A light-addressable potentiometric sensor (LAPS) is a

sensor A sensor is often defined as a device that receives and responds to a signal or stimulus. The stimulus is the quantity, property, or condition that is sensed and converted into electrical signal. In the broadest definition, a sensor is a devi ...

that uses light (e.g.

LED A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (corresp ...

s) to select what will be measured. Light can activate carriers in

semiconductor A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities (" doping") to its crystal structure. When two regions with different doping level ...

History

An example is the pH-sensitive LAPS (range pH4 to pH10) that uses LEDs in combination with (semi-conducting) silicon and pH-sensitive Ta₂O₅ (SiO₂; Si₃N₄) insulator. The LAPS has several advantages over other types of chemical sensors. The sensor surface is completely flat, no structures, wiring or passivation are required. At the same time, the "light-addressability" of the LAPS makes it possible to obtain a spatially resolved map of the distribution of the ion concentration in the specimen. The spatial resolution of the LAPS is an important factor and is determined by the beam size and the lateral diffusion of photocarries in the semiconductor substrate. By illuminating parts of the semiconductor surface, electron-hole pairs are generated and a photocurrent flows. The LAPS is a semiconductor based chemical sensor with an electrolyte-insulator-semiconductor (EIS) structure. Under a fixed bias voltage, the AC (kHz range) photocurrent signal varies depending on the solution. A two-dimensional mapping of the surface from the LAPS is possible by using a scanning laser beam. Optoelectronics Sensors {{tech-stub