At polar oxide heterointerfaces,new and unexpected physical properties which are absent in their individual bulk constituents have triggered intensive research interest.As one sparkling example,the discovery of two dimensional electron gas (2DEG) generated at interface between two band insulators LaAlO3 (LAO) and SrTiO3 (STO),reveals intriguing electronic properties and a rich superconducting phase diagram at low temperature.These significant results promise potential applications of this oxide interface in new generation of electronics.We have fabricated,characterized and theoretically studied polar liquid sensor based on field effect induced transport property modulation of the 2DEG at LaAlO3/SrTiO3 hetero-interface.The results revealed that such sensor is very sensitive to the polar property of liquids.A drop of polar liquid such as water on the sensor surface changes the conducting mechanism of the 2DEG from metallic to semiconducting,while non-polar liquid such as gasoline has negligible effect to the conducing characteristics of the interface.We proposed a sensing mechanism,i.e.,the formation of a metal-semiconductor Schottky junction when the center of LaAlO3 surface is covered with polar molecules of water.The coupling between the polar molecules to the polarization of LAO film results in modulation of band structure and change of transport properties at the LAO/STO interface.In addition,some interesting phenomena such as photoconductivity and gas sensing in this 2DEG system are also observed and analyzed.These results promise the application of the 2DEG at the LAO/STO interface in sensing devices.