Photothermal therapy (PTT) refers to efforts to use electromagnetic radiation (most often in infrared wavelengths) for the treatment of various medical conditions, including cancer.
[citation needed] Huang et al. investigated the feasibility of using gold nanorods for both cancer cell imaging as well as photothermal therapy.
[9] On the other hand, body excretion of non-biodegradable noble metals nanomaterials above 10 nm occurs through the hepatobiliary route in a slow and inefficient manner.
[11] On the other hand, the surface plasmon of excretable gold USNPs is in the UV/visible region (far from the first biological windows), severely limiting their potential application in PTT.
Thus, these nanoscale graphene sheets require a laser power on the lower end of the range used with gold nanoparticles to photothermally ablate tumors.
[16]<[17] The therapeutic treatment used in this study involved the use of nanoscale reduced graphene oxide sheets, nearly identical to the ones used by Robinson et al. (but without any active targeting sequences attached).
[19][20] Organic PTAs including small molecule dyes and conjugated polymers (CPs) have good biocompatibility and biodegradability, but poor photostability.
[19] Among them, small molecule dyes, such as cyanine, porphyrin, phthalocyanine, are limited in the field of cancer treatment because of their susceptibility to photobleaching and poor tumor enrichment ability.
[19] Conjugated polymers with large π−π conjugated skeleton and a high electron delocalization structure show potential for PTT due to their strong NIR absorption, excellent photostability, low cytotoxicity, outstanding PCE, good dispersibility in aqueous medium, increased accumulation at tumor site, and long blood circulation time.
[18][19][20][21] Moreover, conjugated polymers can be easily combined with other imaging agents and drugs to construct multifunctional nanomaterials for selective and synergistic cancer therapy.
[18][22] For conjugated polymers, on the one hand, their unique structures lead to closed stacking of the molecular sensitizers with highly frequent intermolecular collisions which can efficiently quench the fluorescence and intersystem crossing, and thus enhance the yield of nonradiative relaxation.
[22] On the other hand, compared with monomeric phototherapeutic molecules, conjugated polymers possess higher stability in vivo against disassembly and photobleaching, longer blood circulation time, and more accumulation at tumor site due to the enhanced permeability and retention (EPR) effect.
One of the most widely used equations to calculate photothermal conversion efficiency (η) of organic PTAs is as follows: η = (hAΔΤmax-Qs)/I(1-10-Aλ) where h is the heat transfer coefficient, A is the container surface area, ΔΤmax means the maximum temperature change in the solution, Aλ means the light absorbance, I is the laser power density, and Qs is the heat associated with the light absorbance of the solvent.
[18] The D-A assembly system in the conjugated polymers contributes to strong intermolecular electron transfer from the donor to the acceptor, thus bringing efficient fluorescence and intersystem crossing quenching, and improved heat generation.
[27] PPy nanosheets exhibit promising photothermal ablation ability toward cancer cells in the NIR II window for deep-tissue PTT.
C3 was coprecipitated with PEG-PCL and indocyanine green (ICG) to obtain PEG-PCL-C3-ICG nanoparticles for fluorescence-guided photothermal/photodynamic therapy against oral squamous cell carcinoma (OSCC).
[34] Furthermore, with π conjugated structure and different active groups, PDA can be easily combined with various materials to achieve multifunction, such as fluorescence imaging, MRI, CT, PA, targeted therapy etc.
[citation needed] Dopamine-melanin colloidal nanospheres is an efficient near-infrared photothermal therapeutic agent for in vivo cancer therapy.
[36] Wang et al. designed four NIR-absorbing D-A structured conjugated polymer dots (Pdots) containing diketopyrrolo-pyrrole (DPP) and thiophene units as effective photothermal materials with the PCE up to 65% for in vivo cancer therapy.
[39] Pu et al. synthesized PC70BM-PCPDTBT D-A CPs via nanoprecipitation of EA (6,6)-phenyl-C71-butyric acid methyl ester (PC70BM) and ED PCPDTBT (SPs) for PA-guided PTT.
PEDOT:PSS-PEG nanoparticles have high stability in vivo and long blood circulation half-life of 21.4 ± 3.1 h. The PTT in animals showed no appreciable side effects for the tested dose and an excellent therapeutic efficacy under the 808 nm laser irradiation.