This looks like a bizarrely coloured aerial image of a city at night, but in reality it’s something much smaller, and much more fascinating: the tiny scaffolding and organelles that make up a single human cell. Harvard researchers caught this view using a new technique powered by light-up strands of custom-built DNA.
The method, called Exchange-PAINT, uses DNA’s specific binding characteristics to create ultra-sharp images of structures that are too small to be seen with traditional light microscopes. First, scientists coat structures inside the cell with unique DNA tags — one type for the microtubules that form the cell’s internal scaffolding, another to label the mitochondria that provide the cell’s energy, etc. Next, they add free-floating DNA carrying fluorescent molecules, each colour coordinated to a different type of DNA tag. When the two halves bind, the fluorescent molecule lights up — green for the microtubules, purple for the mitochondria, and so on, as seen above.
Perhaps even more fascinating is how the team tested the system. They created 10 unique pieces of tiny folded DNA shaped like the numbers 0 through 9. When the fluorescent DNA labels attached themselves, the result was an image with resolution less than 10 nanometres — one-twentieth the diffraction limit of a light microscope.
With some refining, researchers hope this technique will create ultra-precise images of the processes that go on inside living cells — processes that are too small to directly observe with current techniques. Even if it doesn’t get that far, the imagery created with this DNA method is fascinatingly picturesque. [Harvard]
Pictures: Maier Avendano and Johannes B. Woehrstein / Wyss Institute