Dopamine-Coated Silver Nanoparticles: Therapeutic Agents to Fight Bacteria and Fungi ^†

Multidrug-resistant pathogenic microorganisms have become a serious threat to public health, making it difficult to prevent, treat and fight the infections. This drug resistance is often associated with the overuse and misuse of antibiotics [1]. In this light, silver nanoparticles (Ag-NPs) arise as potential antimicrobial agents for being toxic and lethal against a wide range of microorganisms [2]. In addition, Ag-NPs can also cooperate with other biomolecules, such as polymers with antimicrobial properties to increase their biocidal activity. Among these polymers, dopamine (DA) could be a good alternative to be combined with silver, since it presents great adhesive properties and strong biocompatibility, making it an excellent fit for numerous biological applications [3].

Therefore, for this work, Ag-NP and DA nanoconjugates were formulated based on electrostatic interactions and characterized by UV–Vis spectra measurements, showing a decrease in the silver peak when covered with DA. A scanning electron microscopy (SEM) analysis showed an increase in size when dopamine was conjugated with the Ag-NPs; and Fourier transformed infrared spectroscopy (FTIR) analysis confirmed the presence of DA mixed with the Ag-NPs.

Next, the antimicrobial properties of DA-coated Ag-NPs (Ag-NPs and DA) against the Gram-positive Staphylococcus aureus (S. aureus) and the Gram-negative Escherichia coli (E. coli) bacteria, as well as the antifungal effect against Candida albicans (C. albicans), was assessed and compared with DA and Ag-NPs alone.

So far, the results revealed that Ag-NP and DA nanoconjugates presented higher antibacterial and antifungal effects when compared with Ag-NPs and DA alone. Further experiments will comprise the cytotoxicity evaluation of these nanoparticles, as well the characterization of their ability to successfully deliver drugs and genetic information.