Selective Labeling and Decoration of the Ends and Sidewalls of Single-Walled Carbon Nanotubes Using Mono- and Bispecific Solid-Binding Fluorescent Proteins.

Simple and robust strategies for the noncovalent functionalization of carbon nanostructures with proteins are of considerable interest in hybrid nanomaterials synthesis, part-to-part assembly, and biosensor development. Here, we show that fusion of the Car9 and Car15 carbon-binding peptides to the C-termini of the sfGFP and mCherry fluorescent proteins enables selective labeling of the ends or the sidewalls of single walled carbon nanotubes. By installing a gold-binding peptide or a single cysteine residue in carbon-binding variants of sfGFP, we further produce heterobifunctional solid-binding proteins that support the decoration of nanotubes sidewalls or termini with gold nanoparticles. The approach described here is generic and should prove useful for the controlled assembly of other hybrid materials.

Streamlined Synthesis and Assembly of a Hybrid Sensing Architecture with Solid Binding Proteins and Click Chemistry.

Combining bioorthogonal chemistry with the use of proteins engineered with adhesive and morphogenetic solid-binding peptides is a promising route for synthesizing hybrid materials with the economy and efficiency of living systems. Using optical sensing of chloramphenicol as a proof of concept, we show here that a GFP variant engineered with zinc sulfide and silica-binding peptides on opposite sides of its ß-barrel supports the fabrication of protein-capped ZnS:Mn nanocrystals that exhibit the combined emission signatures of organic and inorganic fluorophores. Conjugation of a chloramphenicol-specific DNA aptamer to the protein shell through strain-promoted azide-alkyne cycloaddition and spontaneous concentration of the resulting nanostructures onto SiO2 particles mediated by the silica-binding sequence enables visual detection of environmentally and clinically relevant concentrations of chloramphenicol through analyte-mediated inner filtering of sub-330 nm excitation light.

Microbial Uptake, Toxicity, and Fate of Biofabricated ZnS:Mn Nanocrystals.

Despite their importance in nano-environmental health and safety, interactions between engineered nanomaterials and microbial life remain poorly characterized. Here, we used the model organism E. coli to study the penetration requirements, subcellular localization, induction of stress responses, and long-term fate of luminescent Mn-doped ZnS nanocrystals fabricated under "green" processing conditions with a minimized ZnS-binding protein. We find that such protein-coated quantum dots (QDs) are unable to penetrate the envelope of unmodified E. coli but readily translocate to the cytoplasm of cells that have been made competent by chemical treatment. The process is dose-dependent and reminiscent of bacterial transformation. Cells that have internalized up to 0.5 µg/mL of nanocrystals do not experience a significant activation of the unfolded protein or SOS responses but undergo oxidative stress when exposed to high QD doses (2.5 µg/mL). Finally, although they are stable in quiescent cells over temperatures ranging from 4 to 42°C, internalized QDs are rapidly diluted by cell division in a process that does not involve TolC-dependent efflux. Taken together, our results suggest that biomimetic QDs based on low toxicity inorganic cores capped by a protein shell are unlikely to cause significant damage to the microbial ecosystem.

A minimized designer protein for facile biofabrication of ZnS:Mn immuno-quantum dots.

A minimized protein consisting of a linear ZnS-binding peptide fused to an antibody-binding domain supports the one-step aqueous synthesis of Mn-doped ZnS nanocrystals that exhibit smaller size, brighter fluorescence and improved antibody-binding relative to those made with the original designer protein.