suspension also potentially the result of the desorption of the protein based coating the next scheme developed in our process towards the present invention is shown in fig2 b it is described in the earlier incorporated by reference applications and used a bifunctional raman reporter molecule to covalently couple the antibody to the particles this scheme improved particle stability and reduced the limit of detection via a lower level of non specific erl u2122 adsorption using this type of erl u2122 we recently reported on the femtomolar detection of prostate specific antigen psa directly in human serum this approach while working with a high level of effectiveness nevertheless required the separate synthesis of the bifunctional reporters bifunctional reports as illustrated in fig2 b therefore work but are expensive and are not normally commercially available which requires synthesis along the way to running the detection analysis this adds time and expense it therefore demonstrates the unfilled need to develop a system which eliminates the need for a separate step requiring synthesis of bifunctional reporter molecules fig2 c introduces a new design for erls u2122 that does eliminate the need for separate synthesis of a bifunctional reporter and yet gets sensitive detection results in this scheme the surface of gold nanoparticles is modified for example with two different thiolates each derived from commercially available compounds one thiolate component has a large raman cross section.