MOTION CAPTURE has been a feature of films for years. Now something similar to the technique, where naturalistic movements are recreated from a handful of lights on actors’ bodies, has found a use in medicine. Huw Summers, from Swansea University, and colleagues have been tagging living cells with fluorescent nanoparticles in order to track cells over multiple generations, which may help understand how cancer cells replicate and respond to drugs.

Available cell-imaging methods include inserting a gene into cells so that they glow green or staining their DNA, but these involve tinkering with the cells’ biology, so any results must be interpreted with caution. A less intrusive option is to use image-recognition software to pick out the outline of a cell in a microscope. Because cells are faint, however, this process is tricky.

Dr Summers’s approach, detailed in a study published in the Public Library of Science, was to use quantum dots. When illuminated, these tiny nanocrystals, just billionths of a metre across, emit light of with a specific wavelength. Conveniently, quantum dots are also small enough to penetrate the cell membrane, creating scores of reflective bubbles scattered throughout the cytoplasm, the gel-like substance which holds the cells' internal structures together.

In a demonstration of the technique, the researchers labelled a few dozen cells and took periodic snapshots of them over 40 hours, using green light to make the quantum dots fluoresce. The result was a time-lapse film of the cells going through multiple divisions. Meanwhile, special software automatically mapped which daugther cells were spawned by the division of which parents. Tracking cell lines, crucial to understanding why some cells respond to drugs and others do not, is something researchers have hitherto had to do by hand, in a time-consuming and labourious process.