Enhanced ion-selective membrane sensors based on a novel electroacoustic measurement approach

This work investigates the mechanical and dielectric properties of an ion-selective membrane based on PDMS:PEG:valinomycin, with a view to creating practical geometries for high performance ion sensing in a variety of realworld settings including healthcare, food industry and agriculture. We focus effort on measuring physical changes in the membrane that can be detected with simple sensors. First a dynamic mechanical analyser instrument was used to determine the effect of potassium ions on the real and imaginary bending storage modulus, loss tangent, glass transition temperature, temperature coefficient of millimeter sized PDMS samples. Second, a microwave dielectric analyser with a coaxial probe fixture was applied to the same sample to isolate dielectric shifts associated with ion uptake, namely the real and imaginary permittivities. These perturbation measurements performed for PDMS, PDMS:PEG and PDMS:PEG:V samples, provide strong evidence that alternatives to traditional electrochemical sensing devices can easily be constructed. Thus a plethora of new acoustic and capacitive sensing geometries arise. Thus there is the opportunity to integrate membranes into quartz crystal microbalance, surface acoustic wave and single-sided capacitance sensors. Some suggestions on suitable dimensions, aspect ratios, operating frequencies are provided.