Stable Encapsulation and Responsive Release of Dyes via Noncovalent Molecular Lock Strategy: A Case Study of Rhodamine B Based Fluorescent Hydrogel Microspheres.

Hydrogel fluorescent microspheres function as versatile tracers with applications spanning across biomedicine, complex plasma systems, hydrodynamics, and drug delivery. However, the controlled release of fluorescent material in hydrogel microspheres is challenging to achieve. The fluorescent hydrogel microsphere (namely poly(ethylene glycol) diacrylate@rhodamine B-tannic acid, PEGDA@RhB-TA) was fabricated by incorporating tannic acid and RhB into PEGDA microspheres. The stable encapsulation and responsive release of RhB can be achieved by leveraging the non-covalent interactions between TA and RhB. RhB was stably encapsulated within PEGDA microspheres through noncovalent interactions (hydrophobic interactions, hydrogen bonding, π-π, and ion-π interactions) between RhB and TA. Both molecular dynamics simulations by GROMACS and experimental results confirmed the noncovalent binding mechanisms between RhB and TA. The microspheres retained RhB following 24 h immersion in a highly concentrated salt solution (1 M NaCl) and exhibited minimal RhB release (7.1%) under heating at 80 °C for 24 h. However, PEGDA@RhB-TA microspheres underwent rapid RhB release in a 50%