Introduction

Photothermal therapy (PTT) is a noninvasive thermal therapy method caused by near-infrared (NIR) light energy excited photothermal agents to selectively achieve cancer cell ablation, which is different from photodynamic therapy in that it is an oxygen-free and reactive oxygen species-free process mediated by photothermal agents^[1]. The photothermal agents play a vital role in the PTT treatment, ideal photothermal agents should have strong absorption efficiency in NIR region, which is the biological tissue transparent window that can effectively convert the absorbed NIR light into heat. In addition, the photothermal agents in PTT should be non-toxic and show high tumor-homing ability, to improve curative effect without producing harmful side effects. MOFs and COFs with good biocompatibility and its tunable property that can easily absorb NIR light energy and open pore channels that allow for the rapid transport of produced heat. Thus, it could be expected that the use of MOFs and COFs is an attractive approach for developing photothermal agents.

Action Mechanism of PTT

Photothermal therapy utilizing photothermal agents generates sufficient heat under laser irradiation to result in notable damage of tumors. When excited by light of a specific wavelength (usually in NIR range), electrons in photothermal agents change from ground state to excited state and then return to its ground state and releases vibrational energy to generate heat, which causes the protein denaturation, alters the multimolecular structures such as membranes and the enzyme complexes, then leading to thermal ablation of cancer cells and subsequent cell death. Primary malignant tumors are more sensitive to temperature changes due to their poor blood circulation, primary malignant, which can be effectively killed when temperature is maintained above 42 °C in 10 min or above 50 °C in only 5 min^[2].

Fig.1 The schematic diagram of photothermal therapy

Application of MOFs and COFs in PTT

Depending on the relationship between photothermal agents and MOFs and COFs, MOFs and COFs-based PTT can be divided into two types: (i) intrinsic photothermal MOFs and COFs, and (ii) Modifications via photothermal agents.

• Intrinsic photothermal MOFs and COFs: Intrinsic photothermal refers to MOFs and COFs that can be directly used as photothermal agents without incorporating extra photothermal agents. For MOFs, prussian blue and its analogues are the important branches of intrinsic photothermal MOFs. Other intrinsic photothermal MOFs is based on the photothermal ability from ligand-to-metal charge transfer mechanism. For example, Yang et al. synthesized a MOFs by using Mn as nodes and IR825 as ligands. Under 808 nm light irradiation, the mass extinction coefficient of MOFs at 808 nm was 78.2 L·g^-1·cm^-1, and the temperature quickly rose to ~52 °C within 5 min, showing great promise in PTT^[3]. For COFs, intrinsic photothermal COF have also been investigated and their photothermal properties can result in highly efficient PTT. Recently, Guo et al. synthesized a radical cation-containing COFs, Py-BPy^+·-COFs, exhibited a remarkable nonradiative relaxation process and photothermal conversion efficiency under irradiation at 808 nm or 1064 nm^[4].

Fig.2 Preparation of Py-BPy^+·-COF

• Modifications via photothermal agents：MOFs and COFs can load photothermal agents to realize photothermal property, which is an easy way to achieve PTT materials. For instance, Cai et al. loaded indocyanine green (ICG) in HA-coated MIL-100(Fe) with a loading content of 40%. In vitro tests manifested that under 808 nm light irradiation for 3 min, the temperature could reach up to 70 °C, and the temperature could remain for 10 min, showing great photothermal property. And its photothermal ability is better than free ICG^[3]. Guo et al. used Fe₃O₄ as a template to successfully prepare a Fe₃O₄@TpBD core-shell COFs material with a photothermal conversion efficiency of up to 21.5% upon 785 nm light irradiation^[4].

What Can Alfa Chemistry Do

MOFs and COFs produced by Alfa Chemistry show great photothermal property when used in photothermal therapy, promoting the development of cancer treatment. Alfa Chemistry also provides customers with professional MOFs and COFs design and customization services, in which our professional technology team has profound research experience in the field of photothermal therapy. No matter what design ideas you have, we will implement them together with you. In addition, we are committed to supporting customers a series of solutions in photothermal therapy using MOFs and COFs. Please contact us immediately to order or cooperate in research and development with high quality and reasonable price.