Probing polymerization dynamics with fluorescent molecular rotors and magnetoelastic sensors

We compared the ability of two different sensors to probe the polymerization dynamics of three popular biopolymers: Polyacrylamide, type-I collagen, and tetramethoxysilane-based sol-gel. The sensors were (1) a magnetoelastic (ME) strip of amorphous metal-glass material performing a viscosity-dependent dampened oscillation after excitation in a radiofrequency magnetic field, and (2) a fluorescent molecular rotor with a viscosity-dependent quantum yield. Both the resonance quality factor Q of the ME strip and the emission intensity of the molecular rotor, exposed to the polymers, were recorded after initiating the polymerization reaction. In polyacrylamide, the Q factor of the ME strip decreased in an exponential fashion, reflecting increased rigidity of the progressively crosslinking monomers. The molecular rotor was quenched by the free-radical donor ammonium persulfate. In collagen gels, increasing crosslinking was accompanied by a marked increase of molecular rotor emission intensity. In contrast, the ME strip showed only a minor decrease in Q. Sol-gel polymerization was accompanied by a decrease of Q of the ME strip. Molecular rotor intensity exhibited a more complex pattern, where hydrolysis and polymerization phases could be distinguished. In conclusion, both the ME strip and the molecular rotors allow monitoring of polymerization processes in real-time. Fluorescent probing of the collagen gelation process and final rigidity is therefore feasible. Finally, both sensors showed a strong reaction in sol-gels, but also appeared to provide information on the dynamics of the gelation process, namely the hydrolysis and crosslinking phase.