Custom Properties Error for Webpart SP 2007

Question

using System;
using System.Runtime.InteropServices;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Serialization;

using System.Data;
using System.Data.SqlClient;


using Microsoft.SharePoint;
using Microsoft.SharePoint.WebControls;
using Microsoft.SharePoint.WebPartPages;

I am using the above header files

public class ApplicationForm : System.Web.UI.WebControls.WebParts.WebPart
    {
        // WebPart Parameter for getting the Connection string
        [
        WebBrowsable(true),
        WebDisplayName("Connection String"),
        Personalizable(PersonalizationScope.User)

        ]
    }

It throws an error for custom attribute:

Error   1   Attribute 'WebBrowsable' is not valid on this declaration type. It is only valid on 'property, indexer' declarations.