Answer:
Geckos use a force not suction to adhere to the surface. This force is van der wall force. The toepad of geckos has many thousand setae that are keratinized and each setae have fine hairs called spatulae.
The van der walls force between the spatulae and the surface helps in the adhesion geckos to the surface. Van der waals is the sum of repulsion and attraction formed during electrostatic interaction. In this force two atoms come to that much close that they create a subtle nuclear attraction.
Apart from Vanderwall force, capillary force also helps in adhesion. Vander wall force play a primary role in adherence on hydrophobic surface.