Ultra-low-powered CNTs-based aqueous shear stress sensors integrated in microfluidic channels

We have developed carbon nanotubes (CNTs) based aqueous shear stress sensors integrated in microfluidic channels. The sensors utilized electronics-grade carbon nanotubes (EGCNTs) as sensing elements, and were built by combining MEMScompatible fabrication technology with AC dielectrophoretic (DEP) technique. The assembled sensing element has a roomtemperature resistance of ∼100 to 200Ω by using the original concentration of 1:1 EG-CNTs in DI-water. The I–V measurements of EG-CNTs show the heating effects of the sensors, and the current required to induce the nonlinearity of EG-CNTs is in the order of 100μA, which implies the operation power of the sensor is in the range of μW. Upon exposure to DI-water flow, the characteristics of the sensor have been investigated at room temperature under constant current (CC) activation mode. It was found that the electrical resistance of the CNT sensors increased linearly with the introduction of constant fluidic shear stress. We have tested the response of the sensors with flow velocity from 0.3 to 3.4m/s. The experimental results show that there is a linear relation between the output resistance change and the flow velocity to the one-third power. This result proved that the CNT sensors work with the same principle as conventional MEMS thermal shear stress sensors but only require ultra-low activation power (∼1μW), which is ∼1000 times lower than that of conventional MEMS thermal shear stress sensor.