Hydrogels offer attractive properties, such as unique softness, biocompatibility and biomimetic performance. Electrodes modified with hydrogels would decrease peak-to-peak noise signals and overcome the limitation of present biosensors in biocompatibility and tissue-to-electrode interaction. In this paper, recent advances on hydrogel-modified electrodes are reviewed. Current preparation methods of hydrogel-modified electrodes are summarized, i.e. dip-coating, covalent binding, electrochemistry and layer-by-layer self-assembly. Furthermore, an overview is given for the application of hydrogels in neural electrodes, enzyme-modified electrodes, redox protein-modified electrodes, pH sensors and other sensors. Finally, the challenges and promising developments of hydrogel-modified electrodes are prospected.

Contents
1 Introduction
2 Preparation methods of hydrogel-modified electrodes
2.1 Dip-coating
2.2 Covalent binding
2.3 Electrochemistry
2.4 Layer-by-layer self-assembly
3 Application of hydrogel-modified electrodes
3.1 Neural electrodes
3.2 Enzyme-modified electrodes
3.3 Redox protein-modified electrodes
3.4 pH sensors
3.5 Other sensors
4 Conclusions and prospects