The recent advances in nanotechnology, combined with modern tools from surface chemistry, have provided a considerable support to the exploration of biorecognition processes. In collaboration with the “Complex Fluids and Molecular Biophysics Lab” of the University of Milan, we have developed a new, straightforward method based on light scattering for the study of ligand-receptor interactions occurring at the surface of “phantom” colloids. The key factor is the use of perfluorinated nanospheres index-matched with water and therefore optically undetectable except when non-fluorinated molecules coat their surface, thus acting as an amplifier of molecular interactions. This label-free Dispersed Phantom Scatterer (DPS) method, has been first assessed through the determination of the binding constant of vancomycin with its peptidic counterpart and the investigation of the antibiotic mechanism of action. In this context, we have highlighted the role of chelate effect and neighbouring hindrance in the activity of this glycopeptide antibiotic. Subsequently, the particles, already optically phantom, have also been made biologically “invisible” through PEG coating and decorated by interacting proteins, thus providing a mean to investigate the biological properties of proteins, once immobilized onto nanostructured surfaces. DPS appears as a new, sensitive and reliable tool for the quantitative determination of protein-ligand, protein-protein and carbohydrate-protein interactions occurring at the surface of nanoparticles.
An alternative approach investigated in our lab to study ligand-receptor interactions makes use of nanoscale magnetic switches. The development of nanosystems applied to rapid and sensitive measurement of biomarkers in fluid samples is a current major goal in diagnostic biomedicine. We develop ligand-functionalized magnetic nanospherical probes, which, due to the reversible alteration of their microaggregation state induced by ligand-receptor specific interaction, are able to sense the occurred biorecognition event as changes in the T2 relaxation time of surrounding water molecules. The method is very sensitive, providing concentration- and time-dependent responses. Furthermore, we have demonstrated that the magnetic assay is able to quantitatively determine the biomarker concentration from T2 linear correlation, thereby supplying a rapid, yet accurate, assay with sensitivity in the nanomolar to femtomolar range, depending on the affinity of the interaction.