Published: April 13, 2011 r2011 American Chemical Society 6099 dx.doi.org/10.1021/la104653s | Langmuir 2011, 27, 6099–6106 ARTICLE pubs.acs.org/Langmuir Adsorption and Desorption Behaviors of DNA with Magnetic Mesoporous Silica Nanoparticles Xu Li, Jixi Zhang, and Hongchen Gu* Nano Biomedical Research Center, Med-X Research Institute, Shanghai Jiao Tong University, 1954 Huashan Road, Shanghai, 200030, China b S Supporting Information I. INTRODUCTION After they were first reported by T. Kresge and co-workers in 1992, 1 mesoporous silica materials have been intensively studied from synthesis to applications. 2À4 Among the numerous ex- plored application areas, a drug delivery system based on the mesoporous structure is an emerging area under development recently. 5 This new application was triggered by the success of synthesis of mesoporous silica nanoparticles (MSNs) in the early 2000s. 6,7 Compared to the former irregularly shaped or bulky mesoporous material, the MSN has a uniform and tunable particle size typically below 100 nm while retaining the various features such as the large surface area, the ordered pore structure, and the super high specific pore volume, which may allow well controllable loading and release of therapeutical medicines. 8À10 The nanometer size of MSN makes the particle potentially suitable for mammalian cells' engulfment and systematic admin- istration for in vivo applications. 11 To date, many efforts have been devoted to exploring the possibilities of MSN as carriers for biomedical purposes, including drug delivery, 12À14 enzyme and protein immobilization, 15À17 bioseparation, 18À20 and so on. It is worth noting that the guest molecules used in these current researches have been mostly focused on small molecules 14 and proteins. 16 Not enough attention has been paid to DNA, a key biomolecule, with regard to its ability lodge inside MSN. To explore the possibility of MSN as a gene delivery vehicle, researchers pretreated MSN with amino silane 21 or cationic polymers. 22À24 With amino functionalized surface, the MSN could interact with DNA through electrostatic force. In further cell experiments, 23,24 it was found that the DNAÀMSN complex were efficient in gene transfection. Unfortunately, DNA adsorption only took place on the external surface of MSN in the above-mentioned studies, whereas the surface area inside meso- pores was not utilized. To date, only a small amount of work has been done on DNA adsorption within mesopores. Fujiwara and co-workers 25 used nitrogen sorption to estimate the pore volume of mesoporous materials before and after DNA adsorption and found that the pore volume of mesoporous silica remarkably decreased after DNA adsorption. They suggested this decrease should be owed to the occupancy of mesopores' inner space by DNA molecules. However, for DNA in mesopores, the decrease of pore volume might not be sufficient because it might also be caused by the residual ions in mesopores. Solberg and Landry 26 observed fluorescently labeled DNA within the pores of their mesoporous silica materials through confocal microscopy. This method tried to observe DNA in mesopores directly. Never- theless, the resolution of optical microscopy was limited at the micrometer level, thus making it impossible to get clear photo- graphs of nanomaterials. Gao and co-workers 27 conducted methylation treatment on the external surface of a surfactant- containing mesoporous material, followed by functionalization Received: November 23, 2010 Revised: March 27, 2011 ABSTRACT: The interaction between DNA and mesopores is one of the basic concerns when mesoporous silica nanoparticle (MSN) is used as a DNA carrier. In this work, we have synthesized a type of mesoporous silica nanoparticle that has a Fe 3 O 4 inner core and mesoporous silica shell. This magnetic mesoporous silica nanoparti- cle (denoted as M-MSN) offers us a convenient platform to manip- ulate the DNA adsorption and desorption processes as it can be easily separated from solution by applying a magnetic field. The DNA adsorption behavior is studied as a function of time in chaotropic salt solution. The maximum amount of adsorbed DNA is determined as high as 121.6 mg/g. We have also developed a method to separate the DNA adsorbed onto the external surface and into the mesopores by simply changing temperature windows. The desorption results suggest that, within the whole adsorbed DNA molecules, about 89.5% has been taken up by M-MSN mesopores. Through the dynamic light scattering experiment, we have found that the hydrodynamic size for M-MSN with DNA in its mesopores is higher than the naked M-MSN. Finally, the preliminary result of the adsorption mechanism study suggests that the DNA adsorption into mesopores may generate more intermolecular hydrogen bonds than those formed on the external surface.