Biosensor and method

A surface Plasmon resonance sensor structure for sensing a target analyte, comprising:

• a metal sensor film having a metal surface,
• a biointerface comprising a monolayer bound to said metal surface, said monolayer formed from a plurality of units, said plurality of units including units with the structure XR—Y wherein:
• (i) X is selected from the group consisting of —S—, —S—S—, —Se—, —Se—Se—, —S—Se—, and mixtures thereof where “—” indicates a chemical bond;
• (ii) R is a carbon backbone of chain length of at least 6 carbon atoms including double or triple bonds along said chain length;
• and
• (iii) Y contains a functional group at a surface of said monolayer,
• wherein said target analyte is bound to said functional group, and
• a plurality of amorphous iron oxide nanoparticles having at least one ligand attached thereto that has structure for binding to said target analyte, wherein said ligand is bound to said target analyte,
• wherein said functional group of said Y is selected from a group consisting of tris-hydroxymethyl ethyl groups, gem-ethyl diol, fluoro gem-propyl diol, and ethylamide.