Surface plasmon resonance of naked gold nanoparticles for photodynamic inactivation of Escherichia coli

Although antimicrobial photothermal inactivation of naked gold nanostructures using powerful pulsed lasers has been previously studied, there are little reports about their photodynamic antimicrobial properties under the irradiation of low-power density continuous wave lasers. Therefore, this paper attempts to fill this gap. In this paper, we studied the effects of a 40-mW/cm² continuous Nd:Yag laser at 532?nm and naked gold nanoparticles on inactivation of Escherichia coli ATCC25922. According to our results, 60?min illumination using the Nd:Yag laser caused a 0.15log reduction of the bacterial viability. Also, the employed gold nanoparticles with an average size of 15?nm were toxic to E. coli ATCC 25922 in the concentrations above 0.5?μg/ml. In addition, synergistic effects of 0.5?μg/ml gold nanoparticles and the light illumination led to a 2.43log reduction of the viability after a 60-min exposure and did not show any considerable temperature change on the media. The obtained results were justified based on the possible interaction mechanisms of low-power density laser lights and naked gold nanoparticles. The paper is proposed as a prelude for future research about localized inactivation of resistant pathogens with minimum side effects on neighbor tissues.