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Recently, humidity sensors have been investigated extensively due to their broad applications in chip fabrication, health care, agriculture, amongst others. We propose a capacitive humidity sensor with a shielding electrode under the interdigitated electrode (SIDE) based on polyimide (PI). Thanks to the shielding electrode, this humidity sensor combines the high sensitivity of parallel plate capacitive sensors and the fast response of interdigitated electrode capacitive sensors. We use COMSOL Multiphysics to design and optimize the SIDE structure. The experimental data show very good agreement with the simulation. The sensitivity of the SIDE sensor is 0.0063% ± 0.0002% RH. Its response/recovery time is 20 s/22 s. The maximum capacitance drift under different relative humidity is 1.28% RH.

The division of aqueous samples into microdroplet arrays has many applications in biochemical and medical analysis. Inspired by biological features, we propose a method to produce picoliter droplet arrays for single-cell analysis based on physical structure and interface. A 0.9 pL droplet array with an RSD (relative standard deviation) less than 6.3% and a density of 49,000 droplets/cm2 was successfully generated on a PDMS chip (polydimethylsiloxane) from a micromachined glass mold. The droplet generation principle of the wetting behavior in the microholes with splayed sidewalls on the PDMS chip by liquid smearing was exploited. The feasibility of the picoliter droplets for bacterial single-cell analysis was verified by the separation of mixed bacteria into single droplets and isolated in situ bacteria propagation.