Since the development of the polarographic electrode by Clark et al. (1953), there has been much progress in the area of sensors, microsensors, and recently nanosensors. Nanomaterials research has energized sensor development eorts by enhancing signal acquisition for both electrochemical (Wang 2005) and optical devices (Bonaccorso et al. 2010). is explosion of technologies includes a large collection of sensors, detectors, and assays for physiological recordings. e nomenclature used for describing these devices is of vital importance, as the attributes and features of sensors, detectors, and assays are quite dierent. e most important characteristics describing performance of these tools are sensitivity, limit of detection, and hysteresis (Table 43.1). Use of the correct terminology is critical, as tools for measuring biophysical transport of molecules at the root-rhizosphere interface must be highly sensitive and selective, with a physiologically relevant limit of detection and little to no hysteresis. e quantitative nature of sensors (which is a major advantage over detectors

and detector arrays) is due to reversible molecular interaction(s) between the recognition element within the sensor and the target analyte.