Photoluminescent hybrid inorganic-protein nanostructures for imaging and sensing in vivo and in vitro

The last decade has seen an exciting confluence of biophotonics with nanotechnology, with nanoparticle-based investigations in life sciences ranging from fundamental biological research to clinical therapeutics. This chapter is focused on photoluminescent nanoparticle-based "bioprobes," designed and built to visualize and probe specific biological processes. Unlike organic dyes and fluorescent proteins, photoluminescent nanoparticles are highly photostable and, depending on the nanomaterial design, exhibit narrow and/or tuneable emission spectra, thereby greatly extending the capabilities of the existing fluorophores. Inorganic materials show photoluminescence independent of environmental conditions, including pH and temperature, while their chemically active surface area provides docking platforms for anchoring targeting and/or cargo biomolecules. Moreover, some types of nanoparticles exhibit unique properties, including enhanced detection/imaging contrast due to long photoluminescence lifetime, and/or an "anti-Stokes" emission wavelength shift. In this review, selected key types of such nanoparticle-based bioprobes are discussed: quantum dots, fluorescent nanodiamonds, nanorubies and upconversion nanoparticles. The chapter aims to demonstrate the power of this bottom-up bio-nanophotonics approach for biological sensing and imaging. The design of photoluminescent nanoparticles, surface activation and bioconjugation are discussed, in addition to the deployment and application of selected bioconjugate structures for specific internalization in cells and living biological tissue.