THYROID-STIMULATING HORMONE ASSAYS BASED ON THE DETECTION OF GOLD CONJUGATES BY SCANNING FORCE MICROSCOPY

Low bulk concentrations of thyroid stimulating hormone (TSH) were dete cted by scanning force microscopy (SFM) using gold-labeled conjugates. Anti-TSH antibodies were covalently bound onto amino-modified silicon oxide wafers, Surface modification was examined by contact-angle meas urements, ellipsometry, PL-ray photoelectron spectroscopy, and SFM, An tibodies were found to form a monolayer of prone molecules with an ave rage surface density of 5000 IgG/mu m(2). TSH molecules were then allo wed to bind to immobilized antibodies, The immunological reaction was quantified by SFM using gold-labeled species. Two scanned force micros copic immunoassays (SFMIA) were compared first, a competitive test whi ch used gold-labeled TSH molecules mixed with free TSH antigens was pe rformed, Afterward, IL sandwich assay was carried out, using gold-labe led anti-TSH antibodies. This latter method was found to be far more s ensitive than competitive SFMIA. Gold conjugates were also found to be of great use to quantify antigens in large volumes by a sandwich test : a sensitivity threshold as low as 0.015 ng of TSH/ml (0.075 mu UI/ml or 6 x 10(-13) M) was estimated. (C) 1998 Academic Press.