Flow rate measurement inside polymer microfluidic systems using carbon nanotube sensors

We have demonstrated a carbon nanotube (CNT) based thermal flow sensor array capable of detecting air flow inside a polymethylmethacrylate (PMMA) micro fluidic chamber. The micro sensors are fabricated on a PMMA substrate using an AC electrophoretic technique to form bundled multi-walled carbon nanotube (MWNT) sensing elements between microelectrodes and then embedded inside the PMMA chamber which is fabricated using SU-8 molding/hot-embossing technique. We have tested the sensors using a hot-film anemometry constant current configuration for dynamic characterization. Preliminary results indicated that the MWNT sensors were capable of sensing input fluid flow variations inside the chamber. We have also measured the I-V characteristic of the resulting device and the results revealed that the sensor could be operated in muW range, which is three orders of magnitude lower than conventional MEMS polysilicon based shear stress sensors. Based on these experimental evidences, we propose that carbon nanotubes is a novel material for fabricating micro flow sensors on polymer substrates - polymer-based devices which may serve as alternative sensors for silicon based flow sensors when bio-compatibility and low-cost applications are required