conference, zmir, 2010 237
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