Hybrid Photonic Nanostructures by In Vivo Incorporation of an Organic Fluorophore into Diatom Algae

Biotechnological processes harnessing living organisms' metabolism are low‐cost routes to nanostructured materials for applications in photonics, electronics, and nanomedicine. In the pursuit of photonic biohybrids, diatoms microalgae are attractive given the properties of the porous micro‐to‐nanoscale structures of the biosilica shells (frustules) they produce. The investigations have focused on in vivo incorporation of tailored molecular fluorophores into the frustules of Thalassiosira weissflogii diatoms, using a procedure that paves the way for easy biotechnological production of photonic nanostructures. The procedure ensures uniform staining of shells in the treated culture and permits the resulting biohybrid photonic nanostructures to be isolated with no damage to the dye and periodic biosilica network. Significantly, this approach ensures that light emission from the dye embedded in the isolated biohybrid silica is modulated by the silica's nanostructure, whereas no modulation of photoluminescence is observed upon grafting the fluorophore onto frustules by an in vitro approach based on surface chemistry. These results pave the way to the possibility of easy production of photonic nanostructures with tunable properties by simple feeding the diatoms algae with tailored photoactive molecules.     

Exploitation of Diatom Frustules for Nanotechnology: Tethering Active Biomolecules

Diatoms are single‐celled microalgae with rigid walls (frustules) composed of amorphous silica. The intricate 3D microstructure of diatoms results in a high surface area formed by myriad pores and channels. The combination of the silica chemistry of the frustule coupled with the high surface area makes it particularly suitable for applications such as microscale total analysis systems. Here it is demonstrated that the diatom frustule can be chemically modified for the attachment of antibodies, and that the attached antibodies retain biological activity. These modified structures have potential applications in antibody arrays and may have use in techniques such as immunoprecipitation. These silica structures are produced in diatoms using only light and minimal nutrients and, therefore, generate an exceptionally cheap and renewable material.     

Genetically Programmed Regioselective Immobilization of Enzymes in Biosilica Microparticles

Diatoms are single‐celled microalgae that produce a large variety of hierarchically porous, silica‐based microparticles as cell wall material. The presence of genetically encoded silica nanopatterns endows the biosilica with favorable properties for a wide range of applications including catalysis, chemical sensing, photonics, and drug delivery. Enhancing the performance of diatom biosilica requires i) a better understanding of the structure–property relationship in this material, and ii) methods that enable the manipulation of the biosilica structure and properties in a targeted manner. Here, genetic engineering of the diatom Thalassiosira pseudonana is employed to immobilize enzymes (glucose oxidase and horseradish peroxidase) into structurally distinct regions of the biosilica, which are termed valves and girdle bands. Remarkably, glucose oxidase in girdle bands exhibits >3‐fold higher catalytic activities compared to its location in valves. It is demonstrated through enzyme accessibility studies, protein engineering, and genetic engineering of biosilica morphology that the divergent enzyme activities are caused by the differences in the inherent silica nanopatterns of valves and girdle bands. This work highlights the importance of silica nanoscale architecture for the activity of immobilized enzymes and provides unprecedented tools for the biotechnological production of silica microparticles with tailored catalytic activities and anisotropic functionalities.     

急性镉中毒大鼠肝脏金属硫蛋白的免疫电镜定位

目的：研究急性镉中毒大鼠肝细胞中金属硫蛋白（ＭＴ）在超微结构水平的分布。方法： 羊抗兔ＩｇＧ－１０ｎｍ胶体金,结合自制的兔抗大鼠ＭＴ抗血清,在灌注固定的急性镉 中毒大鼠肝中,进行ＭＴ的包埋后免疫胶体金电镜定位观察。结果：镉暴露６ｈ大鼠肝细胞中有大量胶体金颗粒分布于胞质与细胞核内,而正常组肝细胞肿中胶体金颗粒数量很少。结论：急性镉中毒６ｈ的大鼠肝细胞中证实已有大量ＭＴ诱导产生,并旅游分布于胞质与细胞     

Biologically Enabled Syntheses of Freestanding Metallic Structures Possessing Subwavelength Pore Arrays for Extraordinary (Surface Plasmon‐Mediated) Infrared Transmission

A scalable wet chemical process has been used to convert the intricate silica microshells (frustules) of diatoms into gold structures that retained the three‐dimensional (3‐D) frustule shapes and fine patterned features. Combined use of an amine‐enriching surface functionalization protocol and electroless deposition yielded thin (<100 nm) conformal nanocrystalline gold coatings that, upon selective silica dissolution, were converted into freestanding gold structures with frustule‐derived 3‐D morphologies. By selecting a diatom frustule template with a quasi‐regular hexagonal pore pattern (Coscinodiscus asteromphalus, CA), gold replica structures possessing such pore patterns were produced that exhibited infrared transmission maxima/reflection minima that were not observed for the starting silica diatom frustules or for flat nonporous gold films; that is, such extraordinary optical transmission (EOT) resulted from the combined effects of the quasi‐periodic hexagonal hole structure (inherited from the CA diatom frustules) and the gold chemistry. Calculated and measured IR transmission spectra obtained from planar gold films with quasi‐periodic hexagonal CA‐derived hole patterns, or with short‐range periodic hexagonal hole patterns, indicated that the enhanced IR transmission exhibited by the gold CA frustule replicas was enabled by the generation and transmission of surface plasmons. This scalable bio‐enabled process provides a new and attractive capability for fabricating self‐supporting, responsive, 3‐D metallic structures for use as dispersible/harvestable microparticles tailored for EOT‐based applications.     

Straightforward Immunosensing Platform Based on Graphene Oxide‐Decorated Nanopaper: A Highly Sensitive and Fast Biosensing Approach

Immunoassays are nowadays a crucial tool for diagnostics and drug development. However, they often involve time‐consuming procedures and need at least two antibodies in charge of the capture and detection processes, respectively. This study reports a nanocomposite based on graphene oxide‐coated nanopaper (GONAP) facilitating an advantageous immunosensing platform using a single antibody and without the need for washing steps. The hydrophilic, porous, and photoluminescence‐quenching character of GONAP allows for the adsorption and quenching of photoluminescent quantum dots nanocrystals complexed with antibodies (Ab‐QDs), enabling a ready‐to‐use immunosensing platform. The photoluminescence is recovered upon immunocomplex (antibody‐antigen) formation which embraces a series of interactions (hydrogen bonding, electrostatic, hydrophobic, and Van der Waals interactions) that trigger desorption of the antigen‐Ab‐QD complex from GONAP surface. However, the antigen is then attached onto the GONAP surface by electrostatic interactions leading to a spacer (greater than ≈20 nm) between Ab‐QDs and GONAP and thus hindering nonradiative energy transfer. It is demonstrated that this simple—yet highly sensitive—platform represents a virtually universal immunosensing approach by using small‐sized and big‐sized targets as model analytes, those are, human‐IgG protein and Escherichia coli bacteria. In addition, the assay is proved effective in real matrices analysis, including human serum, poultry meat, and river water. GONAP opens the way to conceptually new paper‐based devices for immunosensing, which are amenable to point of care applications and automated diagnostics.     

Ultrathin Highly Luminescent Two‐Monolayer Colloidal CdSe Nanoplatelets

Surface effects in atomically flat colloidal CdSe nanoplatelets (NLPs) are significantly and increasingly important with their thickness being reduced to subnanometer level, generating strong surface related deep trap photoluminescence emission alongside the bandedge emission. Herein, colloidal synthesis of highly luminescent two‐monolayer (2ML) CdSe NPLs and a systematic investigation of carrier dynamics in these NPLs exhibiting broad photoluminescence emission covering the visible region with quantum yields reaching 90% in solution and 85% in a polymer matrix is shown. The astonishingly efficient Stokes‐shifted broadband photoluminescence (PL) emission with a lifetime of ≈100 ns and the extremely short PL lifetime of around 0.16 ns at the bandedge signify the participation of radiative midgap surface centers in the recombination process associated with the underpassivated Se sites. Also, a proof‐of‐concept hybrid LED employing 2ML CdSe NPLs is developed as color converters, which exhibits luminous efficacy reaching 300 lm W_opt^?1. The intrinsic absorption of the 2ML CdSe NPLs (≈2.15 × 10⁶ cm^?1) reported in this study is significantly larger than that of CdSe quantum dots (≈2.8 × 10⁵ cm^?1) at their first exciton signifying the presence of giant oscillator strength and hence making them favorable candidates for next‐generation light‐emitting and light‐harvesting applications.     

Strained Interface Defects in Silicon Nanocrystals

The surface of silicon nanocrystals embedded in an oxide matrix can contain numerous interface defects. These defects strongly affect the nanocrystals’ photoluminescence efficiency and optical absorption. Dangling‐bond defects are nearly eliminated by H₂ passivation, thus decreasing absorption below the quantum‐confined bandgap and enhancing PL efficiency by an order of magnitude. However, there remain numerous other defects seen in absorption by photothermal deflection spectroscopy; these defects cause non‐radiative recombination that limits the PL efficiency to <15%. Using atomistic pseudopotential simulations, we attribute these defects to two specific types of distorted bonds: Si‐Si and bridging Si‐O‐Si bonds between two Si atoms at the nanocrystal surface.     

Radiative recombination in Ge<Superscript>+</Superscript>-implanted SiO<Subscript>2</Subscript> films annealed under hydrostatic pressure

Photoluminescence (PL) spectra and PL excitation spectra were recorded at room temperature from SiO₂ films implanted with Ge⁺ ions and annealed at temperature T _a =450–1100°C under hydrostatic pressure P=12 kbar. The emergence of features in the violet and green bands of the PL and PL excitation spectra correlates with the formation of hydrostatically strained Ge nanocrystals. The shift of the PL bands to higher energies, which occurs as the annealing temperature is raised to T _a ≥800°C, can be attributed to a shift of the energy levels related to the radiative recombination centers, which is caused by the increasing deformation potential. The observed PL is accounted for by the enhanced probability of direct radiative transitions in Ge nanocrystals with an X-like conduction band.     

Exciton recombination in δ-doped type-II GaAs/AlAs superlattices

Radiative recombination of excitons in δ-doped type-II GaAs/AlAs superlattices (SLs) is studied experimentally. With an increase in the impurity density in δ-layers from 2×10¹⁰ to 7.5×10¹¹ cm^?2, the integrated intensity of SL photoluminescence (PL) decreases by a factor of 4–6; the intensity of excitonic PL drops considerably (up to 70–80 times), which is accompanied by an increase in the exciton radiative decay rate. Uniform doping of the SL does not result in the exciton PL quenching. Analysis of the temperature dependence and the kinetics of the PL indicate that impurity quenching of the excitonic PL in δ-doped structures is not related to a reduction in the exciton localization energy and cannot be explained by an increase in the density of nonradiative recombination centers. We conclude that the PL quenching is mainly caused by the appearance of built-in electric fields originating from ionized impurities, which hinders the formation of the excitons.     

Efficient and Photostable ZnS‐Passivated CdS:Mn Luminescent Nanocrystals

Efficient and photostable ZnS‐passivated CdS:Mn (CdS:Mn/ZnS core/shell) nanocrystals were synthesized using reverse micelle chemistry. CdS:Mn/ZnS core/shell nanocrystals exhibited much improved luminescent properties (quantum yield and photostability) over organically (n‐dodecanethiol‐) capped CdS:Mn nanocrystals. This is the result of effective, robust passivation of CdS surface states by the ZnS shell and consequent suppression of non‐radiative recombination transitions. The dependence of photoluminescence (PL) intensity has been observed as a function of UV irradiation time for both organically and inorganically capped CdS:Mn nanocrystals. Whereas organically capped CdS:Mn nanocrystals exhibit a significant reduction of PL intensity, CdS:Mn/ZnS core/shell nanocrystals exhibit an increased PL intensity with UV irradiation. XPS (X‐ray photoelectron spectroscopy) studies reveal that UV irradiation of CdS:Mn/ZnS nanocrystals in air atmosphere induces the photo‐oxidation of the ZnS shell surface, leading to the formation of ZnSO₄. This photo‐oxidation product is presumably responsible for the enhanced PL emission, serving as a passivating layer.     

Growth and electronic properties of ZnO epilayers by plasma-assisted molecular beam epitaxy

ZnO thin films were grown on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy (MBE). The crystalline properties of the layers as measured by x-ray diffraction were found to improve with lower growth temperatures, where the full-width at half-maximum (FWHM) of the x-ray rocking curves was shown to be in the range of 100 to 1,100 arcsec. The electronic properties were found to improve for higher growth temperatures, with n-type carrier concentration and electron mobility in the range of 1×10¹⁷ −5×10¹⁸ cm⁻³ and 80–36 cm²/Vs, respectively. Photoluminescence (PL) measurements indicated that growth at higher temperatures provided superior band edge radiative emission, while growth at lower temperatures resulted in significant deep level radiative emission centered at 2.35 eV. Photoconductive decay measurements exhibit a slow decay indicating the presence of hole traps, where Zn vacancies are believed to be the source of both the slow decay and the deep level emission observed in PL spectra.     

Two Distinct Origins of Highly Localized Luminescent Centers within InGaN/GaN Quantum‐Well Light‐Emitting Diodes

The high light‐output efficiencies of In_xGa_1‐xN quantum‐well (QW)‐based light‐emitting diodes (LEDs) even in presence of a large number of nonradiative recombination centers (such as dislocations) has been explained by localization of carriers in radiative potential traps, the origins of which still remain unclear. To provide insights on the highly efficient radiative traps, spectrally resolved photoluminescence (PL) microscopy has been performed on green‐light‐emitting In_0.22Ga_0.78N QW LEDs, by selectively generating carriers in the alloy layers. PL imaging shows the presence of numerous inhomogeneously distributed low‐band‐gap traps with diverse radiative intensities. PL spectroscopy of a statistically relevant number of individual traps reveals a clear bimodal distribution in terms of both band‐gap energies and radiative recombination efficiencies, indicating the presence of two distinct classes of carrier localization centers within the same QW sample. Disparity in their relative surface coverage and photoemission “blinking” characteristics suggests that the deep traps originate from local compositional fluctuations of indium within the alloy, while the shallow traps arise from nanometer‐scale thickness variations of the active layers. This is further supported by Poisson–Schrödinger self‐consistent calculations and implies that radiative traps formed due to both local indium content and interface‐morphology‐related heterogeneities can coexist within the same QW sample.     

Characterization of radiative efficiency in double heterostructures of InGaAsP/InP by photoluminescence intensity analysis

The photoluminescence (PL) intensity of an InGaAsP layer has been investigated as a function of excitation power density over a wide range of five orders. Two samples with n-InP/n-InGaAsP isotype and p-InP/n-InGaAsP heterotype doping have quite different excitation power dependences on PL intensity. The heterotype sample has notable nonlinear dependence. The excitation power dependences of PL intensity are theoretically analyzed. The estimated interface recombination velocity of the InP/InGaAsP heterojunction is found to be very low (smaller than a few cm/sec), compared with that of a GaAs/GaAlAs heterojunction.This PL intensity analysis has been applied to study the effect of an InP buffer layer and thermal degradation of radiative efficiency. The effective non-radiative recombination life time has been estimated as about 2×10⁻⁹ s for the double heterostructure with no buffer layer. Annealing in conditions of low phosphorus pressure leads to degradation of radiative efficiency, and the degradation is attributed to decrease in the nonradiative life time in the quaternary layer rather than increase in the interface recombination velocity. Sufficient phosphorus pressure prevents degradation of radiative efficiency. The correlation between PL intensity and output optical power of the light emitting diode has also been investigated. The PL intensity must be measured at high excitation power if it is to accurately predict the output power as a light emitting diode.     

基于MEMS技术的安培酶免疫传感器研究

该文采用MEMS工艺制备可集成安培酶免疫传感器,用于人免疫球蛋白IgG的检测。该传感器以硅作为基底,铂作为电极,工作电极敏感面积1mm2。SU-8胶形成的微反应池结构使该传感器试剂用量仅为l量级。聚吡咯作为酶与电极之间的电子转移基体聚合于工作电极敏感表面,戊二醛作为交联剂进行抗体(羊抗人IgG)的固定。抗体与酶标抗体(辣根过氧化物酶HRP标羊抗人IgG)对人IgG进行特异性夹心识别,通过检测酶标HRP对底物H2O2催化产生的电流信号实现免疫检测。该传感器工作电压-0.3V,检测下限5ng/ml,线性范围5～255ng/ml,响应时间3min,具有响应快、下限低、试剂用量少、微型化、便于集成等优点。     

Virus‐Tethered Magnetic Gold Microspheres with Biomimetic Architectures for Enhanced Immunoassays

In immunoassays, non‐specific bindings to biosensing surfaces can be effectively prevented by formation of biocompatible and hydrophilic self‐assembled monolayer (SAM) on the surfaces. A thin gold (Au) layer on magnetic microspheres, 15 μm in diameter, enables facile SAM formation and thereby accepts second layer of filamentous virus scaffolds for the immobilization of functional proteins. The merger of the virus and SAM‐Au protected microspheres not only provides exceptionlly dense antibody loading, but also resembles biological cellular structures that enhance ligand‐receptor interactions. Site‐specific biotinylation of filamenous viruses allows formation of free‐standing virus threads (>1.0 × 10¹⁰) on streptavidin‐modified SAM‐Au microspheres. The augmented yield of antibody loading, due to the increased surface to volume ratio, on virus‐modified Au microspheres is confirmed by measuring fluorescence intensities. The bead‐based immunoassays for the detection of cardiac marker proteins exhibit increased sensitivity of virus‐Au microspheres, as low as 20 pg mL^?1 of cardiac troponin I in serum, and extremely low non‐specific adsorption when compared with bare polymer beads. This increased sensitivity due to filamentous morphology and SAM‐Au layer demonstrates the feasibility of merging viruses with non‐biological materials to yield biomimetic tools for the enhanced bead‐based immunoassays.     

Learning from Diatoms: Nature's Tools for the Production of Nanostructured Silica

Diatoms are eukaryotic, unicellular algae that are ubiquitously present in almost any water habitat on earth. Diatoms dominate phytoplankton populations and algal blooms in the oceans. They are responsible for about 25 % of the world's net primary production. Apart from this ecological significance, diatoms are mainly known for the intricate geometries and spectacular patterns of their silica‐based cell walls. These patterns are species specific. They are precisely reproduced in each generation documenting a genetic control of this biomineralization process. Biogenesis of the diatom cell wall is considered to be a paradigm for the controlled production of nanostructured silica. Biochemical studies demonstrated that diatom biosilica is a composite material containing zwitterionic proteins (silaffins) and long‐chain polyamines in addition to silica. Functional studies indicate a crucial role of these organic components in guiding silica precipitation as well as in the formation of species‐specific nanopatterns. These activities can be explained by molecular self‐assembly and phase‐separation processes. Moreover, diatom cell walls also exhibit very exciting properties from the physical point of view: they are extremely stable and they may act as photonic crystals.     

Layer‐By‐Layer Dendritic Growth of Hyperbranched Thin Films for Surface Sol–Gel Syntheses of Conformal,Functional, Nanocrystalline Oxide Coatings on Complex 3D (Bio)silica Templates

Here, a straightforward and general method for the rapid dendritic amplification of accessible surface functional groups on hydroxylated surfaces is described, with focus on its application to 3D biomineral surfaces. Reaction of hydroxyl‐bearing silica surfaces with an aminosilane, followed by alternating exposure to a dipentaerythritol‐derived polyacrylate solution and a polyamine solution, allows the rapid, layer‐by‐layer (LBL) build‐up of hyperbranched polyamine/polyacrylate thin films. Characterization of such LBL‐grown thin films by AFM, ellipsometry, XPS, and contact angle analyses reveals a stepwise and spatially homogeneous increase in film thickness with the number of applied layers. UV–Vis absorption analyses after fluorescein isothiocyanate labeling indicate that significant amine amplification is achieved after the deposition of only 2 layers with saturation achieved after 3–5 layers. Use of this thin‐film surface amplification technique for hydroxyl‐enrichment of biosilica templates facilitates the conformal surface sol–gel deposition of iron oxide that, upon controlled thermal treatment, is converted into a nanocrystalline (～9.5 nm) magnetite (Fe₃O₄) coating. The specific adsorption of arsenic onto such magnetite‐coated frustules from flowing, arsenic‐bearing aqueous solutions is significantly higher than for commercial magnetite nanoparticles (≤50 nm in diameter).     

Synthesis of Highly Luminescent SnO2 Nanocrystals: Analysis of their Defect‐Related Photoluminescence Using Polyoxometalates as Quenchers

Colloidal semiconductor nanocrystals (NCs), called quantum dots (QDs), have been intensively studied because of their excellent photoluminescence (PL) quantum yields. However, commercial QDs such as CdSe and InP contain toxic or expensive rare elements, limiting their sustainable use. This study focuses on nontoxic, stable, and cheap tin oxides, and synthesized luminescent SnO₂ NCs of ≈2 nm in size by a heating‐up method. Tin precursors and diols in a high‐boiling point solvent with oleylamine as the surfactant are heated at 240 °C. SnO₂ NCs show defect‐related photoluminescence at 400–460 nm by excitation at 370 nm, achieving a high quantum yield of more than 60%. The PL intensity is stable even when the NCs are stored in atmospheric air at room temperature for over 1 year. The defect‐related emissions of the SnO₂ NCs are studied using polyoxometalates (POMs) as the PL quencher. POMs efficiently quench the PL emissions by extracting excited electrons from the conduction band and shallow surface defects. The results reveal that PL emissions from SnO₂ NCs are associated with radiative charge recombination via shallow defect levels on the surface and in the bulk, demonstrating the effectiveness of the PL quenching technique using POMs in studying the PL emission mechanism in QDs.     

N‐Type Self‐Assembled Monolayer Field‐Effect Transistors and Complementary Inverters

This work describes n‐type self‐assembled monolayer field‐effect transistors (SAMFETs) based on a perylene derivative which is covalently fixed to an aluminum oxide dielectric via a phosphonic acid linker. N‐type SAMFETs spontaneously formed by a single layer of active molecules are demonstrated for transistor channel length up to 100 μm. Highly reproducible transistors with electron mobilities of 1.5 × 10^?3 cm² V^?1 s^?1 and on/off current ratios up to 10⁵ are obtained. By implementing n‐type and p‐type transistors in one device, a complimentary inverter based solely on SAMFETs is demonstrated for the first time.