Langmuir Analysis of the Binding Affinity and Kinetics for Surface Tethered Duplex DNA and a Ligand–Apoprotein Complex

In this work, the hybridization and dehybridization of ssDNA with 20 bases at gold coated sensor surfaces modified with complementary 20 bases capture probe ssDNA was investigated at 18 °C by quartz crystal microbalance measurements with dissipation monitoring (QCM-D). A sequence of 20 base pairs with a melting temperature of about 64 °C was chosen, since in many biosensor studies the target molecules are DNA or RNA oligomers of similar length. It turned out that at the applied experimental conditions the DNA hybridization was irreversible, and therefore the hybridization and dehybridization process could not be described by the Langmuir model of adsorption. Nevertheless, quantitative dehybridization could be achieved by rinsing the sensor surface thoroughly with pure water. When in contrast the hybridization of a target with only 10 bases complementary to the outermost 10 bases of the 20 bases capture probe was studied, binding and unbinding were reversible, and the hybridization/dehybridization process could be satisfactorily described by the Langmuir model. For the 10 base pair sequence, the melting temperature was about 36 °C. Apparently, for Langmuir behavior, it is important that the experiments are applied at a temperature sufficiently close to the melting temperature of the sequence under investigation to ensure that at least traces of the target molecules are unhybridized (i.e., there needs to be an equilibrium between hybridized and dehybridized target molecules). To validate the reliability of our experimental approach we also studied the reconstitution and disassembly of the flavoprotein dodecin at flavin-terminated DNA monolayers, as according to previous studies it is assumed that the apododecin–flavin system can be well described by the Langmuir model. As a result, this assumption could be verified. Using three different approaches, <i>K</i>_D values were obtained that differ not more than by a factor of 4

Phase Relationships in the BaO–Ga₂O₃–Ta₂O₅ System and the Structure of Ba₆Ga₂₁TaO₄₀

Phase relationships in the BaO–Ga₂O₃–Ta₂O₅ ternary system at 1200 °C were determined. The A₆B₁₀O₃₀ tetragonal tungsten bronze (TTB) related solution in the BaO–Ta₂O₅ subsystem dissolved up to ∼11 mol % Ga₂O₃, forming a ternary trapezoid-shaped TTB-related solid solution region defined by the BaTa₂O₆, Ba_1.1Ta₅O_13.6, Ba_1.58Ga_0.92Ta_4.08O_13.16, and Ba₆GaTa₉O₃₀ compositions in the BaO–Ga₂O₃–Ta₂O₅ system. Two ternary phases Ba₆Ga₂₁TaO₄₀ and eight-layer twinned hexagonal perovskite solid solution Ba₈Ga_4–<i>x</i>Ta_{4+0.6<i>x</i>}O₂₄ were confirmed in the BaO–Ga₂O₃–Ta₂O₅ system. Ba₆Ga₂₁TaO₄₀ crystallized in a monoclinic cell of <i>a</i> = 15.9130(2) Å, <i>b</i> = 11.7309(1) Å, <i>c</i> = 5.13593(6) Å, β = 107.7893(9)°, and <i>Z</i> = 1 in space group <i>C</i>2/<i>m</i>. The structure of Ba₆Ga₂₁TaO₄₀ was solved by the charge flipping method, and it represents a three-dimensional (3D) mixed GaO₄ tetrahedral and GaO₆/TaO₆ octahedral framework, forming mixed 1D 5/6-fold tunnels that accommodate the Ba cations along the <i>c</i> axis. The electrical property of Ba₆Ga₂₁TaO₄₀ was characterized by using ac impedance spectroscopy

Molecular Beacon Modified Sensor Chips for Oligonucleotide Detection with Optical Readout

Three different surface bound molecular beacons (MBs) were investigated using surface plasmon fluorescence spectroscopy (SPFS) as an optical readout technique. While MB1 and MB2, both consisting of 36 bases, differed only in the length of the linker for surface attachment, the significantly longer MB3, consisting of 56 bases, comprised an entirely different sequence. For sensor chip preparation, the MBs were chemisorbed on gold via thiol anchors together with different thiol spacers. The influence of important parameters, such as the length of the MBs, the length of the linker between the MBs and the gold surface, the length and nature of the thiol spacers, and the ratio between the MBs and the thiol spacers was studied. After hybridization with the target, the fluorophore of the longer MB3 was oriented close to the surface, and the shorter MBs were standing more or less upright, leading to a larger increase in fluorescence intensity. Fluorescence microscopy revealed a homogeneous distribution of the MBs on the surface. The sensor chips could be used for simple and fast detection of target molecules with a limit of detection in the larger picomolar range. The response time was between 5 and 20 min. Furthermore, it was possible to distinguish between fully complementary and singly mismatched targets. While rinsing with buffer solution after hybridization with target did not result in any signal decrease, complete dehybridization could be carried out by intense rinsing with pure water. The MB modified sensor chips could be prepared in a repeatable manner and reused many times without significant decrease in performance

Studies of Terbium Bridge: Saturation Phenomenon, Significance of Sensitizer and Mechanisms of Energy Transfer, and Luminescence Quenching

Terbium chain in the form of S → (Tb³⁺)_<i>n</i> → A (S = Ce³⁺ or Eu²⁺, A = Eu³⁺), as a promising energy transfer (ET) approach, has been proposed to enhance Eu³⁺ emission for solid-state lighting. However, the viewpoint of ET from S to A via the terbium chain (Tb³⁺–Tb³⁺–Tb³⁺–...) is very doubtful. Here, hosts of Ba₃Ln­(PO₄)₃, LnPO₄, LnBO₃, and Na₂Ln₂B₂O₇ doped with Ce³⁺ → (Tb³⁺)_<i>n</i> → Eu³⁺ or (Tb³⁺)_<i>n</i> → Eu³⁺ are synthesized to prove the universality of S → (Tb³⁺)_<i>n</i> → A in inorganic hosts and to study the unsolved issues. Saturation distance of Tb³⁺–Eu³⁺, estimated with the empirical data of different hosts, is proposed to be a criterion for determining whether a spectral chromaticity coordinate keeps constant. A branch model is put forward to replace the chain model to explain the role of (Tb³⁺)_<i>n</i> in ET from Ce³⁺ to Eu³⁺ and the necessity of high content of Tb³⁺; the term “terbium bridge” is used to replace “terbium chain”, and the value of <i>n</i> is determined to be two or three. The intensity quenching of Eu³⁺ emission is attributed to the surface defects ascribed to the smaller particles and larger specific surface area rather than the concentration quenching of Tb³⁺. Based on the saturation distance and the mechanism of luminescence quenching, the necessary concentration of Tb³⁺ for (Tb³⁺)_<i>n</i> can be estimated as long as the cell parameters are already known and the luminescent efficiency of Eu³⁺ can be further improved by optimizing the synthesis method to decrease the quantity of surface defects

Phase Relationships in the BaO–Ga₂O₃–Ta₂O₅ System and the Structure of Ba₆Ga₂₁TaO₄₀

Phase relationships in the BaO–Ga₂O₃–Ta₂O₅ ternary system at 1200 °C were determined. The A₆B₁₀O₃₀ tetragonal tungsten bronze (TTB) related solution in the BaO–Ta₂O₅ subsystem dissolved up to ∼11 mol % Ga₂O₃, forming a ternary trapezoid-shaped TTB-related solid solution region defined by the BaTa₂O₆, Ba_1.1Ta₅O_13.6, Ba_1.58Ga_0.92Ta_4.08O_13.16, and Ba₆GaTa₉O₃₀ compositions in the BaO–Ga₂O₃–Ta₂O₅ system. Two ternary phases Ba₆Ga₂₁TaO₄₀ and eight-layer twinned hexagonal perovskite solid solution Ba₈Ga_4–<i>x</i>Ta_{4+0.6<i>x</i>}O₂₄ were confirmed in the BaO–Ga₂O₃–Ta₂O₅ system. Ba₆Ga₂₁TaO₄₀ crystallized in a monoclinic cell of <i>a</i> = 15.9130(2) Å, <i>b</i> = 11.7309(1) Å, <i>c</i> = 5.13593(6) Å, β = 107.7893(9)°, and <i>Z</i> = 1 in space group <i>C</i>2/<i>m</i>. The structure of Ba₆Ga₂₁TaO₄₀ was solved by the charge flipping method, and it represents a three-dimensional (3D) mixed GaO₄ tetrahedral and GaO₆/TaO₆ octahedral framework, forming mixed 1D 5/6-fold tunnels that accommodate the Ba cations along the <i>c</i> axis. The electrical property of Ba₆Ga₂₁TaO₄₀ was characterized by using ac impedance spectroscopy

Critical View on Electrochemical Impedance Spectroscopy Using the Ferri/Ferrocyanide Redox Couple at Gold Electrodes

Electrochemical or faradaic impedance spectroscopy (EIS) using the ferri/ferrocyanide couple as a redox probe at gold working electrodes was evaluated with respect to its ability to monitor consecutive surface modification steps. As a model reaction, the reversible hybridization and dehybridization of DNA was studied. Thiol-modified single stranded DNA (ssDNA, 20 bases, capture probe) was chemisorbed to a gold electrode and treated with a solution of short thiols to release nonspecifically adsorbed DNA before hybridization with complementary ssDNA (20 bases, target) was carried out. Reversible dehybridization was achieved by intense rinsing with pure water. The experimental procedures were optimized by kinetic surface plasmon resonance (SPR) and quartz crystal microbalance with dissipation (QCM-D) measurements to maximize the increase in reflectivity or decrease in frequency upon hybridization before hybridization/dehybridization was also monitored by EIS. In contrast to SPR and QCM-D, repeatable EIS measurements were not possible at first. Combined SPR/EIS and QCM-D/EIS measurements revealed that during EIS the gold surface is seriously damaged due to the presence of CN^– ions, which are released from the ferri/ferrocyanide redox probe. Even at optimized experimental conditions, etching the gold electrodes could not be completely suppressed and the repeatability of the EIS measurements was limited. In three out of four experimental runs, only two hybridization/dehybridization steps could be monitored reversibly by EIS. Thereafter etching the gold electrode significantly contributed to the EIS spectra whereas the QCM-D response was still repeatable. Hence great care has to be taken when this technique is used to monitor surface modification at gold electrodes

Multi-Ligand-Binding Flavoprotein Dodecin as a Key Element for Reversible Surface Modification in Nano-biotechnology

In this paper the multiple (re)programming of protein–DNA nanostructures comprising generation, deletion, and reprogramming on the same flavin-DNA-modified surface is introduced. This work is based on a systematic study of the binding affinity of the multi-ligand-binding flavoprotein dodecin on flavin-terminated DNA monolayers by surface plasmon resonance and quartz crystal microbalance with dissipation (QCM-D) measurements, surface plasmon fluorescence spectroscopy (SPFS), and dynamic AFM force spectroscopy. Depending on the flavin surface coverage, a single apododecin is captured by one or more surface-immobilized flavins. The corresponding complex binding and unbinding rate constants <i>k</i>_on(QCM) = 7.7 × 10³ M^–1·s^–1 and <i>k</i>_off(QCM) = 4.5 × 10^–3 s^–1 (<i>K</i>_d(QCM) = 580 nM) were determined by QCM and were found to be in agreement with values for <i>k</i>_off determined by SPFS and force spectroscopy. Even though a single apododecin–flavin bond is relatively weak, stable dodecin monolayers were formed on flavin-DNA-modified surfaces at high flavin surface coverage due to multivalent interactions between apododecin bearing six binding pockets and the surface-bound flavin-DNA ligands. If bi- or multivalent flavin ligands are adsorbed on dodecin monolayers, stable sandwich-type surface-DNA-flavin-apododecin-flavin ligand arrays are obtained. Nevertheless, the apododecin flavin complex is easily and quantitatively disassembled by flavin reduction. Binding and release of apododecin are reversible processes, which can be carried out alternatingly several times to release one type of ligand by an external redox trigger and subsequently replace it with a different ligand. Hence the versatile concept of reprogrammable functional biointerfaces with the multi-ligand-binding flavoprotein dodecin is demonstrated

Enhancing the Performance of Quantum-Dot Light-Emitting Diodes by Postmetallization Annealing

The effect of postannealing on the device characteristics is systematically investigated. The external quantum efficiency (EQE) of blue quantum-dot light-emitting diodes (QLEDs) is significantly improved from 5.22 to 9.81% after postannealing. Similar results are obtained in green and red QLEDs, whose EQEs are enhanced from 11.47 and 13.60 to 15.57 and 16.59%, respectively. The annealed devices also exhibit a larger current density. The origin of efficiency improvement is thoroughly investigated. Our finding indicates that postannealing promotes the interfacial reaction of Al and ZnMgO and consequently leads to the metallization of the AlZnMgO contact and the formation of the AlO_<i>x</i> interlayer. Because of the metallization of AlZnMgO, the contact resistance is effectively reduced, and thus the electron injection is enhanced. On the other hand, the formation of the AlO_<i>x</i> interlayer can effectively suppress the quenching of excitons by the metal electrode. Because of the enhancement of electron injection and suppression of exciton quenching, the annealed blue, green, and red QLEDs exhibit a 1.9-, a 1.3-, and a 1.2-fold efficiency improvement, respectively. We envision the results offer a simple yet effective method to enhance the charge injection and the efficiency of QLED devices, which would promote the practical application of QLEDs

Multifunctional Silicon Optoelectronics Integrated with Plasmonic Scattering Color

Plasmonic scattering from metallic nanoparticles has been used for centuries to create the colorful appearance of stained glass. Besides their use as passive spectral filtering components, multifunctional optoelectronic applications can be achieved by integrating the nanoscatters with semiconductors that generate electricity using the complementary spectral components of plasmonic colors. To suppress the usual degradation of both efficiency and the gamut of plasmonic scattering coloration in highly asymmetric index configurations like a silicon host, aluminum nanodisks on indium tin oxide (ITO) coated silicon were experimentally studied and demonstrated color sorting in the full visible range along with photocurrent generation. Interestingly, the photocurrents were found to be comparable to the reference devices with only antireflection coatings in spite of the power loss for coloration. Detailed investigation shows that ITO serves as both the impedance matching layer for promoting the backward scattering and schottky contact with silicon, and moreover, plasmonic nanoscatters efficiently harvest the complement spectrum components for charge generation. The present approach combines the capacities of nanoscale color sorting and photoelectric converting at a negligible cost of efficiency, thus providing a broad flexibility of being utilized in various optoelectronic applications including self-powered display, filter-free imaging, and colorful photovoltaics

Highly Thermally Stable Single-Component White-Emitting Silicate Glass for Organic-Resin-Free White-Light-Emitting Diodes

Thermal management is still a great challenge for high-power phosphor-converted white-light-emitting diodes (pc-WLEDs) intended for future general lighting. In this paper, a series of single-component white-emitting silicate SiO₂–Li₂O–SrO–Al₂O₃–K₂O–P₂O₅: Ce³⁺, Tb³⁺, Mn²⁺ (SLSAKP: Ce³⁺, Tb³⁺, Mn²⁺) glasses that simultaneously play key roles as a luminescent convertor and an encapsulating material for WLEDs were prepared via the conventional melt-quenching method, and systematically studied using their absorption spectra, transmittance spectra, photoluminescence excitation and emission spectra in the temperature range 296–498 K, decay curves, and quantum efficiency. The glasses show strong and broad absorption in 250–380 nm region and exhibit intense white emission, produced by in situ mixing of blue-violet, green, and orange-red light from Ce³⁺, Tb³⁺, and Mn²⁺ ions, respectively, in a single glass component. The quantum efficiency of SLSAKP: 0.3%Ce³⁺, 2.0%Tb³⁺, 2.0%Mn²⁺ glass is determined to be 19%. More importantly, this glass shows good thermal stability, exhibiting at 373 and 423 K about 84.56 and 71.02%, respectively, of the observed room temperature (298 K) emission intensity. The chromaticity shift of SLSAKP: 0.3%Ce³⁺, 2.0%Tb³⁺, 2.0%Mn²⁺ is 2.94 × 10^–2 at 498 K, only 57% of the commercial triple-color white-emitting phosphor mixture. Additionally, this glass shows no transmittance loss at the 370 nm emission of a UV-Chip-On-Board (UV-COB) after thermal aging for 240 h, compared with the 82% transmittance loss of epoxy resin. The thermal conductivity of the glass is about 1.07 W/mK, much larger than the 0.17 W/mK of epoxy resin. An organic-resin-free WLEDs device based on SLSAKP: 0.3%Ce³⁺, 2.0%Tb³⁺, 2.0%Mn²⁺ glass and UV-COB is successfully demonstrated. All of our results demonstrate that the presented Ce³⁺/Tb³⁺/Mn²⁺ tridoped lithium–strontium–silicate glass may serve as a promising candidate for high-power WLEDs