How do tumours grow? And how do bacteria transform harmless substances into medical agents? When biophysicists want to understand what is happening in living cells, they have to introduce fluorescent probes or other foreign molecules. There are several ways to overcome the cell wall without causing the cell permanent harm. Physicists at Bielefeld University have developed a particularly gentle method for this: nanoinjection. In a new study to be found in Scientific Reports published by Nature, they show that with this method, nine out of ten cells survive being injected with foreign molecules.