Bacterial resistance to antibiotics is increasing over time. The use of nanomaterial is among the most promising strategies to overcome bacterial resistance. Therefore, nanoparticles (NPs) based treatments have attracted enormous interest because of their excellent antibacterial properties, and limited evidence for resistance. However, not all these NPs are safe in practical applications due to the intrinsic toxicity of the NPs or the released ions. The ideal NP should be highly stable, biocompatible to the mammalian cells yet effective to eradicate wide range of drug resistant bacteria. Gold (Au) is such an ideal material which does not dissociate easily into ions. However, the bulk Au or the AuNPs are not chemically active. In this talk, I shall demonstrate strategies to fabricate antimicrobial AuNPs through precise control of their size down to less than 2 nm. These ultra-small AuNPs are often known as nanoclusters, and exhibits unique molecule like properties such as HOMO-LUMO transition, chirality, magnetism, photoluminescence etc. My talk will cover the structural aspect of these AuNPs, and especially highlight how the surface structure of the ultra-small AuNPs is regulated to trigger their strong antibacterial activities against both Gram negative and Gram positive bacteria.