Coordination bonding-based polydopamine-modified mesoporous silica for sustained avermectin release.

Mesoporous silica nanoparticle (MSN) is a novel vehicle to deliver pesticide. MSN can be modified with different chemical groups to increase its interaction with pesticides. In this study, polydopamine-modified mesoporous silica (MSN-PDA) was prepared through a one-pot method with the addition of dopamine (DA). Copper ions, zinc ions, and iron ions were impregnated on MSN-PDA. In addition, avermectin (AVM) was used as the model drug. We investigated the materials' structure, adsorption and release behaviors, anti-UV properties, as well as their adhesive capability, especially the bridge effect of metal ions, π-π stacking of PDA and electrostatic interaction. The results demonstrated that the above materials possessed spherical morphology with surface areas from 635.833 to 1048.960 m/g. Except for the zinc ions, the complexation with copper and iron ions not only enhanced materials' UV resistance but also increased their adsorption rate and the loading amount of AVM from 133 mg/g to 248 and 243 mg/g, respectively. At pH 3, 7, and 10, the bridge effect of the metal ions demonstrated a cumulative release rate using MSN-PDA not over 30% for AVM in 180 h, while the cumulative release rate for MSN reached its 50% in 60, 90, and 50 h under different pH values, respectively. We further demonstrated that the adhesive effect of PDA could be decreased by metal ions.