Synthesis and characterization of pore size-tunable magnetic mesoporous silica nanoparticles Jixi Zhang a , Xu Li a , Jessica M. Rosenholm a,b , Hong-chen Gu a,⇑ a Nano Biomedical Research Center, Med-X Research Institute, Shanghai Jiao Tong University, 1954 Huashan Road, Shanghai 200030, China b Center for Functional Materials, Department of Physical Chemistry, Abo Akademi University, 3-5 Porthansgatan, Turku FIN-20500, Finland article info Article history: Received 16 December 2010 Accepted 16 May 2011 Available online 23 May 2011 Keywords: Magnetic Mesoporous silica nanoparticles Seeded growth Pore swelling DNA adsorption abstract Magnetic mesoporous silica nanoparticles (M-MSNs) are emerging as one of the most appealing candi- dates for theranostic carriers. Herein, a simple synthesis method of M-MSNs with a single Fe 3 O 4 nano- crystal core and a mesoporous shell with radially aligned pores was elaborated using tetraethyl orthosilicate (TEOS) as silica source, cationic surfactant CTAB as template, and 1,3,5-triisopropylbenzene (TMB)/decane as pore swelling agents. Due to the special localization of TMB during the synthesis pro- cess, the pore size was increased with added TMB amount within a limited range, while further employ- ment of TMB lead to severe particle coalescence and not well-developed pore structure. On the other hand, when a proper amount of decane was jointly incorporated with limited amounts of TMB, effective pore expansion of M-MSNs similar to that of analogous mesoporous silica nanoparticles was realized. The resultant M-MSN materials possessed smaller particle size (about 40–70 nm in diameter), tunable pore sizes (3.8–6.1 nm), high surface areas (700–1100 m 2 /g), and large pore volumes (0.44–1.54 cm 3 /g). We also demonstrate their high potential in conventional DNA loading. Maximum loading capacity of salmon sperm DNA (375 mg/g) was obtained by the use of the M-MSN sample with the largest pore size of 6.1 nm. Ó 2011 Elsevier Inc. All rights reserved. 1. Introduction Multifunctional nanocarriers integrating diagnostic and thera- peutic functions have attracted increasing scientific attention recently [1,2]. The driving force for this trend is the emerging fields of personalized medicine [3,4], molecular imaging [5], and targeted drug delivery [6,7], which can be realized with the aid of promising progress within the field of bionanotechnology and/or nanomedicine. Among the newly explored multifunctional nanocarriers, mag- netic mesoporous silica nanoparticles (M-MSNs) are one of the most potential theranostic platforms [8–10]. M-MSNs not only pos- sess sub-100 nm sizes which meets the requirements of in vivo applications, but also consist of a composite structure enabling syn- ergistic effects through its superparamagnetic nanoparticle core and mesoporous shell structure with short pore channels. In this sense, the magnetic core provides contrast enhancement for MR imaging and can furthermore be magnetically targeted by applying a suitable magnetic field. The mesoporous silica shell can be readily utilized for drug loading, owing to its high surface area, uniform pore size, large amount of available pore volume, along with easily modified silica surface [11,12]. Many recent efforts also include incorporation of more functional components like fluorescent dyes [8,9,13] and cell-receptor moieties [8] into (or onto) the mesopor- ous shell, to impart M-MSNs with optical imaging and tumor tar- geting properties. All the above mentioned attractive properties of M-MSN carri- ers are based on the state-of-the-art synthesis technology progress. Up to now, the liquid-phase seeded growth approach [9,14,15], where pre-existing MNPs are employed as nucleation seeds for the propagation of the mesoporous shell, has become the main M-MSN synthetic process. Hyeon and coworkers first employed cetyltrimethylammonium bromide (CTAB) stabilized single Fe 3 O 4 nanocrystals to synthesize M-MSN with particle sizes of 45– 105 nm [16]. Haynes and coworkers successfully prepared M-MSN with diameters less than 70 nm by using polyvinyl pyrrol- idone (PVP) to improve the phase transfer efficacy of magnetic nanoparticles (MNPs) and avoid interparticle aggregation [13].A critical requirement in the process mentioned above is the in situ transfer of hydrophobic MNPs to an aqueous phase using CTAB. The final size, stability and uniformity of M-MSNs are greatly af- fected by the self-assembly of CTAB/silica mesostructured compos- ites onto CTAB-stabilized MNPs. This seeded growth process is substantially different from the synthesis of pristine mesoporous silica nanoparticles (MSN) in which no seeded growth is taking place [17]. 0021-9797/$ - see front matter Ó 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2011.05.038 ⇑ Corresponding author. Fax: +86 21 6293 2907. E-mail addresses: jixizhang1985@gmail.com (J. Zhang), alxz0907@gmail.com (X. Li), jerosenh@abo.fi (J.M. Rosenholm), hcgu@sjtu.edu.cn (H.-c. Gu). Journal of Colloid and Interface Science 361 (2011) 16–24 Contents lists available at ScienceDirect Journal of Colloid and Interface Science www.elsevier.com/locate/jcis