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Materials

Catch-And-Release Method For Microbots

Scientists devise a pH-controlled system for reversing electrostatic forces between two surfaces, allowing microscale objects to be moved around

by Sophie L. Rovner
September 21, 2009 | APPEARED IN VOLUME 87, ISSUE 38

REVERSING CHARGES
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Adjusting solution pH causes surfaces modified withaminosilanes such as APDMES and APTES to switch between attractive andrepulsive forces.
8738scon_apdmes440.gif
Adjusting solution pH causes surfaces modified withaminosilanes such as APDMES and APTES to switch between attractive andrepulsive forces.

When using a tiny robot to assemble miniature devices such as microelectromechanical systems, surface electrostatic forces come into play. For instance, attractive forces allow a robot’s little gripper to snag a microscopic component and move it into a desired position. But the adhesion can be problematic when the robot is supposed to let go of the component. Researchers in Besançon, France, have now found a simple way to gain better control over these adhesion forces (ACS Appl. Mater. Interfaces, DOI: 10.1021/am900343w). Jérôme Dejeu and colleagues at FEMTO-ST Institute, an affiliate of France’s National Center for Scientific Research, began by assessing interactions in aqueous solutions between an atomic force microscope cantilever and tiny glass spheres or silicon wafers. The researchers coated the cantilever or the wafers with a self-assembled monolayer of an aminosilane. They found that by changing the pH of the solution, they could reverse the charges on the modified surfaces, thereby changing the interaction between the cantilever and the held objects from attractive to repulsive on command.

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