Application of the photothermal-responsive gelatin-based microspheres for controlled release of imidacloprid by helix-coil structural transition mechanism

Abstract

Intelligent controlled release systems (ICRS) are recognized as a feasible and economical way for the highly efficient utilization of agrochemicals. In this work, we developed an intelligent photothermal-responsively controlled-release pesticide particle (IYGCP) based on imidacloprid (IMI, a model pesticide), yeast biochar (YB, adsorbent and photothermal material), gelatin (GE, temperature-responsive polymer), and Ca-alginate (CA, microsphere matrix). Therein, YB with high adsorption property and photothermal conversion capacity was used as a carrier of IMI to avoid the loss of active ingredients, and as an agent to endow the IYGCP platform with unique photothermal-responsive performance. After IMI loading, IMI/YB was scattered and anchored in CA/GE semi-interpenetrating hydrogels by the chelation of sodium alginate and Ca2+. Upon irradiation under simulated sunlight, YB with satisfactory photothermal conversion efficiency can effectively transfer solar energy into thermal energy, induing a free helix-coil structural transition of the un-crossed GE polymers, thereby resulting in changes in microstructure of hydrogel spheres and further enabling a controlled release of IMI encapsulated in the IYGCP. Besides, the composite displayed high control efficacy on corn borers. Consequently, this photothermal-responsive gelatin-based microsphere shows a bright prospect for controlling the release and loss of pesticides.