Synthesis, characterization and biofunctionalization of magnetic gold nanostructured particles Paulina Lloret a , Gloria Longinotti a , Gabriel Ybarra a , Leandro Socolovsky b , Carlos Moina a, * a Instituto Nacional de Tecnologı´a Industrial, San Martı´n, Argentina b Facultad de Ingenierı´a, Universidad de Buenos Aires, Argentina 1. Introduction Nanocrystalline materials have been investigated intensively in the last years, due to their catalytic, optical, electronic, magnetic, and biosensing applications [1–9]. In particular, great efforts have been devoted to obtaining metallic particles with well defined characteristics of size, shape, and structure. So far, several approaches have been developed aiming at the systematic control of crystal size and morphology. The shape-controlled synthesis of particles has been reviewed in Ref. [2] and references therein. The production of highly branched nanoparticles has been reported by several groups [10–16]. However, the controlled preparation of nanostructured particles (NSP) in the submicrometric range with morphological features in the nanoscale remains to be a challenging task. NSP such as nanoflowers, nanourchins and nanostars show potential applications in fields like sensors, biology, catalysis, optics, and surface enhanced Raman spectros- copy (SERS). So far, gold NSP have been obtained mainly deposited onto substrates. Duan et al. [17] reported the fabrication of flowerlike gold nanoparticles electrodeposited onto indium tin oxide as substrates for SERS. Kim et al. [18] combined photoli- thography with electrodeposition to obtain arrays of flowerlike gold nanostructures. On the other hand, synthesis of such nanostructures in solution has proved to be difficult. Guo et al. [19] used a wet chemistry approach to obtain gold nanocorallines with average size of 500 nm, composed of nanorods sized in the 10–100 nm range. Although gold flower-like particles have been grown onto magnetite nanoparticles [20], the controlled production of highly branched NSP with magnetic core has not been yet reported. In this work we present the synthesis, characterization, and chemical modification of magnetic NSP, consisting of a gold urchin-like shell grown onto a magnetic core. The potential application of the NSP as protein carriers for biosensing is shown by electrochemically detecting the horseradish peroxidase enzymatic activity. 2. Experimental 2.1. Preparation of nanostructured particles Magnetite nanoparticles were synthesized by the co-precipita- tion of ferric and ferrous ions. 25 ml of 25% solution of NH 4 OH were added at room temperature to 100 ml of a solution containing 12 g of FeCl 3 and 6 g of FeCl 2 in 0.1% HCl. The precipitate, composed by Fe 3 O 4 , was collected with the aid of a permanent magnet, rinsed with distilled water to eliminate the excess of ferric ion, and dried at 65 8C for an hour. Then, 30 mg of Fe 3 O 4 were added to 80 ml of a solution of toluene containing x ml of oleic acid (Olac) and x ml of oleylamine (Olam), with x = 0.25, 1.25, 2.5 and 5.0, and re- dispersed with ultrasonic agitation during 15 min. A solution of Materials Research Bulletin 48 (2013) 3671–3676 A R T I C L E I N F O Article history: Received 9 January 2013 Received in revised form 14 May 2013 Accepted 16 May 2013 Available online 24 May 2013 Keywords: A. magnetic materials A. nanostructures B. chemical synthesis C. electrochemical measurements A B S T R A C T Magnetic Fe 3 O 4 @Au nanocomposite, nanostructured particles were prepared by depositing gold onto seeds of superparamagnetic iron oxide nanoparticles (SPION). The particles were characterized by SEM, TEM, XRD, visible and near infrared spectroscopy, and magnetic measurements. They were also functionalized and employed as enzymatic carriers for electrochemical biosensing. The nanostructured particles showed an urchin-like, roughly spherical morphology whose surface was covered with nanometric protuberances. The average diameter of the particles could be controlled in the 100–500 nm range by changing the concentration of surfactants (oleylamine and oleic acid) employed in the synthesis. XRD showed a preferential growth of {1 1 1} facets. 3-Mercaptopropionic acid was used to chemically modify the surface of the nanostructured particles and horseradish peroxidase was immobilized onto the gold surface. Attached enzymes showed good activity even after several cycles of magnetic collection, drying, and redispersion. ß 2013 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +54 1174246333; fax: +54 11472463333. E-mail address: moina@inti.gob.ar (C. Moina). Contents lists available at SciVerse ScienceDirect Materials Research Bulletin jo u rn al h om ep age: ww w.els evier.c o m/lo c ate/mat res b u 0025-5408/$ – see front matter ß 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.materresbull.2013.05.066