Crystalline lattices are usually responsible to external mechanical pressures, in particular, when the pressures are extremely high (e.g., tens of GPa). In this presentation, two types of nanomaterials, i.e., silver nanoparticles with closely packed face-centered cubic (fcc) lattices and birnessite-type manganese dioxide (MnO₂) nanosheets with layered crystalline structure, will be discussed. Under high pressure, the highly symmetric fcc silver lattices can be distorted into tetragonal lattice, while the high density of stacking faults in the MnO₂ nanosheets can be squeezed out to improve the lattice symmetry. These results highlight the importance of high pressure for creating new crystalline symmetries in nanomaterials.
This work was performed at the Center for Nanoscale Materials, a U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences User Facility under Contract no. DE-AC02-06CH11357. Use of Advanced Photon Source at Argonne National Laboratory was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract no. DE-AC02-06CH11357.

Advanced photonic devices profit from the design of resonant blackbody metamaterials that can efficiently trap light at selected wavelengths (1) or display topological darkness effects that are extremely promising for high accuracy sensing applications (2). So far, the developed metamaterials have been largely based on noble metal plasmonic nanostructures, the optical resonances of which can be finely tailored by design thus allowing a convenient control of the light trapping or sensing performance. Nevertheless, the insensibility of the intrinsic electronic properties of noble metals to external excitations is a severe limitation in the context of the growing demand of switchable metamaterials for all-optical devices.
Thus, a timely research line has been opened to develop nanostructures with switchable resonant optical properties based on phase transitions, solid-liquid for example. Suitable nanostructures should combine a resonant optical response with a low enough melting point. We have observed polaritonic optical resonances in solid bismuth (Bi) nanostructures in the near ultraviolet to near infrared range (3, 4). In addition, Bi has a low melting point (2700C), and a metallic behavior in the liquid state that allows plasmonic effects. Based on these properties, we have demonstrated very recently spectrally-selective thermo-optical switching in bulk metamaterials based on Bi nanostructures (5). In our presentation, we will provide an overview of the exciting polaritonic and plasmonic properties of solid and liquid Bi nanostructures. Then we will show how these nanostructures can be used to build resonant blackbody metamaterials with switchable light trapping and sensing properties.
1 Hagglund C et al, Nano Letters 13, 3352 (2013)
2 Kravets VG et al, Nature Materials 12,304 (2013)
3 Toudert et al., J. Phys. Chem. C 116, 20530 (2012)
4 Toudert, Nanotechnology Rev. 3, 223 (2014)
5 Jiménez de Castro et al., Appl. Phys. Lett. 105, 113102 (2014)

The global economic and social impacts of counterfeiting result in the loss of 600 billion US Dollars annually. The practice infringes on intellectual property and impinges detrimentally on society, especially in the arenas of health, commerce, and finance. A variety of security technologies have already been developed using innovative security printing materials as crucial anti-counterfeiting measures to deter counterfeiters. Although fluorescent dyes, which can be applied easily to different surfaces inexpensively, have been implemented widely to protect high-value merchandise, government documents, and banknotes, these dyes are familiar to counterfeiters. In response, next-generation fluorescent dyes with properties such as multi-color emission, luminescence up-conversion, fluorescent lifetime encoding and decoding, and stimulus-responsive color-tuning have all been suggested as ways to counteract forgery.
Important considerations, when designing fluorescent security dyes, include (i) tunable emission wavelengths, (ii) stimulus-responsive properties, (iii) susceptibility to mimicry, as well as accessibility, compatibility with current printing technologies and cost. Solid-state fluorescent dyes with tunable and stimulus-responsive emission wavelengths remain challenging to design. Most of the current dyes, which exhibit stimulus-induced spectroscopic changes, are crystalline with slow response times and narrow tunable wavelength windows. Here, we describe a distinctive class of amorphous solid-state fluorescent materials that (i) can be printed as aqueous inks, with a modular supramolecular encryption motif which (ii) provides access to broad-spectrum fluorescent color palettes that (iii) are inherently difficult to reverse engineer, and which (iv) respond rapidly to color-changing chemical authentication.
References:
Ke, C.; Smaldone, R. A.; Kikuchi, T.; Li, H.; Davis, A. P.; Stoddart, J. F., Angew. Chem. Int. Ed., 2013,52, 381-387.
Ke, C.; Strutt, N. L.; Li, H.; Hou, X.; Hartlieb, K. J.; McGonigal, P. R.; Ma, Z.; Iehl, J.; Stern, C. L.; Cheng, C.; Zhu, Z.; Vermeulen, N. A.; Meade, T. J.; Botros, Y. Y.; Stoddart, J. F., J. Am. Chem. Soc., 2013,135, 17019-17030.
Hou, X.; Ke, C.; Cheng, C.; Song, N.; Blackburn, A. K.; Sarjeant, A. A.; Botros, Y. Y.; Yang, Y.-W.; Stoddart, J. F., Chem. Commun. 2014,50, 6196-6199.

Hard rod-like colloidal particles are known to form liquid crystal phases if their aspect ratio is sufficiently high. However, with long-ranged repulsive forces added, the effective repulsive interactions between the rods become increasingly less anisotropic, and the rod-like particles can form a new phase in between that of a crystal and a liquid, which has long-ranged positional order, but no (or short-ranged) rotational order. This phase is called a plastic crystal because it is quite soft. Here, we take two colloidal model systems, namely fluorescently labelled silica rods and silica-coated Au nanorods (AuNRs). In addition, an external electric field can be used to manipulate the rotation of the rods in such systems. Studying the phase behavior and how to manipulate the 3D phases is not only interesting from a fundamental point of view but also important for photonic applications.
Recently, we developed a new model system of micrometer-sized fluorescent silica rods [1] that can be dispersed in the index-matching solvent cyclohexylchloride (CHC), which provides the opportunity to study the above mentioned behavior in real space and real time by confocal microscopy [2]. We found that such silica rods can indeed form the interesting plastic crystal phase in low dielectric media. The 3D lattice on which the rods rotate was found to have a body-centered-cubic (BCC) symmetry. In addition we studied how the phase behavior can be controlled by the application of an external electric field. A transition between a plastic crystal and a full BCC crystal was found, by alternatively switching the electric field on and off.
The second model system consists of AuNRs, which are known to have two separate surface plasmonic resonances, the transverse (TSPR) and longitudinal resonance (LSPR). The TSPR is in the visible wavelength between 500 nm and 550 nm, while the LSPR varies from visible (600 nm) to near IR (>1200 nm), depending on the AuNRs aspect ratio. The AuNRs system therefore has the possibility to realize stronger photonic switching properties. To induce a long-ranged repulsion, the AuNRs were first coated with a shell of silica and grafted with C18 alkane chains and then dispersed in CHC. Similarly to the silica rod system, a plastic crystal phase was also found, with BCC-like positional order. Here fluorescent labelling was not necessary, due to the strong scattering of AuNRs. The alignment under electric field is not fully realized at this stage due to the low aspect ratio of AuNRs after the silica coating. However, preliminary works on particles with a thinner coating are very promising.
[1] A. Kuijk, A. van Blaaderen, and A. Imhof, Synthesis of Monodisperse, Rodlike Silica Colloids with Tunable Aspect Ratio, J. Am. Chem. Soc., 2011, 133, 2346.
[2] B. Liu, T. H. Besseling, M. Hermes, A. F. Demirörs, A. Imhof, and A. van Blaaderen, Switching Plastic Crystals of Colloidal Rods with Electric Fields, Nat. Commun., 2014, 5, 3092.

Fundamental understanding of ligand-receptor interactions is key to the development of effective nanomedicines for early diagnosis and therapy. However, it remains highly challenging to image such interactions in real time due to complexity of native physiological environment. To address this challenge, we have recently developed a class of luminescent plasmonic noble metal nanoparticles by reducing their crystallite size down to electron Fermi wave length through a template-directed growth method. The obtained polycrystal metal nanoparticles exhibit strong surface plasmon absorption, Raman enhancements and robust luminescence. After conjugating a targeting ligand, c-RGD peptide, to the nanoparticles, they can specifically target integrin receptors on U87-MG brain cancers. More importantly, Raman signals became strongly dependent of binding of c-RGD to integrin even in the presence of serum proteins. With these unique optical properties, luminescent plasmonic metal nanoparticles can serve as single-particle sensors for tracking and chemical imaging of ligand-receptor interactions in the real time inside live cells.

Silicon-based photodetectors have been widely used in our daily life, such as digital cameras. Compared to the other semiconductors (e.g., Ge, InGaAs), Si has been widely used due to the cost and easy fabrication process. However, Si has native limitations, such as a poor optoelectronic efficiency at near-infrared (NIR) region due to its band gap energy (ca. 1.12 eV). Thus, few studies focused on developing Si-based NIR photodetectors. Besides, thanks to the localized surface plasmon resonant (LSPR) characteristic of metal nanoparticles (gold, silver), metal nanoparticles doped polymer has widely been investigated. One of the amazing features is the laser-induced heating of the polymer/nanoparticles composites. However, to our best knowledge, no researches focused on light-heating particles by supplying broadband light sources, especially for NIR region.
Herein, we successfully fabricated the silk thin films containing silver nanoparticles (AgNPs) or hollow gold nanoparticles (HGNs), and utilized their ultra-high broadband absorption to develop a novel Si-based NIR photodetector. Firstly, we systematically investigated the optical behaviors of the composite thin films from 350 to 2000 nm with adjusting the particle content embedded in the matrix. Note that the particles could be homogeneously distributed in the matrix (typically, 0-65 wt%) due to the high water solubility of silk. At low metal content, the composite films show an extinctive absorption peak within the visible region corresponding to their LSPR peak in aqueous solutions (414 nm for AgNPs and 803 nm for HGNs). Then, raising the metal content could effectively increase the LSPR absorption due to providing more absorbers. Surprisingly, the absorption at non-LSPR regions also significantly increased. Therefore, we could easily obtain a composite film with ultrahigh broadband absorption (>85% from 350 to 2000 nm). Next, we examined their photoheating behaviors under the illumination of white light sources, such as LEDs and Halogen lamps. We found that the white light source could efficiently induce a photoheating of the plasmonic particles and the final temperature of the composite film could reach >150#730;C. Finally, we integrated the silk/metal nanoparticle composite with a Si-based p-n junction device which is sensitive to temperature. Under a white-light illumination, the light-induced heat can be transferred to the device and can accordingly change the electrical responses of the device, such as the leakage current and the shift of forward bias voltage. Utilizing the high broadband absorption of the composite, especially at NIR region, an innovative silicon-based NIR photodetector can be developed by integrating the photoheating nanocomposite films. The detailed optical, photothermal, and electrical results will be reported in the conference.

In situ detection of premature fracture or crack propagation represents a major challenge in materials failure analysis and would be beneficial for a variety of structural and biological materials applications. Ideally, one would be able to monitor the state of local mechanical properties in real time and with nanoscale spatial precision. Tetrapod quantum dots (tQDs) are an appealing platform for this application as they are three-dimensional, addressable via visible light excitation, and have been shown to exhibit a fluorescence response to mechanical deformation that manifests as a bandgap blueshift under compression and redshift under tension. Interestingly, when incorporated into polymer fibers, tQDs have been limited by only being sensitive to local tension. Here we demonstrate that tQDs can be used as a sensor of compression in films of structural block copolymers, greatly expanding their utility as a pre-fracture diagnostic tool since failure of parts often occurs under compression in the field.
We cast tQD-polymer solutions into bulk films. A fluorescence microscope was used to characterize the stress response. The blue-shifting response has 4 times higher strain (4.5 ± 1.83 meV/strain) and 1000 times higher stress (8.642 ± 3.736 meV/MPa) sensitivity than previous tQD fiber sensors, due to the triaxial stress state in films causing greater stress transfer, and the stronger polymer-nanoparticle interface studied here. We saw excellent stress-strain curve matching between optical and mechanical tests done simultaneously. Uniquely, we find that the full width at half maximum (FWHM) of the spectra decreases in a manner following the stress-strain curve. Also, the FWHM sensitivities, 39.3+-21.5 meV/MPa and -313.02+-148.7 meV/strain, are far higher than previous tQD sensors. The sensor is recyclable with no response change after numerous cycles. The film fabrication is scalable to industrial processing. The tQD is the only nanoparticle able to sense compression, tension, and stress relaxation.
Simulations of tQDs in various stress states reveal that the blue-shifting is due to compression of the tQDs under tension. Thus, this work shows that through microstructural engineering to create local compressive environments, tQDs are capable of sensing local compression in polymers. Furthermore, the tQDs reveal that polymer-nanoparticle interfaces can be under compression during tensile deformation, and that microstructural changes can switch polymer-nanoparticle interface stress from tensile to compressive even under bulk tension. Stress transfer to the nanoparticle has been shown to be far greater under compression. Thus, this result paves paths for engineering of polymer nanocomposites with vastly enhanced mechanical properties.
Using tQDs, stress-sensing is possible in a variety of materials for coatings which herald premature fracture. Applications include detection of premature crack propagation in anti-abrasion coatings and in airframes.

Membranes of organically interlinked gold nanoparticles represent a novel type of functional, nanostructured material exhibiting unique optical and electronic characteristics, which can be tailored by the choice of appropriate crosslinker molecules and particle sizes. During the last two decades these composites received considerable attention, especially due to their potential applications as resistive sensors for gases, chemical vapors^[1,2] or strain^[3] arising from their inherent charge transport mechanisms.
Recently, our group presented a facile route for the time-efficient fabrication of alkanedithiol-interlinked gold nanoparticle membranes on glass substrates based on layer-by-layer spin coating. Furthermore, it was demonstrated that the as-deposited nanometer thin membranes could be lifted-off their initial substrates and transferred to 3d microstructures, rendering the membranes freestanding.^[4] Placement on different microstructures enables various applications of the membranes as novel functional materials for sensors or actuators in micro- and nanoelectromechanical systems (MEMS/NEMS).
Here, we present the current focus of our research, which is the investigation of mechanical and electromechanical properties, as well as potential electromechanical applications of such freestanding alkanedithiol-interlinked gold nanoparticle composites. Recently, a bulge test method was applied for probing the mechanical properties of 1,9-nonanedithiol interlinked gold nanoparticle membranes. In this study, freestanding sections of the latter were deposited on apertures and nitrogen overpressures were applied. The resulting bulges' heights were monitored using atomic force microscopy. From the acquired data, elastic and viscoelastic characteristics of the membrane material were extracted.^[5] We now demonstrate the tunability of the elastic stiffness of the materials by choosing different crosslinker molecules accompanied by changes of the materials' optical and charge transport characteristics. In addition, we are the first to demonstrate the incorporation of these elastic, conductive composite membranes as functional components in electrostatic actuators.
[1] F. J. Ibañez, F. P. Zamborini, Small2012, 8, 174.
[2] N. Olichwer, E. W. Leib, A. H. Halfar, A. Petrov, T. Vossmeyer, ACS Appl. Mater. Interfaces2012, 4, 6151.
[3] M. Segev-Bar, H. Haick, ACS Nano2013, 7, 8366.
[4] H. Schlicke, J. H. Schröder, M. Trebbin, A. Petrov, M. Ijeh, H. Weller, T. Vossmeyer, Nanotechnology2011, 22, 305303.
[5] H. Schlicke, E. W. Leib, A. Petrov, J. H. Schröder, T. Vossmeyer, J. Phys. Chem. C2014, 118, 4386.

Tetrapod nanocrystal geometry is sterically demanding, while the core and the arms can possess the quantum confinement effect allowing optical properties tuning. Recent advances in nanoparticle synthesis allow composition of different materials in the tetrapod quantum dots (tQD), particularly, the core of the tQD can be made of CdSe and the arms can be grown as CdS. The arms can transfer mechanical stress to the quantum confined core and the core structural deformation influences its electronic levels. This work presents systematic large scale ab initio investigation of the optical response on different kinds of deformations in CdSe/CdS tQD. We provide specific conditions under which tQD show red or blue shift in the fluorescent spectra that can be used for local stress-sensing.

Shape memory materials (SMMs) are characterized by the ability to recover their original shape from a significant and quasi-plastic deformation when a particular stimulus is applied. In this study, some reduced graphene oxide (rGO) compounds are shown to have shape memory effect (SME) and shape change effect (SCE) via first-principles density functional theory calculations. We find that some of the rGO crystal structures intrinsically have two stable phases/states. Applying an electric field perpendicular to the basal plane of the stable rGO phase leads to a huge plastic in-plane contraction deformation of 15% as a result of phase transformation from the stable to the metastable phase, whereas a mechanical force in parallel to the basal plane can revert the metastable rGO to its original shape (the stable phase/state), completing a whole shape memory cycle. In addition, a reversible elastic SCE deformation in excess of 5% is observed in some of the rGO crystals. It is found that the SME/SCE behaviour primarily depends on the oxygen concentration in the rGO compounds. These rGO could be the thinnest SME and SCE materials ever reported, which might find huge application potentials as micro/nano-actuators in the micro/nanoelectromechanical systems.

Photocatalytic activity of Portland cement pastes added with nanoparticles of titanium
oxynitride (TiO_2-xN_x), previously synthesized by nitriding nano TiO2 powders was studied.
Adding different percentages of TiO_2-xN_x (0.5%, 1%, 3%, 5%) to cement samples
degradation of NO and Rhodamine B were evaluated, resulting in a notable reduction of
these even low substitution levels using visible light (lambda; #707; 380 nm) as a source of light
radiation for activating the catalyst. The effect of cure time (65 hours and 28 days), the
porosity of the cement paste (water/cement ratio of 0.5 and 1.0) and its hydration products is also
considered in the yield of nanoparticles Titanium oxynitride (TiO_2-xN_x) to be supported in
the cementitious matrix.

Metal nanoparticles with well-defined structural characteristics serve as an important tool to probe the nature of heterogeneous catalysis. To date, researchers have uncovered many important factors governing the catalytic performance of nanoparticle catalysts, including composition, shape, size, surface/interface effects and so on. Despite these remarkable advances, it remains largely underexplored to apply the ripping nanotechnology to organic reactions, so as to improve the reactivity and selectivity of known reactions, and perhaps more importantly to enable organic reactions that are not readily accessible by homogeneous catalysis. In the first part of this talk we will introduce our new synthetic methods for various well-defined nanoparticles. In the second part, we will discuss how we exploited these syntheses towards obtaining catalysts with new activity and/or improved selectivity in a range of organic transformations [1-5].
References
1. Wu, Y. E.; Li, Y. D.; et al. J. Am. Chem. Soc. 2014, In Press.
2. Duan, H. H.; Li, Y. D.; et al. Nature Commun. 2014, 5, 3093.
3. Li, L. L.; Li, Y. D.; et al. Angew. Chem. Int. Ed. 2013, 52, 11049.
4. Wu, Y. E.; Li, Y. D.; et al. J. Am. Chem. Soc. 2013, 135, 12220.
5. Wu, Y. E.; Li, Y. D.; et al. Angew. Chem. Int. Ed. 2012, 51, 12524.

Inorganic nanoparticle/organic hybrid materials attract increasing attentions because of their beneficial properties of each phase. In situ formation of functional nanoparticles (NPs) is one of the suitable methods for the synthesis of NP-based hybrid materials. The authors reported the syntheses and properties of ferrite nanoparticle (NP)/organic hybrids from metal-organics [1,2]. This paper describes the one-pot synthesis of magneto-responsive nanomaterials via the in situ process. Rod-like assembled magnetite (Fe₃O₄) NPs were successfully synthesized in a one-pot process using a polysiloxane template derived from a dialkoxysilane. The assembly was constructed using the thiol-ene click reaction between thiol groups on the polysiloxane chain and allyl groups on Fe₃O₄ NPs. The thiol-containing polysiloxane chain and the allyl-containing Fe₃O₄ NPs were synthesized by the hydrolysis-condensation of dialkoxysilane derivative and iron (III) allylacetylacetonate, respectively. The hybrid was analyzed by FT-IR, DTA-TG, powder XRD, TEM-EDX, VSM, and magnetorheometer. Fe₃O₄ NPs of around 5 nm were uniformly dispersed on the siloxane rods, and exhibited neither remanent magnetization nor coercivity. The EDX analysis supported the uniform dispersion of Si, and S on the siloxane rods. A fluid containing a dispersion of rod-like assembled Fe₃O₄ NPs showed yield stress even without the application of an external magnetic field, whereas spherical Fe₃O₄ NPs exhibited no yield stress. The rod-like assembled Fe₃O₄ NPs on anisotropic siloxane clearly exhibited typical magneto-rheological behavior. The rod-like assembly of Fe₃O₄ NPs resulted in more marked magneto-rheological behavior than the spherical Fe₃O₄ NPs.
1. K. Hayashi, W. Sakamoto, and T. Yogo, J .Mag. Mag. Mater., 321, 450 (2009).
2. T. Hosoya, W. Sakamoto, and T. Yogo, J.Mater. Sci.49, 5093 (2014).

Hybrid nanoarchitectures are among the most promising nanotechnology-enabled materials for biomedical applications. Interfacing of nanoparticles with external stimuli-activated materials gives rise to the structures with unique multiple functionality. Superparamagnetic iron oxide nanoparticles particles SPION are widely employed in the biology and in developing of advanced medical technologies. Polymeric micelles offer the advantage of multifunctional carriers which can serve as delivery vehicles carrying nanoparticles, hydrophobic chemotherapeutics and other functional materials and molecules. Stimuli-responsive polymers are especially attractive since their properties can be modulated in a controlled manner. We demonstrate that temperature-responsive magnetic nanomicelles can serve as thermal energy and cargo carriers with controlled drug release functionality [1, 2]. We investigate the interaction between the hybrid magnetic nanomicelles engineered for controlled payload delivery with various biological models, including cell and animal. The distribution of a platinum complex on subcellular level is visualized using hard X-ray fluorescence microscopy with unprecedented level of detail at sub-100 nm spatial resolution. By employing the magnetic functionality of the micelles and additionally loading them with a near infrared fluorescent dye, we magnetically target them to a tumor site in a live animal xenografted model which allows to visualize their biodistribution in vivo . [1] D-H. Kim, E. A. Vitol, J. Liu, S. Balasubramanian, D. J. Gosztola, E. E. W. Cohen, V. Novosad, E. A. Rozhkova, Stimuli-Responsive Magnetic Nanomicelles as Multifunctional Heat and Cargo Delivery Vehicles, Langmuir, 29, 7425minus;7432 (2013)
[2] E. A. Vitol , E. A. Rozhkova , V. Rose , B. D. Stripe , N. R. Young , E. E. W. Cohen , L. Leoni, V. Novosad, Efficient Cisplatin Pro-Drug Delivery Visualized with Sub-100 nm Resolution: Interfacing Engineered Thermosensitive Magnetomicelles With a Living System, Adv. Mater. Interfaces, 1400182 (2014)

supramolecular self-assemblies, which are often formed as a result of spontaneous process of inherently disordered molecular units into stable ordered structures, are ubiquitous in nature. the nature of the supramolecular assemblies and the essence for their formation is on the basis of noncovalent bonding, such as hydrogen bonds or electrostatic interactions. aggregations, such as micelles, nanofibers, nanoribbon, nanotube and thin films, are the examples that are made use of this concept. the aggregations are found very promising in the field of sensing, drug delivery, and diagnostics, which have been attracted to many researchers in biomedicine.
in this work, azobenzene (az)-containing amphiphilic phosphates with various structures (x-az-y-6-pc) were successfully systhesized. then, supramolecular assemblies as fibers and vesicles formed from spontaneous self-assembly of azobenzene-containing amphiphilic phosphates aqueous solution were explored. combination of ch3o-az-o-6-pc and o2n-az-n(ch3)-6-pc in water led to aggregation of fibers, and combination of ch3o-az-o-6-pc and o2n-Az-o-6-pc in water led to aggregation of vesicles in the progress of electrostatic interaction. uv and visible light were carried out to study their light-stimulus-responsive behavior. the irreversible disassembly of fibers occurred upon uv light, while the reversible disassembly and reassembly of vesicles could be induced by uv and visible light. furthermore, the changes of the morphology from fibers to vesicles were found to be facilitated by adding thf. the size of the vesicles was also demonstrated to be able to control in the range of nano-scale. finally, the release behavior of calcein within the vesicle lumen was studied upon uv light, giving a release yield 89%.

Magnetic nanoparticles have been extensively investigated over the last decade for magnetic separation, controlled drug release, as MRI contrast agents and MPI tracers, as well as for magnetic hyperthermia. Here, we report on the fabrication of a novel magnetic polymer nanocomposite material comprised of iron oxide nanoparticles embedded in ultra-high molecular weight polyethylene (UHMWPE), which exhibits superparamagnetic behavior and has the ability to induce localized heating upon excitation with an alternating-current (AC) magnetic field. The magnetic polymer nanocomposite is chemically stable in both aqueous and organic solvents, in contrast to free standing iron oxide nanoparticles that can undergo degradation in solution. Moreover, since the iron oxide nanoparticles are immobilized in the UHMWPE matrix, we can decouple the effects of Brownian relaxation in the AC magnetic field- triggered heat generation process. Besides providing a good platform for the study of magnetic hyperthermia in nanoparticle immobilizing matrices, these magnetic polymer nanocomposites have great potential for biomedical applications due to their biocompatible nature.

Hybrid composites, which made from two or more constituent materials with significantly different physical or chemical properties, take many advantages of each substance. Hexagonal boron nitrides (h-BN) have been attracted great interests as promising materials for advanced electronic devices due to their high thermal conductivity and electrical insulation. In particular, the h-BN exhibits anisotropic characters, where its thermal conductivity is much higher within the basal planes than perpendicular to them. However, a development of the practicable technologies is still making slow progress due to a lack of ways for deriving a maximized device performance from anisotropic properties of the h-BN. In this study, we fabricated iron oxide (Fe₃O₄)-coated h-BN platelets to operate under a magnetic field. Fe₃O₄ nanoparticles (NPs) were synthesized on h-BN surfaces by co-precipitation of Fe³⁺ and Fe²⁺ with a base. Magnetic properties of Fe₃O₄-coated h-BN platelets were controlled with feeding amounts of iron sources. The Fe₃O₄-coated h-BN platelets were aligned either horizontally or vertically to the film plane within the polymer matrix, depending on the direction of magnetic flux with high anisotropy. Fe₃O₄-coated h-BN/epoxy composites exhibited exceptional performance in terms of in-plane thermal conductivity. We believe that these Fe₃O₄-coated h-BN platelets can be potentially used for electronic applications such as semiconductors, chip package substrates and printed circuit boards because of its excellent dielectric and thermal properties.

Manipulation of droplet is of significant interest for a broad range of applications from lab on a chip to bioinspired functional surfaces. To control and actuate droplet, micro- or nanopatterned surfaces have been suggested as a passive approach in which unique structural features or chemical gradients enable liquid wetting and spreading into specific directions. While these approaches allow for a control over liquid wetting and spreading without external power sources, they are typically slow and not reversible. A set of active droplet manipulation techniques have also been proposed, which include electrowetting, dielectrophoresis, surface acoustic waves and thermocapillary force. As compared with the passive techniques, the active ones provide an enhanced controllability over a droplet position and motion in a fast and reliable manner. Especially, the electrowetting method has demonstrates its versatility in microfluidic systems as it enables precise manipulation of discrete droplets through programmed path. Nonetheless, the electrowetting platform requires formation of electrodes and external power source for the manipulation of liquid droplet, which limits the scalability and applicability of the technique.
To this end, magnetically actuating surfaces with micro- or nanoscale structures have a great potential to be used for the active manipulation of droplet because of their reversible and instantaneous structural tunability in response to remote and non-intrusive magnetic field. However, previous droplet manipulation approaches based on the magnetic force are mostly limited to the transition of wetting state without the ability to control the position and motion of discrete droplet. Although studies of the positional control of droplet has been reported, they added magnetic nanoparticles into the droplet for the magnetic control, which significantly limits the broad applications of the techniques.
Here, we present a simple yet novel approach to control the motion of discrete droplet on a magnetic responsive flexbile film that has reversibly actuating hierarchical structures on the surface. In this approach, a discrete droplet of pure water can be fastly manipulated into arbitrary target locations on the flexible film only with a permanat magnet, eliminating the needs for predefined electrodes or magnetic particle mixing with a droplet. The dynamically actuated hierarchical pillar arrays on the film are formed by moldess self-assembly of mixture solution of uncurd PDMS and magnetic particles under a magnetic field. The resulting magnetic responsvie film shows reliable actuating capabilities with immediate field-responses and maximum tilting angles of ~90°. Furthermore, the magnetic responsive surfaces exhibits superhydrophobic properties regardless of tilting angles of the structures.

Recently our group has been focused on medical applications of various uniform-sized nanoparticles. Using 3 nm-sized iron oxide nanoparticles, new non-toxic MRI contrast agent was realized for high resolution MRI of blood vessels down to 0.2 mm. We fabricated tumor pH-sensitive magnetic nanogrenades composed of self-assembled iron oxide nanoparticles and pH-responsive ligands for theranostic application, enabling the visualization of small tumors of < 3 mm via pH-responsive T1 MRI and fluorescence imaging and superior photodynamic therapeutic efficacy in highly drug-resistant heterogeneous tumors. We synthesized tumor pH-sensitive nanoformulated triptolide coated with folate targeting ligand to treat hepatocellular carcinoma (HCC), which has one of the worst prognosis for survival as it is poorly responsive to both conventional chemotherapy and mechanism directed therapy.

Magnetic nanoparticles have shown great potential in nanomedicine, including as contrast agents for magnetic resonance imaging (MRI), heat flux generation for magnetic hyperthermia, and cell-based therapy monitoring. Specific targeting is one of the critical steps to realize all these potential applications. In this presentation we report a facile and linker-free method for the conjugation of anti-GD2 antibodies to iron oxide nanoparticle surfaces. The antibody conjugated nanoparticles exhibited highly selective targeting on GD2-positive neuroblastoma cells. Most importantly, the antibody conjugated nanoparticles were capable of transporting from cell membranes into cytosols, providing a promising platform to load the cancer-curing drug on and perform targeted therapy.

Magnetic polymer networks are a new class of soft polymer materials with properties modulated by magnetic field leading to emerging applications. In this context we elaborated new magnetic sensitive nanocomposite biopolymer-based networks by introducing functionalized magnetic nanoparticles in uncrosslinked aqueous solutions of sodium alginate. Magnetic nanoparticles of maghemite have been synthesized by the polyol process and further functionalized with dopamine and 3-aminopropyl-triethoxysilane bearing NH2 functional groups and able to bind the nanoparticles. IR spectroscopy con#64257;rmed the grafting, whereas X-ray di#64256;raction and transmission electron microscopy did not show either structural or microstructural change on the iron oxide particles. 57Fe Mo#776;ssbauer spectrometry allowed, giving a quantitative assessment of the bonding preferences of dopamine on the iron oxide surfaces, the π-donor character of this ligand to be experimentally evidenced for the #64257;rst time [1]. These results are supplemented by ab initio modelling.
The development of a new original device allowed the measurements of mechanical properties under continuous magnetic field. A significant and reversible enhancement of viscoelastic moduli and viscosity at low shear rate has been clearly evidenced [2] and could be explained by intramolecular electrostatic interactions between the positively charged NH3+ groups present at the surface of the magnetic nanoparticles and the negatively charged carboxylate groups (COO-) of sodium alginate chains. This assumption is supported by microscopic observation showing magnetic-induced structures in the nanocomposite materials. Perspectives of the work are discussed.
[1] J. Fouineau, K. Brymora, L. Ourry, F. Mammeri, N. Yaacoub, F. Calvayrac, S. Ammar-Merah, J.-M. Greneche. Synthesis, Mo#776;ssbauer Characterization, and Ab Initio Modeling of Iron Oxide Nanoparticles of Medical Interest Functionalized by Dopamine. J. Phys. Chem. C (2013) 117, 14295.
[2] C. Galindo-Gonzalez, S. Gantz, L. Ourry, F. Mammeri, S. Ammar-Merah, A. Ponton. Elaboration and rheological investigation of magnetic sensitive nanocomposite biopolymer networks, Macromol (2014) 47, 3136.

In this study we fabricated a novel class of magnetic polymer composite materials through incorporating iron oxide nanoparticles into an ultra-high molecular weight polyethylene matrix. The resulting composite material can serve as a platform to study the magnetic behavior of immobilized iron oxide nanoparticles in response to an external alternating-current (AC) magnetic field. Using this model, we explore how to tune the magnetic properties of the nanoparticles by tailoring their size, shape, and composition to enhance their magnetic response to an AC field while they are embedded in a rigid polymer matrix. Furthermore, in order to increase the loading of magnetic nanoparticles without compromising the mechanical properties of the polymer support, we are systematically modifying the surface chemistry of the nanoparticles to improve the interfacial interactions between the magnetic nanoparticles and the UHMWPE matrix. The information gathered from these studies will provide valuable knowledge on the design and development of highly sensitive magnetic imaging tracers and effective hyperthermia therapeutic agents for targeted therapy with magnetic nanoparticles immobilized on the sites of interests.

Engineered magnetic nanomaterials offer an unprecedented level of functionality in fundamental studies and applied research. While the mainstream of reports deals with chemically synthesized nanoparticles with sizes in the range of tens of nm, an alternative approach based on the top-down physical methods commonly used in microelectronics is also of interest [1, 2]. Microfabricated particles offer the advantage of higher values of the magnetization of saturation while maintaining almost no net magnetization in the absence of magnetic field due to formation of spin-vortex or antiferromagnetic ground states. In this talk we will discuss the basic mechanisms governing their magnetic properties, as well as review some of the recent attempts to employ such particles for the MRI contrast enhancement, targeted drug delivery and triggered release, separation, hyperthermia, and magneto-mechanical actuation.
[1] W. Hu, et al., “High-moment antiferromagnetic nanoparticles with tunable magnetic properties”. Advanced Materials, 20, 1479-1483 (2008).
[2] D-H. Kim, et al., “Biofunctionalized magnetic-vortex microdiscs for targeted cancer-cell destruction”, Nature Materials, vol. 9 (2): 165-171 (2010).

Magnetic nanowires (NWs) have been demonstrated as functional tools for biomedical applications such as nanorobotic targeted drug delivery [1], anti-biofouling [2], and biosensing [3]. Depending on the application, it is essential to tune the magnetic properties of NWs. A strategy for tailoring the magnetic properties of NWs is by alternating magnetic and non-magnetic segments within the NW architecture [3]. FeCo NWs, whose magnetic properties are expected to be tailored by inserting non-magnetic Cu layers, attract our attention since their high saturation magnetization and unique magnetostrictive properties make them promising candidates for biomedical applications [4]. In this study, we have systemically studied the synthesis of FeCo/Cu segmented NWs, investigated the influence of segmentation on their magnetic properties and demonstrated the on-demand drug release performance. The NWs were fabricated by electrodeposition in anodic aluminium oxide (AAO) templates. By varying the synthesis conditions we could successfully control the composition and thickness of each segment. The influence of non-magnetic Cu segment size on magnetization was simulated using Nmag micromagnetics solver and experimentally verified by vibrating sample magnetometer (VSM) measurements and magnetic force microscopy (MFM) observations. The results show that the easy-axis of magnetization is reversed when Cu segments (100 nm) are larger than FeCo segments (15 nm). Finally the influence of magnetic tunability on the drug release performance of the NWs was studied. For this purpose, we chose a protein as our model drug and studied the protein adsorption-release performance of three types of NWs, namely fully magnetic (FeCo), segmented (FeCo/Cu), and fully non-magnetic (Cu). Application of an external oscillating magnetic field showed that protein release was drastically increased for the fully magnetic and segmented NWs, where as release stayed the same for fully non-magnetic NWs. The results suggest that magnetic stimulation of FeCo/Cu NWs can induce on-demand drug release performance due to their magnetic tunability.
[1] M. A. Zeeshan, S. Pané, S. K. Youn, E. Pellicer, S. Schuerle, J. Sort, S. Fusco, A. M. Lindo, H. G. Park, B. J. Nelson, Adv. Funct. Mater. 2013, 23, 823.
[2] K. M. Ainslie, G. Sharma, M. A. Dyer, C. A. Grimes, M. V. Pishko, Nano Lett. 2005, 5, 1852.
[3] H. T. Huang, T. R. Ger, Y. H. Lin, Z. H. Wei, Lab Chip 2013, 13, 3098.
[4] D. Hunter, W. Osborn, K. Wang, N. Kazantseva, J. Hattrick-Simpers, R. Suchoski, R. Takahashi, M. L. Young, A. Mehta, L. A. Bendersky, S. E. Lofland, M. Wuttig, I. Takeuchi, Nat. Comm. 2011, 2, 518.

Remote heating of thermo-responsive polymers that exhibit reversible swelling/shrinking properties is desirable for the triggered release applications such as targeted drug delivery. This can be realized by the heating-effect produced in magnetic nanoparticles (MNP)/hydrogels composites when they are exposed to external alternating radiofrequency (RF) magnetic fields [1]. In the linear response model for RF heating the mechanism for temperature increase is attributed to Neel and Brownian responses of the MNPs of sizes smaller than about 20 nm [2]. The model describes the flipping of the magnetic moment within the MNP in response to the alternating magnetic field, known as the Neel response, as being dependent on the anisotropy, size and thermal energy of the MNP. The rotation of the MNP in response to the alternating magnetic field, known as the Brownian response, is dependent on the viscosity of the sample, hydrodynamic size, and thermal energy. Samples of hydrogel solutions were made in which polymer and MNP concentrations are varied. We use the linear response model for hyperthermia to describe how the heating rates of polymer samples transition from being Neel to Brownian dominated as the polymer concentration increases. This is made possible, in a separate experiment, by using the same Fe₃O₄ nanoparticles dispersed in a sample of agarose to prevent their Brownian motion thus giving their Neel relaxation time of 2.93 X 10^-8 s and 3.15 X 10^-8 s at MNP concentration of 2 mg/mL and 3 mg/mL respectively. In particular, we find that as the stimuli-responsive polymer content increases from 0.3 wt. % to 1.0 wt. % the Brownian relaxation time increases from 6.56 X 10^-8 s to 1.12 X 10^-6 s respectively. The systematic remote triggering of the transition temperature in polymer gels using Fe₃O₄ nanoparticles we report on will be valuable for a fundamental understanding to researchers using these stimuli-responsive hydrogels for drug delivery applications. The analysis of sample heating rates using the linear response model shows how the hyperthermic heating mechanism changes as polymer content increases due in part to increasing viscosity of samples.
[1]. T. -Y. Liu, S. -H. Hu, D. -M. Liu, S. -Y. Chen, I. -W. Chen, Nano Today, 2008, 4, 52-65.
[2]. Q. A. Pankhurst, J. Connolly, S. K. Jones, J. Dobson, J. Phys. D: Appl. Phys. 2003, 36, R167-R181

Magnetic field can be employed as an effective tool for assembling colloidal nanostructures into functional materials, controlling their properties, and fabricating novel nanoscale devices. The key is to induce well controlled particle-field interactions or particle-particle magnetic interactions. In this presentation, I will use a number of examples recently developed in my group to demonstrate that magnetic field can be utilized for dynamically tuning the optical properties of nanostructured materials, such as diffraction of photonic crystals, birefringence of liquid crystals, and surface plasmon resonance of metallic nanostructures. By taking advantage of our tailored syntheses of well defined nanostructured building blocks, we show that such dynamic tuning can be realized through effective control over the assembly and disassembly behaviors or the orientation of the nanostructures using magnetic fields.

Self-assembly, driven by non-covalent interactions is the fundamental mechanism behind the formation of cellular machineries that perform essential functions of life. It has been found that interaction anisotropy dictates the structural complexity and functional specificity of naturally occurring cellular machineries. This finding stimulates research efforts based on anisotropy to design and control the self-assembly of nanoparticles into well-defined two-dimensional (2D) and 3D complex structures, which may provide a low-cost, programmable paradigm to synthesize functional solid-state materials that are not easily accessible via conventional methods. For example, these materials can exhibit properties inherited from their individual nanoparticle constituents as well as collective properties induced from the coupling effects between their constituents. In the current literature, the discovered collective properties of nanoparticle superlattices include spin-dependent electron transport, vibrational coherence, enhanced conductivity, tandem catalysis, reversible metal-to-insulator transitions, enhanced ferro- and ferrimagnetism, tunable magneto-transport, and efficient charge transport.
To overcome this difficulty, here we report a new synthesis for making needle-like CdSe/CdS supercrystals, which is based on the preparation of CdSe/CdS nanorods exhibiting a static structure with hydrophobic anisotropy through surface functionalization with 1,12 dodecanediamine. Because 1,12-dodecanediamine ligands are primarily functionalized onto the side faces of CdSe/CdS nanorods, their bottom and top faces exhibit more hydrophobicity than their side faces due to the hydrophilicity of amine groups. Therefore, the hydrophobic anisotropy of the resultant nanorods leads to the formation of needle-like superparticles through a process of self-assembly of these nanorods. Significantly, the surface treatment of 1,12-dodecanediamine requires only 10 min, and the quality of the resulting needle-like superparticles is comparable to that of those made using octylamine treatment for 6 to 7 days. In addition, because the 1,12-dodecanediamine functionalized nanorods exhibit a static hydrophobicity-anisotropic structure, the synthesis here can yield needle-like superparticles with diameters of (2.00±0.43)×100 nm, which is about five times narrower than those needle-like superparticles (1.1±0.3)×1000 nm made using the octylamine treatment. These narrower superparticles are important in their applications as energy-down conversion LEDs because a narrower size can minimize the light loss caused by Rayleigh scattering, which is important for their use as energy down-conversion phosphors in manufacturing polarized light-emitting diodes.

Super hydrophobic surfaces play a key role in self-cleaning materials, enhancement of heat transfer and drag reducing surfaces. In these cases the superhydrophobic character is predefined by the chemistry and morphology of the surface. In this study, we demonstrate a fully-reversible transition between Cassie-Baxter and Wenzel states of a substrate with pillar morphology via acoustic pressure. Acoustic cavitation is used to promote nucleation and growth of gas bubbles directly on an immersed hydrophobic pillar substrate and the same method, together with mild vacuum, to cause the air film entrapped in between the pillars to collapse. We show that this method is solely driven by the nucleation and coalescence of nano to micro bubbles at the solid-liquid interface. In addition, a proposed model for the transition in both directions is presented. This model is based on bubble nucleation theory and on energy calculations and is qualitatively not substrate specific. The influence of the surface geometry on the energy barrier for the transition and the stability of each of the states are discussed as well. This technique provides an insight into the transition between the Cassie and Wenzel states and is promising for the design of surfaces with underwater tailored adhesiveness for trapping micro to nano particles or gas bubbles and can be used to engineer tribological materials.

Metal Organic Responsive Frameworks (MORFs) are a proposed new class of smart material consisting of a metal organic framework (MOF) with photoisomerizing linkers that fold in response to light. These would permit new light responsive materials with properties such as photoactuation, photo-tunable rigidity, and photo-tunable porosity. However, conventional MOF architectures are too rigid to allow isomerization of photoactive moieties. We propose a new computational approach for designing MOF linkers to have the required mechanical properties to permit photoisomer folding that uses concepts from de novo molecular design and engineering design automation. Here we show how this approach can be used to design folding linkers with the necessary flexibility to be actuated by photoisomerization and used to design MORFs with desired functionality.

The incorporation of light-responsive groups into metal-organic frameworks (MOFs) is an alluring idea and the potential applications are endless — gas adsorption/desorption for carbon sequestration, chemical sensing, catalysis and drug delivery are only a few examples — and withal the synthesis of metal-organic responsive frameworks (MORFs) is in its infancy. The rigidity of MOFs is at the heart of the problem in that it constrains the photoisomers and thus hinders isomerization. We propose a computational approach that relies on density functional theory to determine the role of constraint on photoisomerization by mapping force curves computed along transition paths. In addition to understanding the constraint mechanisms we submit that the geometric constraint of the framework can be used as an advantage in successfully designing a new class of responsive, shape-shifting materials.

Polymer fibers, elastomers, and shape memory polymers containing embedded magnetite (Fe₃O₄) nanoparticles or gold nanorods can undergo shape changes or bending in response to applied magnetic fields or light. Chains of magnetic nanoparticles embedded in polymers can be formed through magnetic field-directed self-assembly during solvent casting or bulk polymerization. The magnetic anisotropy of the Fe₃O₄ nanoparticle chains causes an enhanced magnetic response along the chaining direction, which imparts an anisotropic bending response to composites in applied magnetic fields. For composites of gold nanorods in shape memory polymers, heat generated by the gold nanorods can drive shape changes in the polymer. Our recent results in the magnetic and photothermal actuation of polymers through the use of embedded chains of Fe₃O₄ nanoparticles and gold nanorods and nanoparticles will be discussed.

Magnetic nanoparticles are being proposed as nanoscale heaters in applications such as magnetic fluid hyperthermia and magnetically triggered drug release. These applications are often touted on the potential advantages of delivering heat at the nanoscale, in close proximity to biological structures. However, macroscopic continuum heat transfer analyses indicate there should be no advantage to deliver heat using nanoparticles and that there is a lower limit to the volume of tissues that can be selectively heated to the hyperthermia range using magnetic nanoparticles. In contrast with the theory, recent experiments from our group and others indicate that nanoscale thermal effects due to energy dissipation by magnetic nanoparticles in alternating magnetic fields indeed exist. In this talk I will address this controversy from the point of view of theory and experiments, and discuss potential biomedical applications of nanoscale thermal effects due to magnetic nanoparticles.

Live optical recordings of action potentials can help visualize neuron dynamics and interactions, advancing efforts to map the brain. Both the potential difference across the cell membrane (~100mV) and mechanical movement of the dendritic spine (~0.6mu;m) are signals that if translated into light, could advance current brain imaging techniques. Lanthanide-doped upconverting nanoparticles are promising optical recorders because they operate in the near infrared (NIR) and emit photons in visible wavelengths, enabling deeper tissue penetration and background-free imaging. Additionally, upconverters do not suffer from problems of genetically encoded voltage indicators such as photobleaching and blinking.
Here, we present two new lanthanide-based platforms for the optical detection of voltage and pressure respectively: 1) 2-20% erbium-doped barium titanate (BaTiO₃:Er) and 2) 0-30% manganese, 2% erbium, and 18/20% ytterbium-doped sodium yttrium fluoride (Mn-doped NaYF₄:Er/Yb). In both systems, the local crystal field of the lanthanide ions is altered by an external stimulus, resulting in emission modulation. First, we synthesize single crystalline cubic-phase BaTiO₃:Er (2-20%) using a hydrothermal reaction in an autoclave. The synthesis results in monodisperse nanoparticles with sizes from 6-20 nm and shapes including cubes and spheres. After heating the particles at 500-700 degrees, we detect visible upconversion from Er under 980nm illumination. We investigate the voltage sensitivity of our particles by applying a voltage bias with piezorespone force microscopy (PFM) in atomic force microscopy (AFM). This technique allows for targeted and localized probing in order to achieve comparable electric fields of 10²-10³ kV/cm across neuron membranes. Upon an external voltage, titanium ions shift tetragonally and alter the local crystal field of the erbium dopant, changing the probability of its radiative transitions. Combining spectroscopy with AFM, we explore voltage-induced emission changes of single BaTiO₃:Er nanoparticles. Secondly, we synthesize both cubic and hexagonal Mn-doped NaYF₄:Er/Yb with Mn doping concentrations ranging from 0-30% and constant Er (2%) and Yb (18/20%) doping. In this system, there is rapid energy transfer from Er (⁴S_3/2) to Mn (⁴T₁), which enhances emission intensity of the ⁴F_9/2 to ⁴I_15/2 transition at 660nm in erbium. Under 980nm illumination, we collect spectra to determine the doping concentration effects on the upconversion intensity for the two phases. Then, using a diamond anvil cell to exert pressures of ~1GPa, we observe intensity changes and spectral shifts in emission. We also investigate the release of pressure in determining whether changes are reversible and therefore compatible for multiple action potential recordings. Our results demonstrate the feasibility of upconverting nanoparticles for detection of biologically-relevant voltages and pressures with the potential for dynamic, deep-tissue optical brain imaging.

A permanent magnet with large energy product can store high energy density. Such a magnet is required to have a large coercivity and a high magnetic moment. In this talk, I will summarize our efforts in using solution phase chemistry and self-assembly to fabricate monodisperse magnetic nanoparticles and nanocomposite magnets. I will highlight the synthesis of FePt, FePd, SmCo as well as Fe and CoFe nanoparticles and their assemblies into composite nanostructures. I will then describe how to achieve efficient exchange-coupling between magnetically hard and soft phases within the composite structure via either core/shell structure or controlled thermal annealing. Our work demonstrates the great advantage of using chemical synthesis and self-assembly to fabricate exchange-spring nanocomposite magnets for high performance permanent magnet applications.

The encapsulation of inorganic nanoparticles by polymers is a frequently used approach to improve the nanoparticle colloidal stability, to change the surface functionality and to achieve hybrid materials with multifunctional properties. Of particular interest are coatings with responsive polymers since they allow for externally triggered switching of materials properties. In case of plasmonic nanoparticle cores the responsive character of such a shell can be used to tune the optical properties of the system. However the optical response is highly sensitive to the polymer shell morphology, thickness and dielectric contrast.
In this contribution we present a detailed study on the nature of cross-linked, thermoresponsive polymer shells using, for the first time, four different scattering approaches to elucidate the density profile of the shells. Each scattering method provides unique information about the temperature-induced changes of shell thickness in terms of hydrodynamic radius and radius of gyration, the pair-distance distribution functions of the shells as well as the dynamic network fluctuations. Only a combination of these different scattering techniques allows to develop a morphological model of the core-shell particles. We further demonstrate control of the cross-linker distribution in core-shell synthesis by semi-batch precipitation copolymerization. Conducting the polymerization in three steps, we show for the first time that the polymer shell thickness can be successively increased without affecting the shell morphology and response behavior.
[1] M. Dulle, S. Jaber, S. Rosenfeldt, A. Radulescu, S. Förster, P. Mulvaney, M. Karg, submitted

Stimuli-responsive crosslinked polymers, hydrogels can change their volume significantly in response to small alterations of certain environmental parameters. As a network of soft polymers, hydrogel can be chemically adjusted to provide a large assortment of sensitivities as diverse as humidity, temperature, light, mechanical stress, magnetic or electric field, pH, glucose and other molecular species. It is also possible to finely tune the sensitivity and selectivity of each stimulus by tailoring polymer composition or geometry.
Due to these properties, many hydrogel-based sensing designs have been developed with high performance demonstrated, including photonic crystals, hydrogel gratings and SPR sensors. Yet it is still challenging to fabricate a hydrogel sensing system that simultaneously satisfies the requirements of cost, robustness, sensitivity and versatility. To fulfill this goal, we&’ve developed an interferometry-based hydrogel sensing platform.
Well-controlled hydrogel features deposited onto a reflective substrate (e.g. silicon wafer) appear certain colors as a result of light interference. By incorporating catalysts or reactants into the gel feature, our system is able to respond to various external stimuli, resulting in changes in its apparent color. This color change can be easily observed by either naked eyes or optical detectors, which provides a measurable, stimuli-dependent quantity. We&’ve applied this in several chemical sensing applications, including quantitatively determining urea, alcohol, glucose and heavy metal concentrations. Fast response and high sensitivity have been demonstrated upon 1 µM level of analyte injection in miliseconds. Theoretical mechanical and optical calculation has validated the experimental results and also provides insights for system design and optimization.
Compared to other sensing techniques involving hydrogel or responsive polymers, our system doesn&’t require complex or expensive fabrication procedure, can work under extreme conditions (e.g. fully dehydrated environment) and allows selectively detection of many analytes by proper gel modifications. By spatially patterning gel features with different responsiveness, high throughput sensing arrays that detect any arbitrary combination of analytes may be further developed. We believe that our technique is an important development of externally actuated responsive nanomaterials with wide applications in environment and (bio)medicine.

Core-shell encapsulation is frequently limited by the degree of tunability of the system, which is usually addressed by adding unnecessary complexity in the form of composite systems. However, to address these limitations, we recently reported cationic cyclopolymerization of o-vinylbenzaldehydes initiated by boron trifluoride to generate acid-sensitive poly(o-(α-alkyl)vinylbenzaldehyde). Herein we describe preparation of core-shell microcapsules (mu;Cs) using flow-focusing microfluidic techniques with shells composed of poly(o-(α-methyl)vinylbenzaldehyde) (PMVB) that release their payload in response to dilute aqueous acid solution. Release profiles of encapsulated fluorescein isothiocyanate-labeled dextran from mu;Cs are controlled by varying the proton concentration and shell-wall thickness. SEM studies indicate the system&’s unique reversible release mechanism involves porosity changes in the shell wall due to micro-crack formation, and we will discuss some of the ongoing applications.

Photonic crystals (PhC) are composite materials made by periodically ordered media possessing different refractive index. The interaction between light and these highly ordered dielectric lattices generates a photonic band structure characterized with forbidden propagation frequencies. This feature is widely exploited in optoelectronic devices such as lasers, light emitting diodes, waveguides, solar cells, displays and color-responsive sensors.
Among possible PhC geometries, multilayered 1D structures are the simplest in terms of fabrication and modeling. In recent years, there has been substantial interest in fabricating PhCs using polymer building blocks thanks to their mechanical flexibility, low cost and ease of preparation. However, it is very challenging to achieve high dielectric contrast and mutual polymer processability simultaneously [1].
For PhC-based sensing applications, highly porous structures are required to allow analyte penetration within the dielectric lattice. Indeed, porous 3D opals and inorganic nanoparticles multilayers have proven suitable for the detection of molecules in both liquid and gas phases [2-4], whereas so far the low permeability of amorphous polymers has hindered detection of gas and vapors by simple 1D-polymer PhCs.
In this work we establish a new strategy to increase 1D-polymer PhCs responsivity to gases and vapors, where constituent polymer layers are modified by loading with a nanofiller that increases both refractive index and permeability. We loaded polystyrene with surface-modified ZnO nanoparticles grown by solvothermal route and used it to fabricate 1D PhC with near-infrared photonic band-gap. This strategy allowed observing diffraction peaks up to the fifth order, in excellent agreement with light polarization and angle of incidence dependence modelled by transfer matrix method. Such structure shows a ten-fold increase of optical responsivity to solvent vapors compared to multilayers fabricated with un-doped matrices, opening up new opportunieties for the development of low-cost colorimetric gas sensors.
[1] L. Frezza, M. Patrini, M. Liscidini, and D. Comoretto, J. Phys. Chem. C,115, 19939 (2011).
[2] X. Xu, A. V. Goponenko, and S. A. Asher, J. Am. Chem. Soc.,130, 3113, (2008).
[3] S. Colodrero, M. Ocaña, A. R. González-Elipe, and H. Míguez, Langmuir,24, 9135, (2008 ).
[4] R. Pernice, G. Adamo, S. Stivala, A. Parisi, A. C. Busacca, D. Spigolon, M. A. Sabatino, L. D'Acquisto, and C. Dispenza, Opt. Mater. Express,3, 1820, (2013).