The invention relates to methods and compositions of detecting a biological marker in a sample. In certain embodiments, the methods and compositions comprise a first binding agent that specifically binds to a biological marker in a sample; a second binding agent linked to a first polymer, wherein the second binding agent specifically binds to the first binding agent; a third binding agent linked to a second polymer, wherein the third binding agent specifically binds to the second binding agent; and a detectable substance. In certain embodiments the biological markers are detected immunologically.