Light-addressable Potentiometric Sensor

Light-Addressable Potentiometric Sensors are widely used in biochemical and biophysical applications. The principle of operation of the LAPS is similar to that of the EIS capacitor. The LAPS uses photo excitation of the semiconductor to probe the surface potential at the insulator-electrolyte interface. The semiconductor is addressed by a modulated flux of (infrared) photons: this flux results in the generation of hole-electron pairs in the semiconductor. The photogenerated pairs lead to an alternating current that can be measured by means of an external circuit.This paper has introduced the principle and application of LAPS, which is controlled by a computer and communicate by IEEE-488. A physical study of the device is presented here to gets the physical model of the LAPS. Utilizing the least square, we also obtain the mathematical model of the actual frequency response. Comparing the physical model and mathematic model, the optimization of its design can be realized. Simulation and optimization results are presented, focused on the basic knowledge of the system identification, which can be used in the future. A new type of thin film LAPS based on chalcogenide glass-sensitive materials was developed by means of silicon planar technology and thermal evaporation technique. The physical layer structure and the stoichiometric composition of the deposited glass materials have been investigated using transmission electron microscopy. Depending on the conventional "two-electrodes" measuring set-up, these novel thin film sensors possess certain sensitivity towards heavy metals of seawater. The obtained results are compared to measurements performed with conventional bulk ion-selective electrodes, built-up of the same layer composition. The new sensitive materials deposited on LAPS with electron beam thermal evaporation meet the requirements for fabricating miniaturised sensor devices and can be employed in environmental control such as detection of heavy metal ions.