A coating of sugar could help nanoparticles deliver molecules to fight widespread tumours, according to research on mice. The team’s nanoparticles, which contain gene-silencing molecules that can inhibit cancerous growth, are designed to be injected into the bloodstream and taken up primarily by tumour cells. The nanoparticles also manage not to create troublesome reactions from the immune system. The nanoparticles, which are small enough to pass through blood vessels into the surrounding tissue, are taken up by cancerous cells because they carry a molecular tag that binds to receptors found on tumours. The agent consists of small interfering RNA (siRNA). When the agent is taken up by a tumor cell, it inhibits expression of the tumour-growth gene, and the cell stops multiplying. Other attempts to carry siRNA to tumours have used nanoparticles made of lipids. But in some mouse studies, these particles provoked an immune response, which would make the approach difficult to use in humans.