On September 13, 2022, the European Union (EU) Observatory for Nanomaterials (EUON) published a Nanopinion entitled “Can the Brain’s Gatekeeper Fight a Nano-Attack?” by Dr. Eugenia (Éva) Valsami-Jones, Professor of Environmental Nanoscience at the University of Birmingham, who co-authored an article entitled “Biotransformation modulates the penetration of metallic nanomaterials across an artificial blood–brain barrier model.” The researchers set out to explore systematically how different nanoparticle properties play a role in their potential to be transported across the blood-brain barrier (BBB). To be able to test their hypotheses, they constructed a model BBB inside a special permeable well, on which human cells representative of the BBB were cultured and tested to ensure their function precisely replicated that of the real barrier. The researchers then investigated what factors affect the ability of a number of model nanoparticles, specifically cerium oxide, iron oxide, zinc oxide, and silver in different particle sizes and shapes, to cross the model BBB. Valsami-Jones states that the researchers discovered that silver and zinc oxide nanoparticles, “which are often used in consumer goods, including healthcare products, have the potential to cross the BBB and enter the brain in the form of both particles and dissolved ions, depending on the size, shape and exposure concentration.” These nanoparticles can also affect cellular function and integrity of the BBB. The study revealed how nanoparticles may gain access to the brain and how they might bypass the brain’s guardian BBB. According to Valsami-Jones, “[t]he knowledge acquired can help make the use of nanoparticles safer, by ensuring, for example, that properties that facilitate crossing of the BBB are designed out of products that could come to direct contact with our bodies. In contrast, if nanoparticles are used as vehicles for drug delivery, for example in order to fight diseases such as Parkinson’s and Alzheimer’s, then we should design in the properties that give them easy passage through the BBB.”