public static bool ContainsRus(string TestString)
{
    return
        Regex.IsMatch(TestString, @"[а-я]", RegexOptions.IgnoreCase);
}

public static bool ContainsRusOrSpace(string TestString)
{
    return
        Regex.IsMatch(TestString, @"[а-я]|\s", 	RegexOptions.IgnoreCase);
}