Silver nanoparticles (AgNPs) with size ranging from 7 to 70 nm were synthesized using ascorbic acid-citrate seed-mediated growth approach at room temperature. The 8 nm silver particles were prepared using gallic acid in alkaline conditions and used as seed to prepare AgNPs. The presence of ascorbic acid and citrate allows the regulation of size and size distribution of the nanoparticles. The increase in free silver ion-to-seed ratio (Ag+/Ag0) resulted in the changes of particle shape from spherical to pseudo-spherical and minor cylindrical shape. Further repetitive seeding approach resulted in the formation of pseudo-spherical particles with higher polydispersity index and minor distributions of tetrahedral particles. Citrate-capped AgNPs were stable and did not agglomerate upon centrifugation. The effect of AgNPs on biofilm reduction was evaluated using static culture on 96 well microtiter plates. Results showed that AgNPs with the smallest average diameter were the most effective in the reduction of P. aeruginosa biofilm colonies, which accounted for 90% of removal. The biofilm removal activities of the nanoparticles were found to be concentration independent particularly for the concentration within the range of 80 to 200 µg/ml.