Multifunctional Fe 3 O 4 /ZnO core-shell nanoparticles for photodynamic therapy Juan.C. Beltran Huarac * , M.S. Tomar * , S.P. Singh ** , Oscar Perales-Perez **, *** , L. Rivera *** and S. Peña *** * Department of Physics, University of Puerto Rico at Mayagüez; Mayagüez-Puerto Rico, juan.beltran1@upr.edu , maharaj.tomar@upr.edu ** Department of Engineering Science & Materials, University of Puerto Rico at Mayagüez; Mayagüez- Puerto Rico, surinder.singh@upr.edu , oscarjuan.perales@upr.edu *** Department of Chemistry, University of Puerto Rico at Mayagüez; Mayagüez-Puerto Rico, luis.rivera100@upr.edu , sandraluengas@yahoo.es ABSTRACT We synthesized Fe 3 O 4 /ZnO core-shell structure as a multifunctional platform for photodynamic therapy (PDT). The magnetic properties of these nanostructures will enable magnetically driven targeting as well delivery of photosensitizer deep in tumor tissues. Reactive oxygen species (ROS) generation capability of ZnO will help to kill cancer cells through oxidative stress. Fe 3 O 4 /ZnO core-shell nanostructures were synthesized via a simple method in aqueous phase. X-ray diffraction (XRD) patterns showed the presence of both, Fe 3 O 4 and ZnO phases that suggests the development of a core-shell. Photoluminescence (PL) measurements displayed the excitonic emission of ZnO, at around 380 nm, in co-existence with a weak and broad defect- related green emission. Energy Dispersive X-ray Spectroscopy (EDS) indicated the presence Zn species on the crystal surface at variable amounts, which were dependent on the shell thickness. The generation of singlet oxygen species under UV irradiation has been verified using DPBF (1,3-diphenylisobenzofuran) as quencher for singlet oxygen. Quantum yield (QY) of singlet oxygen generated by core-shell nanoparticles was found to be 28%, suggesting the potential application of these core–shell nanostructures in PDT. Keywords: magnetite, zinc oxide, heterostructured nanoparticles; singlet oxygen, photoluminescence. 1 INTRODUCTION PDT is an emerging cancer treatment modality that involves the use of a photoactive drug, a photosensitizer (PS) and light. The light interacts with photosensitizer and generates singlet oxygen, responsible for killing of cancer cells selectively [1-2]. The possibility of promoting the singlet oxygen quantum yield by using QDs alone or combined with conventional photo-sensitizers, opens new possibilities for cancer therapy [ 3]. Recent studies on QDs for PDT applications have been centered on CdSe or CdTe and CdSe/ZnS core/shell QDs. The enhanced generation of singlet oxygen from CdSe QDs linked to Pc4 PS has been verified along with the capability of bare CdSe to sensitize molecular oxygen [4]. Derfus et al. also verified the QDs cytotoxicity mediated by UV irradiation [5]. Bakalova’s group has confirmed the potential of CdSe QDs anti-CD conjugates to sensitize leukemia cells to UV irradiation and/or to reinforce the effect of conventional PS trifluoperazine sensitizer [6]. These studies suggested that semiconductor QDs dots and QDs-PS platform will enhance the effectiveness of PDT generation and application in selective destruction of cancer cells. However, these most promising Cd-based QDs structures are considered to be most cytotoxic. Therefore, design and development of biocompatible, non-toxic QDs and their evaluation as direct sensitizers or QD/PS conjugate for PDT in cancer become indispensable. In the present work, we have synthesized multifunctional Fe 3 O 4 /ZnO core-shell nanoparticles and evaluated their capability to generate singlet oxygen. The photochemical activity of Fe 3 O 4 /ZnO nanoparticles has been investigated in presence of 1,3- diphenylisobensofuran (DPBF), a singlet oxygen quencher, in methanol [7]. 2 EXPERIMENT 2.1 Materials Iron (II) chloride tetrahydrate FeCl 3 ∙4H 2 O, Iron (III) chloride hexahydrate, FeCl 3 ∙6H 2 O, sodium hydroxide NaOH, zinc acetate dihydrate Zn(OOCCH 3 ) 2 ∙H 2 O, lithium hydroxide monohydrate LiOH∙H 2 O, zinc nitrate hexahydrate, Zn(NO 3 ) 2 ∙6H 2 O, 1,3-diphenylisobensofuran (DPBF, 97%), Methylene Blue (MB) 99%, Rose Bengal (RB) 95%, nitric acid ACS reagent 70%, hydrochloric acid ACS reagent 37%, and ammonium hydroxide NH 4 OH (14.5 M) were of reagent grade and used without further purification. Acetone and ethanol were of chemical grade. 2.2 Synthesis of Fe 3 O 4 /ZnO core-shell nanoparticles Fe 3 O 4 superparamagnetic nanocores were prepared and treated with sodium citrate according to available methods NSTI-Nanotech 2010, www.nsti.org, ISBN 978-1-4398-3415-2 Vol. 3, 2010 405