Abstract
Antibacterial photodynamic therapy (aPDT) utilizes reactive oxygen species such as singlet oxygen (1O2) and free radicals via photosensitizers, which are light and light-sensitive agents, to reduce bacterial infections. It has been utilized as a treatment for dental diseases in place of antibiotic therapies. However, aPDT does not always cause the desired therapeutic effect due to the instability of organic photosensitizers and the formation of bacterial biofilms. To promote the antibacterial and antibiofilm effects of aPDT, we have proposed a lysozyme (Lys)-gold nanoclusters (Au NCs)/rose bengal (Lys-Au NCs/RB) conjugate as a novel photosensitizer. This conjugate was found to effectively impede the growth of both gram-positive and gram-negative bacteria when exposed to white light-emitting diode (LED) irradiation. The photoexcited Lys-Au NCs/RB showed significantly higher antibacterial activity than photoexcited Lys-Au NCs or RB alone. The synergistic effect is a result of the combination of Lys (an antibacterial protein) and enhanced 1O2 generation related to resonance energy transfer (RET) in the Au NCs/RB conjugate. Photoexcited Lys-Au NCs/RB increased the effects of aPDT in a dose- and time-dependent manner. Furthermore, the photoexcited Lys-Au NCs/RB successfully decreased Streptococcus mutans biofilm formation. However, in contrast, it did not have a negative effect on the proliferation, adhesion, or spread of mammalian cells, indicating low cytotoxicity. Lys-Au NCs/RB is a novel photosensitizer with low cytotoxicity that is capable of bacterial inactivation and the suppression of biofilm formation, and could help to improve dental treatments in the future.
Highlights
Antibacterial photodynamic therapy is widely used alongside oral disinfection therapies, including those for caries, endodontic disease, periodontitis, and peri-implantitis
We evaluated whether Lys-Au lysozyme-Au nanoclusters (NCs)/rose bengal (RB) with white light-emitting diode (LED) irradiation exerted antibacterial and antibiofilm activities against oral bacteria, and in particular, when supported by the resonance energy transfer (RET) mechanism
Upon conjugation of RB with Lys-Au NCs, the RB absorption was observed at approximately 550 nm, in addition to absorption at less than 450 nm by Lys-Au NCs; the absorbance of RB in the conjugates increased with the ratio of RB to Lys-Au NCs (Figure 1B)
Summary
Antibacterial photodynamic therapy (aPDT) is widely used alongside oral disinfection therapies, including those for caries, endodontic disease, periodontitis, and peri-implantitis. To assess the time-dependent effects of LED irradiation, S. mutans suspensions supplemented with the Lys-Au NCs/RB conjugate (at 0 (absence) or 1 μg/mL) were subjected to white LED irradiation for 0, 30, 60, and 90 s.
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