2.4 Antibacterial tests
To examine the minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) of different sized
AgNPs, the procedure specified by Ruparelia et al. was followed (ESI, S1†). The effect of AgNPs on bacterial growth
kinetics was measured at 600 nm, as increase in absorbance using a spectrophotometer. The experiment included a positive control (flask containing AgNPs and nutrient media, without inoculum) and a negative control (flask containing inoculum and nutrient media, without AgNPs). The absorbance values for experimental fiasks (containing nutrient media, inoculum and AgNPs) were corrected by deducting the corresponding absorbance values for the positive controls. All the experiments were carried out in triplicate. Disk diffusion tests were done to determine the size-selective bacterial sensitivity towards AgNPs, as marked by their zone of inhibition (ZoI). As discussed by Ruparelia et al., AgNPs impregnated on filter paper disks (5 mm diameter) were placed on an agar plate having uniform bacterial suspension (E. coli. MTCC 443, 104 to 105 CFU ml1). The culture plates were then incubated at 35 C for 24 hours and the ZoI was measured using photographic images of the agar plates having a clear zone.