Enzyme-Responsive Phosphate-Crosslinked Microgels with Enhanced Foliar Adhesion and Insecticide Stability: An Approach for Sustained Insecticide Delivery and Increased Plant Growth

Stimuli-responsive, biodegradable polymeric carriers have emerged as a promising platform for the effective utilization of agrochemicals to address the challenge of environmental pollution. In this work, we present the fabrication of 3,4-dihydroxyhydrocinnamic acid (DC)-functionalized cellulose-based microgels (DC-CelP MGs) crosslinked with phosphate moieties for the sustained release of the imidacloprid (Im) insecticide. These microgels are ∼220 nm in diameter and can degrade in the presence of cellulase enzyme available in soil and salivary glands of insects. Im@DC-CelP MGs exhibit 8.6% loading efficiency and 65% encapsulation efficiency for Im. Im@DC-CelP MGs display ∼76 and ∼94% Im release in the presence of 10 and 15 U cellulase enzyme over 160 h, respectively. Notably, the encapsulation of Im in Im@DC-CelP MGs significantly improves its photostability. The developed microgels show good foliar adhesion on Chinese cabbage leaves, which is beneficial to reduce the insecticide loss by rain. Furthermore, in contrast to bare Im_UV and Confidor_UV, Im@DC-CelP MGs_UV are able to retain the insecticidal activity of Im against the green peach aphid (Myzus persicae) even after UV treatment for 12 h. Additionally, the presence of phosphate-based crosslinking units render these microgels as potential sources of P. Experimental results reveal that the spraying of the Im@DC-CelP MG formulation improves seed germination and overall plant growth in Chinese cabbage, with no visible phytotoxic effects. Also, acid phosphatase activity in Chinese cabbage roots is reduced upon treatment with DC-CelP MGs and Im@DC-CelP MGs, suggesting the availability of P upon degradation of DC-CelP MGs by the cellulase enzyme in soil. Moreover, no phytotoxicity in the case of potato plants further indicates the wider applicability of the developed microgels. Overall, these results exhibit that the developed microgel carriers with enhanced foliar adhesion and insecticide stability along with the slow release feature for P can act as a promising platform for sustainable agriculture practices.