Enhancing the UV Radiation Protection of Bacillus thuringiensis Formulation using Sulfur Quantum Dots: A Biotechnological Approach

Abstract Low stability against ultraviolet (UV) radiation is one of the drawbacks of biological pesticides such as Bacillus thuringiensis (Bt). The persistence of Bt crystals against insect pests is thus deactivated. Bt plays a key role in the control of microbial pests. In this study, Bt spores and crystals were protected from UV radiation by sulfur quantum dots (SQDs). These were synthesized by treating sublimated sulfur powders with an alkali using polyethylene glycol 400 (PEG-400). Their effect on the formulation of Bt was investigated to improve its resistance to UV radiation. Excellent aqueous dispersibility and superior photostability were observed for the synthesized SQDs. Properly dispersed SQDs with mean size distributions of 3.27 nm and 6.07 nm were obtained for 120 and 72 h, respectively. The findings indicate that SQDs perform very well in encapsulated formulations prepared by the Pickering emulsion method compared to non-encapsulated formulations. Spore viability and mortality of second-instar Ephestia kuehniella larvae under UV-A radiation were studied. The unique properties of SQDs are believed to reduce the degradation of Bt against UV radiation. Our results showed that these SQDs can be used to improve the stability and resistance of Bt in SQD-stabilized microcapsule formulations.