Metal-based nanomaterials (NM) find applications today in the biomedical field for imaging, sensing, and therapy. Moreover, due to the possibility to functionalize their surface, they offer scope for theranostics applications, in which imaging properties, targeting agents, and drugs are carried by a single nano-platform. Therefore, it is crucial to assess the stability of these engineered nanomaterials in in vitro biological models, in order to contribute to the design of biocompatible functional NM with intact optical properties and ideally no toxicity.

Synchrotron techniques as X-ray Fluorescence (XRF) micro/nano-imaging and X-ray Absorption Spectroscopy (XAS) are unique experimental techniques that can reveal the fate of metallic NM in cells and tissues. XRF micro/nano-imaging provides the biodistribution, down to the sub-cellular level, of native and exogenous elements, allowing for the visualization of the trafficking pathways of the NM and of the target cellular compartments. XAS interrogates a selected metal and provides information about its chemical state. Therefore, it is an invaluable tool to disclose the physicochemical transformations of metallic NM in vivo/in cellulo, as it detects not only intact NM but also their degradation products, which are most often optically silent.

We will present two studies making use of synchrotron techniques to unravel the biotransformations of two distinct NM formulations. The first focuses on Ag nanoparticles (NP), which are extensively used as antibacterial agents in medical devices such as catheters, wound dressing, and implants. We investigated the transformations of Ag NP, as a function of the coating, in a hepatic cell line, including in 3D cultures mimicking liver functions. This approach allowed us to follow the in cellulo dissolution and the distribution of Ag species until biliary excretion. [1, 2]

The second example concerns indium phosphide (InP) –based quantum dots (QD): these nanocrystals exhibit a narrow and tunable photoluminescence peak in the UV/Visible range, which makes them excellent candidates for biosensing and theranostics. We probed their transformations in the polyp Hydra vulgaris, an invertebrate animal model. Although InP QDs proved stable in vitro, even after 24 h at acidic pH, we highlighted their fast and almost complete degradation in less than 3 h in vivo. [3]  

In summary, we propose a panel of experimental tools that enable the investigation of the in cellulo and in vivo stability of metal-based nanomaterials for nanomedicine.