UV/enzyme dual responsive photosensitizer-loaded 4-(Phenylazo)benzoic Acid-mPEG nanosystem for enhanced photodynamic insecticide efficacy

To improve photostability and enhance utilization rate and reduce pest resistance, a new strategy based on the combination of photodynamic insecticide action and stimulus-responsive polymer micelles is developed. 4-(phenylazo)benzoic acid (PBA)-modified poly(ethylene glycol) monomethyl ether (mPEG) conjugate is prepared by the esterification reaction of mPEG and PBA, and followed by self-assembly in aqueous solution to obtain polymeric nanoparticles. TEM shows that the nanoparticles have a core-shell structure and an average diameter of 78 nm. DLS shows that the nanoparticles are stability in water solution but can change their structure in response to UV light and/or esterase stimulation. The photodegradation of Protoporphyrin IX (PpIX) encapsulated in the nanoparticles can be effectively inhibited because of aggregation-caused quenching effect, whose maximum photodegradation rate is about 20.54% after 8 h exposure to daylight compared with the complete photodegradation of free PpIX. UV light and/or esterase stimulus can trigger PpIX release and result in a high photodynamic activity. Compared with free PpIX, the PpIX-loaded nanoparticles show a higher phototoxicity to insect cells and the daylight pretreatment has little influence on the phototoxicity.