This may sound like science fiction, but virtually every other possibility has been exhausted. Gecko feet do not have gland cells, so they can't be adhering by some kind of secreted glue. So a change of perspective was required. Rather than looking at the feet of the gecko, researchers have been looking at the surfaces they cross. In the 1960s, German Uwe Hiller found that the stickiness of a gecko increased with the 'surface energy' of what the creature was scuttling across.
Surface energy is a measure of the 'roughness' of a surface at the atomic scale.
A high-energy surface is loosely packed, with a lot of loose atomic bonds hanging around. Many of the properties of water, such as its high boiling point, can be explained by van der Waals forces that bind water molecules into loose, short-term associations. It has taken another 30 years for Hiller's amazing idea to be substantiated. Gecko feet aren't smooth. Each seta ends in a fringe of up to 1,000 submicroscopic hairs called 'spatulae'.