Solidcontact

Solidcontact is a term used in electrochemistry to describe an electrode architecture in which the ion-selective membrane of an ion-selective electrode (ISE) is directly interfaced with a solid conductive transducer layer, eliminating the need for a liquid junction and inner filling solution. This arrangement allows ion activity to be converted into an electrical signal through a solid material rather than through a liquid-contact pathway, enabling the creation of fully solid-state sensors.

Common solid-contact materials include conducting polymers such as PEDOT:PSS and polypyrrole, carbon-based materials like graphene and carbon nanotubes, porous carbon, and various metal oxides or composites. The solid-contact layer typically acts as a transducer that facilitates charge transfer, providing either capacitive or mixed transduction mechanisms to convey the ion signal to the underlying electronic circuitry.

Advantages of solid-contact electrodes include the potential for fully solid-state, compact, and flexible sensors that are easier to manufacture and handle, with reduced risk of leakages and membrane drying. They can also offer improved mechanical stability and compatibility with miniaturized and portable analytical platforms, as well as easier integration with microfabrication processes.

Challenges remain, however. Potential drift over time can arise from slow redox processes at the solid contact or from changes at the interface. The formation of a thin water layer under the membrane can still occur if the contact is not properly designed, compromising stability. Reproducibility and long-term stability of the solid-contact layer, along with selectivity and fouling resistance, are active areas of research.

Applications of solid-contact ISEs span environmental monitoring, clinical diagnostics, and industrial process control, including sensors for ions such as Na+, K+, Ca2+, Cl−, and nitrate, often in conjunction with microfluidic or wearable systems.