A chemisorption-based microcantilever chemical sensor for the detection of trimethylamine

This paper presents a new method for detecting trimethylamine (TMA) in gas and liquid phases using a piezoresistive microcantilever sensor functionalized with a self-assembled monolayer (SAM). The microcantilever consists of two silicon dioxide layers and a single crystalline silicon piezoresistor in-between. This configuration allows microcantilevers to achieve high sensitivity because of the low stiffness of silicon dioxide and the high piezoresistive coefficients of single crystalline silicon. The surface of the microcantilever is chemically functionalized with a self-assembled monolayer of 11-mercaptoundecanoic acid (11-MUA) via Au–SH covalent bonding on a gold film deposited on the microcantilever. The 11-MUA SAM adsorbs TMA through hydrogen bonding between the SAM and TMA molecules, and the microcantilever is deflected by the changes in the surface stress as a result of the hydrogen bonding based chemisorption. Experimental results show that the deflection of the microcantilever depends on the concentration of TMA, and the minimum detection limits of 10 mg/L for liquid TMA and 1.65 μg/L for gas TMA are achieved. The selectivity of TMA with respect to ethanol, acetone, and butanone is also investigated.