That is the best method. Other wise loss the StringBuilder and use something like following

        using (MemoryStream ms = new MemoryStream()) {
            using (StreamWriter sw = new StreamWriter(ms, Encoding.Unicode)) {
                sw.WriteLine("dirty world.");
            }
            //do somthing with ms
        }

That is the best method. Other wise loss the StringBuilder and use something like following:

using (MemoryStream ms = new MemoryStream()) 
{
    using (StreamWriter sw = new StreamWriter(ms, Encoding.Unicode))
    {
        sw.WriteLine("dirty world.");
    }
    //do somthing with ms
}