**Preface to "Light-Addressing and Chemical Imaging Technologies for Electrochemical Sensing"**

Visualizing chemical components in a specimen is an essential technology in many branches of science and practical applications. While optical methods based on indicators or fluorescent dyes are widely used in biological and medical sciences, various electrochemical methods have also been developed to meet specific requirements.

A major class of electrochemical imaging techniques employs a scanning electrode to access local electrochemistry, as in the cases of scanning electrochemical microscopy (SECM) and electrochemical scanning tunneling microscopy (EC-STM). Another class of electrochemical imaging techniques relies on semiconductor devices with the capability of spatially-resolved sensing. Two types of such sensing devices have been extensively studied and applied in various fields, i.e., arrayed sensors and light-addressed sensors. An ion-sensitive field-effect transistor (ISFET) array and a charge-coupled device (CCD) ion image sensor are examples of arrayed sensors. They take advantage of semiconductor microfabrication technology to integrate a large number of sensing elements on a single chip, each representing a pixel to form a chemical image. A light-addressable potentiometric sensor (LAPS), on the other hand, has no pixel structure. A chemical image is obtained by raster-scanning the sensor plate with a light beam, which can flexibly define the position and size of a pixel. This light-addressing approach is further applied in other LAPS-inspired methods. Scanning photo-induced impedance microscopy (SPIM) realized impedance mapping and light-addressable electrodes/light-activated electrochemistry (LAE) realized local activation of Faradaic processes.

This book is a compilation of eight articles dealing with state-of-the-art technologies of light-addressing/chemical imaging devices and their application to biology and materials science. It offers graduate students, academic researchers, and industry professionals insight into different up-to-date examples. If this book gives the readers the idea of what should come next, it is our great pleasure.

> **Tatsuo Yoshinobu, Michael J. Sch ¨oning** *Editors*
