Trace TNT Vapor Detection with an SAM-functionalized Piezoresistive SiO2 Microcantilever

Presented is an ultra-sensitive piezoresistive SiO
₂
microcantilever sensor for trace TNT detection. A thin single crystalline silicon piezoresistor is encapsulated in a SiO
₂
cantilever for on-chip electric readout. The cantilever can lead to a more sensitive characteristic compared with conventional silicon cantilever because of a much lower Young's modulus of SiO
₂
. Moreover, fully covered by SiO
₂
, the piezoresistor behaves a much lower current leakage relative noise comparing to those with p-n junction isolation. In addition to the performance improvement of the cantilever sensor, an optimized self-assembled monolayer (SAM) of 6-mercaptonicotinic acid (6-MNA) is immobilized on the cantilever as specifically sensitive coating to capture TNT molecules and, then, causes surface stress for piezoresistive detection. Experimental results shows that the sensor yields a rapid, reversible and reproducible response to TNT vapor, and can achieve a detection limit of about 20-30 ppt.