Set target audience to Quick Launch item programmatically

SPSecurity.RunWithElevatedPrivileges(delegate()

               {

                   using (SPSite spSite = new SPSite(siteUrl))

                   {

                       using (SPWeb spWeb = spSite.OpenWeb())

                       {                           

                           //First delete all the items in quick launch

                           for (int i = spWeb.Navigation.QuickLaunch.Count - 1; i > -1; i--)

                           {

                               if (spWeb.Navigation.QuickLaunch[i].Title == "Admin Panel")

                                spWeb.Navigation.QuickLaunch[i].Delete();                            

                           }

                           spWeb.Update();

                           //Add items to Quick Launch

                           //Quick Launch item - Meeting Work Space

                           //SPList lst = spWeb.Lists[Constants.LstContacts];//"Contacts"

                           SPNavigationNodeCollection nodes = spWeb.Navigation.QuickLaunch;

                           string TargetGroups = "2-Project Admin";

                           SPNavigationNode navNode2 = newSPNavigationNode("Admin Panel","/sites/Projects/BHEL/Pages/adminpanel.aspx",true);

                           nodes.AddAsLast(navNode2);

                           if (navNode2.Properties.Contains("Audience"))

                           {

                               //// Set Property

                               navNode2.Properties["Audience"] = TargetGroups;

                           }

                           else

                           {

                               //// Add Property

                               navNode2.Properties.Add("Audience", TargetGroups);

                           }

                           navNode2.Update();

                          

                           spWeb.Update();

                       }

                   }

               });