REGEX to match the exact word in the string, ignoring case.

 string keyword="ankit";
 string str="my name is ankit";


 if (Regex.Match(str.Trim().ToLower(), @"\b" + keyword.Trim().ToLower() + @"\b", RegexOptions.Singleline | RegexOptions.IgnoreCase).Success)
{
      // if matches
}
else
{
     // if not matches
} 



Here, in 'if' condition "Success" is used to the condition is true or not, just like "==true"