how to make ICollection serializable .net 4.0

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serialization

I am creating a web service to fetch the employee data. I am using EF 4.0 and have created a serializable employeewrapper class accessible in webservice.
I need help in serializing the foreign key relationship classes to access the related data as well.

How to make Designation and Client serializable?

Currently my code is:

[Serializable]
    public class EmployeeWrapper
    {
        public string FirstName { get; set; }
        public string MiddleName { get; set; }
        public short DesignationId { get; set; }

        public virtual Designation Designation { get; set; }
        public virtual ICollection<Client> Client { get; set; }

        public EmployeeWrapper()
        {
    		this.Client = new HashSet<Client>();
        }
    }