Pinaceae Pine Resins (Black Pine, Shore Pine, Rosin, and Baltic Amber) as Natural Dielectrics for Low Operating Voltage, Hysteresis-Free, Organic Field Effect Transistors.

Four pinaceae pine resins analyzed in this study: black pine, shore pine, Baltic amber, and rosin demonstrate excellent dielectric properties, outstanding film forming, and ease of processability from ethyl alcohol solutions. Their trap-free nature allows fabrication of virtually hysteresis-free organic field effect transistors operating in a low voltage window with excellent stability under bias stress. Such green constituents represent an excellent choice of materials for applications targeting biocompatibility and biodegradability of electronics and sensors, within the overall effort of sustainable electronics development and environmental friendliness.

Sensitive and high laser damage threshold substrates for surface-enhanced Raman scattering based on gold and silver nanoparticles.

Surface-enhanced Raman scattering (SERS) is a sensitive and fast technique for sensing applications such as chemical trace analysis. However, a successful, high-throughput practical implementation necessitates the availability of simple-to-use and economical SERS substrates. In this work, we present a robust, reproducible, flexible and yet cost-effective SERS substrate suited for the sensitive detection of analytes at near-infrared (NIR) excitation wavelengths. The fabrication is based on a simple dropcast deposition of silver or gold nanomaterials on an aluminium foil support, making the design suitable for mass production. The fabricated SERS substrates can withstand very high average Raman laser power of up to 400 mW in the NIR wavelength range while maintaining a linear signal response of the analyte. This enables a combined high signal enhancement potential provided by (i) the field enhancement via the localized surface plasmon resonance introduced by the noble metal nanomaterials and (ii) additional enhancement proportional to an increase of the applicable Raman laser power without causing the thermal decomposition of the analyte. The application of the SERS substrates for the trace detection of melamine and rhodamine 6G is demonstrated, which shows limits of detection smaller than 0.1 ppm and analytical enhancement factors on the order of 104 as compared to bare aluminium foil.

Synthesis and Spatial Order Characterization of Controlled Silica Particle Sizes Organized as Photonic Crystals Arrays.

The natural occurrence of precious opals, consisting of highly organized silica particles, has prompted interest in the synthesis and formation of these structures. Previous research has shown that a highly organized photonic crystal (PhC) array is only possible when it is based on a low polydispersity index (PDI) sample of particles. In this study, a solvent-only variation method is used to synthesize different sizes of silica particles (SiPs) by following the traditional sol-gel Stöber approach. The controlled rate of the addition of the reagents promoted the homogeneity of the nucleation and growth of the spherical silica particles, which in turn yielded a low PDI. The opalescent PhC were obtained via self-assembly of these particles using a solvent evaporation method. Analysis of the spatial statistics, using Voronoi tessellations, pair correlation functions, and bond order analysis showed that the successfully formed arrays showed a high degree of quasi-hexagonal (hexatic) organization, with both global and local order. Highly organized PhC show potential for developing future materials with tunable structural reflective properties, such as solar cells, sensing materials, and coatings, among others.

Hollow Silica Microparticles Based on Amphiphilic Polyphosphazenes.

Hollow microparticles are important materials, offering a larger surface area and lower density than their solid counterparts. Furthermore, their inner void space can be exploited for the encapsulation and release of guest species in a variety of applications. Herein, we present phosphazene-based silica hollow microparticles prepared via a surfactant-free sol-gel process through self-assembly of the alkoxysilyl-containing polymer in water-ethanol solution. Solely, a silane-derived polyphosphazene was used as the precursor for the microparticle formation, without additional classical silica sources. These novel hollow silica-based microparticles were prepared without surfactant, using a designed amphiphilic polyphosphazene for the particle formation made by two components, a hydrophilic unit consisting of 3-mercaptopropyl(trimethoxysilane), and a hydrophobic unit (dodecanethiol) attached to the double bonds from the poly(allylamine)phosphazene backbone via a thiol-ene photoreaction. Due to these two functionalities, a "vesicle"-like self-assembled structure was formed in the reaction medium, which could be then utilized for the microparticle preparation. The influence of NaOH during the synthesis was shown to affect the size and the wall thickness of the microparticles. This effect may enhance the possibilities to tailor such microparticles for drug delivery purposes or for future controlled release of other substances, such as drugs, fragrances, or anticorrosive pigments.

Lanthanide (Eu, Tb, La)-Doped ZnO Nanoparticles Synthesized Using Whey as an Eco-Friendly Chelating Agent.

Strategies for production and use of nanomaterials have rapidly moved towards safety and sustainability. Beyond these requirements, the novel routes must prove to be able to preserve and even improve the performance of the resulting nanomaterials. Increasing demand of high-performance nanomaterials is mostly related to electronic components, solar energy harvesting devices, pharmaceutical industries, biosensors, and photocatalysis. Among nanomaterials, Zinc oxide (ZnO) is of special interest, mainly due to its environmental compatibility and vast myriad of possibilities related to the tuning and the enhancement of ZnO properties. Doping plays a crucial role in this scenario. In this work we report and discuss the properties of undoped ZnO as well as lanthanide (Eu, Tb, and La)-doped ZnO nanoparticles obtained by using whey, a by-product of milk processing, as a chelating agent, without using citrate nor any other chelators. The route showed to be very effective and feasible for the affordable large-scale production of both pristine and doped ZnO nanoparticles in powder form.

Reversible Speed Regulation of Self-Propelled Janus Micromotors via Thermoresponsive Bottle-Brush Polymers.

Invited for the cover of this issue is the group of Ian Teasdale and Yolanda Salinas at the Johannes Kepler University Linz. The image depicts the self-propelled Janus micromotors reported in this work. Read the full text of the article at 10.1002/chem.202004792.

Reversible Speed Regulation of Self-Propelled Janus Micromotors via Thermoresponsive Bottle-Brush Polymers.

This work reports a reversible braking system for micromotors that can be controlled by small temperature changes (≈5 °C). To achieve this, gated-mesoporous organosilica microparticles are internally loaded with metal catalysts (to form the motor) and the exterior (partially) grafted with thermosensitive bottle-brush polyphosphazenes to form Janus particles. When placed in an aqueous solution of H2 O2 (the fuel), rapid forward propulsion of the motors ensues due to decomposition of the fuel. Conformational changes of the polymers at defined temperatures regulate the bubble formation rate and thus act as brakes with considerable deceleration/acceleration observed. As the components can be easily varied, this represents a versatile, modular platform for the exogenous velocity control of micromotors.

Hybrid Porous Microparticles Based on a Single Organosilica Cyclophosphazene Precursor.

Porous organosilica microparticles consisting of silane-derived cyclophosphazene bridges were synthesized by a surfactant-mediated sol-gel process. Starting from the substitution of hexachlorocyclotriphosphazene with allylamine, two different precursors were obtained by anchoring three or six alkoxysilane units, via a thiol-ene photoaddition reaction. In both cases, spherical, microparticles (size average of ca. 1000 nm) with large pores were obtained, confirmed by both, scanning and transmission electron microscopy. Particles synthesized using the partially functionalized precursor containing free vinyl groups were further functionalized with a thiol-containing molecule. While most other reported mesoporous organosilica particles are essentially hybrids with tetraethyl orthosilicate (TEOS), a unique feature of these particles is that structural control is achieved by exclusively using organosilane precursors. This allows an increase in the proportion of the co-components and could springboard these novel phosphorus-containing organosilica microparticles for different areas of technology.

Synthesis conditions influencing formation of MAPbBr3 perovskite nanoparticles prepared by the ligand-assisted precipitation method.

This work reports on an optimized procedure to synthesize methylammonium bromide perovskite nanoparticles. The ligand-assisted precipitation synthetic pathway for preparing nanoparticles is a cost-effective and promising method due to its ease of scalability, affordable equipment requirements and convenient operational temperatures. Nevertheless, there are several parameters that influence the resulting optical properties of the final nanomaterials. Here, the influence of the choice of solvent system, capping agents, temperature during precipitation and ratios of precursor chemicals is described, among other factors. Moreover, the colloidal stability and stability of the precursor solution is studied. All of the above-mentioned parameters were observed to strongly affect the resulting optical properties of the colloidal solutions. Various solvents, dispersion media, and selection of capping agents affected the formation of the perovskite structure, and thus qualitative and quantitative optimization of the synthetic procedure conditions resulted in nanoparticles of different dimensions and optical properties. The emission maxima of the nanoparticles were in the 508-519 nm range due to quantum confinement, as confirmed by transmission electron microscopy. This detailed study allows the selection of the best optimal conditions when using the ligand-assisted precipitation method as a powerful tool to fine-tune nanostructured perovskite features targeted for specific applications.

Trends in Degradable Mesoporous Organosilica-Based Nanomaterials for Controlling Drug Delivery: A Mini Review.

The last few years of enhancing the design of hybrid mesoporous organosilica nanoparticleshas allowed their degradation under specific pathologic conditions, which finally is showing a lightin their potential use as drug delivery systems towards clinical trials. Nevertheless, the issueof controlling the degradation on-demand at cellular level still remains a major challenge, even if ithas lately been addressed through the incorporation of degradable organo-bridged alkoxysilanesinto the silica framework. On this basis, this mini review covers some of the most recent examplesof dierent degradable organosilica nanomaterials with potential application in nanomedicine,from degradable non-porous to mesoporous organosilica nanoparticles (MONs), functionalized withresponsive molecular gates, and also the very promising degradable periodic mesoporous organosilicamaterials (PMOs) only consisting of organosilica bridges.

Anti-Stokes photoluminescence study on a methylammonium lead bromide nanoparticle film.

Photon cooling via anti-Stokes photoluminescence (ASPL) is a promising approach to realize all-solid-state cryo-refrigeration by photoexcitation. Photoluminescence quantum yields close to 100% and a strong coupling between phonons and excited states are required to achieve net cooling. We have studied the anti-Stokes photoluminescence of thin films of methylammonium lead bromide nanoparticles. We found that the anti-Stokes photoluminescence is thermally activated with an activation energy of ∼80 meV. At room temperature the ASPL up-conversion efficiency is ∼60% and it depends linearly on the excitation intensity. Our results suggest that upon further optimization of their optical properties, the investigated particles could be promising candidates for the demonstration of photon cooling in thin solid films.

Visible Light Photocleavable Ruthenium-Based Molecular Gates to Reversibly Control Release from Mesoporous Silica Nanoparticles.

Herein we present hybrid mesoporous silica nanomaterials (MSN) with visible light-sensitive ruthenium complexes acting as gates. Two different [Ru(bpy)2L1L2]2+ complexes were investigated by grafting [Ru(bpy)2(4AMP)2](PF6)2 (RC1) and [Ru(bpy)2(PPh3)Cl]Cl (RC2) via two or one ligands onto the surface of mesoporous silica nanoparticles (MSNs), to give MSN1-RC1 and MSN2-RC2, respectively. The pores were previously loaded with a common dye, safranin O, and release studies were conducted. The number and position of the ligands were shown to influence the photocages behavior and thus the release of the cargo. Release studies from MSN1-RC1 in acetonitrile showed that in the dark the amount of dye released was minimal after 300 min, whereas a significant increase was measured upon visible light irradiation (ca. 90%). While successful as a photochemically-controlled gated system, RC1 was restricted to organic solvents since it required cleavage of two ligands in order to be cleaved from the surface, and in water only one is cleaved. Release studies from the second nanomaterial MSN2-RC2, where the complex RC2 was bound to the MSN via only one ligand, showed stability under darkness and in aqueous solution up to 180 min and, rapid release of the dye when irradiated with visible light. Furthermore, this system was demonstrated to be reversible, since, upon heating to 80 °C, the system could effectively re-close the pores and re-open it again upon visible light irradiation. This work, thus, demonstrates the potential reversible gate mechanism of the ruthenium-gated nanomaterials upon visible light irradiation, and could be envisioned as a future design of photochemically-driven drug delivery nanosystems or on/off switches for nanorelease systems.

Dual stimuli-responsive polyphosphazene-based molecular gates for controlled drug delivery in lung cancer cells.

A switchable silane derived stimuli-responsive bottle-brush polyphosphazene (PPz) was prepared and attached to the surface of mesoporous silica nanoparticles (MSNs). The hybrid polymer with PEG-like Jeffamine® M-2005 side-arms undergo conformational changes in response to both pH and temperature due to its amphiphilic substituents and protonatable main-chain, hence were investigated as a gatekeeper. Safranin O as control fluorophore or the anticancer drug camptothecin (CPT) were encapsulated in the PPz-coated MSNs. At temperatures below the lower critical solution temperature (LCST), the swollen conformation of PPz efficiently blocked the cargo within the pores. However, above the LCST, the PPz collapsed, allowing release of the payload. Additionally, protonation of the polymer backbone at lower pH values was observed to enhance opening of the pores from the surface of the MSNs and therefore the release of the dye. In vitro studies demonstrated the ability of these nanoparticles loaded with the drug camptothecin to be endocytosed in both models of tumor (A549) and healthy epithelial (BEAS-2B) lung cells. Their accumulation and the release of the chemotherapeutic drug, co-localized within lysosomes, was faster and higher for tumor than for healthy cells, further, the biocompatibility of PPz-gated nanosystem without drug was demonstrated. Tailored dual responsive polyphosphazenes thus represent novel and promising candidates in the construction of future gated mesoporous silica nanocarriers designs for lung cancer-directed treatment.

Mesoporous Silica Micromotors with a Reversible Temperature Regulated On-Off Polyphosphazene Switch.

The incorporation of an extraneous on-off braking system is necessary for the effective motion control of the next generation of micrometer-sized motors. Here, the design and synthesis of micromotors is reported based on mesoporous silica particles containing bipyridine groups, introduced by cocondensation, for entrapping catalytic cobalt(II) ions within the mesochannels, and functionalized on the surface with silane-derived temperature responsive bottle-brush polyphosphazene. Switching the polymers in a narrow temperature window of 25-30 °C between the swollen and collapsed state, allows the access for the fuel H2 O2 contained in the dispersion medium to cobalt(II) bipyridinato catalyst sites. The decomposition of hydrogen peroxide is monitored by optical microscopy, and effectively operated by reversibly closing or opening the pores by the grafted gate-like polyphosphazene, to control on demand the oxygen bubble generation. This design represents one of the few examples using temperature as a trigger for the reversible on-off external switching of mesoporous silica micromotors.

Cyclic Peptide Stabilized Lead Halide Perovskite Nanoparticles.

Combining the unique properties of peptides as versatile tools for nano- and biotechnology with lead halide perovskite nanoparticles can bring exceptional opportunities for the development of optoelectronics, photonics, and bioelectronics. As a first step towards this challenge sub 10 nm methylammonium lead bromide perovskite colloidal nanoparticles have been synthetizes using commercial cyclic peptide Cyclo(RGDFK), containing 5 amino acids, as a surface stabilizer. Perovskite nanoparticles passivated with Cyclo(RGDFK) possess charge transfer from the perovskite core to the peptide shell, resulting in lower photoluminescence quantum yields, which however opens a path for the application where charge transfer is favorable.

Biocompatible Phenylboronic-Acid-Capped ZnS Nanocrystals Designed As Caps in Mesoporous Silica Hybrid Materials for on-Demand pH-Triggered Release In Cancer Cells.

Biocompatible ZnS-based nanocrystals capped with 4-mercaptophenylboronic acid (ZnS@B) have been size-designed as excellent pH-responsive gatekeepers on mesoporous silica nanoparticles (MSNs), which encapsulate fluorophore safranin O (S2-Saf) or anticancer drug epirubicin hydrochloride (S2-Epi) for delivery applications in cancer cells. In this novel hybrid system, the gate mechanism consists of reversible pH-sensitive boronate ester moieties linking the nanocrystals directly to the alcohol groups from silica surface scaffold, avoiding tedious intermediate functionalization steps. The ∼3 nm size of the ZnS@B nanocrystals was tailored to allow efficient sealing of the pore voids and achieve a "zero premature cargo release" at neutral pH (7.4). The system selectively released the cargo in acidic conditions (pH 5.4 and 3.0) because of the hydrolysis of the boronate esters, which unblocked the pore voids. Delivery of the cargo by off-on cycles was demonstrated by changes in pH from 7.4 to 3.0, showing its potential pH-switching behavior. Cellular uptake of these nanocarriers within human cervix adenocarcinoma (HeLa) cells was achieved and the controlled release of the chemotherapeutic drug epirubicin was shown to occur within the endogenous endosomal/lysosomal acidified cancer cell microenvironment and further diffused into the cytosol. Cytotoxicity tests done on the mesoporous support without cargo and covalently linked with ZnS@B nanocrystals as caps were negative, suggesting that the proposed system is biocompatible and can be considered as a very promising drug nanocarrier.

Pseudorotaxane capped mesoporous silica nanoparticles for 3,4-methylenedioxymethamphetamine (MDMA) detection in water.

Mesoporous silica nanoparticles loaded with fluorescein and capped by a pseudorotaxane, formed between a naphthalene derivative and cyclobis(paraquat-p-phenylene) (CBPQT4+), were used for the selective and sensitive fluorogenic detection of 3,4-methylenedioxymethamphetamine (MDMA).

Molecularly Imprinted Polymer Coated Quantum Dots for Multiplexed Cell Targeting and Imaging.

Advanced tools for cell imaging are of great interest for the detection, localization, and quantification of molecular biomarkers of cancer or infection. We describe a novel photopolymerization method to coat quantum dots (QDs) with polymer shells, in particular, molecularly imprinted polymers (MIPs), by using the visible light emitted from QDs excited by UV light. Fluorescent core-shell particles specifically recognizing glucuronic acid (GlcA) or N-acetylneuraminic acid (NANA) were prepared. Simultaneous multiplexed labeling of human keratinocytes with green QDs conjugated with MIP-GlcA and red QDs conjugated with MIP-NANA was demonstrated by fluorescence imaging. The specificity of binding was verified with a non-imprinted control polymer and by enzymatic cleavage of the terminal GlcA and NANA moieties. The coating strategy is potentially a generic method for the functionalization of QDs to address a much wider range of biocompatibility and biorecognition issues.

Smart Polymeric Nanoparticles as Emerging Tools for Imaging--The Parallel Evolution of Materials.

The field of imaging has developed considerably over the past decade and recent advances in the area of nanotechnology, in particular nanomaterials, have opened new opportunities. Polymeric nanoparticles are particularly interesting and a number of novel materials, characterized by stimuli-responsive characteristics and fluorescent tagging, have allowed visualization, intracellular labeling and real-time tracking. In some of the latest applications the nanoparticles have been used for imagining of tumor cells, both in vivo and ex vivo.

Chromo-fluorogenic detection of nitroaromatic explosives by using silica mesoporous supports gated with tetrathiafulvalene derivatives.

Three new hybrid gated mesoporous materials (SN3 -1, SNH2 -2, and SN3 -3) loaded with the dye [Ru(bipy)3 ](2+) (bipy=bipyridine) and capped with different tetrathiafulvalene (TTF) derivatives (having different sizes and shapes and incorporating different numbers of sulfur atoms) have been prepared. The materials SN3 -1 and SN3 -3 are functionalized on their external surfaces with the TTF derivatives 1 and 3, respectively, which were attached by employing the "click" chemistry reaction, whereas SNH2 -2 incorporates the TTF derivative 2, which was anchored to the solid through an amidation reaction. The final gated materials have been characterized by standard techniques. Suspensions of these solids in acetonitrile showed "zero release", most likely because of the formation of dense TTF networks around the pore outlets. The release of the entrapped [Ru(bipy)3 ](2+) dye from SN3 -1, SNH2 -2, and SN3 -3 was studied in the presence of selected explosives (Tetryl, TNT, TNB, DNT, RDX, PETN, PA, and TATP). SNH2 -2 showed a fairly selective response to Tetryl, whereas for SN3 -1 and SN3 -3 dye release was found to occur with Tetryl, TNT, and TNB. The uncapping process in the three materials can be ascribed to the formation of charge-transfer complexes between the electron-donating TTF units and the electron-accepting nitroaromatic explosives. Finally, solids SNH2 -2 and SN3 -1 have been tested for Tetryl detection in soil with good results, pointing toward a possible use of these or similar hybrid capped materials as probes for the selective chromo-fluorogenic detection of nitroaromatic explosives.