Functionalized TiO2 nanoparticles as labels for immunoassay

We designed a versatile inorganic probe based on functionalized TiO2 nanoparticles for labeling immunoreagents and developing immunological tests. Similarly to enzymatic probes traditionally used in immunoassay, the TiO2 probe could be covalently linked to antigens or antibodies and exploited as the signal reporter in immunoassays. The TiO2 probe allowed revealing the rate of antigen-antibody complex formation by promoting the oxidation of a suitable chromogenic substrate with absorption in the visible. We demonstrated the suitability of the TiO2 probe as a label for immunoassay by coupling it to human serum albumin and developing a direct competitive assay to measure micro- and macro-albuminuria for diabetes diagnosis. The developed TiO2-based assay showed high sensitivity (detection limit 1.4 mg/l), wide dynamic range (6-1270 mg/l) and acceptable precision (within- and between-assay coefficient of variation %<20%) and accuracy (75-95 %) for measuring albumin in human urine. The method is fully compatible with materials and equipment of standard enzyme immunoassay (except for the need of UV irradiation), while the inorganic probe is more robust towards chemical and physical conditions and shows better long term stability compared to enzymes