Water-soluble, cyclodextrin-modified semiconductor quantum dots - A novel class of chemical and biological sensors

This thesis work is an effort to realize the development of a semiconductor quantum dot based chemical and biological sensor. It involves the combination of various projects completed during the course of this study related to receptor modified semiconductor nanoparticles. In the first project a simple one pot approach has been developed for the synthesis of CdS nanoparticles. Cyclodextrin modified CdS particles showed good water solubility and were stable over a very long period of time. Host-Guest chemistry of these cyclodextrin modified quantum dots has been studied with different ferrocene compounds. Up to 90% fluorescence quenching was achieved, when ferrocene carboxylate was present in solution with CdS particles. For the first time the reversibility of fluorescence has been studied using receptor modified CdS quantum dots.;Even though US particles showed excellent water solubility and stability over different pH range, the quantum yield of these particles was less than 1%. In order to obtain higher quantum yield nanoparticles a simple method was developed for preparing core-shell structured CdSe/CdS particles. These core-shell structured particles has been modified with monothiolated beta-cyclodextrin and very stable. Quantum yields up to 46% could be obtained upon photoactivation. Even after several days of photoactivation the particles maintained their stability. In order to use these particles in a biological environment, the effect on optical properties by ionic strength and pH have also been studied. When tested with ferrocene compounds, these particles showed ten fold sensitivity than CdS particles.;In another project an efficient fluorescent sensor has been developed for the detection of neurotransmitters by using monothiolated beta-cyclodextrin modified CdSe/CdS particles. The presence of excess ascorbic acid in the solution containing millimolar concentration of dopamine did not affect the fluorescence detection. Molecular recognition studies of other amine neurotransmitters have also been conducted with these particles.