Gold nanoparticles have been used as a probe for the detection of various aminoglycosidic antibiotics like streptomycin, gentamycin and neomycin. The nature of interaction between these drugs and gold nanoparticles has been probed by various analytical techniques like UV-vis, FT-IR, TEM, etc. Such studies can be used for the determination of drugs in drug formulations. Further in vitro antibacterial activities of drugs capped Au nanoparticles (Au@drugs) were investigated against various strains of Gram positive and Gram negative organisms viz. Staphylococcus aureus, Micrococcus luteus, E. Coli and Pseudomonas aeruginosa. Our results suggest that gold nanoparticles could act as an effective drug carrier in drug delivery system. © 2006 Elsevier B.V. All rights reserved.