Nano-Chemo-Mechanical Sensor Array Platform for High Throughput Selective Coating Material Search

Microcantilever (MC) sensors can detect the presence of chemical vapors at very low concentrations based on the surface stress changes generated by the interactions between probe and target molecules on their surfaces [1-2]. The magnitude of the surface stress change depends on the type of interaction taking place which include hydrogen bonding, electrostatic, van der Waals forces, etc. Pinnaduwage et al [2] demonstrated detection of explosive materials at ultra low concentrations (10-30 ppt) using single MC AFM tip coated with a thiol (-SH) self assembled monolayer (SAM). They were able to get highly sensitive and reproducible signals from their MC sensor while detecting chemicals like PETN, RDX, etc. However, they did not demonstrate the specificity of the coating material to explosive materials. Most types of chemical sensors (metal oxide, conductive polymer, carbon nano tube or belt sensors) are known to respond to interfering chemical agents in a similar manner as the target. Bietsch et al [3] used a set of MC’s (1D array) coated with different types of polymers as chemical sensing layers to try and identify unique deflection signatures for each target chemical. The performance of such sensors is expected to degrade during long term usage as the binding force between the polymer coating and the silicon cantilever structure is weak. Furthermore, polymer coating layers are in general not selective to specific target vapors since they have limited chemical and structural information due to the simple repetition of same chemical structure. To increase the selectivity for a particular target vapor, it is necessary to develop coating materials, which have enough chemical/structural information and long term stability specifically for that target. To expedite the screening process for testing several coating materials in parallel, we need a high throughput sensor array platform.