Nanoemulsions loaded with compound photosensitisers: synergistic photodynamic inactivation effects of curcumin and riboflavin tetra butyrate

Antimicrobial photodynamic therapy (aPDT) is an effective method in the field of sterilisation. Singlet oxygen (O-1(2)) is an important substance in photodynamic sterilisation that needs to be detected. It involves energy transfer from an excited photosensitiser to surrounding oxygen molecules to produce cytotoxic O-1(2) species, a process termed as type II reaction. Traditional photodynamic sterilisation for fresh produce generally involves only a single photosensitiser and uses nanoemulsions coating to make the photosensitiser work better. This allows the emulsion to produce only a limited amount of reactive oxygen species (ROS) in the presence of light, such that the bactericidal effect is limited. We have innovatively compounded two photosensitisers and stored them as nanoemulsions. The composite photosensitiser produces relatively higher ROS and the nanoemulsions have good stability as well as rheological properties, and the photosensitisers are well coated in the emulsions. In summary, nanoemulsions based on composite photosensitisers showed synergistic activity in controlling the growth of Staphylococcus aureus, which provides a novel approach for raw sterilisation to maintain food safety.