Cloneable Selenium Nanoparticles As Multi-modal Bio-imaging Contrast Agents

A cloneable NanoParticle (cNP) is an inorganic nanoparticle that is synthesized by a protein. The protein determines the elemental composition, size, morphology, and other properties of the nanoparticle. Here, we describe the use of a cloneable Selenium NanoParticle (cSeNP) as a cloneable imaging contrast agent in electron microscopy, fluorescence microscopy, and X-ray computed tomography. Combined, these three imaging modalities produce images of biological length scales spanning meters to angstroms but are difficult to correlate. The cSeNP is comprised of an NADPH dependent enzyme that reduces selenodiglutathione to zerovalent Se precipitates. SeNP binding peptides fused to the enzyme ligate the Se precipitates, retain them at the enzyme, and regulate SeNP size to ~5 nm inside cells. The cSeNP-protein can be genetically fused to any protein-of-interest, creating a chimeric protein-of-interest-cSeNP. The cSeNPs endow the protein-of-interest with distinguishable contrast in X-ray and EM images, due to the contrast of SeNPs in these imaging modalities relative to biological background. The cSeNPs can react spontaneously with transition metals such as Znn+ or Cun+, forming fluorescent metal-selenides, imageable in florescence microscopy. The cSeNP, therefore, represents a cloneable imaging contrast agent that facilitates location and correlation of proteins-of-interest across all biological length scales.