Image copyright EPFL Image caption The new markers light up the cellular skeleton by attaching to the proteins tubulin (shown here in green) or actin

Scientists have developed new tools for looking at structural proteins in action inside our cells.

The two fluorescent markers will "switch on" when they bind to actin or tubulin, the building blocks of the cellular "skeleton".

Because they are safe and stable, the new markers can be added directly to cells in culture.

This makes for brilliant, live pictures of the architecture of living cells, reported in the journal Nature Methods.

Image copyright EPFL Image caption Actin is the basis of many cellular structures and can be seen here as rings along axons - the fibrous limbs extending from live neurons

A large team led by researchers from the Ecole Polytechnique Fédérale de Lausanne (EPFL) built on a previous discovery of a fluorescent molecule that only emits light when attached to the charged surface of a protein.

They coupled this marker to two different compounds, which specifically stick to the two most important structural proteins in nearly all cells.

Image copyright EPFL Image caption The researchers photographed the tubulin within a tiny but crucial structure called the centrosome, seen here in red, no more than 200nm (0.0002 millimetres) in diameter

The new tools emit light at far-red wavelengths, which is easily separated from background light and allows very detailed photographs to be taken using a microscopic technique called "super-resolution" imaging.

Image copyright EPFL Image caption The super-resolution images depict various structures including microtubules, important cell components built from tubulin

Importantly, they easily pass into live cells and can be used at very low concentrations that are not toxic.

"You just add them directly into your cell culture, and they are taken up by the cells," said Prof Kai Johnsson, one of the study's authors.