Recent Advances in Green Metallic Nanoparticles for Enhanced Drug Delivery in Photodynamic Therapy: A Therapeutic Approach

Abstract

Globally, cancer is one of the leading causes of death among men and women, it is characterized by the unregulated proliferation of tumor cells. Some of the common risk factors associated with cancer development include the consistent exposure of body cells to carcinogenic agents such as alcohol, tobacco, toxins, gamma rays and alpha particles. Besides the above-mentioned risk factors, conventional therapies such as radiotherapy, and chemotherapy have also been linked to the development of cancer. Over the past decade, tremendous efforts have been invested in the synthesis of eco-friendly green metallic nanoparticles (NPs), and their medical application. Comparatively, metallic NPs have greater advantages over conventional therapies. Additionally, metallic NPs can be functionalized with different targeting moieties e.g., liposomes, antibodies, folic acid, transferrin, and carbohydrates. Herein, we review and discuss the synthesis, and therapeutic potential of green synthesized metallic NPs for enhanced cancer photodynamic therapy (PDT). Finally, the advantages of green hybridized activatable NPs over conventional photosensitizers (PSs) and the future perspectives of nanotechnology in cancer research are discussed in the review. Furthermore, we anticipate that the insights offered in this review will inspire the design and development of green nano-formulations for enhanced image-guided PDT in cancer treatment.

Keywords: cancer; nanoparticles; photodynamic therapy; photosensitizer; theranostic.

Figure 1

Modified Jablonski energy diagram depicting the underlying photophysical and photochemical reactions of PSs in photodynamic diagnosis (PDD) (a) and photodynamic therapy (PDT) (b).

Figure 2

Schematic representation of surface plasmon resonance (SPR) of metallic nanoparticles (NPs). Photoexcitation and relaxation of plasmonic NPs generate localized surface plasmon resonance (LSPR) (a–c). Post-irradiation, plasmonic NPs may undergo two major processes, i.e., radioactive decay /or non-radioactive decay (b,c). Radioactive decay can either lead to far-field light scattering into adjacent nanostructures, or/electromagnetic fields, i.e., near-field (a,b). Alternatively, LSPR can undergo a non-radioactive decay process in which intraband or/interband excitation levels within the conduction band of a metallic NP can result in the generation of hot electrons (c). The interactions of high energy hot electrons with molecular oxygen (O₂) can result in the generation of cytotoxic reactive oxygen species (ROS). Further, the electronic energy states of hot electrons and holes are depicted by the colors red and green respectively (c).

Figure 3

Schematic representation of the synthesis and characterization of green metallic nanoparticles.

Figure 4

Schematic diagram representing green synthesis of Lip-ZnPcS₄ and characterization techniques.

Figure 5

Schematic representation of hybridized liposome encapsulated silver nanoparticles (Ag NPs) functionalized with activatable PS.

Figure 6

A schematic diagram illustrating the administration and therapeutic effects of functionalized nanoparticles in cancer PDT.