Micro‐photoluminescence of single living diatom cells

Diatoms are single‐celled microalgae that possess a nanostructured, porous biosilica shell called a frustule. This study characterized the micro‐photoluminescence (μ‐PL) emission of single living cells of the photosynthetic marine diatom Thalassiosira pseudonana in response to UV laser irradiation at 325 nm using a confocal Raman microscope. The photoluminescence (PL) spectrum had two primary peaks, one centered at 500–510 nm, which was attributed to the frustule biosilica, and a second peak at 680 nm, which was attributed to auto‐fluorescence of photosynthetic pigments. The portion of the μ‐PL emission spectrum associated with biosilica frustule in the single living diatom cell was similar to that from single biosilica frustules isolated from these diatom cells. The PL emission by the biosilica frustule in the living cell emerged only after cells were cultivated to silicon depletion. The discovery of the discovery of PL emission by the frustule biosilica within a single living diatom itself, not just its isolated frustule, opens up future possibilities for living biosensor applications, where the interaction of diatom cells with other molecules can be probed by μ‐PL spectroscopy. Copyright © 2016 John Wiley & Sons, Ltd.     

Scalable,Self‐Aligned Printing of Flexible Graphene Micro‐Supercapacitors

Graphene micro‐supercapacitors (MSCs) are an attractive energy storage technology for powering miniaturized portable electronics. Despite considerable advances in recent years, device fabrication typically requires conventional microfabrication techniques, limiting the translation to cost‐effective and high‐throughput production. To address this issue, we report here a self‐aligned printing process utilizing capillary action of liquid inks in microfluidic channels to realize scalable, high‐fidelity manufacturing of graphene MSCs. Microstructured ink receivers and capillary channels are imprinted on plastic substrates and filled by inkjet printing of functional materials into the receivers. The liquid inks move under capillary flow into the adjoining channels, allowing reliable patterning of electronic materials in complex structures with greatly relaxed printing tolerance. Leveraging this process with pristine graphene and ion gel inks, miniaturized all‐solid‐state graphene MSCs are demonstrated to concurrently achieve outstanding resolution (active footprint: <1 mm², minimum feature size: 20 µm) and yield (44/44 devices), while maintaining a high specific capacitance (268 µF cm^–2) and robust stability to extended cycling and bending, establishing an effective route to scale down device size while scaling up production throughput.     

3D‐Printed Stretchable Micro‐Supercapacitor with Remarkable Areal Performance

While stretchable micro‐supercapacitors (MSCs) have been realized, they have suffered from limited areal electrochemical performance, thus greatly restricting their practical electronic application. Herein, a facile strategy of 3D printing and unidirectional freezing of a pseudoplastic nanocomposite gel composed of Ti₃C₂T_x MXene nanosheets, manganese dioxide nanowire, silver nanowires, and fullerene to construct intrinsically stretchable MSCs with thick and honeycomb‐like porous interdigitated electrodes is introduced. The unique architecture utilizes thick electrodes and a 3D porous conductive scaffold in conjunction with interacting material properties to achieve higher loading of active materials, larger interfacial area, and faster ion transport for significantly improved areal energy and power density. Moreover, the oriented cellular scaffold with fullerene‐induced slippage cell wall structure prompts the printed electrode to withstand large deformations without breaking or exhibiting obvious performance degradation. When imbued with a polymer gel electrolyte, the 3D‐printed MSC achieves an unprecedented areal capacitance of 216.2 mF cm^?2 at a scan rate of 10 mV s^?1, and remains stable when stretched up to 50% and after 1000 stretch/release cycles. This intrinsically stretchable MSC also exhibits high rate capability and outstanding areal energy density of 19.2 µWh cm^?2 and power density of 58.3 mW cm^?2, outperforming all reported stretchable MSCs.     

Facile and Scalable Preparation of Ruthenium Oxide‐Based Flexible Micro‐Supercapacitors

Tremendous efforts have been invested in the development of the internet of things during the past 10 years. Implantable sensors still need embedded miniaturized energy harvesting devices, since commercialized thin films and microbatteries do not provide sufficient power densities and suffer from limited lifetime. Therefore, micro‐supercapacitors are good candidates to store energy and deliver power pulses while providing non‐constant voltage output with time. However, multistep expensive protocols involving mask aligners and sophisticated cleanrooms are used to prepare these devices. Here, a simple and versatile laser‐writing procedure to integrate flexible micro‐supercapacitors and microbatteries on current‐collector‐free polyimide foils is reported, starting from commercial powders. Ruthenium oxide (RuO₂)‐based micro‐supercapacitors are prepared by laser irradiation of a bilayered tetrachloroauric acid (HAuCl₄ · 3H₂O)–cellulose acetate/RuO₂ film deposited by spin‐coating, which leads to adherent Au/RuO₂ electrodes with a unique pillar morphology. The as‐prepared microdevices deliver 27 mF cm^?2/540 F cm^?3 in 1 m H₂SO₄ and retain 80% of the initial capacitance after 10 000 cycles. This simple process is applied to make carbon‐based micro‐supercapacitors, as well as metal oxide based pseudocapacitors and battery electrodes, thus offering a straightforward solution to prepare low‐cost flexible microdevices at a large scale.     

Micro‐CT X‐rays do not fragment DNA in preserved bird skins

Most zoological systematics studies are currently based on morphological features, molecular traits or a combination of both to reconstruct animals’ phylogenetic history. Increasingly, morphological studies of museum specimens are using X‐ray computed tomography to visualize internal morphology, because of its ‘non‐destructive’ nature. However, it is not known whether CT can fragment the size of DNA extracted from museum specimens, as has been demonstrated to occur in living cells. This question is of paramount importance for collections based research because X‐rays may reduce the amount of data obtainable from specimens. In our study, we tested whether exposure of museum bird skins to typical CT X‐ray energies (for visualization of the skeleton) increased DNA strand fragmentation, a key factor for the success of downstream molecular applications. For the present study, we extracted DNA from shavings of 24 prepared and dried bird skins (100⁺ years) footpads before and after CT scanning. The pre‐ and post‐CT fragmentation profiles were assessed using a capillary electrophoresis high‐precision instrument (Agilent Bioanalyzer). Comparison of the most common strand length in each DNA sample (relative mass) revealed no significant difference unexposed and exposed tissue (paired t‐test p = 0.463). In conclusion, we found no further quantifiable degradation of DNA strand length under standard X‐ray exposure obtained from our bird skins sample. Differences in museum preservation techniques probably had a greater effect on variation of pre‐CT DNA fragmentation.     

Acquired tolerance of tomato (Lycopersicon esculentum cv. Micro‐Tom) plants to cadmium‐induced stress

The effects of varying concentrations of cadmium (Cd) on the development of Lycopersicon esculentum cv. Micro‐Tom (MT) plants were investigated after 40 days (vegetative growth) and 95 days (fruit production), corresponding to 20 days and 75 days of exposure to CdCl₂, respectively. Inhibition of growth was clearly observed in the leaves after 20 days and was greater after 75 days of growth in 1 mM CdCl₂, whereas the fruits exhibited reduced growth following the exposure to a concentration as low as 0.1 mM CdCl₂. Cd was shown to accumulate in the roots after 75 days of growth but was mainly translocated to the upper parts of the plants accumulating to high concentrations in the fruits. Lipid peroxidation was more pronounced in the roots even at 0.05 mM CdCl₂ after 75 days, whereas in leaves, there was a major increase after 20 days of exposure to 1 mM CdCl₂, but the fruit only exhibited a slight significant increase in lipid peroxidation in plants subjected to 1 mM CdCl₂ when compared with the control. Oxidative stress was also investigated by the analysis of four key antioxidant enzymes, which exhibited changes in response to the increasing concentrations of Cd tested. Catalase (EC 1.11.1.6) activity was shown to increase after 75 days of Cd treatment, but the major increases were observed at 0.1 and 0.2 mM CdCl₂, whereas guaiacol peroxidase (EC 1.11.1.7) did not vary significantly from the control in leaves and roots apart from specific changes at 0.5 and 1 mM CdCl₂. The other two enzymes tested, glutathione reductase (EC 1.6.4.2) and superoxide dismutase (SOD, EC 1.15.1.1), did not exhibit any significant changes in activity, apart from a slight decrease in SOD activity at concentrations above 0.2 mM CdCl₂. However, the most striking results were obtained when an extra treatment was used in which a set of plants was subjected to a stepwise increase in CdCl₂ from 0.05 to 1 mM, leading to tolerance of the Cd applied even at the final highest concentration of 1 mM. This apparent adaptation to the toxic effect of Cd was confirmed by biomass values being similar to the control, indicating a tolerance to Cd acquired by the MT plants.     

Micro‐RNAs meet epigenetics to make for better brains

Recent studies have highlighted the importance of regulatory non‐coding RNAs and epigenetics in controlling the differentiation of somatic stem cells. Two major pathways characterize these fields: micro‐RNAs (miRNAs) and DNA methylation. In this issue of EMBO Reports, Lv et al show that during mammalian corticogenesis, miR‐15b inhibits cytosine demethylation by targeting Tet3, a key methylcytosine dioxygenase. This leads to the epigenetic downregulation of cyclin D1. As a result, cell cycle and differentiation of neural progenitors are altered, promoting their switch to neurogenesis. Hence, Lv et al elegantly bring together miRNAs and DNA methylation in the cell cycle control of neural progenitors and neurogenesis.     

3D Printing Quasi‐Solid‐State Asymmetric Micro‐Supercapacitors with Ultrahigh Areal Energy Density

A 3D printing approach is first developed to fabricate quasi‐solid‐state asymmetric micro‐supercapacitors to simultaneously realize the efficient patterning and ultrahigh areal energy density. Typically, cathode, anode, and electrolyte inks with high viscosities and shear‐thinning rheological behaviors are first prepared and 3D printed individually on the substrates. The 3D printed asymmetric micro‐supercapacitor with interdigitated electrodes exhibits excellent structural integrity, a large areal mass loading of 3.1 mg cm^?2, and a wide electrochemical potential window of 1.6 V. Consequently, this 3D printed asymmetric micro‐supercapacitor displays an ultrahigh areal capacitance of 207.9 mF cm^?2. More importantly, an areal energy density of 73.9 µWh cm^?2 is obtained, superior to most reported interdigitated micro‐supercapacitors. It is believed that the efficient 3D printing strategy can be used to construct various asymmetric micro‐supercapacitors to promote the integration in on‐chip energy storage systems.     

Micro‐ and Mesoporous Carbide‐Derived Carbon–Selenium Cathodes for High‐Performance Lithium Selenium Batteries

Nanocomposites of selenium (Se) and ordered mesoporous silicon carbide‐derived carbon (OM‐SiC‐CDC) are prepared for the first time and studied as cathodes for lithium‐selenium (Li‐Se) batteries. The higher concentration of Li salt in the electrolytes greatly improves Se utilization and cell cycle stability. Se‐CDC shows significantly better performance characteristics than Se‐activated carbon nanocomposites with similar physical properties. Se‐CDC also exhibits better rate performance and cycle stability compared to similarly produced sulfur (S)–CDC for Li/S batteries.     

Micro‐ and nano‐scale mineralogical characterization of Fe(II)‐oxidizing bacterial stalks

Neutrophilic, microaerobic Fe(II)‐oxidizing bacteria (FeOB) from marine and freshwater environments are known to generate twisted ribbon‐like organo‐mineral stalks. These structures, which are extracellularly precipitated, are susceptible to chemical influences in the environment once synthesized. In this paper, we characterize the minerals associated with freshwater FeOB stalks in order to evaluate key organo‐mineral mechanisms involved in biomineral formation. Micro‐Raman spectroscopy and Field Emission Scanning Electron Microscopy revealed that FeOB isolated from drinking water wells in Sweden produced stalks with ferrihydrite, lepidocrocite and goethite as main mineral components. Based on our observations made by micro‐Raman Spectroscopy, field emission scanning electron microscopy and scanning transmission electron microscope combined with electron energy‐loss spectroscopy, we propose a model that describes the crystal‐growth mechanism, the Fe‐oxidation state, and the mineralogical state of the stalks, as well as the biogenic contribution to these features. Our study suggests that the main crystal‐growth mechanism in stalks includes nanoparticle aggregation and dissolution/re‐precipitation reactions, which are dominant near the organic exopolymeric material produced by the microorganism and in the peripheral region of the stalk, respectively.     

Graphitic Carbon Nitride Induced Micro‐Electric Field for Dendrite‐Free Lithium Metal Anodes

Uncontrolled dendrites resulting from nonuniform lithium (Li) nucleation/growth and Li volume expansion during charging cause serious safety problems for Li anode‐based batteries. Here the coating of nickel foam with graphitic carbon nitride (g‐C₃N₄) to have a 3D current collector (g‐C₃N₄@Ni foam) for dendrite‐free Li metal anodes is reported. The lithiophilic g‐C₃N₄ coupled with the 3D framework is demonstrated to be highly effective for promoting the uniform deposition of Li and suppressing the formation of dendrites. Both density functional theory calculations and experimental studies indicate the formation of a micro‐electric field resulting from the tri‐s‐triazine units of g‐C₃N₄, which induces numerous Li nuclei during the initial nucleation stage, effectively guiding the following Li growth on the 3D Ni foam to be well distributed. Furthermore, the 3D porous framework is favorable for absorbing any volume change and stabilizing the solid–electrolyte interphase layer during repeated Li plating/stripping. As such, a Li metal anode based on the g‐C₃N₄@Ni foam has a remarkable electrochemical performance with a high Coulombic efficiency (98% retention after 300 cycles), an ultralong lifespan up to 900 h, as well as a low overpotential (<15 mV at 1.0 mA cm^?2) at a Li deposition of 9.0 mA h cm^?2.     

Advanced Electrode Materials Comprising of Structure‐Engineered Quantum Dots for High‐Performance Asymmetric Micro‐Supercapacitors

Micro‐supercapacitors (MSCs) as a new class of energy storage devices have attracted great attention due to their unique merits. However, the narrow operating voltage, slow frequency response, and relatively low energy density of MSCs are still insufficient. Therefore, an effective strategy to improve their electrochemical performance by innovating upon the design from various aspects remains a huge challenge. Here, surface and structural engineering by downsizing to quantum dot scale, doping heteroatoms, creating more structural defects, and introducing rich functional groups to two dimensional (2D) materials is employed to tailor their physicochemical properties. The resulting nitrogen‐doped graphene quantum dots (N‐GQDs) and molybdenum disulfide quantum dots (MoS₂‐QDs) show outstanding electrochemical performance as negative and positive electrode materials, respectively. Importantly, the obtained N‐GQDs//MoS₂‐QDs asymmetric MSCs device exhibits a large operating voltage up to 1.5 V (far exceeding that of most reported MSCs), an ultrafast frequency response (with a short time constant of 0.087 ms), a high energy density of 0.55 mWh cm^?3, and long‐term cycling stability. This work not only provides a novel concept for the design of MSCs with enhanced performance but also may have broad application in other energy storage and conversion devices based on QDs materials.     

Micro‐Solid Oxide Fuel Cell Membranes Prepared by Aerosol‐Assisted Chemical Vapor Deposition

Free‐standing electrolyte membranes for low‐temperature micro‐solid oxide fuel cells (micro‐SOFCs) are prepared by aerosol‐assisted chemical vapor deposition (AA‐CVD), a cost‐effective, non‐vacuum thin‐film deposition technique. Thin, yttria‐stabilized zirconia (YSZ) membranes (50–400 nm) as well as bilayer membranes of YSZ and gadolinia‐doped ceria are prepared at temperatures of 600 °C and below. AA‐CVD, which is a gas‐phase deposition method, allows for the synthesis of precursor‐free crystalline layers, thereby limiting the development of tensile stress. High membrane survival rates of around 90% are thus obtained. The columnar structure of the electrolyte ensures high oxygen‐ion conductivity and results in negligible ohmic losses. Using sputtered platinum electrodes, the demonstration of a micro‐SOFC based on AA‐CVD electrolyte is achieved and first power density data of 166 mW cm^‐2 at 410 °C is obtained.     

Micro‐structured Devices for Chemical Sensing of Flavor and Fragrance

The aim of this study was to design, develop and test an integrated micro‐analytical system. Of special interest are micro‐fluidic and micro‐sensor applications in the field of chemical analysis, such as the optical detection of parameter changes, optical recognition of component profiles and technological micro‐reaction applications. For this purpose, a modular system was developed, which enables the realization of various application cases in an uncomplicated manner, and to execute (via serial or parallel combination of components) usually not compatible tasks. Software components were developed to control the measuring procedure as well as to execute the data interpretation up to a chemometrical discriminant analysis. Application is directed to the production and product control in life sciences mainly for food, natural products, cosmetics and pharmaceutics.     

Micro‐ to nanostructure and geochemistry of extant crinoidal echinoderm skeletons

This paper reports the results of micro‐ to nanostructural and geochemical analyses of calcitic skeletons from extant deep‐sea stalked crinoids. Fine‐scale (SEM, FESEM, AFM) observations show that the crinoid skeleton is composed of carbonate nanograins, about 20–100 nm in diameter, which are partly separated by what appears to be a few nm thick organic layers. Sub‐micrometre‐scale geochemical mapping of crinoid ossicles using a NanoSIMS ion microprobe, combined with synchrotron high‐spatial‐resolution X‐ray micro‐fluorescence (μ‐XRF) maps and X‐ray absorption near‐edge structure spectroscopy (XANES) show that high Mg concentration in the central region of the stereom bars correlates with the distribution of S‐sulphate, which is often associated with sulphated polysaccharides in biocarbonates. These data are consistent with biomineralization models suggesting a close association between organic components (including sulphated polysaccharides) and Mg ions. Additionally, geochemical analyses (NanoSIMS, energy dispersive spectroscopy) reveal that significant variations in Mg occur at many levels: within a single stereom trabecula, within a single ossicle and within a skeleton of a single animal. Together, these data suggest that physiological factors play an important role in controlling Mg content in crinoid skeletons and that great care should be taken when using their skeletons to reconstruct, for example, palaeotemperatures and Mg/Ca palaeo‐variations of the ocean.