Antibacterial efficacy of acridine derivatives conjugated with gold nanoparticles

Adsorption of acridine derivatives viz. 9-aminoacridine hydrochloride hydrate (9AA-HCl), acridine yellow (AY), acridine orange (AO), and proflavine (Pro) on citrate stabilized gold nanoparticle surface were studied using different analytical techniques like UV-vis absorption spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and transmission electron microscopy (TEM). The amine moiety of acridine derivative binds strongly to the gold nanoparticles as confirmed by spectroscopic studies. The plasmon band observed for the wine red colloidal gold at 525 nm in the UV-vis spectrum is characteristic of gold nanoparticles. However, with the addition of acridine derivatives the intensity of the absorption band at 525 nm decreases and a new peak emerges at red-end region - a signature of formation of gold-drug complex. The TEM images show the average size of citrate stabilized gold nanoparticles as 15-20 nm, which becomes larger in the presence of various drugs due to aggregation. From the thermogravimetric analyses (TGA) we have measured the number of drug molecules attached per gold nanoparticle (AuNP). These gold nanoparticles are very important as drug delivery vehicles and for clinical applications it is necessary to understand their activity in vivo. The antibacterial efficacy of drugs coated gold nanoparticles were studied against various strains of Gram positive and Gram negative bacteria. Among the four drugs, 9AA-HCl and AO showed antibacterial activity and for both of them the AuNP conjugated drug showed better antibacterial efficacy than the bare drug. Because of the high penetrating power and large surface area of Au(0), a single gold nanoparticle can adsorb multiple drug molecules, hence this total entity acts as a single group against the bacteria.