Cooperative Doping in Ultrasmall BaF₂ Nanocrystals for Multimodal ¹⁹F‑MRI and CT Applications

Nanostructured metal fluorides (nanofluorides) are an emerging type of inorganic nanocrystals (NCs) with unique physiochemical properties for advanced applications. One recent demonstration used water-dispersed ultrasmall CaF2 nanofluorides as imaging agents that combined the advantages of inorganic NCs with the benefit of background-free 19F-magnetic resonance imaging (19F-MRI). Nevertheless, obtaining small nanofluorides with a face-centered cubic crystal structure, where all fluorides are magnetically equivalent to result in a single 19F NMR signal, is challenging for other types of nanofluorides, preventing their use in 19F-MRI. Here, we show the development of ultrasmall, water-dispersed, barium fluoride (BaF2) NCs for bioimaging applications. By doping BaF2 with two types of lanthanides, diamagnetic-La3+ and paramagnetic-Sm3+, we were able to control the morphology and 19F-MR properties of the final La,Sm:BaF2 (termed LaSamBa) formulation. The fine-tuning of the La3+ content enabled us to obtain monodispersed 4.5 nm NCs, and control over the Sm3+ content provided LaSamBa with very short T1 relaxation properties (ca. 100 ms) needed for enhanced 19F-MRI sensitivity. This type of nanofluorides was examined in two different imaging modalities (i.e., 19F-MRI and CT), benefiting from their single 19F-NMR signal and the high atomic number of barium atoms, respectively. As their 19F chemical shift significantly differs from that of other nanofluorides (e.g., CaF2 and SrF2), LaSamBa expanded the nanofluoride library for future multitarget 19F-MRI studies

Image-based visual hull of a tennis racket

Researchers are often interested in tracking object movement in sport. This could be useful to identify equipment designs that match the technique of players. Previously, stereo camera systems have been used to track markers attached to striking implements to measure their movement in three dimensions. However, manual selection of markers on the image plane can be time consuming and inaccurate. There is potential however to reduce these drawbacks associated with marker-based analysis by tracking a striking implement using its visual hull. The closest geometric approximation of an object that can be reconstructed using only its silhouette images is its visual hull. Early applications of visual hulls include size and shape estimation of objects such as stones. Recently, subject specific visual hulls constructed from multiple camera views combined with anatomical tracking algorithms have measured human motion through markerless motion capture. However, multiple camera systems are not practical for real play conditions in most sports. The application of visual hulls to measure movements of striking implements used in sport has not yet been explored. A set of calibrated views of a tennis racket were captured and segmented into binary images to obtain silhouettes. The visual hull of a tennis racket was constructed by intersection of the volume of space formed by back-projecting the silhouettes from all input views. This research is the first stage in the development of a system that measures movement of a striking implement in real play conditions by combining its visual hull with footage from a single camera

Genetically Engineered MRI-Trackable Extracellular Vesicles as SARS-CoV‑2 Mimetics for Mapping ACE2 Binding <i>In Vivo</i>

The elucidation of viral-receptor interactions and an understanding of virus-spreading mechanisms are of great importance, particularly in the era of a pandemic. Indeed, advances in computational chemistry, synthetic biology, and protein engineering have allowed precise prediction and characterization of such interactions. Nevertheless, the hazards of the infectiousness of viruses, their rapid mutagenesis, and the need to study viral-receptor interactions in a complex in vivo setup call for further developments. Here, we show the development of biocompatible genetically engineered extracellular vesicles (EVs) that display the receptor binding domain (RBD) of SARS-CoV-2 on their surface as coronavirus mimetics (EVsRBD). Loading EVsRBD with iron oxide nanoparticles makes them MRI-visible and, thus, allows mapping of the binding of RBD to ACE2 receptors noninvasively in live subjects. Moreover, we show that EVsRBD can be modified to display mutants of the RBD of SARS-CoV-2, allowing rapid screening of currently raised or predicted variants of the virus. The proposed platform thus shows relevance and cruciality in the examination of quickly evolving pathogenic viruses in an adjustable, fast, and safe manner. Relying on MRI for visualization, the presented approach could be considered in the future to map ligand-receptor binding events in deep tissues, which are not accessible to luminescence-based imaging