In vivo near-infrared imaging using ternary selenide semiconductor nanoparticles with 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. A lot of work remains ahead to provide medical practitioners with solid proof of the potential advantages of this imaging technique over well-established ones such as magnetic resonance imaging or nuclear imaging. To do so, one of the key objectives is to improve the optical performance of dedicated contrast agents, thus improving the resolution and penetration depth achievable with in vivo imaging. In the present study, we move along this direction and report on the use of AgInSe₂ nanoparticle-based contrast agents (nanocapsules) for fluorescence imaging. The use of a Ag₂Se seeds-mediated synthesis method allows stabilizing an uncommon orthorhombic crystal structure. This structure 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 in vitro–and show superior brightness compared with well-established and widely used Ag₂S nanoparticles. Imaging experiments point to the great potential of the novel AgInSe₂-based nanocapsules for high-resolution, whole-body in vivo imaging. In particular, their extended permancence time within blood vessels make them especially suitable for prolonged imaging of the cardiovascular system.