Method for detecting a change in molecular tumbling of an electron-spin labelled system (1) in solution. Nuclear spins of the entire solution are measured in solution using Overhauser dynamic nuclear polarization in a first reference measurement, and then nuclear spins of said electron-spin labelled system (1) and of at least one further molecule (3, 11, 13-16) aggregated and/or linked with at least one of said electron-spin labelled systems (1) and not present in said first measurement, or said electron-spin labelled systems (1) under different conditions or in a different environment than in the first measurement, are measured in solution using Overhauser dynamic nuclear polarization in a second measurement. A difference in Overhauser dynamic nuclear polarization enhancement spectrum between said first and second measurements is taken as a measure of the change in molecular tumbling of said electron-spin labelled system (1) and/or of the presence of an aggregate of said at least one further molecule (3, 11, 13-16) aggregated and/or linked with at least one of said electron-spin labelled systems (1).