%0 Journal Article
%T The Effect of Multidentate Biopolymer Based on Polyacrylamide Grafted onto Kappa-Carrageenan on the Spectrofluorometric Properties of Water-Soluble CdS Quantum Dots
%A Ghasem Rezanejade Bardajee
%A Zari Hooshyar
%A Yousof Pourhasan
%J International Journal of Spectroscopy
%D 2011
%I Hindawi Publishing Corporation
%R 10.1155/2011/954252
%X A new fluorescent composite based on CdS quantum dots immobilized on the multidentate biopolymer matrix is prepared through the graft copolymerization of the acrylamide onto kappa-Carrageenan. A variety of techniques like thermogravimetric analysis (TGA), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR) was used to confirm the structure of the obtained samples. To investigate the spectrofluorometric properties, fluorescence spectroscopy of the obtained quantum dots was studied. 1. Introduction Semiconductor quantum dots (QDs), also called nanocrystals (NCs), have gained increasing attention in the past decade [1¨C3]. They have been widely investigated because of their potential use in sensors [4], laser materials [5], thin-film light-emitting devices (LEDs) [6¨C8], and biological labels. Among numerous possible applications of QDs, biological labeling will be pointed out [9, 10]. QDs exhibit larger photostability than organic dyes used routinely, since narrow excitation spectra of conventional dye molecules make difficult simultaneous excitation in most cases. However, QDs display size-dependent tunable florescence (FL) with broad excitation spectra and narrow emission band widths, which span the visible spectrum. This property of QDs allows simultaneous excitation of several particle sizes at a single wavelength, and therefore they facilitate multicolor experiments [11¨C14]. In addition, QDs have high photochemical stability, excellent resistance to chemical degradation and photodegradation, and good florescence quantum yields. For most biological applications of QDs, their water solubility is indispensable. Three different approaches can be used to prepare water-soluble semiconductor QDs: ligand exchange [15, 16], encapsulation into a water-soluble shell (i.e., the silica or phospholipids) [17, 18], and surface coating with polymers [19, 20]. In comparison, silica encapsulation produces good stability but with larger sizes which are about tens of nanometers to several micrometers [21]. In ligand exchange, the stability of the nanocrystals is limited by the stability of ligands on the QD surfaces. The proper choice of ligand is therefore crucial in order to achieve functionality and retain the optical properties of the QDs, and it usually limits the final application range of the QDs [22]. In this context, polymers may be used as suitable substitutes for the small organic ligand molecules due to their good stability on the surface of QDs [23]. A number of strategies were developed to obtain polymer-coated QDs:
%U http://www.hindawi.com/journals/ijs/2011/954252/