University of Massachusetts, Amhearst,
Keywords: nanoparticles synthesis, bio sensing
Summary:Nanocrystals of II-VI compound semiconductors, such as CdSe and ZnSe, and core-shell structures based on them have unique properties, including size-tunable photoluminescence, narrow emission spectrum, broad excitation, high brightness, high extinction coefficients, and excellent photochemical stability. These materials have a wide range of novel applications, including medical diagnostics, high color definition display technologies and solar energy conversion. ZnSe nanocrystals are particularly attractive, because they do not contain toxic heavy metal ions, such as Cd2+, and can be doped relatively easily with transition metal ions, such as Mn2+ and Cu2+, thus enabling further tuning of their optoelectronic properties. We have developed a technique for growing II-VI nanocrystals that employs microemulsions and liquid crystals as templates for controlling both size, shape and size distribution of the nanocrystals. Kinetic Monte Carlo simulations of the process revealed the underlying mechanisms of particle nucleation and growth while Density Functional Theory calculations provided insights on doping mechanisms and enabled tuning of the nanocrystal growth and doping techniques. Extraction of the nanocrystals from the templates, annealing, and coating of their surfaces with molecules containing specific functional units enabled their stabilization in aqueous solutions and conjugation with biomolecular probes for applications in medical diagnostics. A new class of optical biosensors based on ZnSe nanocrystals has been developed for rapid quantitative detection of molecular or biological targets in solution. The biosensors have high sensitivity and selectivity by utilizing changes in the fluorescence emission spectra of ZnSe nanocrystals induced by the binding of the probes to the target biomolecules. Detection of single-base DNA mutations and separation-free assays that enable rapid quantitative detection of proteins in solution will be discussed as examples. These biosensors are attractive for developing miniaturized lab-on-a-chip portable devices that could enable rapid multiplexed detection of several biological targets for medical, environmental, and food safety applications.