How to use SampleGrad in Unity shader

The code in hlsl but I can't use it. Unity says "sampler2D object does not have methods" There's the detail [SampleGrad (DirectX HLSL Texture Object)][1] The article relate to [A Closer Look At Parallax Occlusion Mapping][2] [1]: https://msdn.microsoft.com/en-us/library/windows/desktop/bb509698(v=vs.85).aspx [2]: http://www.gamedev.net/page/resources/_/technical/graphics-programming-and-theory/a-closer-look-at-parallax-occlusion-mapping-r3262