The antimicrobial activity of silver nanoparticles has been extensively studied in the last years. Such nanoparticles constitute a potential and promising approach for the development of new antimicrobial systems especially due to the fact that several microorganisms are developing resistance to some already existing antimicrobial agents, therefore making antibacterial and antimicrobial studies on alternative materials necessary to overcome this issue. Silver nanoparticle concentration and size are determining factors on the antimicrobial activity of these nano systems. Heparin is a polysaccharide that belongs to the glycosaminoglycans (GAGs) family, molecules formed by a base disaccharide whose components are joined by a glycosidic linkage that is a repeating unit along their structure. It is highly sulfated making it a negatively charged material that is also widely used as an anticoagulant in Medicine because its biocompatibility besides it is also produced within the human body, specifically in the mast cells. Heparin alone possesses antimicrobial activity although it has not been studied very much in detail, it only has been demonstrated that it inhibits E. coli, P. aeruginosa, S. aureus and S. epidermidis, so taking this into account, this study is dedicated to assess UV photochemically-synthesized (λ=254 nm) heparin-based silver nanoparticles antimicrobial activity using the agar disk diffusion method complemented by the broth microdilution method to estimate de minimum inhibitory concentration (MIC), that is the lowest concentration at which an antimicrobial will inhibit visible growth of a microorganism. The strains used were the ones aforementioned to assess the antimicrobial activity degree these heparinbased nanoparticles exhibit.
A photochemical-based method in which UVA light (λ=366 nm) is used for synthesizing gold nanoparticles is presented
by irradiating gold (III) chloride hydrate (HAuCl<sub>4</sub>) in the presence of pharmaceutical-grade heparin sodium (PGHEP) as
a reducing and stabilizing agent in aqueous solution. Different HAuCl<sub>4</sub> to PGHEP concentration ratios were exposed to UVA for up to seven hours. The as-synthesized nanoparticles were characterized by UV-VIS and Raman spectroscopy, transmission electron microscopy (TEM), and pH measurements. The synthesized AuNPs present spherical as well as anisotropic shapes, such as oval, triangular, hexagonal sheets, rods, and some other faceted forms, with dimensions ranging from 20 nm to 300 nm. All obtained products show good temporal stability in solution. Surface plasmons differ when varying HAuCl<sub>4</sub> to PGHEP concentration ratio. The obtained samples exhibit two absorption peaks, one in the region between 500-600 nm, and another one in the near-IR between 900-1200 nm; both peaks shift to longer
wavelengths and increase their absorption intensity as the HAuCl4 to PGHEP concentration ratio increase. TEM images
show the change in nanoparticles yield as well as the shape and sizes change depending on HAuCl<sub>4</sub> to PGHEP
concentration ratio variation. Ph measurements suggest that acidic media promote anisotropic nanoparticle formation.
Raman spectroscopy was used to find out which heparin sodium main groups attached to the nanoparticles surface, and
in what amount. In summary, it is found that when modifying the reactants concentrations and keeping the UV
exposition time as the only fixed parameter, different nanoparticles with distinctive characteristics can be attained.