Femtomolar detection of autoantibodies by magnetic relaxation nanosensors.

The development of nanosystems applied to rapid and sensitive measurement of biomarkers in fluid samples is a current major goal in diagnostic biomedicine. In this article, we report the accurate and reliable detection of anti-HSA (human serum albumin) antibodies by protein-functionalized magnetic nanospherical probes due to the reversible alteration of their microaggregation state induced by protein antibody-specific interaction, sensed as changes in the T(2) relaxation time of surrounding water molecules. Once the optimal parameters were adjusted, the method proved to be very sensitive, providing concentration- and time-dependent responses. Furthermore, we demonstrate that the developed immunoassay is able to quantitatively determine the biomarker concentration from T(2) linear correlation, thereby supplying a rapid, yet accurate, assay with sensitivity in the femtomolar range. The high susceptibility and stability of these magnetic nanoparticles, as well as their accessible synthetic preparation, make these nanosensors a promising new tool for versatile and effective medical diagnostics.