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 ch arge 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, th e entire cantilever can be immersed in buffer solutions and cleaned with st rong acids without degrading its electrical response. As an example, we dem onstrate that the device can reproducibly detect adsorption of positively c harged poly-L-lysine (PLL) on silicon dioxide. We also demonstrate that PLL adsorption and pH can be measured in discrete solutions by scanning the ca ntilever through parallel, distinct streams within a microfluidic channel a rray. (C) 2001 American Institute of Physics.