Preparation and Photodynamic Antimicrobial Activity of Tetra(4-carboxyphenoxy)-Phthalocyaninatozinc(II) Loaded Gelatin Microspheres

Antimicrobial photodynamic therapy (APDT) based on photosensitizers has emerged as an alternative treatment to antibiotics. However, the poor water solubility and tendency to aggregate of photosensitizers severely impede the widespread application of APDT. Therefore, in this study, tetra(4-carboxyphenoxy)-phthalocyaninatozinc(II)-loaded gelatin microspheres (TPZnPc-GMs) were prepared by using a water-in-oil emulsion cross-linking method. The carboxyl groups in TPZnPc and gelatin were employed to coordinate with Cu²⁺ ions. The microspheres were characterized by using Fourier transform infrared spectroscopy, scanning electron microscopy and UV-visible spectroscopy. Results demonstrated the successful loading of TPZnPc into TPZnPc-GMs with a loading rate of 0.6%. The average particle size of TPZnPc-GMs was 1.6 μm, and TPZnPc remained its monomeric form within these microspheres. The TPZnPc-GMs solution, when exposed to red light (630-710 nm), produced singlet oxygen. When co-cultured with Gram-positive Bacillus subtilis (B. subtilis), the TPZnPc-GMs solution at a concentration of 1 mg/mL exhibited 65% photodynamic bactericidal rate. The photodynamic bactericidal rate of 100% was achieved when its concentration was improved to 3 mg/mL.