Self-assembly of PbS hollow sphere quantum dots via gas–bubble technique for early cancer diagnosis Masoud Mozafari a,b,n , Fathollah Moztarzadeh b , Alexander M. Seifalian c,d , Lobat Tayebi a a Helmerich Advanced Technology Research Center, School of Material Science and Engineering, Oklahoma State University, OK 74106, USA b Biomaterials Group, Faculty of Biomedical Engineering (Center of Excellence), Amirkabir University of Technology, P.O Box 15875-4413, Tehran, Iran c Centre for Nanotechnology & Regenerative Medicine, UCL Division of Surgery & Interventional Science, University College London, London, UK d Royal Free Hampstead NHS Trust Hospital, London, UK article info Available online 30 December 2011 Keywords: Lead sulfide Quantum dot Hollow sphere Gas–liquid interface aggregation mechanism Cancer detection abstract Quantum dots (QDs) with their unique optical properties have attracted widespread interest in cancer diagnosis and therapy. Due to their ability to absorb and emit light very efficiently, lead sulfide (PbS) hollow spheres with nanometer-to-micrometer dimensions having tailored structural, optical, and surface properties represent an important class of QDs that are potentially useful for early cancer detection. In this study, PbS hollow sphere QDs have been successfully synthesized using a template- free and green method. The formation of hollow structures was explained by a gas–liquid interface aggregation mechanism, in which the formation of SO 2 gas bubbles plays a key role. The synthesized samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray analyzer (EDX), photoluminescence (PL) and Fourier transform infrared spectroscopy (FTIR). The results demonstrate that the PbS hollow spheres possess good optical quality with strong luminescence properties, which indicate their capabilities for the simultaneous detection of multiple cancer biomarkers in blood assays and cancer tissue biopsies. & 2011 Elsevier B.V. All rights reserved. 1. Introduction Early screening of cancer is desirable as most tumors are detectable only when they reach to a certain size containing millions of cells already in metastatic stage. Currently employed diagnostic techniques are insufficiently sensitive and specific to detect most types of early-stage cancers. Moreover, these assays are labor intensive, time consuming, expensive and without multiplexing capability. From other point of view, quantum dot (QD) based detection is rapid, easy, cost effective and quick point- of-care screening of cancer markers. In the past few years, QD nanocrystals (NCs) have attracted broad attention since they have represented quantum confinement effects and size-dependent characteristics in contrast with the bulk counterparts [1]. There- fore, shape and size of inorganic NCs are well known to have important influence on their widely varying electrical and optical properties. Nowadays, metal sulfide semiconductor NCs, particu- larly PbS QDs are of great interest because of their wide applica- tions. By carefully designing and controlling of different parameters, it is possible to manipulate the optical and electronic properties of these materials for specific technological applica- tions. In principle, the electronic and optical properties of semi- conductor NCs are tunable by varying their morphology and size. Thus, rational control over the configuration of semiconductors has become a hot topic in recent material research field. Among all semiconductor NCs, PbS is important due to its small direct energy gap (i.e. 0.41 eV at 300 K for bulk PbS) and a large excitation Bohr radius of 18 nm. The band gap can be blue shifted to the spectral region of 0.7–1.5 mm (1.77–0.82 eV) upon lowering the diameter of the PbS NCs below the size of the excitonic Bohr radius, due to quantum confinement effect. This fact makes lead sulfide appropriate for telecommunication requirements and optical switches [2]. In nano and micro-scale morphologies, hollow spheres are particularly important because of their specific structures and potential applications. The synthesis and characterization of such materials, especially of inorganic materials hollow spheres, has aroused research interests lately [3–6]. They show special struc- tures, optical and surface properties with wide potential applica- tions in transportation systems of carriers, photonic crystals, filling agents, catalysts, microreactors and fuel cells [7–11]. Different preparation methods of hollow spheres have been reported, including the templating method using silicon dioxide Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/jlumin Journal of Luminescence 0022-2313/$ - see front matter & 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jlumin.2011.12.054 n Corresponding author at: Helmerich Advanced Technology Research Center, School of Material Science and Engineering, Oklahoma State University, OK 74106, USA. Tel.: þ1 918 594 8634; fax: þ1 270 897 1179. E-mail address: masoud.mozafari@okstate.edu (M. Mozafari). Journal of Luminescence 133 (2013) 188–193