ORIGINAL PAPER Synthesis of gold nanoparticles under highly oxidizing conditions Tanja Jurkin 1 & Martina Guliš 2 & Goran Dražić 3 & Marijan Gotić 1 Received: 26 October 2015 /Accepted: 22 February 2016 /Published online: 8 March 2016 # Springer International Publishing Switzerland 2016 Abstract Gold nanoparticles (AuNPs) were synthesized in a microemulsion water/Triton X-100/1-pentanol/cyclohexane using various reducing agents. Basically, three microemulsion syntheses of AuNPs were studied: (i) one using a strong chem- ical reducing agent (NaBH 4 ), (ii) another using γ-irradiation under moderately strong reducing/oxidizing conditions, and (iii) yet another under highly oxidizing conditions (with the addition of NaOH aqueous solution). All the three were per- formed at room temperature. When a strong chemical reduc- ing agent NaBH 4 was used in the microemulsion, gold crys- tallites 11.7 nm in size were obtained, as determined on the basis of X-ray powder diffraction line broadening. The γ-irradiation of nitrogen-saturated microemulsion at the acidic pH produced AuNPs about 12 nm in size, which under the isolation by centrifugation aggregated into large preconcentrated AuNPs about 150 nm in size. These AuNPs possess thixotropic properties. The microemulsion stirred at room temperature and at the pH < 7 under oxidizing conditions did not produce gold nanoparticles. Under the identical exper- imental conditions and at the pH > 7 (stronger oxidizing con- ditions), well-dispersed AuNPs 12 nm in size were formed. The microemulsion synthesis of AuNPs in the alkaline range but not at an acidic pH was explained by the oxidation of alcohol groups (–OH) into carbonyl groups (>C=O) due to the catalytic action of hydroxyl ions and gold. In parallel with the catalytic oxidation of alcohol groups in microemulsion, the Au(III) were reduced with the subsequent formation of gold nanoparticles. The synthesis of AuNPs in 1-pentanol by adding the aqueous NaOH solution at room temperature with- out using microemulsions confirmed the role of the base- catalyzed oxidation of alcohols in the formation of AuNPs. Based on the findings in this study, we propose the base- catalyzed alcohol oxidation at room temperature as a new, simple, and versatile synthesis route for obtaining gold nano- particles. The results of this study suggest that the classical approach of using a reducing agent for the synthesis of AuNPs is not a determining factor, since a diametrically opposite ap- proach to the synthesis of AuNPs can be used, namely, stim- ulating the oxidation of the functional organic groups in close proximity to gold ions. Keywords Gold nanoparticles . Microemulsion . Alcohol . Oxidizing conditions . Base catalyzed . Cloud point extraction Introduction Gold nanoparticles (AuNPs) are widely used in analytical chemistry [1, 2], in biomedicine [3, 4], and as catalysts [5–9]. In biomedicine, AuNPs are used as biosensors [10, Electronic supplementary material The online version of this article (doi:10.1007/s13404-016-0179-3) contains supplementary material, which is available to authorized users. * Marijan Gotić gotic@irb.hr Tanja Jurkin tjurkin@irb.hr Martina Guliš martina.gulis@gmail.com Goran Dražić goran.drazic@ki.si 1 Division of Materials Chemistry, Ruđer Bošković Institute, Bijenička 54, Zagreb, Croatia 2 Faculty of Chemical Engineering and Technology, University of Zagreb, Marulićev trg 19, 10000 Zagreb, Croatia 3 Laboratory for Materials Chemistry, National Institute of Chemistry, Hajdrihova 19, SI-1001 Ljubljana, Slovenia Gold Bull (2016) 49:21–33 DOI 10.1007/s13404-016-0179-3