The Photodynamic Antibacterial Activity Properties of a Series of Indium(III) Porphyrins and their Gold and Silver Nanoparticle Conjugates

In(III) tetraarylporphyrin complexes with 4-thiomethylphenyl (1-InPor), thien-3-yl (2-InPor), thien-2-yl (3-InPor) and 5-bromothien-2-yl (4-InPor) meso-aryl rings have been synthesized and characterized. The complexes have been conjugated to gold and silver nanoparticles (AuNPs and AgNPs). The photodynamic antimicrobial chemotherapy (PACT) activities of 1-4-InPor and their AuNP and AgNP conjugates have been investigated against both planktonic bacteria and biofilms of Gram-(+) S. aureus and Gram-(-) E. coli. 2.5 mu g.mL(-1) solutions of 1-4-InPor exhibited favorable PACT activities against planktonic S. aureus with high Log(10) reduction values in the 4.28-7.69 range upon 75 min photoirradiation with a Thorlabs M625L3 LED (240 mW.cm(-2)) mounted onto the illumination chamber of a Modulight 7710 medical laser system to provide a dose at the well-plate of 86 mJ.cm(-2).min(-1). In contrast, low values in the 1.4-1.9 range were obtained against E. coli with 10 mu g.mL(-1) solutions. 1-4-InPor exhibited relatively low PACT activity against the biofilm cells of S. aureus and E. coli. Conjugation of 1-4-InPor to AgNPs and AuNPs significantly enhanced the PACT activities. This is demonstrated by the complete eradication of planktonic S. aureus at shorter irradiation times with high Log(10) values>7.69 and moderate Log(10) values>2 against planktonic E. coli for the meso-thienylporphyrin conjugates.