Learning from Nature: Bioinspired Chlorin-Based Photosensitizers Immobilized on Carbon Materials for Combined Photodynamic and Photothermal Therapy

Abstract

Chlorophylls, which are chlorin-type photosensitizers, are known as the key building blocks of nature and are fundamental for solar energy metabolism during the photosynthesis process. In this regard, the utilization of bioinspired chlorin analogs as photosensitizers for photodynamic therapy constitutes an evolutionary topic of research. Moreover, carbon nanomaterials have been widely applied in photodynamic therapy protocols due to their optical characteristics, good biocompatibility, and tunable systematic toxicity. Herein, we review the literature related to the applications of chlorin-based photosensitizers that were functionalized onto carbon nanomaterials for photodynamic and photothermal therapies against cancer. Rather than a comprehensive review, we intended to highlight the most important and illustrative examples over the last 10 years.

Natural Photosensitizers in Antimicrobial Photodynamic Therapy

“…Natural molecules such as chlorophyll, heme, and cobalamin are known groups of tetrapyrrolic macrocycles and are considered “pigments of life” [ 106 ]. Porphyrin and chlorins are the most commonly used PSs for PDT studies.…”

“…Porphyrin has an absorption band in the region of 400 nm (Soret band) and other small bands in the region of 630 nm. Chlorin-type PSs have a strong absorption band in the violet–blue region (380–450 nm, B or Soret band) and a moderate band in the red region (600–700 nm, Q band) [ 106 ]. Most bacteriochlorins show a strong absorption in the NIR region but exhibit low stability and conversion to chlorin and/or porphyrin precursors [ 106 , 107 ].…”

“…Chlorins generate a large amount of singlet oxygen, but their poor solubility and instability in the presence of light, acids, and bases limit their application [ 24 ]. However, many chlorin PS applications in the microbial control of seeds, plant disease, and multidrug resistance have been reported [ 97 , 106 , 107 ]. Chlorophyllin sodium salt at low (1 µM) or high (15 mM) concentrations showed effective antimicrobial properties upon exposure to light intensities of 96 and 148 W/m 2 [ 101 , 102 ].…”

“…PSs are obtained by natural extraction or by semisynthetic or synthetic methods. For instance, chlorin-based PSs have been produced from chlorophyll using several methods: Direct isolation of natural chlorophylls from plants [ 124 , 125 ]; Synthesis of chlorin-based PSs by hydrogenation, annulation, cycloaddition, breaking, and mending of porphyrin precursor [ 126 , 127 , 128 , 129 ]; Semisynthesis of chlorin-based PSs from natural chlorophylls [ 130 ]; and De novo synthesis of gem-dialkylchlorins using a reduced ring of the acyclic precursors of chlorin [ 106 , 131 ]. …”

“…De novo synthesis of gem-dialkylchlorins using a reduced ring of the acyclic precursors of chlorin [ 106 , 131 ].…”