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 μg.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 μg.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.