Use @ symbol in regex search as keyword in C#

Question

Created an extension method and it works for normal words but When I added an @ as part of search keyword it stopped working. Can someone help?

public static class Extensions
{
        public static string ReplaceWholeWord(this string inputString, string oldValue, string newValue)
        {
            string pattern = @"\b@test\b"; // @"\b$\b".Replace("$",oldValue);
            return Regex.Replace(inputString, pattern, newValue);
        }
}


static void Main(string[] args)
        {
            string input = "@test, and @test but not testing.  But yes to @test";

            input = input.ReplaceWholeWord("@test", "text");

            Console.WriteLine(input);

        }