Comparative analysis of antibacterial and antibiofilm potential of chemically- and green laser-produced gold and silver nanoparticles against dental pathogens

Abstract

Objectives

This study compared antibacterial and antibiofilm effectiveness of chemically (chem_) and pulsed laser ablation-synthesized (laser_) gold (Au) and silver (Ag) nanoparticles (NPs), namely chem_AuNPs, chem_AgNPs, laser_AuNPs, and laser_AgNPs, against four Streptococcus species (S. mutans, S. mitis, S. sanguinis, and S. gordonii), essential for cariogenic biofilm development.

Design

Nanoparticles were characterized for size and stability using dynamic light scattering (DLS) and transmission electron microscopy (TEM). Their antibacterial and antibiofilm activities were tested in microdilution and crystal violet assays, respectively. Ex vivo evaluation of the nanoparticles antibiofilm activity was performed against a four-species biofilm on enamel discs by quantifying CFU. Scanning electron microscopy was used to visualize the reduction in biofilm mass on enamel discs treated with laser_Au and Ag nanoparticles.

Results

TEM showed nanoparticle sizes ranging 5.89–18.49 nm. DLS revealed the stability of NPs colloid solutions, with ζ-potential approximately −30 mV over 21 days. All NPs exhibited strong antibacterial activity, with MIC values of 56.9–120.6 μg mL-1 for chem_AuNPs and 1.9–30.8 μg mL-1 for all the rest. The evaluation of NPs potential in biofilm prevention showed the following trend in activity: laser_AuNPs>laser_AgNPs>chem_AuNPs>chem_AgNPs. AuNPs, regardless of synthesis method, were as effective as the positive control (chlorhexidine-mouthwash) against the multispecies biofilm settled on enamel discs, while AgNPs were nearly twice as efficient.

Conclusions

AuNPs and AgNPs could be alternatives for managing cariogenic bacteria both planktonic and within biofilms. Laser_AgNPs, being more efficient than commercial mouthwash, seem to be the most valuable candidate.