Reliable Calibration-Free Long-Term Ion Monitoring

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With funding from the Chemical Measurement and Imaging (CMI) program in the Division of Chemistry, Professor Philippe Buhlmann and coworkers at the University of Minnesota-Twin Cities will seek to address a major failure mode of current ion sensors, which is the delamination of ionophore-doped polymeric sensing membranes from underlying platform substrates when exposed to repeated mechanical stress. In macro-sized devices, delamination can be avoided by mechanical means such as screw lids and O-rings, but that is not possible in miniaturized devices. Miniaturized devices are better suited for on-line monitoring and are more affordable for broader impact applications. The attachment of ionophore-doped sensing membranes with chemical bonds to the sensor platform material and the transducer layer that separates the sensing membranes from the underlying electron conductors is crucial to the development of electroanalytical sensors that (i) do not fail catastrophically by membrane delamination and (ii) exhibit minimal signal drift in long-term in-situ monitoring. Covalent attachment of the sensing membrane opens a venue to calibration-free sensors with long lifetimes, as they are needed for long-term measurements in the environment, in industrial processes, and for health monitoring.In this research project, the Buhlmann team at the University of Minnesota aims to achieve the covalent attachment of ionophore-doped polymeric sensing membranes to inert plastics and conductive carbon materials. This will be achieved using chemically resistant, plasticizer-free and biocompatible polymeric membrane materials, nanoporous carbon solid contacts, and redox buffers for the fabrication of robust potentiometric solid-state sensors for calibration-free long-term monitoring. The covalent attachment of the sensing membrane using chemical grafting and photo- or plasma-initiated in-situ polymerization as used in this project is a very general approach that does not suffer from the disadvantages of silyl chemistry, which has been used for this purpose in the past. In particular, it is suitable for a range of substrates from polyesters, polyurethanes, and polyolefins to fluoropolymers. If successful, this approach will eliminate the need for frequent recalibration of potentiometric ion sensors, which requires a constant supply of calibration solutions and either complex fluid handling systems or trained personnel. Thus, the project has the potential for broad scientific impact across a wide range of ion sensor applications from academia, to industry to government laboratories.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.