An Electrochemical Impedance-Based Flexible Flow Sensor With Ultra-Low Limit of Detection

In this paper, we design and fabricate a flexible micro thermal flow sensor with an ultra-low limit of detection (LOD) based on the electrochemical impedance (EI) transduction principle. Two sensing modes, single pair of electrodes (SE) mode and dual pairs of electrodes (DE) mode, were systematically investigated through the proposed theoretical and CFD models. Accordingly, the EI-based flow sensor was designed and fabricated on a
$100 \boldsymbol {\mu } \text{m}$
thick polyimide (PI) substrate to guarantee its flexibility and biocompatibility. For the ionic solution (0.9% NaCl) flow from
$0 \boldsymbol {\mu } \text{m}$
/s to
$110 \boldsymbol {\mu } \text{m}$
/s, the fabricated flexible flow sensor achieves the highest sensitivity of 523 PPM/(
$\boldsymbol {\mu } \text{m}$
/s) within a linear range of 0~
$45 \boldsymbol {\mu } \text{m}$
/s when it works in SE mode, while its sensitivity increases to 637 PPM/(
$\boldsymbol {\mu } \text{m}$
/s) when it operated in DE mode. The high sensitivity achieved by the developed sensor enables it detection of ultra-low solution flow as low as
$4.9 \boldsymbol {\mu } \text{m}$
/s and
$5.5 \boldsymbol {\mu } \text{m}$
/s in SE and DE modes, respectively. In short, this developed highly sensitive EI-based flow sensor will be a very useful device for the measurement of ultra-low fluid flow in microfluidic and biomedical applications.