<p>Triazolium-based ionic liquids (ILs) with varying alkyl chain lengths and counter ions were employed as tunable capping and stabilizing agents for the controlled synthesis of silver nanoparticles (Ag NPs) via NaBH₄ reduction in aqueous medium. The formation of nanoparticles was confirmed by UV–vis spectroscopy, which revealed a progressive redshift of surface plasmon resonance (408–431&#xa0;nm) with the length of the alkyl chain. X-ray diffraction was used to determine the crystalline Ag NPs, and zeta potential values were found to be +57 to +81&#xa0;mV which indicates excellent colloidal stability because of increased surface charge. SEM analysis revealed that there were mostly spherical nanoparticles with a minor aggregation. The Gram-positive (<i>Staphylococcus aureus</i>, MRSA, <i>Bacillus subtilis</i>) and Gram-negative (<i>Escherichia coli</i>, <i>Klebsiella pneumoniae</i>) Gram-negative antimicrobial activity depended significantly on the length of alkyl chain, with the highest activity indicated by the [OMTr123][Br]-Ag NPs. It is important to note that <i>E. coli</i> was resistant to the inhibition, but <i>K. pneumoniae</i> was not. The lower activity against Gram-negative bacteria is explained by the existence of outer membrane barriers, a decreased accessibility of surface-bound IL moieties, and steric/diffusion constraints. These findings underscore the importance of ionic liquid structure in regulating the stability and antibacterial activity of nanoparticles.</p> Graphical abstract <p></p>