Chemically functional semiconductor nanocrystals: Electrochemistry and self-assembly on surfaces

Semiconductor nanocrystals (i.e., Quantum Dots, QDs) exhibit size-dependent emission properties and have synthetically adjustable ligand shells, making them interesting materials for applications ranging from luminescent displays to biomolecular tags. In this paper, the electrochemical properties of two types of nanocrystal are studied with an emphasis on the effect of core/shell vs core structures. The band gap energy of CdSe particles, measured using optical spectroscopy, was shown to increase slightly with the application of a ZnSe shell, as expected based on the increased energy required to transfer an electron through the shell material. The electrochemically determined band gaps are overestimated in the case of CdSe/ZnSe core/shell nanoparticles, reflecting the band gap of the ZnSe shell. Finally, QDs were self-assembled onto gold surfaces by electrostatic and covalent attachment, and their presence confirmed by fluorescence spectroscopy. The high intensity of emitted light shows that the QDs can be self-assembly onto metallic surfaces, without energy transfer quenching of the luminescence.