Antimicrobial photodynamic activity and cytocompatibility of Au₂₅(Capt)₁₈ clusters photoexcited by blue LED light irradiation

Abstract

Antimicrobial photodynamic therapy (aPDT) has beneficial effects in dental treatment. We applied captopril-protected gold (Au 25 (Capt) 18 ) clusters as a novel photosensitizer for aPDT. Photoexcited Au clusters under light irradiation generated singlet oxygen ( 1 O 2 ). Accordingly, the antimicrobial and cytotoxic effects of Au 25 (Capt) 18 clusters under dental blue light-emitting diode (LED) irradiation were evaluated. 1 O 2 generation of Au 25 (Capt) 18 clusters under blue LED irradiation (420–460 nm) was detected by a methotrexate (MTX) probe. The antimicrobial effects of photoexcited Au clusters (0, 5, 50, and 500 μg/mL) on oral bacterial cells, such as Streptococcus mutans, Aggregatibacter actinomycetemcomitans , and Porphyromonas gingivalis , were assessed by morphological observations and bacterial growth experiments. Cytotoxicity testing of Au clusters and blue LED irradiation was then performed against NIH3T3 and MC3T3-E1 cells. In addition, the biological performance of Au clusters (500 μg/mL) was compared to an organic dye photosensitizer, methylene blue (MB; 10 and 100 μg/mL). We confirmed the 1 O 2 generation ability of Au 25 (Capt) 18 clusters through the fluorescence spectra of oxidized MTX. Successful application of photoexcited Au clusters to aPDT was demonstrated by dose-dependent decreases in the turbidity of oral bacterial cells. Morphological observation revealed that application of Au clusters stimulated destruction of bacterial cell walls and inhibited biofilm formation. Aggregation of Au clusters around bacterial cells was fluorescently observed. However, photoexcited Au clusters did not negatively affect the adhesion, spreading, and proliferation of mammalian cells, particularly at lower doses. In addition, application of Au clusters demonstrated significantly better cytocompatibility compared to MB. We found that a combination of Au 25 (Capt) 18 clusters and blue LED irradiation exhibited good antimicrobial effects through 1 O 2 generation and biosafe characteristics, which is desirable for aPDT in dentistry.

Photo/electrocatalysis and photosensitization using metal nanoclusters for green energy and medical applications

“…16B). 89 The following section includes discussion of several strategies to improve the 1 O 2 generation efficiency and PDT activity of Au NCs by using: (i) atomically precise size control, (ii) NIR activation for deep-tissue treatments, (iii) aggregation-induced emission (AIE), (iv) resonance energy transfer (RET), and (v) forming nanocomposites with other nanomaterials for multimodal synergistic therapy (Fig. 17).…”

Antibacterial and Antibiofilm Photodynamic Activities of Lysozyme-Au Nanoclusters/Rose Bengal Conjugates

“…Previously, Miyata et al compared the biocompatibility properties of Au NCs and a conventional organic dye, MB, at clinically relevant antibacterial concentrations. 19 This study showed that exposure to MB decreased the viability of fibroblastic and osteoblastic cells; exposure to Au NCs did not. It is thus important that the cytotoxicity of organic dyes in aPDT be reduced.…”

Recent Development of Gold Nanoparticles as Contrast Agents for Cancer Diagnosis

“…These studies confirmed the great potential of AuNCs as fluorescence imaging agents for cancer diagnosis. Moreover, due to their optical properties, the AuNCs can be activated by light to produce reactive oxygen species, making them good candidates as photosensitizers for photodynamic therapy of cancers [ 105 , 106 ].…”