Semiconductor II-VI Quantum Dots with Interface States and Their Biomedical Applications

Nanocrystals of group II-VI semiconductors, known as quantum dots (QDs), in which electrons and holes are three dimensionally confined within the exciton Bohr radius of the material, are characterized by the exceptional optical properties, such as broad absorption and sharp emission bands as well as size-tunable photoluminescence in the visible spectral range. The most popular are CdSe/ZnS QDs due to their bright and unique emission with the wide excitation spectra and narrow emission bandwidths (Bailey et al., 2004; Dybiec et al., 2007; Jamieson et al., 2007; Kune et al., 2001; Norris et al., 1996; Tessler et al., 2002). The II-VI QDs have been investigated in versatile photonic applications including solar cells (Choi et al., 2006; Kongkanand et al., 2008; Lopez-Luke et al., 2008), optical fibre amplifiers (Liu et al., 2007), color displays using light-emitting diode arrays (Huang et al., 2008: Klude et al., 2002; Zhao et al., 2006), optical temperature probes (Liang et al., 2006; Walker et al., 2003), as well as in biology and medicine (Alivisatos et al., 2005; Grodzinski et al., 2006; Hoshino et al., 2007; Murcia et al., 2008; Portney & Ozkan, 2006; Wang et al., 2007). Note that metal, semiconductor, polymer and ceramic nanoparticles in general have gained essential interest for biological and medical applications (Brigger, et al., 2002). Polymer and ceramic nanoparticles have been widely used as drug carriers, whereas metal nanoclusters and semiconductor QDs have been applied mainly for imaging and therapy. Among various nanoparticles, semiconductor QDs attracted much attention due their exceptional optical properties. In comparison with organic dyes and fluorescent proteins, the semiconductor quantum-confined core/shell nanostructures, such as CdSe/ZnS QDs, are brighter, more stable against photo bleaching, have multicolor emission in dependence on core sizes and can be excited for this emission with a single light source. The size-tunable properties allow one to choose an emission wavelength that is well suited to experimental conditions and to synthesize the QD-based probe by using an appropriate semiconductor materials and nanocrystal sizes. In biology and medicine the semiconductor QDs have been used: for the fluorescence resonance energy transfer (FRET) analysis (Bailey et al., 2004; Jamieson et al., 2007; Zhang et al., 2005), in gene technology (Gerion et al., 2002; Han et al., 2001; Pathak et al., 2001), fluorescent labeling of cellular proteins (Dubertret et al., 2002; Dubertret et al., 2003; Hanaki