Programmable chiral nanocolloids

Nanoparticles promise a variety of application in energy, medicine, and biology. However, most nanoparticlesâ material composition and shape cannot be tuned and so functions have thus far been limited. Moreover they are often also chemically unstable in solution. Therefore, the overall goal of this thesis is to develop nanoparticles whose function and shape can be programmed and that can be corrosion protected, and to then apply these nanoparticles to sensing tasks in complex biological fluids. A special focus of this thesis is chiral nanostructures. A promising technique to address this is physical vapour shadow growth, namely nano glancing angle depo-sition (nanoGLAD). This scheme allows the design of new three-dimensional (3D) hybrid nanoparticles as it permits the control over both the shape and material composition of the nanoparticles. Although this method offers the possibility to grow nanoparticles that are functionally programmed, it has so far not al-lowed the use of many materials that are chemically unstable in solution, which limits the scope of poten-tial applications. This thesis starts with describing the nanoGLAD growth procedure. A first application is the wafer-scale patterning of unconventional nanoshapes, e.g. tri-layer particles, holes, rings, and hollow domes, which are not possible using state of the art 3D nanofabrication methods (chapter 2). Then, in conjunction with atom-ic layer deposition (ALD), this thesis shows how the nanoGLAD scheme can be adapted for the fabrication of â3D core-shell nanoparticles and nanocolloidsâ using unstable and reactive materials. The key concept here is that the core consists of the unstable material which is grown such that the shell contains no voids or defects (chapter 3). Notably, the shapes that can be grown include symmetry-broken chiral nanoparti-cles, which possess unique spectral properties that make them useful for sensing applications. This thesis uses chiral nanocolloids to realise extremely sensitive plasmonic nanosensors and nanocolloids that can also be used as a nanomechanical probes for active nanorheology. By forming a composite of two materials during growth â one that gives a strong plasmonic response and the other to tune the compositeâs dielec-tric function â plasmonic nanoparticles are presented that show record local surface plasmon resonance (LSPR) sensitivities to date (chapter 4). With the same alloying principle a plasmonic and a ferromagnetic material are combined. The resulting âchiral + plasmonic + ferromagneticâ particles can be actuated using a magnetic field and this is used to measure the viscosity of blood plasma in the presence of blood cells. The viscosity of blood serum is an important disease indicator, but the measurement using commercial rheome-ters requires the separation of the blood cells. This is not needed in the nanorheological measurements shown in this thesis (chapter 5).

New Analytical Methods for Size Fractionated, Quantitative, and Element Specific Analysis of Metallic Engineered Nanoparticles in Aerosols and Dispersions

Harald Hagendorfer

The application of engineered nanoparticles (ENP) increased almost exponentially during the last decade. Next to carbon based ENP, metal based ENP are the next most commonly employed. Utilization of such particles for medical applications, remediation of toxic substances, consumer products, new materials, and numerous other fields has been reported already. Despite their extraordinary success and implementation, concerns have been raised about possible negative effects in humans and the environment. Once released, ENP are easily distributed via the atmosphere and the aquatic environment where an exposure to organisms can occur. To understand ENP release, life cycle (fate), and exposure as well as to evaluate their toxicological mechanisms, appropriate, media-specific (aerosols and dispersions) analytical methods are required. First, the development of a new set-up to determine ENP in aerosols is presented. For this purpose online (SMPS) and offline (electrostatic sampling on TEM grids) aerosol particle measurement techniques were combined. The aim was to study the release and fate of metallic ENP from commercial available spray products. Method development and verification was performed employing a well characterized aqueous Ag-NP spray product. The investigations have shown that the method offers the possibility to determine size, and element -specific nanoparticle release. Furthermore information about particle morphology and quantity could be obtained. It was revealed, that the release of nanoparticles strongly depends on the type of spray. Pump sprays did not show to produce airborne ENP in the aerosol, whereas propellant gas sprays released nanoparticles in substantial quantities. The release of nanoparticles was correlated with the droplet size distributions generated from the different spray types. Following method development, the setup was applied to determine ENP release of commercial available sprays, indicated to contain ENP. The obtained data was useful to model the consumer exposure of ENP from such products. Second, a set-up to determine ENP in dispersions was developed. For this purpose an asymmetric flow field flow fractionation (A4F) apparatus was coupled to an UV/Vis, light scattering- and inductively coupled plasma mass spectrometric (ICPMS) detector, simultaneously. In the beginning, method development and systematic investigations of prospects and limitations was performed employing well-characterized Au nanoparticles (Au-NP). The investigation revealed that A4F is a versatile separation technique for metallic ENP. In contrast, size determination with the A4F system, derived from the retention times of nanoparticles in the chromatogram, was erroneous. Unspecific interaction of ENP with the A4F channel membrane led to retention time shifts resulting in biased size information. For this reason, online dynamic light scattering (DLS) was employed and it offered a reliable determination of nanoparticle dimensions. Determination of nanoparticle concentration also proved to be to be problematic. Unspecific loss of nanoparticles in the A4F separation channel led to insufficient recovery prevented direct quantification of nanoparticles. To overcome this problem an alternative method was employed. With ICPMS after ultracentrifugation, quantification of the ionic and particulate -fraction of metallic ENP dispersions was possible. Validation of the set-up was performed with certified Au-NP reference materials obtained from NIST and results showed excellent agreement. Combining both of these new methods provided a comprehensive understanding of the metallic ENP systems. After method development with well defined nanoparticle systems, the set-up was tested for its applicability to "real world" samples. First, the characterization of commercial available, polydisperse, commercial Ag nanoparticle (Ag-NP) products was performed. The new developed set-up allowed obtaining an element specific, mass, and number size distribution. Furthermore, Ag-NP concentrations as well as the toxicological relevant ionic Ag concentration could be determined. Figures of merit compared to transmission electron microscopy (TEM) and batch-DLS results were in good agreement and the new method was advantageous in terms of analysis time and reliability. Furthermore the possibility to characterize SiO2 coated Au nanoparticles (Au@SiO2) was investigated. These particles are employed for Shell-Isolated Nanoparticle Enhanced Raman Spectroscopy (SHINERS). It was shown that in terms of particle size characterization, the method provided excellent data. However, determination of Si concentrations to calculate the shell thickness of such particles was impeded by the poor A4F peak shape as well as the high Si background in ICPMS. In conclusion, both setups show great potential for the characterization of metallic ENP either in aerosols or dispersions, respectively.

EPFL2011

High-aspect ratio three-dimensional photoresin-based microstructures doped with luminescent nanocrystals

Jürgen Brugger, Vahid Fakhfouri

Incorporation of nanoparticles into photostructurable polymer materials enables the engineering of novel, highly integrated micro/nanosystems (MEMS/NEMS) with enhanced intrinsic functional properties. For instance, nanoparticles with (semi)conducting, optical or magnetic properties can be incorporated into polymers in order to convey their inherent functionalities to the final material, which can then be exploited for sensor and actuator applications. The current challenge is two-fold: (a) the incorporation of the functional nanoparticles into the polymer matrix and (b) the maintaining of the structurability of photosensitive polymers by UV lithography. In this paper we present a novel approach to further advance this field by combining luminescent nanocrystals (NCs) of cadmium selenide coated by a shell of zinc sulfide (CdSe@ZnS) with epoxy-based photosensitive resins. This class of material is well-known for polymer MEMS applications due to its superb structurability by UV lithography and mechanical properties. Here, colloidal methods have been used to provide luminescent CdSe@ZnS NCs with tunable size, exhibiting size-dependent optoelectronic properties. The presence of an organic ligand shell makes the NCs soluble in organic solvents and thus enables their processing and incorporation into polymers. The luminescent NCs (4.7 nm) were successfully incorporated in the epoxy-based resin by exploiting their solubility in a suitable common solvent. The NC-doped resin has been spin-coated on a silicon wafer, baked, exposed to UV light through a mask and developed. The same processing was applied to un-doped resin used as reference material. The obtained structures were inspected by means of optical, scanning electron, fluorescent and atomic force microscopy, as well as surface profilemetry. The results confirm the overall UV-structuring capability of the modified polymer. The emission properties of the NCs were demonstrated to be retained upon incorporation in the resin and spin coating. The luminescent properties of the NCs were retained after patterning by UV photolithography, although some aggregation of NCs was observed. The presence of organic ligand shell at the colloidal NC surface shows to be relevant for the subsequent processing of the doped photo-resin. The presented route looks promising for the microfabrication of polymer MEMS with inherent functionalities. Further optimization needs to be implemented also in view of a possible extension to incorporation of different types of colloidal NCs.

2006

Fe3O4 nanoparticles and nanocomposites with potential application in biomedicine and in communication technologies: Nanoparticle aggregation, interaction, and effective magnetic anisotropy

Yves Leterrier, Tommaso Nardi, Marco Sangermano

Magnetite nanoparticles with a size of 5-6 nm with potential impact on biomedicine and information/communication technologies were synthesized by thermal decomposition of Fe(acac)(3) and subsequently coated with a silica shell exploiting a water-in-oil synthetic procedure. The as-produced powders (comprised of either Fe3O4 or Fe3O4@silica nanoparticles) were mixed with a photocurable resin obtaining two magnetic nanocomposites with the same nominal amount of magnetic material. The static magnetic properties of the two nanopowders and the corresponding nanocomposites were measured in the 10 K-300 K temperature range. Magnetic measurements are shown here to be able to give unambiguous information on single-particle properties such as particle size and magnetic anisotropy as well as on nanoparticle aggregation and interparticle interaction. A comparison between the size distribution functions obtained from magnetic measurements and from TEM images shows that figures estimated from properly analyzed magnetic measurements are very close to the actual values. In addition, the present analysis allows us to determine the value of the effective magnetic anisotropy and to estimate the anisotropy contribution from the surface. The Field-cooled/ zero field cooled curves reveal a high degree of particle aggregation in the Fe3O4 nanopowder, which is partially reduced by silica coating and strongly decreased by dissolution in the host polymer. In all considered materials, the nanoparticles are magnetically interacting, the interaction strength being a function of nanoparticle environment and being the lowest in the nanocomposite containing bare, well-separate Fe3O4 particles. All samples behave as interacting superparamagnetic materials instead of ideal superparamagnets and follow the corresponding scaling law. (C) 2014 AIP Publishing LLC.

American Institute of Physics2014