Pluronic? P-123 as a reductant and stabilizing agent for gold nanoparticles (AuNPs) combined with methylene blue for photodynamic and photothermal therapy

The search for more effective drugs and therapies for the treatment of microbial diseases has driven the development of nanomedicine in recent years. In this sense, the present work shows the combination of photodynamic therapy (PDT) and photothermal therapy (PTT) using the photoactive drugs: methylene blue (MB) and gold nanoparticles (AuNPs). The ABA triblock Pluronic (R) P-123 copolymer was employed both as a micellar nanocarrier and reductant/stabilizing agent for AuNPs. The synthesis of gold nanoparticles (AuNPs) was carried out in situ through the redox process of AuCl3 gold salt in the presence of different concentrations of P-123 ranging from 0.25 % to 8.00 % ( % w/V) following the solid dispersion method. The MB was incorporated into the copolymeric micellar system by passive and active incorporation methods. In general, the system containing 1.00 % and 2.00 % (w/V) of P-123 was the more efficient and reproducible to obtain P-123/AuNPs/MB samples. The AuNPs synthesized presented plasmonic resonance peaks ranging from 535 to 554 nm, characteristic of spherical AuNPs. Dynamic Light Scattering and transmission electronic microscopy confirm the structure of the polymeric micelle around 20 nm and the AuNPs 3 nm diameters. The fluorescence emission showed to be dependent on the excitation wavelength, a promising feature for biological applications, especially when considering an image-guided diagnosis. Furthermore, the Stern-Volmer study by fluorescence quenching with iodide showed that active incorporation favors greater internalization of MB at the hydrophobic core of the micelle. On the other hand, the passive incorporation method placed MB in the most hydrophilic region in the micelle. The photodynamic effect was confirmed by singlet oxygen generation using ABDA as a probe. Thermal Lens spectroscopy and heating studies also confirms the heat generation by the system. In addition, the results point to synergism both in the generation of 1O2 and heat. The in vitro susceptibility of the samples was evaluated in Candida albicans strain. Better antifungal activity was observed in the sample of 2.00 % P-123/AuNPs/MB by Passive incorporation, illuminated with red and green LEDs. The biological study in bacteria strains of E. coli and S. aureus has shown that both percentages of P-123 with MB and AuNPs/MB by passive incorporation were efficient in controlling the evaluated bacteria. In this way, the present work showed promise for the treatment of antimicrobials through the combined therapy of PDT and PTT.