ToLower is not working for me.

Question

Hello:
I am trying to lower case a string, can someone help? The ones in red and underlined are the issue.
 
string Object_ID = "";
string Object_Type = "";
string Object_ID_LowerCase = "";
string Object_Type_LowerCase = "";
Object_ID = ((TextBox)sender).Name;
Object_ID_LowerCase = Object_ID.ToLower;
Object_Type = ((TextBox)sender).GetType();
Object_Type_LowerCase = ((TextBox)sender).GetType();