Micro-rheology: evaluating the rigidity of the microenvironment surrounding antibody binding sites

The microscopic rigidity of structural elements of the cell and of the extracellular matrix control the genetic expression of factors that control critical aspects of malignancy including metastasis and neoangiogenesis. Methods of measuring the rigidity in vitro are being developed and exploited to explore the mechanisms involved. But no methods that function in vivo are available. We demonstrate proof of concept that the stiffness of the microenvironment surrounding bound magnetic nanoparticles can be measured using the shape of the spectra of the magnetization induced by a harmonic applied field. The microscopic region where the stiffness is measured can be selected by selecting the antibody binding sites for which the nanoparticles are targeted. In other applications, the same signal from the nanoparticles has been measured in vivo at very low concentrations so the methods demonstrated here should be capable of measuring low concentrations in vivo as well. The ability to measure the rigidity in vivo will enable the links between genetic control and rigidity to be explored in the complex in vivo environment for the first time.