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Li K.,Institute of Materials Research and Engineering of Singapore | Liu B.,Institute of Materials Research and Engineering of Singapore | Liu B.,National University of Singapore
Chemical Society Reviews | Year: 2014

Polymer encapsulated organic nanoparticles have recently attracted increasing attention in the biomedical field because of their unique optical properties, easy fabrication and outstanding performance as imaging and therapeutic agents. Of particular importance is the polymer encapsulated nanoparticles containing conjugated polymers (CP) or fluorogens with aggregation induced emission (AIE) characteristics as the core, which have shown significant advantages in terms of tunable brightness, superb photo- and physical stability, good biocompatibility, potential biodegradability and facile surface functionalization. In this review, we summarize the latest advances in the development of polymer encapsulated CP and AIE fluorogen nanoparticles, including preparation methods, material design and matrix selection, nanoparticle fabrication and surface functionalization for fluorescence and photoacoustic imaging. We also discuss their specific applications in cell labeling, targeted in vitro and in vivo imaging, blood vessel imaging, cell tracing, inflammation monitoring and molecular imaging. We specially focus on strategies to fine-tune the nanoparticle property (e.g. size and fluorescence quantum yield) through precise engineering of the organic cores and careful selection of polymer matrices. The review also highlights the merits and limitations of these nanoparticles as well as strategies used to overcome the limitations. The challenges and perspectives for the future development of polymer encapsulated organic nanoparticles are also discussed. © 2014 the Partner Organisations.


Wang F.,Institute of Materials Research and Engineering of Singapore | Wang F.,National University of Singapore | Liu X.,Institute of Materials Research and Engineering of Singapore | Liu X.,National University of Singapore
Accounts of Chemical Research | Year: 2014

ConspectusLanthanide-doped nanoparticles exhibit unique luminescent properties, including large Stokes shift, sharp emission bandwidth, high resistance to optical blinking, and photobleaching, as well as the unique ability to convert long-wavelength stimulation into short-wavelength emission. These attributes are particularly needed for developing luminescent labels as alternatives to organic fluorophores and quantum dots. In recent years, the well-recognized advantages of upconversion nanocrystals as biomarkers have been manifested in many important applications, such as highly sensitive molecular detection and autofluorescence-free cell imaging. However, their potential in multiplexed detection and multicolor imaging is rarely exploited, largely owing to the research lagging on multicolor tuning of these particles.Lanthanide doping typically involves an insulating host matrix and a trace amount of lanthanide dopants embedded in the host lattice. The luminescence observed from these doped crystalline materials primarily originates from electronic transitions within the [Xe]4fn configuration of the lanthanide dopants. Thus a straightforward approach to tuning the emission is to dope different lanthanide activators in the host lattice. Meanwhile, the host lattice can exert a crystal field around the lanthanide dopants and sometimes may even exchange energy with the dopants. Therefore, the emission can also be modulated by varying the host materials. Recently, the advance in synthetic methods toward high quality core-shell nanocrystals has led to the emergence of new strategies for emission modulation. These strategies rely on precise control over either energy exchange interactions between the dopants or energy transfer involving other optical entities.To provide a set of criteria for future work in this field, we attempt to review general and emerging strategies for tuning emission spectra through lanthanide doping. With significant progress made over the past several years, we now are able to design and fabricate nanoparticles displaying tailorable optical properties. In particular, we show that, by rational control of different combinations of dopants and dopant concentration, a wealth of color output can be generated under single-wavelength excitation. Strikingly, unprecedented single-band emissions can be obtained by careful selection of host matrices. By incorporating a set of lanthanide ions at defined concentrations into different layers of a core-shell structure, the emission spectra of the particles are largely expanded to cover almost the entire visible region, which is hardly accessible by conventional bulk phosphors. Importantly, we demonstrate that an inert-shell coating provides the particles with stable emission against perturbation in surrounding environments, paving the way for their applications in the context of biological networks. © 2014 American Chemical Society.


Liu X.,National University of Singapore | Liu X.,Institute of Materials Research and Engineering of Singapore
Angewandte Chemie - International Edition | Year: 2012

Morphologies Ala carte: A kinetic control strategy has been utilized to fabricate bimetallic nanoparticles. Using cubic Pd nanocrystals as seeds and a syringe pump that enables precise control over precursor injection rate, it is possible to synthesize Pd-Ag bimetallic nanoparticles with tailored shapes (see picture: dimers, eccentric hybrid bars, and core-shell structures) and tunable localized surface plasmon resonances. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Zeng H.C.,National University of Singapore | Zeng H.C.,Institute of Materials Research and Engineering of Singapore
Accounts of Chemical Research | Year: 2013

Despite significant advancements in catalysis research, the prevailing catalyst technology remains largely an art rather than a science. Rapid development in the fields of nanotechnology and materials chemistry in the past few decades, however, provides us with a new capacity to re-examine existing catalyst design and processing methods. In recent years, " nanocatalysts" has become a term often used by the materials chemistry and catalysis community. It refers to heterogeneous catalysts at nanoscale dimensions. Similar to homogeneous catalysts, freestanding (unsupported) nanocatalysts are difficult to separate after use. Because of their small sizes, they are also likely to be cytotoxic and pose a threat to the environment and therefore may not be practical for industrial use. On the other hand, if they are supported on ordinary catalyst carriers, the nanocatalysts would then revert to act as conventional heterogeneous catalysts, since chemists have known active metal clusters or oxide particles in the nanoscale regime long before the nanotechnology era. To resolve this problem, we need new research directions and synthetic strategies.Important advancements in catalysis research now allow chemists to prepare catalytic materials with greater precision. By controlling particle composition, structure, shape, and dimension, researchers can move into the next phase of catalyst development if they can bridge these old and new technologies. In this regard, one way seems to be to integrate active nanostructured catalysts with boundary-defined catalyst supports that are "not-so-nano" in dimension. However, these supports still have available hierarchical pores and cavity spaces. In principle, these devices keep the essence of traditional "catalyst-plus-support" type systems. They also have the advantages of nanoscale engineering, which involves both high level design and integration processes in their fabrication. Besides this, the active components in these devices are small and are easy to integrate into other systems. For these reasons, we refer to the final catalytic devices as integrated nanocatalysts (INCs).In this Account, we describe the current status of nanocatalyst research and introduce the various possible forms of design and types of integration for INC fabrication with increasing compositional and structural complexities. In addition, we discuss present difficulties and urgent issues of this research and propose the integration of the INCs into even more complex "supracatalysts" for future research. © 2012 American Chemical Society.


Regulacio M.D.,Institute of Materials Research and Engineering of Singapore | Han M.-Y.,Institute of Materials Research and Engineering of Singapore | Han M.-Y.,National University of Singapore
Accounts of Chemical Research | Year: 2010

The ability to engineer the band gap energy of semiconductor nanocrystals has led to the development of nanomaterials with many new exciting properties and applications. Band gap engineering has thus proven to be an effective tool in the design of new nanocrystal-based semiconductor devices. As reported in numerous publications over the last three decades, tuning the size of nanocrystalline semiconductors is one way of adjusting the band gap energy. On the other hand, research on band gap engineering via control of nanocrystal composition, which is achieved by adjusting the constituent stoichiometries of alloyed semiconductors, is still in its infancy. In this Account, we summarize recent research on colloidal alloyed semiconductor nanocrystals that exhibit novel composition-tunable properties. Alloying of two semiconductors at the nanometer scale produces materials that display properties distinct not only from the properties of their bulk counterparts but also from those of their parent semiconductors. As a result, alloyed nanocrystals possess additional properties that are composition-dependent aside from the properties that emerge due to quantum confinement effects. For example, although the size-dependent emission wavelength of the widely studied CdSe nanocrystals can be continuously tuned to cover almost the entire visible spectrum, the near-infrared (NIR) region is far outside its spectral range. By contrast, certain alloy compositions of nanocrystalline CdSexTe1-x, an alloy of CdSe and CdTe, can efficiently emit light in the NIR spectral window. These NIR-emitting nanocrystals are potentially useful in several biomedical applications. In addition, highly stable nanocrystals formed by alloying CdSe with ZnSe (i.e., ZnxCd1-xSe) emit blue light with excellent efficiency, a property seldom achieved by the parent binary systems. As a result, these materials can be used in short-wavelength optoelectronic devices. In the future, we foresee new discoveries related to these interesting nanoalloys. In particular, colloidal semiconductor nanoalloys that exhibit composition-dependent magnetic properties have yet to be reported. Further studies of the alloying mechanism are also needed to develop improved synthetic strategies for the preparation of these alloyed nanomaterials. © 2010 American Chemical Society.


Grant
Agency: European Commission | Branch: FP7 | Program: CP | Phase: ICT-2009.8.7 | Award Amount: 9.63M | Year: 2011

AtMol will establish comprehensive process flow for fabricating a molecular chip, i.e. a molecular processing unit comprising a single molecule connected to external mesoscopic electrodes with atomic scale precision and preserving the integrity of the gates down to the atomic level after the encapsulation. Logic functions will be incorporated in a single molecule gate, or performed by a single surface atomic scale circuit, via either a quantum Hamiltonian or a semi-classical design approach. AtMol will explore and demonstrate how the combination of classical and quantum information inside the same atomic scale circuit increases the computing power of the final logic circuit. Atomic scale logic gates will be constructed using atom-by-atom manipulation, on-surface chemistry, and unique UHV transfer printing technology. The AtMol research programme necessitates the state-of-the-art UHV atomic scale interconnection machines comprising, within one integrated UHV system, a surface preparation chamber, a UHV transfer printing device, an LT-UHV-STM (or a UHV-NC-AFM) for atomic scale construction, a FIM atomic scale tip apex fabrication device and a multi-probe system with its companion SEM or optical navigation microscope. Only three of these systems exist worldwide and they are each housed within the laboratories members of the AtMol consortium. These systems will be used to interconnect molecular logic gates one-by-one in a planar atomic scale multi-pad approach on the top, atomically reconstructed, surface of the wafer. For this molecular chip, the back face of the wafer will incorporate nano-to-micro-scale interconnections using nanofabricated vias which pass through the substrate to the top face. The hybrid micro-nano back interconnect approach to be developed in the AtMol project will enable the full packaging of the molecular chip preserving the surface atomic scale precision of the gates.


Roberts A.D.,University of Liverpool | Roberts A.D.,Institute of Materials Research and Engineering of Singapore | Li X.,Institute of Materials Research and Engineering of Singapore | Zhang H.,University of Liverpool
Chemical Society Reviews | Year: 2014

The development of the next generation of advanced lithium-ion batteries (LIBs) requires new & advanced materials and novel fabrication techniques in order to push the boundaries of performance and open up new and exciting markets. Structured carbon materials, with controlled pore features on the micron and nanometer scales, are explored as advanced alternatives to conventional graphite as the active material of the LIB anode. Mesoporous carbon materials, carbon nanotube-based materials, and graphene-based materials have been extensively investigated and reviewed. Morphology control (e.g., colloids, thin films, nanofibrous mats, monoliths) and hierarchical pores (particularly the presence of large pores) exhibit an increasing influence on LIB performance. This tutorial review focuses on the synthetic techniques for preparation of porous carbon spheres and carbon monoliths, including hydrothermal carbonization, emulsion templating, ice templating and new developments in making porous carbons from sustainable biomass and metal-organic framework templating. We begin with a brief introduction to LIBs, defining key parameters and terminology used to assess the performance of anode materials, and then address synthetic techniques for the fabrication of carbon spheres & monoliths and the relevant composites, followed, respectively, by a review of their performance as LIB anode materials. The review is completed with a prospective view on the possible direction of future research in this field. © 2014 The Royal Society of Chemistry.


Zhang S.-Y.,Institute of Materials Research and Engineering of Singapore | Regulacio M.D.,Institute of Materials Research and Engineering of Singapore | Han M.-Y.,Institute of Materials Research and Engineering of Singapore
Chemical Society Reviews | Year: 2014

The ability of nanoscopic materials to self-organize into large-scale assembly structures that exhibit unique collective properties has opened up new and exciting opportunities in the field of nanotechnology. Although earlier work on nanoscale self-assembly has focused on colloidal spherical nanocrystals as building blocks, there has been significant interest in recent years in the self-assembly of colloidal nanocrystals having well-defined facets or anisotropic shapes. In this review, particular attention is drawn to anisotropic one-dimensional (1D) nanocrystals, notably nanorods and nanowires, which can be arranged into a multitude of higher-order assembly structures. Different strategies have been developed to realize self-assembly of colloidal 1D nanocrystals and these are highlighted in the first part of this review. Self-assembly can take place (1) on substrates through evaporation control, external field facilitation and template use; (2) at interfaces, such as the liquid-liquid and the gas-liquid interface; and (3) in solutions via chemical bonding, depletion attraction forces and linker-mediated interactions. The choice of a self-assembly approach is pivotal to achieving the desired assembly configuration with properties that can be exploited for functional device applications. In the subsequent sections, the various assembly structures that have been created through 1D nanocrystal self-assembly are presented. These organized structures are broadly categorized into non-close-packed and close-packed configurations, and are further classified based on the different types of 1D nanocrystal alignment (side-by-side and end-to-end), orientation (horizontal and vertical) and ordering (nematic and smectic), and depending on the dimensionality of the structure (2D and 3D). The conditions under which different types of arrangements are achieved are also discussed. This journal is © the Partner Organisations 2014.


A comparative DFT (IEFPCM/PBE0/DGDZVP) study of the Rh-catalysed, enantioselective 1,4-addition of phenylboronic acid to 2-cyclohexenone with 11 known cyclic, chiral 1,4- and 1,5-diene ligands reveals a common pathway involving a transition state-less binding (EB) of 2-cyclohexenone to a [(diene)Rh-Ph] intermediate in a multitude of orientations leading to carborhodation (CR) via two competing, diastereomeric transition states (TS), which collapse to α-rhodioketones and then by further conformational reorganization to Rh-oxa-π-allyls. The energy difference between CR-TSs determines the enantioselectivity. DFT-predicted energy difference values are in good to excellent agreement with those derived from experimental enantiomeric excess values. Enantioselectivity was shown to be determined by a cooperative action of crossed diene coordination (measured by the angle formed by the two Rh-coordinated CC bonds in the ligand) and steric repulsion of the ligand substituents (e.g., phenyl) and 2-cyclohexenone. The cooperative effect is the strongest in the hitherto unknown 3,7-diphenylbicyclo[3.3.0]octa-2,6-diene, which was predicted to give the highest enantioselectivity of all ligands studied. This journal is © The Royal Society of Chemistry 2013.


Kantchev E.A.B.,Institute of Materials Research and Engineering of Singapore
Chemical Communications | Year: 2011

A density functional theory study of the addition of phenylboronic acid to cyclohexenone catalyzed by chiral 1,4-diene-Rh(i) catalyst reveals that 1,4-addition is thermodynamically preferred. The enthalpy-driven enantioselection occurs during the carborhodation step and not the enone binding step, as previously proposed. The chiral ligand selectively destabilizes the disfavored transition state by making it "more early". © 2011 The Royal Society of Chemistry.

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