Antimicrobial photodynamic therapy and the advances impacted by the association with nanoparticles

Microbial resistance to antibiotics, antifungals, and virucides is one of today's most significant public health problems. Antimicrobial Photodynamic Therapy (aPDT) is a prominent therapeutic strategy for infection control that does not cause microbial resistance to treatment. Its microbial eradication potential is significantly increased when aPDT is associated with nanotechnology. aPDT causes cell death due to photophysical and photochemical events derived from the interaction between a photosensitive agent (PS), a light at an appropriate wavelength, and the oxygen in the medium. Its main product, reactive oxygen species (ROS), leads to the death of microorganisms in and around the irradiated PS. However, the low water solubility, instability, and low microbial internalization of PSs with high quantum yield diminish the effectiveness of the aPDT. Nanoparticles emerge to overcome these limitations. They have been shown to increase the photodynamic activity of PSs and potentially target their delivery to infected sites, increasing the selectivity of the therapy. This review addresses the main constraints of bacteria, fungi, and viruses to the effectiveness of aPDT and discusses how nanotechnology can overcome these difficulties. Current studies that used polymeric, lipid, and metallic nanoparticles associated with aPDT were raised, and the significant advances impacted by them were critically discussed. Among the microorganisms eliminated by nanoparticles-associated aPDT, Methicillin-Resistant Staphylococcus aureus (MRSA) bacteria in planktonic culture and the form of biofilms, and fungi such as Candida albicans, stand out. The nanoparticle-associated aPDT increases the chances of success of oral cavity treatments, such as those that affect the root canal, and cutaneous, such as dermatophytosis. The use of aPDT against viruses such as HSV-1 and HIV, including Sars-CoV-2, has also shown promising results. The selectivity and effectiveness of aPDT are strictly related to the characteristics of the PS-loaded nanoparticle. It is essential to know the microorganism and the place it is installed to select the nanocarrier properly.