Summary: The FIII9'10 domain pair is an antibody light chain mimic which we serendipitously found binds IGFBP-5, a therapeutic target in late stage prostate cancer. An immunoassay using self-assembling FIII9'10 (¿capture¿) proteins is proposed for detection of IGFBPs, and Biacore data suggest high MW PEG-thiols will form a suitable brush-border support on gold surfaces. Neutron reflectivity will fully characterise the PEG/protein surfaces and progress development of the immunoassay. Objectives: 1) acquire magnetic contrast neutron reflectivity data for high MW PEG-thiol layers on gold, determining PEG layer thickness and coverage in each case; 2) subsequently adsorb self-assembling FIII9'10 proteins to the PEG-derivatised gold surfaces and characterise protein layer thickness and surface coverage; 3) test surface functionality by incubation with IGFBP-5 and layer characterisation.