Nanoanalytical Insights into the Stability, Intracellular Fate, and Biotransformation of Metal-Organic Frameworks

Systematic Comparison of Commercial Uranyl-Alternative Stains for Negative- and Positive-Staining Transmission Electron Microscopy of Organic Specimens

Negative- and positive-staining transmission electron microscopy (ns/psTEM) is a cornerstone of research and diagnostics, enabling nanometer-resolution analysis of organic specimens from nanoparticles to cells without requiring costly cryo-equipment. For nearly 70 years, uranyl salts like uranyl acetate (UA) have been the gold-standard ns/psTEM-stains. However, mounting safety concerns due to their high toxicity and radioactivity have led to stricter regulations and expensive licensing requirements. Consequently, there is an urgent global demand for safer, more sustainable stains that deliver uranyl-comparable, high-quality ns/psTEM. Here, the commercially available stain-alternatives UranyLess, UAR, UA-Zero, PTA, STAIN 77, Nano-W, NanoVan, and lead citrate are systematically assessed against UA. The stains are evaluated regarding their contrast, resolution, stain-distribution, and ease-of-use in ns/psTEM across a diverse sample set, including polymethylmethacrylate-nanoplastics, phosphatidylcholine-liposomes, Influenza-A viruses, globular ferritin, fibrillar pyruvate kinase amyloids, and human lung-carcinoma cell-sections. It is shown that for this variety of samples, a ready-to-use uranyl-alternative is commercially available with comparable or even superior ns/psTEM-performance to UA using an efficient staining-protocol. Furthermore, the GUIDE4U tool is developed for the fast identification of the appropriate uranyl-replacements for each sample of interest, saving ns/psTEM-users time and costs while ensuring excellent staining results for ultrastructural analysis, thereby further catalyzing the use of safer stains.

Safety Landscape of Therapeutic Nanozymes and Future Research Directions

Oxidative stress and inflammation are at the root of a multitude of diseases. Treatment of these conditions is often necessary but current standard therapies to fight excessive reactive oxygen species (ROS) and inflammation are often ineffective or complicated by substantial safety concerns. Nanozymes are emerging nanomaterials with intrinsic enzyme-like properties that hold great promise for effective cancer treatment, bacterial elimination, and anti-inflammatory/anti-oxidant therapy. While there is rapid progress in tailoring their catalytic activities as evidenced by the recent integration of single-atom catalysts (SACs) to create next-generation nanozymes with superior activity, selectivity, and stability, a better understanding and tuning of their safety profile is imperative for successful clinical translation. This review outlines the current applied safety assessment approaches and provides a comprehensive summary of the safety knowledge of therapeutic nanozymes. Overall, nanozymes so far show good in vitro and in vivo biocompatibility despite considerable differences in their composition and enzymatic activities. However, current safety investigations mostly cover a limited set of basic toxicological endpoints, which do not allow for a thorough and deep assessment. Ultimately, remaining research gaps that should be carefully addressed in future studies are highlighted, to optimize the safety profile of therapeutic nanozymes early in their pre-clinical development.

Catalytically Active Ti-Based Nanomaterials for Hydroxyl Radical Mediated Clinical X-Ray Enhancement

Nanoparticle radioenhancement offers a promising strategy for augmenting radiotherapy by locally increasing radiation damage to tumor tissue. While past research has predominantly focused on nanomaterials with high atomic numbers, such as Au and HfO2, recent work has revealed that their radioenhancement efficacy decreases considerably when using clinically relevant megavoltage X-rays as opposed to the orthovoltage X-rays typically employed in research settings. Here, radiocatalytically active Ti-based nanomaterials for clinical X-ray therapy settings are designed. A range of candidate materials, including TiO2 (optionally decorated with Ag or Pt nanoseeds), Ti-containing metal-organic frameworks (MOFs), and 2D Ti-based carbides known as Ti3C2Tx MXenes, is investigated. It is demonstrated that these titanium-based candidates remain consistently performant across a wide energy spectrum, from orthovoltage to megavoltage. This sustained performance is attributed to the catalytic generation of reactive oxygen species, moving beyond the simple physical dose enhancements associated with photoelectric effects. Beyond titania, emergent materials like titanium-based MOFs and MXenes exhibit encouraging results, achieving dose-enhancement factors of up to three in human soft tissue sarcoma cells. Notably, these enhancements are absent in healthy human fibroblast cells under similar conditions of particle uptake, underscoring the selective impact of titanium-based materials in augmenting radiotherapy across the clinically relevant spectral range.

Cellular Alterations Due to Direct and Indirect Interaction of Nanomaterials with Nucleic Acids

Deoxyribonucleic acid (DNA) represents the main reservoir of genetic information in the cells, which is why it is protected in the nucleus. Entry into the nucleus is, in general, difficult, as the nuclear membrane is a selective barrier to molecules longer than 40 kDa. However, in some cases, the size of certain nanoparticles (NPs) allows their internalization into the nucleus, thus causing a direct effect on the DNA structure. NPs can also induce indirect effects on DNA through reactive oxygen species (ROS) generation. In this context, nanomaterials are emerging as a disruptive tool for the development of novel therapies in a broad range of biomedical fields; although their effect on cell viability is commonly studied, further interactions with DNA or indirect alterations triggered by the internalization of these materials are not always clarified, since the small size of these materials makes them perfectly suitable for interaction with subcellular structures, such as the nucleus. In this context, and using as a reference the predicted interactions presented in a computational model, we describe and discuss the observed direct and indirect effects of the implicated nanomaterials on DNA.