Nanoscale metal-organic frameworks (NMOFs) based on Gd3+ centers and benzenedicarboxylate and benzenetricarboxylate bridging ligands were synthesized using reverse microemulsions and characterized using SEM, PXRD, and TGA. These NMOFs exhibit extraordinarily large R1 and R2 relaxivities because of the presence of up to tens of millions of Gd3+ centers in each nanoparticle and are thus efficient T1 and T2 contrast agents for MRI. The NMOFs can also be made highly luminescent by doping with Eu3+ or Tb3+ centers. The results from this work suggest that NMOFs can be used as potential contrast agents for multimodal imaging.

Pt-containing nanoscale coordination polymer (NCP) particles with the formula of Tb2(DSCP)3(H2O)12 (where DSCP represents disuccinatocisplatin), NCP-1, were precipitated from an aqueous solution of Tb3+ ions and DSCP bridging ligands via the addition of a poor solvent. SEM and TEM images showed that as-synthesized NCP-1 exhibited a spherical morphology with a DLS diameter of 58.3 +/- 11.3 nm. NCP-1 particles were stabilized against rapid dissolution in water by encapsulation in shells of amorphous silica. The resulting silica-coated particles NCP-1' exhibited significantly longer half-lives for DSCP release from the particles (a t1/2 of 9 h for NCP-1' with 7 nm silica coating vs t1/2 of 1 h for as-synthesized NCP-1). In vitro cancer cell cytotoxicity assays with the human colon carcinoma cell line (HT-29) showed that internalized NCP-1' particles readily released the DSCP moieties which were presumably reduced to cytotoxic Pt(II) species to give the Pt-containing NCPs anticancer efficacy superior to the cisplatin standard. The generality of this degradable nanoparticle formulation should allow for the design of NCPs as effective delivery vehicles for a variety of biologically and medically important cargoes such as therapeutic and imaging agents.

Manganese-containing nanoscale metal-organic frameworks (NMOFs) with controllable morphologies were synthesized using reverse-phase microemulsion techniques at room temperature and a surfactant-assisted procedure at 120 degrees C with microwave heating. The nanoparticles were characterized using a variety of methods including SEM, TEM, TGA, PXRD, and ICP-MS. Although the nanoparticles gave a modest longitudinal relaxivity (r1) on a per Mn basis, they provided an efficient vehicle for the delivery of large doses of Mn2+ ions which exhibited very high in vitro and in vivo r1 values and afforded excellent MR contrast enhancement. The particle surface was also modified with a silica shell to allow covalent attachment of a cyclic RGD peptide and an organic fluorophore. The cell-targeting molecules on the Mn NMOFs enhanced their delivery to cancer cells to allow for target-specific MR imaging in vitro. The MR contrast enhancement was also demonstrated in vivo using a mouse model. Such core-shell hybrid nanostructures provide an ideal platform for targeted delivery of other imaging and therapeutic agents to diseased tissues.

Metal-organic frameworks (MOFs) are an interesting class of materials which have been exploited on the bulk scale for a number of applications, including gas adsorption 1 and catalysis. 2 We have recently described a general method for preparing nanoscale MOFs (NMOFs) using reverse microemulsions and have demonstrated their utility as magnetic resonance imaging contrast agents. 3 Owing to their tunable nature, we believe that NMOFs have potential in a variety of other imaging, biosensing, biolabeling, and drug delivery applications. The successful application of NMOFs in these areas will critically depend on our ability to modify and functionalize their surfaces to engender stability, biocompatibility, and specific functionality. To date, however, there have been no reports on the surface modification or functionalization of MOF materials.Coating nanostructures with a silica shell via sol-gel or microemulsion-based methods has enabled the synthesis of an array of core-shell nanocomposites, such as silica-coated superparamagnetic metal oxides, 4 quantum dots, 5 gold, 6 carbon nanotubes, 7 and organic polymers. 8 The silica shell as a surface coating offers several advantages, including enhanced water dispersibility, biocompatibility, and the ability to further functionalize the core-shell nanostructures via the co-condensation of siloxy-derived molecules. Herein, we describe a general method for synthesizing a new class of nanocomposites with an NMOF core and a silica shell. We also demonstrate the ability to control the release of metal constituents from silica-coated NMOFs and to further functionalize them for the luminescence sensing of dipicolinic acid (DPA), which is a major constituent of many pathogenic spore-forming bacteria.NMOFs of the composition Ln(BDC) 1.5 (H 2 O) 2 , 1, where Ln=Eu 3+ , Gd 3+ , or Tb 3+ and BDC=1,4-benzenedicarboxylate, were synthesized using a reverse microemulsion system as previously described (1′ is used to designate Eu-doped Gd(BDC) 1.5 (H 2 O) 2 in Scheme 1). 3 This synthesis allowed for the aspect ratios of nanorods 1 to be reproducibly tuned from 2.5 to 40 by adjusting the water to surfactant molar ratio, W. We then used a strategy developed by van Blaaderen et al. to deposit silica on NMOFs whose surfaces had been modified with polyvinylpyrrolidone (PVP). 9 Treatment of as-synthesized 1 with PVP (MW=40000) in situ for 12 h led to highly dispersible PVP-coated nanorods.TEM showed that PVP-functionalized Ln(BDC) 1.5 (H 2 O) 2 nanoparticles, 2, synthesized at W=5 had a rod-like morphology with dimensions approximately 100 nm in length by 40 nm in width (Figure 1b). The polydispersity of nanoparticles of 2 was low and their particle size wlin@unc.edu. Supporting Information Available: Experimental procedures and 17 figures. This material is available free of charge via the Internet at http://pubs.acs.org. and morphology corresponded well to those of 1. 3 Nanoparticles of 2 with an aspect ratio as high as 40 were also synthesized in high yield at W=15. NIH Public AccessNanoparti...

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The coordination-directed assembly of metal ions and organic bridging ligands has afforded a variety of bulk-scale hybrid materials with promising characteristics for a number of practical applications, such as gas storage and heterogeneous catalysis. Recently, so-called coordination polymers have emerged as a new class of hybrid nanomaterials. Herein, we highlight advances in the syntheses of both amorphous and crystalline nanoscale coordination polymers. We also illustrate how scaling down these materials to the nano-regime has enabled their use in a broad range of applications including catalysis, spin-crossover, templating, biosensing, biomedical imaging, and anticancer drug delivery. These results underscore the exciting opportunities of developing next-generation functional nanomaterials based on molecular components.

Lighting things up: Multifunctional silica nanoparticles containing a luminescent core and a paramagnetic coat are prepared, and their utility as multimodal imaging probes is demonstrated in vitro. Monocyte cells can be labeled with the hybrid nanoparticles with greater than 98 % efficiency and do not experience measurable toxicity even at a high loading of 0.123 mg per 5000 cells.

Multifunctional nanoparticles (MFNPs) have shown great promise as new probes for biomedical imaging and carriers for drug delivery. 1 MFNPs can not only carry large payloads of imaging and/or therapeutic agents, but also be rendered target-specific by conjugation to affinity molecules which have avidity for cell surface markers. Although a number of strategies have been developed to synthesize target-specific MFNPs, most of them rely on covalent attachment of affinity molecules to their surfaces. 2 Since such bioconjugation steps can be tedious, there exists a need for new synthetic strategies toward imaging and/or therapeutic MFNPs that can specifically target diseased cells. Herein we wish to report a noncovalent, electrostatic layer-by-layer (LbL) self-assembly strategy for the synthesis of cancer-specific MFNPs that are efficient contrast agents for multimodal imaging. TEM images indicated alternate deposition of 1 and PSS onto the nanoparticles (Figure 1a-c); the average diameters for NP1A, NP3A, and NP6A are 37±1, 41±1, and 43±2 nm, respectively.