Dual-signal detection of trypsin using controlled aggregation of conjugated polymer dots and magnetic nanoparticles

We developed a new ensemble for trypsin sensing by manipulating an aggregation of conjugated polymer dots (CPdots) and magnetic nanoparticles (MNPs) that generates dual signals of fluorescence and spin-spin relaxation (T₂)-based magnetic resonance imaging (MRI). Upon addition of trypsin, the dual signals were induced by the aggregation of CPdots with MNPs, generating MNPs-induced fluorescence quenching (or fluorescence color change), as well as a change in MRI relaxivity because of the increase in the size of aggregated MNPs. The MNPs played a role in the quencher for the fluorescence-related ensemble and in the MRI-signal generator for the magnetic property-related ensemble. The presence of polypeptide on the surface of CPdots was essential for the formation and destruction of the aggregates of CPdots and MNPs. Different fluorescence colors could be obtained by suitable selection of CPdots and polypeptide in terms of “turn-off” and “fluorescence color-changeable” modes.