Cantilever arrays: A universal platform for multiplexed label-free bioassays

Microcantilevers have caught great attention as label-free and ultra-sensitive biological sensors. When molecular adsorption occurs on only one surface of cantilever, the resulting differential surface stress leads to cantilever bending, thus providing a method of detecting molecular adsorption (Figure 2.1). How does the transduction from molecular adsorption to surface stress change occur? Though the underlying science of the transduction is yet to be completely understood, the thermodynamic argument suggests that the reaction-induced free energy reduction on one cantilever surface is balanced by the strain energy increase due to bending, such that at equilibrium the free energy of the whole system reaches the minimum [11]. In other words, the penalty of increasing the strain energy must be compensated by a larger reduction in free energy due to reaction, reflecting the interplay between mechanics and chemistry. Hence, the cantilever bending can be construed as a measure of free energy reduction due to the chemical reaction on one surface. What isworth noting is that because free energy reduction is common for all reactions, the cantilever-based sensing is universal platform for studying reactions. The ability of analyzing molecules without the use of optical or radioactive labels makes this approach rather attractive for biology and medicine.