Fluorescent Nanocrystals and Proteins

Abstract

Colloidal semiconductor nanocrystals (NCs) have recently gained recognition as versatile bioprobes for advanced molecular and cellular imaging techniques. Fluorescent NCs may in fact overcome some of the typical limitations presented by organic fluorophores, owing to high photobleaching threshold, good chemical stability, broad absorption spectrum, along with the peculiar possibility of accurately tuning their spectral properties (thanks to their size-dependent emission spectrum). The fluorescence of NCs can be precisely tuned in the whole visible spectrum or even the near-infrared region, thus covering a very wide spectral range (from 400 nm to 2.2 μm). The broad absorption spectrum permits efficient excitation at any wavelength shorter than the emission peak, while maintaining the same characteristic narrow, symmetric emission spectrum, regardless of the excitation wavelength. Such spectral feature allows excitation of different sizes of NCs by means of a single wavelength of light, resulting in many fluorescent colors that may be detected simultaneously. Interestingly, a number of reliable procedures to transfer semiconductor nanocrystals from hydrophobic solutions to aqueous environment have been recently developed, in order to exploit NCs as fluorophores in biological processes, which obviously occur in aqueous environments. This chapter illustrates several demonstrations of protein–NCs hybrid systems that have been recently developed by several groups. The implementation of different