LDC2112: the LDC2112 chip work as a simple digital sensor

Jiahui,

The LDC2112 can indeed be used to sense the presence or absence of conductive materials, which includes many metals.
For more detailed information, please see the Inductive sensing FAQ for answers to frequent questions, app notes and other info on using inductive sensors like the LDC2112.
The LDC2112 data sheet has detailed info on device settings, and the LDC2112 EVM User's Guide provides useful information as well. 
Please see the Inductive Sensing Blogs for general guidance and strategies for using inductive sensors.

Regards,
John