For the synthesis of spherical Au nanoparticles (NPs), Turkevich method is very popular. However, in this method the citrate reduction of gold is carried out at high temperature, which is often a draw back. Herein, we describe a near room-temperature synthesis of cetyltrimethylammonium bromide (CTAB) stabilized spherical Au NPs of various sizes in a novel one-step synthesis protocol. We show that, in a growth solution containing CTAB, HAuCl 4 and ascorbic acid, nucleation can be induced by the

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... ddition of AgNO 3 . This allowed us to eliminate the necessity of the presence of seed particles for NP growth. We show that NP size is strongly influenced by the CTAB to Ag molar ratio in the reaction medium. By tuning the CTAB to Ag molar ratio the sizes of the NPs can be tuned from 8 to 64 nm. Owing to the ease of synthesis and superior properties, CTAB stabilized NPs can replace the conventional citrate capped NPs for many applications.