Robust microfabricated field-effect sensor for monitoring molecular adsorption in liquids

We show that a microfabricated field-effect sensor located at the terminus of a freestanding cantilever can detect surface potential changes resulting from the adsorption of charged molecules in an aqueous environment. The charge sensitive region, defined by lightly doped silicon, is embedded within the heavily doped silicon cantilever. Since both the electrical trace and sensitive region are passivated with thermally diffused silicon dioxide, the entire cantilever can be immersed in buffer solutions and cleaned with strong acids without degrading its electrical response. As an example, we demonstrate that the device can reproducibly detect adsorption of positively charged poly-L-lysine ~PLL! on silicon dioxide. We also demonstrate that PLL adsorption and pH can be measured in discrete solutions by scanning the cantilever through parallel, distinct streams within a microfluidic channel array. © 2001 American Institute of Physics. @DOI: 10.1063/1.1423776#