Light-Addressable Potentiometric Sensors for Quantitative Spatial Imaging of Chemical Species

Abstract

A light-addressable potentiometric sensor (LAPS) is a semiconductor-based chemical sensor, in which a measurement site on the sensing surface is defined by illumination. This light addressability can be applied to visualize the spatial distribution of pH or the concentration of a specific chemical species, with potential applications in the fields of chemistry, materials science, biology, and medicine. In this review, the features of this chemical imaging sensor technology are compared with those of other technologies. Instrumentation, principles of operation, and various measurement modes of chemical imaging sensor systems are described. The review discusses and summarizes state-of-the-art technologies, especially with regard to the spatial resolution and measurement speed; for example, a high spatial resolution in a submicron range and a readout speed in the range of several tens of thousands of pixels per second have been achieved with the LAPS. The possibility of combining this technology with microfluidic devices and other potential future developments are discussed.

Multi‐Well Sensor Platform Based on a Partially Etched Structure of a Light‐Addressable Potentiometric Sensor

“…The reduced thickness of the semiconductor layer inside a well is in favor of higher spatial resolution and enhancement of the signal strength . As schematically illustrated in Figure b, the spatial resolution is determined by lateral diffusion of photocarriers generated on the back surface . In a simplified model, the spatial resolution is given by , where L p is the diffusion length of minority carriers and d is the thickness of the semiconductor layer .…”

“…As schematically illustrated in Figure b, the spatial resolution is determined by lateral diffusion of photocarriers generated on the back surface . In a simplified model, the spatial resolution is given by , where L p is the diffusion length of minority carriers and d is the thickness of the semiconductor layer . A smaller d enhances the spatial resolution and increases the signal strength due to the reduced loss of photocarriers by recombination in the course of diffusion.…”

“…Therefore, the current gain becomes lower as the ratio of the transit time to the period of modulation becomes larger. By thinning the sensor plate, therefore, a larger photocurrent signal is obtained even at a high frequency . Enhancement of the sensor signal implies the possibility of reducing the measurement time to obtain a high signal‐to‐noise ratio required to guarantee the precision in pH measurement.…”

“…A light‐addressable potentiometric sensor (LAPS) is a kind of semiconductor‐based (bio)chemical sensor, which can measure the concentration of ions in a solution with the help of the field effect in the semiconductor . The sample solution and the sensor plate are components of a field‐effect structure or an EIS (electrolyte–insulator–semiconductor) structure, in analogy to a MIS (metal–insulator–semiconductor) structure.…”

A Gas‐Sensitive SPIM Sensor for Detection of Ethanol Using SnO2 as Sensing Element

“…Fortunately, the light‐addressable potentiometric sensor (LAPS) has been extensively developed since its first report by Hafeman et al in 1988, which provided a label‐free method of detection of chemical species in a spatially resolved manner owing to its light‐addressability . A LAPS and similar techniques called a surface photovoltage (SPV) sensor or a light‐pulse technique have been applied to the detection and quantification of H 2 and NO .…”