Biopotential measurements are done using different types of specialized electrodes. The work of these recording electrodes is to couple the ionic potentials generated inside the body to an electronic instrument.
Biopotential electrodes are classified either as non-invasive (skin surface) or invasive (for example microelectrodes or wire electrodes).
Related: Types of Electrodes used in Medical Instrumentation
Biopotential Measurements must be carried out using high-quality electrodes to minimize artifacts and ensure that the measured signal is accurate, stable, and undistorted. Body fluids are very corrosive to metals, so not all metals are acceptable for biopotential sensing. Moreover, some materials are toxic to living tissues. For implantable applications, relatively strong metal electrodes are typically used that are made from example stainless steel or noble materials such as gold or from various alloys such as platinum-tungsten, platinum-iridium, titanium-nitride or iridium-oxide. These electrodes do not react chemically with tissue electrolytes and therefore minimize tissue toxicity. Unfortunately, they give rise to large interface impedances and unstable potentials.
Related: Sources of Biomedical Signals
External monitoring electrodes can use non-noble materials such as silver with lesser concerns of biocompatibility, but they must deal with the large skin interface impedance and the unstable biopotential.
Additional considerations in the design and selection of biopotential electrodes are cost, shelf life, and mechanical characteristics.
Related: Types of Transducers used in Medical Measurements
