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.