Inside every cell, things are constantly meeting and parting. Some pairs hold tight, like Velcro, while others barely touch, like pollen on the wind. These fleeting touches, where the binding strength is comparable to a grain of salt dissolving in a glass of water, govern many of the cell's signals and decisions. But studying them is nearly impossible: to detect such a weak embrace, you need a huge number of molecules in one place, and you can't crank their concentration up to the required levels: you hit physical limits.

The researchers changed tactics. Instead of cramming more and more molecules into the test tube, they shrank the test tube itself, or rather, the part where molecules can meet. A vast hall where two people wander for hours without noticing each other becomes a tiny room where a meeting is inevitable. The role of such a room was played by nanoscale cavities assembled from DNA (like origami, but made of genetic material). The volume became so small that even rare molecules collided frequently, and weak interactions became noticeable.

The method allowed measuring the affinity (binding strength) between a protein and a short peptide chain — about 10 millimolar, which was previously beyond reach. Moreover, the substances were used in amounts a thousand times smaller than usual: femtomoles (millionths of a billionth of a mole) per well. A standard plate reader gave a clear signal with a huge sensitivity margin. What's more, they found compounds that don't bind tightly themselves but change the rules of engagement — making weak contacts more likely, like oiling door hinges so the door closes faster.

In this way, the scientists turned the long-vague notions of "local concentration" and "proximity effect" into precise, controllable quantities. This opens the door to studying a whole class of biological phenomena that were previously invisible to instruments. And perhaps to creating drugs that work not through crude blocking, but through fine-tuning molecular encounters.