Figure 1 - Electrochemcial etched Macropores in p-type Silicon
Figure 1 - Electrochemcial etched Macropores in p-type Silicon
The large internal surface area of porous silicon is also electrically active. This property results from the presence of surface states capable of transfering charge
into the silicon skeleton therefore changing the conductive and capacitive properties of porous silicon. When polar molecules, such as organic solvents, are present on the surface
of porous silicon changes in the charge distribution can also give rise to modifications in the electrical properties. These are two possible mechanisms that have been considered to
explain the electrical activity of porous silicon. Although the precise mechanism has not been identified, the common consesnus is that the surface of porous silicon is sensitive to the
presence of charge. This implies that the electrical sensing properties of porous silicon can be extended one step further from the well characterized pH response to the detection of
molecular events. Hybridization of a single strand DNA to its complementary sequence produces a charged double helical structure. When this event takes place in the porous silcon matrix
it can be identified as a change in capacitance and conductance in real time.
An essential step to consider porous silicon for sensing applications is to be able to deliver the analytes in a controlled manner. The compatibility of porous silicon with standard IC technology opens
the possibility to integrate microfluidic paths with the sensing substrate over the same plataform. Electrocapillarity and electro-osmotic effects can be used to drive small volumes of analyte allowing
a simulateous access to several sensing sites which is the basis of microsensor array