A living cell is an immensely complicated chemical machine, working with thousands of interacting molecules, and we haven't got an instruction manual.
Usually, if you're given a machine you don't understand, you prod it and see what happens. One of the biological equivalents of this is to introduce new molecules into a cell, and then study the consequences.
Unfortunately for biochemists, a cell is bounded by a membrane, which is deliberately structured to filter the molecules entering or leaving the cell.
Scientists already have ways to get around this by genetically altering cells so that they produce certain molecules, by doing some clever chemistry or even by injecting molecules directly into cells by hand. But these are very laborious processes and sometimes only work for certain types of chemicals.
Now, Alex Shalek from Harvard University and his collegues have developed a far easier method. They have taken vertical silicon nanowires, essentially a forest of little silicon spikes a few tens of nanometres across and about 100 nanometres high, and covered them in molecules they want to inject into the cells.
Then they put cells on top and they slowly settle down over about an hour and are penetrated by the nanowires. Once this has happened, whatever was covering the nanowire is now inside 95% of the cells. The cells seem perfectly happy in this state and have been grown for several weeks with no apparent ill effects, despite being impaled on multiple silicon spikes.
The team have used this technique to successfully inject DNA, RNA, peptides, proteins, and small molecules into many different types of cells and also detected the effects of the molecules within these cells. The technique means that it's also possible to experiment on hundreds of cells at once so you can get good statistical data on the results.
More recently the team have even been able to ink-jet print hundreds of small patches of different chemicals, and combinations of chemicals at different concentrations, onto a slide. This has allowed them to do hundreds of different experiments all at once and even remove the cells, intact, at the end of the experiment, opening up the possibility of doing multiple experiments on the same cell.
It is unlikely this approach could be used therapeutically, but instead it provides a very powerful way to learn about living cells.