Harnessing photo-responsive azobenzene-functionalized chitosan nanomicelles for UV protection of photosensitive pesticides

Photosensitive pesticides are susceptible to ultraviolet (UV) light, leading to their easy photodegradation and short half-life under natural conditions. In this context, it is highly desired to develop novel pesticide formulations with UV protection efficiency. In this study, a photo-responsive amphiphilic chitosan-based copolymer (mPEG-CS-AZO) was synthesized successfully by the grafting of poly(ethylene glycol) as the hydrophilic chains, and azobenzene moieties that serve as both hydrophobic and photo-responsive constituents. The mPEG-CS-AZO was characterized with 1 H NMR, FTIR, and the critical micelle concentration (CMC) value was determined to be 0.01 mg/mL. mPEG-CS-AZO nanomicelles can be formed spontaneously by the self-assembly in aqueous solution, which were used for the loading of avermectin (AVM), a representative photosensitive pesticide with poor water solubility. The mPEG-CS-AZO nanomicelles can act as UV protector for the loaded AVM, with a retention rate of 57.37 % following 60 h of UV exposure, attributing to that the irradiated UV light can be consumed through the efficient azobenzene trans-cis isomerization. The AVM release profiles fit the first-order model quite well. Therefore, the mPEG-CS-AZO nanomicelles can be applied as potential prospective carriers for photosensitive pesticides with the purpose of UV protective efficiency and sustained release.