Dear colleges,

in these days we're struggeling with the following Problem:

With a microfluidic device, PDMS-microchannels with a measuring chamber, bonded to a glass-wafer with Ti/Au-Electrodes, we face a drift of impedance values by measuring 5% citric acid solutions over time (we stopped measung-process after 90minutes)

First of all: Do you have an own idea what could cause this?

Here are our assumptions:

- H2O-Molecules of the solution diffuse constantly into the PDMS-Network, while leaving the acid Ions Behind, which increases the ion-density in the measuring chamber.

- The geometry of the measuring-chamber could result in unwanted turbolences, that influence the measuring process

Is there a way to prevent or decrese the amount of water diffusing into the PDMS?

Do you have some completely different ideas, how you'd solve this?

The idea is to investigate if there's a dependance of the measured impedance to the Flow-Speed of the fluid.

I attached a picture of the measuring chamber with the Ti/Au-electrodes

Channelwidth/Hight: 200um/350um

Chamberwidth: 2mm

PDMS: (Classical) Silgard 182 10:1

Thank you in advance!