Practice question

In electrophysiology toolkit, signal origin defines method classification. Patch-clamp directly measures ionic currents crossing membrane, voltage-sensitive dyes like ANEP translate electric field into fluorescence change, positron emission tomography detects photons from tracer annihilation. Each reports either electrical or radioactive signal. Approaches based on pH-sensitive probes monitoring proton concentration changes reflect acid-base chemistry, not primary electrophysiological current or potential. Among listed categories, no standard electrophysiological imaging or recording principle operates inherently as pH-sensitive chemical detector, making none appropriate for that classification in this context.