Nanostructures for Antimicrobial and Antibiofilm Photodynamic Therapy

Abstract

Unprecedented explosion of research in the field of nanotechnology has gained importance in the treatment, prevention, and eradication of antibiotic-resistant bacterial strains. The emerging multidrug-resistant bacteria (MDRB) pose a major threat to the modern health-care system. The MDRB strains cannot be treated with conventional antibiotics due to their rapid mutations and resistance. Antibiotic-resistant bacteria that produce biofilm are responsible for approximately 700,000 deaths each year. One of the biggest problems faced by research society is to find alternatives to combat the increasing number of resistant variants. Photodynamic therapy (PDT) was established recently and remains a successful treatment modality for infectious diseases caused by microbial strains and biofilms. Light-mediated inactivation through photodynamic therapy provides new dimensions to eradicate antibiotic-resistant microbes. Antimicrobial photodynamic therapy (aPDT) has gained interest in nanotechnology where the effectiveness of photosensitizers (PS) can be enhanced by the use of nanoparticles (NPs). In the last two decades, different techniques have been raised for aPDT in combination with nanoparticles. Nanoparticles are used in aPDT either as photosensitizing agents or as PS delivery agents. Nanoparticles used in aPDT improve the dispersion and selective delivery of PS to the target cells. Over last decades, various nanoparticles are utilized in aPDT as nanocarriers. Polymeric nanovehicles, nanomicelles, and liposome are used to encapsulate PS molecules. The inorganic metallic nanoparticles are extensively studied for the photoinactivation of resistant microorganisms and their biofilms. The four types of combinations between nanoparticles and PS are categorized as nanoparticles embedded with PS, nanoparticles with PS bound to the surface, nanoparticles as the PS, and PS alongside nanoparticles. Nanoparticles have enhanced the activity of aPDT by encapsulating the PS in nanoparticles or binding the PS on the surface of nanoparticles covalently. The photoactive nanoparticles were successful as antimicrobial agents and more effective against antibiotic-resistant microbial strains and their biofilms.