Nanophotonics of quantum dot-protein composites

Summary form only given. Quantum dot nanocrystals (QD) have been the versatile tool of nanophotonic applications with their size tunable narrow emission spectrum and broad-band excitation characteristics. Compared to the conventional dye molecules, they exhibit a longer lifetime, which makes convenient tools to be employed in nonradiative energy transfer applications. QDs can be utilized for the formation of protein/peptide based nanohybrids facilitating nonradiative energy transfer for nanophotonic applications, e.g., sensing and imaging. In such a system protein will be basically benefit from the fluorescence lifetime of the quantum dots while QDs will benefit from the biocompatibility feature of the proteins. In addition to these, many modifications can be made on proteins through protein/genetic engineering for a better functionality. To probe these possibilities, we investigated/tested two systems for sensing. In the first approach, we achieved a layer-by-layer assembled QDs embedded into polypeptide multilayer, where we succeeded lifetime modifications of the QDs as a function of a protease activity. In the second approach a nanohybrid of QD and photoprotein was realized. Using protein engineering, a trypsin cleavage site and a tag for the attachment of photoprotein on the QD surface was inserted to the photoprotein. The lifetime of the photoprotein was enhanced through nonradiative energy transfer from QD to photoprotein. Bioactivity of a trypsin protease was detected using this system, through lifetime change of the nanohybrid as a result of removal of photoprotein from the quantum dot surface.