The reversible binding of hydrophobically end-capped poly(ethylene glycol)s to poly-β-cyclodextrin-coated gold surfaces: a surface plasmon resonance investigation

Polymers of β-cyclodextrin (β-CD) bearing amino groups (poly-β-CD-NH₂) were grafted to gold surfaces by two different procedures. Hydrophobically end-capped model-polymers were adsorbed onto resulting (poly-β-CD-NH₂)-coated sensor chips by formation of inclusion complexes. Their adsorption onto the surface was followed in real time by surface plasmon resonance (SPR). Multilayered structures obtained by inclusion of adamantyl-modified poly(ethylene glycol)s (Ad-PEG) into immobilized β-cyclodextrin cavities were highly stable in aqueous media. Conditions leading to the regeneration of initial (poly-β-CD-NH₂)-coated surfaces were studied by SPR. Regeneration by competitors such as polymers of β-cyclodextrin was possible. However, it was found to be a complex mechanism involving two opposite phenomena depending on the structure and composition of the (poly-β-CD-NH₂) layer. Complete desorption of the bound Ad-PEG layer was also observed after exposure of the multilayered structures to organic solvents or sodium dodecylsulfate (SDS).     

电导率测量合成氨冷凝液中氨浓度的应用

测定合成氨生产过程中的工艺冷凝液的回收利用是一项很重要的节能措施。但是合成氨系统的冷凝液往往由于管壁渗漏,使少量氨以游离状或铵盐形式存在于冷凝液中。而为了确保合成氨系统工艺冷凝液回收装置回收的工艺冷凝液不影响后续工序的正常运行,工艺冷凝液中氨等杂质的含量必须控制在一定的范围内,因此精确测定冷凝液中氨含量是回收利用冷凝液的先决条件。测定工艺冷凝液中氨离子用选择电极等测定法,该方法在工艺中受温度、压力和膜头密封等因素的影响使其不能正常与运行、且仪器价格昂贵。我公司采用电导率和氨根离子之间的浓度关系诺模图快速准确地反映合成氨冷凝液浓度值,满足合成氨冷凝液回收装置的运行要求。     

Interrogation of surface plasmon resonance sensors using temporally stretched ultrashort optical pulses

We propose a novel technique that has the potential to realize interrogation of surface plasmon resonance (SPR) sensors at very high speed. In contrast to the incoherent light source used in the traditional wavelength interrogation schemes, a broadband coherent laser generating short optical pulses at a high repetition rate is used along with a highly dispersive optical element. The dispersion causes strong broadening of the optical pulses, and the temporal pulse shape could exactly resemble the spectral distribution of the pulses due to the induced linear chirp. Therefore, by measuring the changes in the pulse shapes with a single high-speed photodetector, the spectral response of the SPR sensor can be obtained for each input pulse and the interrogation speed could reach the repetition rate of the pulse train. This could enable SPR measurements at the speed of tens of MHz or higher, which is well beyond that of other current SPR interrogation techniques. We experimentally demonstrate that, by measuring the variations in the pulse shapes of the chirped pulses, sensitive SPR measurements can be made. Implementing this scheme with a femtosecond fiber laser and other fiber optic components also show the potential to realize more compact and integrated SPR systems.     

Label-free sensitive optical detection of polychlorinated biphenyl (PCB) in an aqueous solution based on surface plasmon resonance measurements

A label-free, ultrasensitive method for the optical detection of polychlorinated biphenyl (PCB) is described. The detection mechanism for PCB is based on PCB-induced conformational changes of immobilized Cytochrome c (Cyt c) on an Au thin film altering the local dielectric function of the supported Cyt c, which can be detectable by surface plasmon resonance (SPR) spectroscopy. Results showed that the confirmations of Cyt c changed in a very sensitive way depend on PCB concentrations as confirmed by circular dichroism (CD) measurements and atomic force microscope (AFM) observations. Based on the results, we investigated the PCB-sensitive detection performance of the self-assembling Cyt c monolayer surface by SPR. On exposure to PCB, the reflectance R at the SPR angle of the supported Cyt c showed a sensitive and systematic increase with increasing PCB concentrations. The limit of detection was as low as 0.1 ppb and the responses completed within 10 min.     

On the interaction of oxygen with Nb(110) and Nb(750)

The interaction of Nb(110) and Nb(750) with oxygen has been studied using LEED, AES, SIMS and ELS. The Nb single-crystal samples contained an amount of ≈ 0.1 at.% oxygen dissolved in the bulk as determined by microhardness measurements. Segregation of oxygen from the bulk to the surface results in a very complex LEED pattern on Nb(110) which corresponds to about two thirds of a monolayer of chemisorbed oxygen. Oxygen segregation causes the Nb(750) surface to break up into (110) terraces and (310) steps with a minimum length of ≈ 50 Å. At temperatures below ≈ 200°C, a very thin oxide layer builds up when admitting oxygen from the gas phase to the surfaces. For P_O2 ⩽ 5 × 10^-8 Torr, the film teaches its final thickness of 5–6 Å after exposures to several hundred Langmuirs. AES, SIMS and ELS measurements suggest that the topmost layer of the oxide consists of a highly irregular two-dimensional network of NbO₆ octahedra linked together in a way to yield the stoichiometry of Nb₂O₅. At temperatures > 250°C the oxide film decomposes rapidly, probably by oxygen diffusion into the bulk, and the complex chemisorbed oxygen overlayer is restored.     

Novel e-nose for the discrimination of volatile organic biomarkers with an array of carbon nanotubes (CNT) conductive polymer nanocomposites (CPC) sensors

We report the original design of a new type of electronic nose (e-nose) consisting of only five sensors made of hierarchically structured conductive polymer nanocomposites (CPC). Each sensor benefits from both the exceptional electrical properties of carbon nanotubes (CNT) used to build the conductive architecture and the spray layer by layer (sLbL) assembly technique, which provides the transducers with a highly specific 3D surface structure. Excellent sensitivity and selectivity were obtained by optimizing the amount of CNT with five different polymer matrices: poly(caprolactone) (PCL), poly(lactic acid) (PLA), poly(carbonate) (PC), poly(methyl methacrylate) (PMMA) and a biobased polyester (BPR). The ability of the resulting e-nose to detect nine organic solvent vapours (isopropanol, tetrahydrofuran, dichloromethane, n-heptane, cyclohexane, methanol, ethanol, water and toluene), as well as biomarkers for lung cancer detection in breath analysis, has been demonstrated. Principal component analysis (PCA) proved to be an excellent pattern recognition tool to separate vapour clusters.     

Optical parameters of calix[4]arene films and their response to volatile organic vapors

The Langmuir-Blodgett (LB) technique was employed to produce thin LB films using an amphiphilic calix-4-resorcinarene onto different substrates such as quartz, gold coated glass and quartz crystals. The characteristics of the calix LB films are assessed by UV-visible, quartz crystal microbalance (QCM) and surface plasmon resonance (SPR) measurements. UV-vis and QCM measurements indicated that this material deposited very well onto the solid substrates with a transfer ratio of >0.95. Using SPR data, the thickness and refractive index of this LB film are determined to be 1.14 nm/deposited layer and 1.6 respectively. The sensing application of calixarene LB films towards volatile organic vapors such as chloroform, benzene, toluene and ethanol vapors is studied by the SPR technique. The response of this LB film to saturated chloroform vapor is much larger than for the other vapors. The response is fast and fully recoverable. It can be proposed that this sensing material deposited onto gold coated glass substrates has a good sensitivity and selectivity for chloroform vapor. This material may also find potential applications in the development of room temperature organic vapor sensing devices.     

Comparative analysis of QCM and SPR techniques for the optimization of immobilization sequences

One of the most remarkable procedures to immobilize some biological molecules onto surfaces is the use of self-assembled monolayers (SAMs). The aim of this work is to analyse the influence of formation conditions in the detection capability of two different SAMs. With this purpose two techniques have been implemented: the Quartz Crystal Microbalance with Dissipation (QCM-D) and the Surface Plasmon Resonance (SPR). Thus, several parameters usually involved in the SAM protocols have been characterized, i.e. the nature of the thiolated acid. The influence of its concentration and incubation time has been also taken into account. For the validation of these biological layers, the polymyxin B sulfate salt (PmB), as ligand, and the lipopolysaccharide (LPS), as analyte, have been used. It is demonstrated that both in the QCM and the SPR, the use of SAM improves significantly the detection and immobilization of the target compound and an optimum SAM formation protocol is provided.     

Manufacture of robust surface plasmon resonance fiber optic based dip-probes

Surface plasmon resonance (SPR) spectroscopy has been conducted on both prism and fiber optic (FO) based sensors for several years. This technique measures the refractive index (RI) of a solution or layer adsorbed to a thin (50 nm) Au layer on the sensor substrate. To date a succinct set of protocols have not been published regarding the optimization of fiber-based SPR dip-probe sensors. Such sensors would allow application of SPR to a wider variety of applications. This paper focuses on consideration of the choice of fiber, isolation of the mirror from the sensing area, and orientation of the probes in the metal layer sputter deposition chamber in the manufacture of SPR dip-probes for reproducibility and robustness. Optimization of the process yields sensors with a batch to batch reproducibility as low as 0.5 nm in the location of the SPR spectral minima. Further study of RI measurements by the same probe over 2 months show these SPR dip-probes have a long shelf-life. A selection of probes was exposed to various solutions to monitor their drift. The data shows the probes’ response indicated a lowering of the RI measured over a period of 3 or 7 days depending on the probe type. Evidence of surface porosity and damage upon exposure to hydrothermal water seems to indicate these sensors are prone to chemical attack. Further research is needed to characterize this attack and allow creation of more robust sensors.     

Simulation of satellite water vapour lidar measurements: Performance assessment under real atmospheric conditions

A lidar simulator has been applied to assess the performances of a satellite water vapour differential absorption lidar (DIAL) system. Measurements performed by the airborne Deutsches Zentrum für Luft-und Raumfahrt (DLR) water vapour DIAL on 15 May 2002 during ESA's Water Vapour Lidar Experiment (WALEX), in combination with PSU/NCAR Mesoscale Model (MM5) output, were used to obtain backscatter and water vapour fields with high resolution and accuracy. These data and model output serve as input for the simulator, allowing for the performance of satellite DIAL under highly-inhomogeneous atmospheric conditions including clouds to be assessed. The airborne measurements show an intrusion of stratospheric air into the troposphere, and MM5 data used above the DLR Falcon airplane flight altitude are characterized by very high upper tropospheric humidity levels, comparable to those associated with strong mid-latitude transport events from the troposphere to the lowermost stratosphere. Results of the simulator reveal that the maximum systematic error does not exceed 5% up to 16 km, except in the presence of thick cirrus and mid level clouds with an optical thickness up to 2 and, occasionally, inside the dry stratospheric intrusion, while the random error is less than 20% up to 16 km when spatial measurement resolutions are applied that follow the World Meteorological Organization (WMO) threshold observational requirements for numerical weather prediction (NWP). The bias is even smaller if a drier upper troposphere/lower stratosphere (UTLS) region from a reference atmosphere is considered. The results confirm the capability of satellite water vapour DIAL systems to retrieve thin structures of the tropospheric water vapour and particle backscatter fields, as well as its capability to provide low bias and random error measurements even in the presence of clouds.     

Polyisoprene-nanostructured carbon composite (PNCC) organic solvent vapour sensitivity and repeatability

In this paper highly structured carbon black (HSCB) dispersion method effect on polyisoprene-nanostructured carbon composite (PNCC) organic solvent vapour (OSV) sensitivity is presented. PNCC has been produced using two different HSCB dispersion techniques: (1) dry method: the HSCB dispersed in polyisoprene mixing ingredients by cold rolling and (2) wet method: the HSCB dispersed in chloroform by ultrasonic homogenizer and mixed with solution of rubber in chloroform by magnetic stirring. The sensitivity to OSV of the obtained PNCC is tested by holding the samples in vapour of toluene or ethyl acetate and measuring in situ electrical resistance, mass, and length of the sample. Obtained results indicate two mechanisms of the change of electrical resistance in PNCC. Repeatability of the response of PNCC is tested in case of toluene vapour.     

De-Noising Brain MRI Images by Mixing Concatenation and Residual Learning (MCR)

Brain magnetic resonance images (MRI) are used to diagnose the different diseases of the brain, such as swelling and tumor detection. The quality of the brain MR images is degraded by different noises, usually salt & pepper and Gaussian noises, which are added to the MR images during the acquisition process. In the presence of these noises, medical experts are facing problems in diagnosing diseases from noisy brain MR images. Therefore, we have proposed a de-noising method by mixing concatenation, and residual deep learning techniques called the MCR de-noising method. Our proposed MCR method is to eliminate salt & pepper and gaussian noises as much as possible from the brain MRI images. The MCR method has been trained and tested on the noise quantity levels 2% to 20% for both salt & pepper and gaussian noise. The experiments have been done on publically available brain MRI image datasets, which can easily be accessible in the experiments and result section. The Structure Similarity Index Measure (SSIM) and Peak Signal-to-Noise Ratio (PSNR) calculate the similarity score between the denoised images by the proposed MCR method and the original clean images. Also, the Mean Squared Error (MSE) measures the error or difference between generated denoised and the original images. The proposed MCR de-noising method has a 0.9763 SSIM score, 84.3182 PSNR, and 0.0004 MSE for salt & pepper noise; similarly, 0.7402 SSIM score, 72.7601 PSNR, and 0.0041 MSE for Gaussian noise at the highest level of 20% noise. In the end, we have compared the MCR method with the state-of-the-art de-noising filters such as median and wiener de-noising filters.     

Comparison of surface plasmon resonance spectroscopy and quartz crystal microbalance for human IgE quantification

Surface plasmon resonance (SPR) and quartz crystal microbalance (QCM) have been known independently as surface sensitive analytical devices capable of label-free and in situ bioassays. In this study a SPR device and a 10 MHz QCM sensor are employed for the study of human IgE and anti-human IgE-binding reactions upon immobilizing the latter on the gold electrodes. The SPR and QCM response curves to the antibody immobilization and antigen binding are similar in shape but different in time scale, reflecting different resonation principles. Through optimization of the anti-human IgE coating, both the SPR and QCM sensors could detect IgE in a linear range from 5 to 300 IU/ml. Although the intrinsic sensitivity of the SPR device is five times of the 10 MHz QCM, the IgE detection sensitivity of the two methods is, however, different only in a factor of 2. The acceptable QCM sensitivity for the IgE detection is attributed to the fact that QCM measures the sum of molar mass of a protein layer and the entrapped water. Although both the devices use open, stand still liquid cell, and all the measurements are performed at room temperature, the SPR reproducibility and reliability are better than QCM, as the QCM frequency is more sensitive to temperature fluctuations, press changes and mechanical disturbances.     

Highly accurate and sensitive surface plasmon resonance sensor based on channel photonic crystal waveguides

A highly sensitive surface plasmon resonance (SPR) sensor based on channel photonic crystal waveguide (PCW) is proposed. The PCW is based on widely used lithographic and nano-fabrication compatible materials like TiO₂ and SiO₂. Gold has been used as a SPR active metal. By rigorously optimizing the different waveguide parameters, we have shown that there is significant transfer of modal power around phase-matching or resonance wavelength which has been utilized to design a compact and highly sensitive sensor for lab on chip. The ultra narrow width (∼765 pm for an interaction length of 10 mm) of surface plasmon resonance curve and sensitivity as high as 7500 nm-RIU⁻¹ will open a new window for bio-chemical sensing applications.     

Error estimation and adaptive procedures based on superconvergent patch recovery (SPR) techniques

Summary  The paper discusses error estimation and adaptive finite element procedures for elasto-static and dynamic problems based on superconvergent patch recovery (SPR) techniques. The SPR is a postprocessing procedure to obtain improved finite element solutions by the least squares fitting of superconvergent stresses at certain sampling points in local patches. An enhancement of the original SPR by accounting for the equilibirum equations and boundary conditions is proposed. This enhancement improves the quality of postprocessed solutions considerably and thus provides an even more effective error estimate. The patch configuration of SPR can be either the union of elements surrounding a vertex node, thenode patch, or, the union of elements surrounding an element, theelement patch. It is shown that these two choices give normally comparable quality of postprocessed solutions. The paper is also concerned with the application of SPR techniques to a wide range of problems. The plate bending problem posted in mixed form where force and displacement variables are simultaneously used as unknowns is considered. For eigenvalue problems, a procedure of improving eigenpairs and error estimation of the eigenfrequency is presented. A postprocessed type of error estimate and an adaptive procedure for the semidiscrete finite element method are discussed. It is shown that the procedure is able to update the spatial mesh and the time step size so that both spatial and time discretization errors are controlled within specified tolerances. A discontinuous Galerkin method for solving structural dynamics is also presented.     

In place merging of satellite based atmospheric water vapour measurements

Atmospheric water vapour plays a key role in the climatology of the Earth. It has traditionally been measured using radiosondes for reasons of instrumental simplicity but these offer limited opportunities for spatial and continuous measurements of dynamic water vapour changes over large areas of the Earth's atmosphere. Efforts have recently turned to using satellite remote sensing instruments with different spectral and spatial capabilities to derive measurements of total water vapour content in atmospheric columns or simply precipitable water. The merging of remote sensing data with different spectral and spatial capabilities can result in large biases when independent measurements are not nested correctly to produce the final product. Consequently, such merging of data must take into account the intrinsic time dynamics of measured parameters. In this paper, the impact of atmospheric water vapour dynamics on the merging of satellite-based retrieval of precipitable water estimates is investigated by comparing independent measurements obtained at different spatial resolutions from the High Resolution Infrared Sounder (HIRS) and the Advanced Very High Resolution Radiometer (AVHRR). Correlations are used to infer optimal merging parameters depending on the observational conditions. The authors conclude that the merging technique reproduces HIRS-based retrievals in cloud-free and partly cloudy locations from AVHRR soundings.     

Kelvin Probe measurements of polymer coated gold substrates: Mechanism studies

The origin of work-function changes induced in polymer/metal structures (polyacrylic acid (PAA), ammonium and sodium polyacrylate) upon ammonia exposure is studied. To understand and explain the mechanism systematic measurements of uncoated and polymer coated metals are performed in Kelvin Probe (KP) setups. Additional data have been acquired through gravimetric and electrochemical experiments (cyclic voltammetry (CV)). The results obtained confirm that the field effect sensitive processes are taking place at the metal/polymer interface and allow their modelling. The intrinsic sensitivity of metallic samples upon ammonia exposure is influenced by the presence of coating polymers, by their ability to sorb water and to keep the metal surface wet or dry.     

Highly sensitive detection of HCl gas using a thin film of meso-tetra(4-pyridyl)porphyrin coated glass slide by optochemical method

The meso-tetra(4-pyridyl)porphyrin (MTPyP) deposited on glass slide by dip coating was used as a solid state sensor for HCl gas detection by optochemical method. Exposure of MTPyP coated glass slide to HCl gas results in the formation of protonated meso-tetra(4-pyridyl)porphyrin (PMTPyP). UV-vis and fluorescence spectral methods were used to study the protonation of MTPyP both in solution and on solid state. The absorption spectrum of MTPyP modified glass slide shows an intense Soret band at 427 nm, which is shifted to 470 nm upon exposure to HCl gas. The concentration of HCl gas was monitored from the absorbance changes of Soret band of PMTPyP at 470 nm. The detection limit of the solid state sensor was found to be 0.01 ppm. The recovery rate of the solid state was very fast and it was monitored by UV-vis and fluorescence techniques with successive exposure to HCl gas and ammonia vapor with nitrogen gas. The planarity and energy of the molecule have changed after exposed to HCl gas which was confirmed by ab-intio calculation using Gaussian software. The response of the solid state sensor towards HCl gas was highly stable for several months.     

Surface plasmon resonance detection of small molecule using split aptamer fragments

It was difficult to detect small molecules directly using conventional surface plasmon resonance (SPR) biosensors since the changes of refractive index, which was resulted by binding small molecules, were usually small. In this paper, split aptamer fragments were used for the construction of SPR biosensor to determine small molecule such as adenosine with high sensitivity. An aptamer for adenosine was designed to be two flexible ssDNA pieces, one was tethered on Au film and the other was modified on Au nanoparticles (AuNPs). In the presence of adenosine, two ssDNA pieces reassembled into the intact aptamer structure and the AuNPs-labeled adenosine-aptamer complex was formed on the Au film. Then, the resonance wavelength shift was enhanced obviously, due to the electronic coupling between the localized plasmon of AuNPs and the surface plasmon wave associated with Au film. The results confirmed that this biosensor could detect adenosine with high sensitivity and selectivity. The limitation of detection (LOD) of this SPR biosensor was ca. 1.5 pM, which was an approximately ca. 2-3 order of magnitude lower than that of those SPR biosensors which utilized competitive methods.     

SAWSA-LPR: Astochastic search strategy for estimation of maximum likelihood DNA phylogenetic trees

In the spirit of the “grand challenge”, this paper covers the development of novel concepts for inference of large phylogenies based on the maximum likelihood method, which has proved to be the most accurate model for inference of huge and complex phylogenetic trees. Here, a novel method called Leaf Pruning and Re-grafting (LPR) has being presented, which is a variant of standard Sub-tree Pruning and Re-grafting (SPR) technique. LPR is a systematic approach where only unique topologies are generated at each step. Various stochastic search strategies for estimation of the maximum likelihood (ML) tree have also being proposed. Here, simulated annealing has been combined with steepest accent method to improve the quality of the final tree obtained. All the current simulated annealing approaches are used with simple hill climbing method to avoid the large number of repeated topologies that are normally generated by SPR. This easily leads to local maxima. However in the present study steepest accent with simulated annealing by way of LPR (SAWSA-LPR) has being used; the chances of returning local maxima has being significantly reduced. A straightforward and efficient parallel version of simulated annealing with steepest accent to accelerate the process of DNA phylogenetic tree inference has also being presented. It was observed that the implementation of the algorithm based on random DNA sequences gave better results as compared to other tree construction methods.