Periodontitis, an inflammatory disease of the gums that destroys the foundation on which teeth rest. Deterioration of periodontal ligaments (PDLs), the development of periodontal pockets, and the resorption of alveolar bone are hallmarks. Pockets may get infected with periodontitis because of the proliferation of microflora, especially anaerobes, which cause a loss of clinical connection, and the deterioration of alveolar bone ^[1]

Photodynamic therapy (PDT) is a form of phototherapy involving photochemistry, photophysics, and photobiology. PDT as a noninvasive method for tumor treatment, differing from surgery, radiotherapy and chemotherapy, is less toxic, short-term, non-resistant to the drug. Therefore, PDT has been already applied in skin cancer , squamous cell carcinoma, prostate cancer, breast cancer, cervical cancer, lung cancer , and much other cancer prevention and treatment, which becomes more highly focused.^[2]

It employs photosensitizers that are excited by appropriate light in the presence of oxygen, to generate cytotoxic reactive oxygen species (ROS), especially singlet oxygen. The ROS exerts toxic actions on periodontal pathogens in either planktonic cultures or biofilm status to substantially reduce the bacterial colonization without side effects and drug resistance. effective for antibacterial treatment of deep periodontal pockets, when excitation light with large penetration depth is involved to trigger PDT effect, which is difficult to reach by mechanical approaches.^[3]

The clinical evidence points out two significant limitations of current phototherapeutic interventions: restricted penetration of photosensitizer and light propagation inside the dentinal tubules, which confines aPDT to marginal efficiency in vivo which are overcome by nano platform based photosensitisers. The use of nano-based platforms to enhance photosensitizers’ penetration . The application of nanoscale science has been serving a link between engineering/technology and medicine/dentistry to produce efficient platforms for the delivery of photosensitizers in target dysbiotic biofilms which are located 5-7mm depth in pocket. The mobility and bioavailability of nanoparticles will largely depend upon their diffusion coefficients, which will be related to their size and physicochemical characteristics, and the nature of the biofilm. Metallic nanoparticles have a high surface-to-volume ratio, which guides the ability of such material to interact with the bacterial membrane to induce bactericidal action ^{[3 ]}

Zinc is an indispensable trace element for humans and plays a crucial role in regulating cellular metabolism and homeostasis. ZnO NPs can be easily biodegraded and absorbed in the body and thus have been listed as generally recognized as a safe (GRAS) material by the Food and Drug Administration (FDA)^[5]

ZnO nanoparticles are a newer type of promising candidate because of its high safety, low price, lack of polluting effects, and good stability against air and sunlight. the combination of their excellent catalytical and antimicrobial properties together with their biocompatibility makes ZnO nanostructures promising materials for tissue regeneration, bacterial resistance, and wound dressing.  Zn 2+ ions released from ZnO nanostructures not only have the ability to stimulate bone formation in vitro but can also enhance keratinocyte migration toward a wound site and promote healing. the excellent electronic properties of ZnO nanostructures make them suitable for the fabrication of biosensors, and their unique photoluminescent properties, such as a tunable emission wavelength, together with their high aqueous stability and high quantum yield (QY) make ZnO-based quantum dots (QDs) promising candidates as bioprobes for cell and tissue imaging ^[6]

zinc oxide nanoparticles (ZnONPs), belonging to the family of semiconducting metal oxide, are used as photosensitizers in aPDT. The photoresponse of ZnO consists of two parts: a rapid process of photogeneration and recombination of electron-hole pairs and a slow process attributed to the oxygen adsorption and Photodesorption on the film surface as well as the grain boundaries. ZnO NPs, such as the promising arrangement of its electronic structure, light absorption properties, and charge transport characteristics, make it possible to use it as a photosensitizer. ZnO NPs get photocatalyzed under both ultra-violet and visible light irradiation, releasing ROS, which eventually causes bacterial cell death ^[7]