research:

Adsorption-Induced Stress

Molecular adsorption when confined to one side of a cantilever results in cantilever bending [1]. Cantilever bending is attributed to be due to adsorption-induced variation in surface free energy.

Based on that observation, we have demonstrated many novel chemical, physical and biological sensors over the course of the last 8 years. Adsorption-induced forces can be easily detected on so called "real surfaces" such as the surface of a silicon microcantilever manufactured by standard processes used for micro-electro-mechanical systems (MEMS).

The realization that many molecular phenomena result in mechanical responses at the nanoscale promises to bring about a revolution in the field of chemistry and biology. Indeed, it can be said that detecting the mechanical forces that accompany chemical and biological reaction at nanoscale provides a new paradigm for molecular recognition.

In addition to cantilever bending, the resonance response can be used for monitoring interactions. If the cantilever is of the micron scale in size, then the resonance frequency varies sensitively as a function of molecular adsorption onto its surface. Chemical selectivity can be achieved by coating the cantilevers with selective molecules. It is postulated that the cantilever bending depends on the changes in surface free energy while the resonance frequency variation is normally due to mass loading (both specific and nonspecific adsorption). The minimum detectable adsorbed mass on a cantilever sensor can be increased by orders of magnitude by varying the force constant of the mechanical structure.

References

[1]: Appl. Phys. Lett. 64, 2894, 1994