The ultrasensitive detection of cancer in its earliest stage would greatly help the ensuing treatment process, and therefore various imaging modalities and image-enhancing methods are being developed.[1] In particular, metal oxide nanoparticles prove to be promising contrast agents in magnetic resonance imaging (MRI) for the ultrasensitive detection of cancer, and the principles for enhancing MRI contrast have been deciphered recently.[2] For example, it is advantageous to employ superparamagnetic metal oxide nanoparticles with high magnetization values (emu g À1 ) for improved T 2 image contrast.[3] In addition, clusters of superparamagnetic nanoparticles exhibit greater T 2 contrast abilities than individual nanoparticles.[4] Therefore, the clustering of magnetic nanoparticles with high magnetization values is advantageous because of both improved T 2 contrast and the frugal usage of targeting moieties. For enhanced T 1 contrast, nanoparticles should have numerous high-spin metal ions exposed on the surface for facilitated interactions with the surrounding water molecules. [5,6] This calls for the use of smaller nanoparticles with a high surface-to-volume ratio, but simply using a high number of small nanoparticles is not compatible with the frugal usage of targeting moieties. In the case of large nanoparticles, the non-exposed metal ions in the core cannot contribute to the MRI T 1 contrast; the T 1 -weighted image obtained with metal ions is much poorer than that from conventional ion-based contrast agents.We reasoned that the highest surface area for a nanoparticle of a given diameter would be provided by an urchinlike morphology as shown in Figure 1. As a model system to prove our concept, manganese oxides were investigated that had been previously used as an MRI T 1 contrast agent. This system is particularly interesting because of the easy conversion of MnO to Mn 3 O 4 and the different stabilities of these two manganese oxide phases under physiological conditions. It is envisaged that the MnO nanoparticle trapped in the thin shell of an urchin-shaped stable Mn 3 O 4 phase can be unloaded in the form of Mn II ions to the low-pH sites (< pH 7) in the tumor. While the low pH of tumor cells has been exploited for the fabrication of numerous activatable drug-delivery systems, [7] a nanoparticle-based pH-activatible MRI agent is unprecedented to our knowledge. The combination of the T 1 contrast effect from the empty Mn 3 O 4 urchin shell with a high surface area and the released Mn II ions should make the MnO@Mn 3 O 4 nanourchin a powerful MRI T 1 contrast agent. Herein we report the synthesis of the MnO@Mn 3 O 4 nanourchin through facet-selective etching as well as its successful application as a pH-responsive activatable T 1 contrast agent,

Hollow Mn-doped iron oxide nanocontainers, formed by a novel one-pot synthetic process, fulfill the dual requirements of delivering an effective dose of an anticancer drug to tumor tissue and enabling image-contrast monitoring of the nanocontainer fate through T2 -weighted magnetic resonance imaging, thereby determining the optimal balance between diagnostic and therapeutic moieties in an all-in-one theranostic nanoplatform.

By understanding the structural relationship among three shape-controlled Rh nanostructures, namely, {111} nanotetrahedrons, {111} tetrahedral nanoframes, and <111> skeletal nanotetrapods, we could prepare novel hierarchical dendritic Rh nanostructures with <111> Rh arms as linkers between tetrahedral shaped nanocrystals.

Nanoparticles and their composites hold great promise for advances in bio-, energy-, and environment-related fields. The properties of nanoparticles depend on composition, phase, dimension, and exposed crystal facets, and thus control over these parameters is crucial for nanoparticles to have desired properties. The process of nanoparticle formation is affected by various kinetic and thermodynamic parameters, which are determined by the intricate interplay of precursors, surfactants, and reaction temperature.

The ultrasensitive detection of cancer in its earliest stage would greatly help the ensuing treatment process, and therefore various imaging modalities and image-enhancing methods are being developed. [1] In particular, metal oxide nanoparticles prove to be promising contrast agents in magnetic resonance imaging (MRI) for the ultrasensitive detection of cancer, and the principles for enhancing MRI contrast have been deciphered recently. [2] For example, it is advantageous to employ superparamagnetic metal oxide nanoparticles with high magnetization values (emu g À1 ) for improved T 2 image contrast. [3] In addition, clusters of superparamagnetic nanoparticles exhibit greater T 2 contrast abilities than individual nanoparticles. [4] Therefore, the clustering of magnetic nanoparticles with high magnetization values is advantageous because of both improved T 2 contrast and the frugal usage of targeting moieties. For enhanced T 1 contrast, nanoparticles should have numerous high-spin metal ions exposed on the surface for facilitated interactions with the surrounding water molecules. [5,6] This calls for the use of smaller nanoparticles with a high surface-to-volume ratio, but simply using a high number of small nanoparticles is not compatible with the frugal usage of targeting moieties. In the case of large nanoparticles, the non-exposed metal ions in the core cannot contribute to the MRI T 1 contrast; the T 1weighted image obtained with metal ions is much poorer than that from conventional ion-based contrast agents.We reasoned that the highest surface area for a nanoparticle of a given diameter would be provided by an urchinlike morphology as shown in Figure 1. As a model system to prove our concept, manganese oxides were investigated that had been previously used as an MRI T 1 contrast agent. This system is particularly interesting because of the easy conversion of MnO to Mn 3 O 4 and the different stabilities of these two manganese oxide phases under physiological conditions. It is envisaged that the MnO nanoparticle trapped in the thin shell of an urchin-shaped stable Mn 3 O 4 phase can be unloaded in the form of Mn II ions to the low-pH sites (< pH 7) in the tumor. While the low pH of tumor cells has been exploited for the fabrication of numerous activatable drug-delivery systems, [7] a nanoparticle-based pH-activatible MRI agent is unprecedented to our knowledge. The combination of the T 1 contrast effect from the empty Mn 3 O 4 urchin shell with a high surface area and the released Mn II ions should make the MnO@Mn 3 O 4 nanourchin a powerful MRI T 1 contrast agent. Herein we report the synthesis of the MnO@Mn 3 O 4 nanourchin through facet-selective etching as well as its successful application as a pH-responsive activatable T 1 contrast agent, Figure 1. a) Schematic diagram of a low-surface-area truncated cube and a high-surface-area urchin. b) Representation of the unloading of core MnO content from the urchin-shaped MnO@Mn 3 O 4 nanoparticle at low pH.