How to send binary messages with QPID

I am attempting to enclose a binary message in C++ and trying to receive it
at C#
here is what I am doing
in my c++
std::string ser = obj.SerializeAsString();
response.setContent(ser); //This is a message type;

and in C#

String resp = response.GetContent();
byte[] bytes = System.Text.Encoding.UTF8.GetBytes(resp);
obj = obj.CreateBuilder().MergeFrom(bytes).Build();

any suggestion on what I might be doing wrong ? I am using google protocol
buffer from serializat in C++ and deserialization in C#