Get a JS to a Page load parameter

I have this function in javascript that is within a .aspx that opens a .aspx called Aplicaciones_Usuarios.aspx

 $(document).ready(function () {
            $('#MasterContent_ui_rprApp_ui_hlkApp_0').click(function (e) {



                alert($(this).attr('text'));

                window.open("Aplicaciones_Usuarios.aspx?Url=" + $(this).attr('text'),"Aplicaciones");
            });


        });

The text is obtained from a label which is the following:

<label ID="ui_hlkApp" runat="server" style="cursor:pointer;" text='<%# Eval("URL")%>'> <%# Eval("DESCRIPCION") %> </label>

So I need to get the parameter text of my function js and pass it to Aplicaiones_Usuarios.aspx because there I have a iframe where the src has to have what the parameter text has.

<iframe id="iframe1" runat="server" src="Url" style="width:100% !important">

    </iframe>

This is my Page load :

public string Url;

protected void Page_Load(object sender, EventArgs e)
{

        Url = Request.QueryString["Url"];

}

I tried it that way but it sends me an error.