In Vivo Near-Infrared Imaging Using Ternary Selenide Semiconductor Nanoparticles with an Uncommon Crystal Structure

The implementation of in vivo fluorescence imaging as a reliable diagnostic imaging modality at the clinical level is still far from reality. Plenty of work remains ahead to provide medical practitioners with solid proof of the potential advantages of this imaging technique. To do so, one of the key objectives is to better the optical performance of dedicated contrast agents, thus improving the resolution and penetration depth achievable. This direction is followed here and the use of a novel AgInSe₂ nanoparticle-based contrast agent (nanocapsule) is reported for fluorescence imaging. The use of an Ag₂ Se seeds-mediated synthesis method allows stabilizing an uncommon orthorhombic crystal structure, which endows the material with emission in the second biological window (1000-1400 nm), where deeper penetration in tissues is achieved. The nanocapsules, obtained via phospholipid-assisted encapsulation of the AgInSe₂ nanoparticles, comply with the mandatory requisites for an imaging contrast agent-colloidal stability and negligible toxicity-and show superior brightness compared with widely used Ag₂ S nanoparticles. Imaging experiments point to the great potential of the novel AgInSe₂ -based nanocapsules for high-resolution, whole-body in vivo imaging. Their extended permanence time within blood vessels make them especially suitable for prolonged imaging of the cardiovascular system.