public class JsonHelper
    {   
        /// <summary>
        /// JSON Serialization
        /// </summary>
        public static string JsonSerializer<T>(T t)
        {
            DataContractJsonSerializer ser = new DataContractJsonSerializer(typeof(T));
            MemoryStream ms = new MemoryStream();
            ser.WriteObject(ms, t);
            string jsonString = Encoding.UTF8.GetString(ms.ToArray());
            ms.Close();
            return jsonString;
        }
        /// <summary>
        /// JSON Deserialization
        /// </summary>
        public static T JsonDeserialize<T>(string jsonString)
        {
            DataContractJsonSerializer ser = new DataContractJsonSerializer(typeof(T));
            MemoryStream ms = new MemoryStream(Encoding.UTF8.GetBytes(jsonString));
            T obj = (T)ser.ReadObject(ms);
            return obj;
        }
    }

// usage
// collection
            IList<Person> pList = new List<Person>(){
                new Person(){ firstName="chutchai.kp", email="chutchai.kp@gmail.com", grade=13},
                new Person(){ firstName="chutchai", email="chutchai.kp@gmail.com", grade=13},
                new Person(){ firstName="kp", email="chutchai.kp@gmail.com", grade=13}
            };

            // to string
            string jsonString = JsonHelper.JsonSerializer<IList<Person>>(pList);             
            Console.WriteLine(jsonString); // output ***

            // to object
            var obj = JsonHelper.JsonDeserialize<IList<Person>>(jsonString);

            Console.Read();