Photoelectrochemical sensor is a dynamically developed and promising analytical method, based on the photoelectrochemical process and chemical or biological probing recognition. Benefitting from the separation of the excitation source (light) and electrochemical detection signal (photocurrent), the photoelectrochemical sensor possesses many intrinsic advantages, such as higher sensitivity with low background signals, simpler and low-cost instruments, and inherent miniaturization. It has received an increasing attention and shows an extensive application potential in rapid and high-throughput biological and chemical assays. Under light irradiation, the photocurrent is recorded on the basis of the electron transfer among the photoelectrochemical materials in excited state, electrode surface, and electrolyte. Depending on the photocurrent change resulting from the interactions between various sensing elements and their target analytes, the quantitative photocurrent-analyte relationship is obtained. There are two key portions in the development of photoelectrochemical sensor: the fabrication of the photosensitive layer and the assembly of the molecular recognition layer at the transducer surface. The design and fabrication of photosensitizer, deriving from photoelectrochemically active species and the exploitation of exquisite sensing mechanisms are of extreme importance in the achievements of acceptable sensitivity. In this paper, the sensing principle of photoelectrochemical sensor, lasted applications, design and fabrication of photosensitizer and developments of sensing strategies are reviewed.

Contents
1 Photoelectrochemistry and photoelectrochemical process
2 Introduction to photoelectrochemical sensor
3 Photoelectrochemically active species for the design and fabrication of photoelectrochemical sensor
3.1 Organic photovoltaic molecule
3.2 Conducting polymer
3.3 Inorganic semiconductor and its composites
3.4 Other photovoltaic materials
4 Signal generating mechanism and sensing strategies
4.1 Direct charge transmission and redox reaction
4.2 Signal-off strategy derived from steric hindrance based on molecular recognition
4.3 Enzymatic inhibition and enzymatic catalysis
4.4 Local surface plasma resonance (LSPR) of noble metal nanoparticles and energy transfer in exciton-plasmon interaction (EPI)
4.5 Other probing strategies
5 Prospective of photoelectrochemical sensor