Many particles and cells are known to be able to float. At the liquid surface, surface tension exists. This forms an energy barrier which can be harnessed for manipulation purposes.

Selective single particle handling with high degrees of controllability, precision, and delicateness are sought after for operations such as sorting, isolation, and placement. We have demonstrated an approach [1] that operates based on a droplet dispensed directly above a selected particle floating on the liquid surface to cause it to sink. The mode of sinking appears to be based on the detachment of the particle from the liquid interface with an applied force. This method offers the desired attributes of particle handling and is amenable to the incorporation of automation to speedily accomplish the selective handling of multiple particles.

 

1. L. Xu, T.W. Ng, A. Neild, Delicate selective single particle handling with a float-sink scheme. Applied Physics Letters. 94 (2009) 034104.