Bio/chemical detection in liquid with self-sensing Pr-Oxi-Lever (piezo-resistive SiO2 cantilever) sensors

The paper presents a self-sensing microcantilever for bio/chemical detection in liquid. The developed silicon piezoresistance encapsulated SiO2 cantilever (Pr-Oxi-Lever) is with the electric interconnection wires insulated by a SU-8 coating layer for specifically detecting bio/chemical molecules in liquid environment. Functionalized with specific sensing terminals, siloxane-based molecule layer is directly modified on the cantilever SiO2 surface via reliable Si–O covalent bond. Instead of the previously used thiol self-assembly molecule layers that show long-term instability, the modified siloxane sensing layer secures long-term sensitivity stability and long working life. The sensors have been successfully used for detection of 2.5% aqueous tetramethylammonium hydroxide (TMAH) and avidin at 10−11 mol/mL trace level. An interesting phenomenon of opposite surface-stress sensing signals for different-sized target-molecules is experimentally observed. A simple model is proposed for preliminary explanation of this phenomenon.