Fluorescent polyelectrolytes as protein sensors

This review discusses recent advances in protein sensing using fluorescent polyelectrolytes that are mainly water‐soluble conjugated polymers. A quencher‐labeled substrate or fluorophore‐labeled substrate is generally used as a probe. In the presence of an enzyme, the linker between substrate and quencher/fluorophore is cleaved and fluorescence of the polymer is either ‘turned on’ or ‘turned off’. Fluorescence behavior of these conjugated polymers is highly sensitive to conformation of the polymeric chains. Since upon binding with proteins the conformation is perturbed and fluorescence is affected, these polyelectrolytes have been used to study conformational changes in proteins. The conformation‐dependent fluorescence is also a limitation for these sensors in some cases and non‐conjugated polyelectrolytes have been shown to provide an alternative. Copyright © 2006 Society of Chemical Industry     

Polyurethane-acrylate based films as humidity sensors

Fluorescence spectroscopy, together with a conventional gravimetric method, were employed to study the mechanism and kinetics of water diffusion in UV-cured polyurethane-acrylate based adhesive films doped with organic fluorescent sensors. The diffusion of water through the films followed Fick's law during almost the whole mass sorption curve. Whilst the fluorescence data showed that boundary conditions are more complex and Fickian behaviour is only observed after different periods, depending on the molar volume of the fluorescent probe and the adhesive composition. The influence of hydrophilic monomers is discussed. Good correlation between diffusion coefficients by both methods is obtained in the range where water uptake is diffusion controlled.

The fluorescence of the studied probes or labels in these films shows high sensitivity to humidity, good long-term stability and fast response time. Therefore, it appears that these doped films can be used as efficient humidity sensors.     

Freestanding chemiresistive polymer composite ribbons as high-flux sensors

Chemiresistive polymer composite ribbons that function as chemical detectors were produced from solution-cast films of polymers and carbon composites. An array with multiple polymer sensor threads was exposed to dimethyl methyl phosphonate, a nerve agent simulant, and different interferents in the vapor phase. Principal component analysis was used to differentiate between the analytes. The response of the ribbon sensors as a function of the carbon composite and the host polymer source was investigated. The freestanding threads/sensors were mounted into a cell perpendicular to the gas flow to provide little pressure drop and were imbedded into fabrics to provide an example of a small, low-cost, wearable chemical sensor. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Single-walled carbon nanotube/Nafion composites as methanol sensors

Single-walled carbon nanotube (SWCNT)/Nafion composite films were fabricated on an interdigitated electrode by using a simple casting method. Nafion acts as a polymer backbone to give stable and homogeneous cast thin films. The potential use of the composites as sensors of methanol concentration in water was investigated. The composites are operative even at ambient temperatures, and respond quickly to concentration changes. The resistance increases significantly with increasing concentration between 0.5 M and 4 M. The composites may be useful as a material to measure the concentration of methanol for direct fuel cells.     

Hybrid carbon nanostructured ensembles as chemiresistive hydrogen gas sensors

Hybrid carbon nanostructures consisting of graphene nanoplatelets (GNPs) interspersed with multiwalled carbon nanotubes (MWCNTs) were synthesized by solution phase mixing of their parent aqueous dispersions. To further arrest the aggregation of GNPs, crystalline nanoparticles of a noble metal (Pt) were dispersed in situ by chemical reduction. This ensemble of the metal decorated hybrid structure was solubilized using Nafion and a simple drop casting method was employed to fabricate the sensor. In addition to the remarkable stability and repeatability, the sensor also showed an enhanced sensitivity of ∼17% to a low concentration of 4 vol.% hydrogen in air, at room temperature. The improved sensitivity due to Nafion solubilization could be explained by a dual mechanism of hydrogen dissociation. Variations in the sensor properties with change in hydrogen concentrations and temperature were studied. The kinetics of hydrogen adsorption in the sensor could be well explained by the Avrami–Erofeev model. From the Arrhenius plot of the rate constants, the activation energy was determined to be ∼24 kJ/(mol H). Effect of morphology of the bare hybrid structure was systematically investigated by varying the weight ratios of GNPs and MWCNTs.     

Development of mini-cyclones as the size-selective inlet of miniature particle detectors

The recent development of miniature particle detectors stems from the demanding need to monitor/measure particles, especially nanoparticles, at the personal level for epidemiological studies or studies investigating the interaction among genes and environmental factors, including particulates. Light scattering and electrical mobility techniques have been implemented in these mini-devices for monitoring submicron particles. The presence of large particles in the sampling stream, however, affects the performance of these mini-detectors. Prototype mini-cyclones were thus developed as a size selective inlet for mini-particle detectors. In this study two “quarter-sized” mini-cyclones were designed to remove particles larger than 1.0 and 0.3 μm at a flow rate of 0.3 lpm, and their performance was experimentally evaluated. The performance of prototypes was also compared with that of existing personal sampling cyclones. Further, empirical models to estimate the performance of the prototype mini-cyclones (i.e., the 50% cutoff particle size and pressure drop) were also established. The developed linear regression model can thus serve as the tool for the future design of mini-cyclones with the similar size and configuration.     

Pre-imidized photoimageable polyimide as a dielectric for high density multichip modules

Issues relating to the fabrication of complex multichip modules were investigated from a manufacturability perspective. The use of a preimidized photosensitive polyimide reduces the number of processing steps, thus making it a desirable dielectric material. Factors influencing the polyimide resolution, stress, and feature profile were studied both by experimentation and modeling. Thermal cure cycles for polyimide baking were optimized for solvent resistance, polyimide mechanical properties, and process throughput. Studies were also done on polyimide interactions with metal depositions, including adhesion and polyimide surface damage. Results of this research are shown as embodied in a fabricated 1.4 Gbit/s optical transceiver multichip module.     

Methods and Applications of In Silico Aptamer Design and Modeling

Aptamers are nucleic acid analogues of antibodies with high affinity to different targets, such as cells, viruses, proteins, inorganic materials, and coenzymes. Empirical approaches allow the design of in vitro aptamers that bind particularly to a target molecule with high affinity and selectivity. Theoretical methods allow significant expansion of the possibilities of aptamer design. In this study, we review theoretical and joint theoretical-experimental studies dedicated to aptamer design and modeling. We consider aptamers with different targets, such as proteins, antibiotics, organophosphates, nucleobases, amino acids, and drugs. During nucleic acid modeling and in silico design, a full set of in silico methods can be applied, such as docking, molecular dynamics (MD), and statistical analysis. The typical modeling workflow starts with structure prediction. Then, docking of target and aptamer is performed. Next, MD simulations are performed, which allows for an evaluation of the stability of aptamer/ligand complexes and determination of the binding energies with higher accuracy. Then, aptamer/ligand interactions are analyzed, and mutations of studied aptamers made. Subsequently, the whole procedure of molecular modeling can be reiterated. Thus, the interactions between aptamers and their ligands are complex and difficult to understand using only experimental approaches. Docking and MD are irreplaceable when aptamers are studied in silico.     

核酸适配体在光生化检测中的应用

核酸适配体是一小段经体外筛选得到的寡核苷酸序列,能与相应的配体进行高亲和力和强特异性的结合。本文根据核酸适配体在检测靶物质时获得光信号的机理,将核酸适配体在光生化的检测方法进行分类,并评述了‘这些检测方法的优缺点及核酸适配体在生物检测中的发展前景。     

Carbon nanotubes as Raman sensors of vulcanization in natural rubber

A method has been developed to synthesize composites with cross-linked natural rubber (NR) and dispersed single-wall carbon nanotubes (SWNT). The mechanical response of the NR samples was observed to change as a function of the amount of sulfur used for cross-linking, based on the number density of cross-links resulting from the vulcanization process. The relationship between SWNTs D^∗ wavenumber shift and the amount of sulfur have been obtained by means of Raman spectroscopy. The cross-link densities of the NR and SWNT/NR samples have been calculated from uniaxial stress-strain measurements, and plotted as the function of the amount of added sulfur. Comparison of the results from mechanical measurements and Raman spectroscopic measurements showed that SWNT Raman sensors are sensitive to the cross-link density in natural rubber and can be used to evaluate the cross-linking process of rubbery materials.     

Application of hand-held mobility spectrometers as sensors in manufacturing industries

Ion mobility spectrometers (IMS) are small, lightweight, extremely robust devices with low power requirements, no moving parts, no absolute requirement for gases or vacuums, that can be operated atambient temperatures and pressures, and yet are capable of measuring vapour phase concentrations of organic chemicals at very low levels (sub-μg/l). IMS are capable of analysing complex mixtures and producing a simple spectral output. Volatile components produce measurable negative and positive product ions in the spectrometer through chemical ionization. The spectra produced are essentially the vapour phase fingerprints of the target molecules/mixture. Quantitative data can be obtained provided instrument response is within the linear dynamic range of these instruments, but most practical applications of IMS have used the technology in a qualitative manner in situations which require just an above/below threshold or positive/ negative response.In the manufacturing industry there are many examples where the aroma/odour of raw materials has safety or product quality implications. IMS was not developed to replace traditional methods of analysis, e.g. GC/MS or sensory panels, but rather to provide a rapid, qualitative response complementary to more established methods. This paper reports on the use of a hand-held ion mobility spectrometer to characterize the vapours produced by volatile organic compounds,fresh herbs and retail spice mixtures at ambient temperature and pressure. The results show that by monitoring in both ion acquisition modes, ion mobility spectrometers are capable of discriminating between a wide range of products.     

Impedance spectra analysis to characterize interdigitated electrodes as electrochemical sensors

Interdigitated electrode (IDE) arrays have been used widely for electrochemical impedance spectroscopy (EIS). Here, we present an in-depth analysis of interdigitated electrode impedance spectra. Such an analysis is necessary for the identification of the contribution of each interdigitated electrode circuit element to the impedance change. We also discuss the importance of the solution conductivity in impedance spectroscopy showing that the use of low conductivity solutions is advantageous when inter-digit solution resistance and geometric capacitance need to be monitored.     

Nanoporous carbons as gas sensors: Exploring the surface sensitivity

Ammonia sensing properties of a poly(sodium 4-styrene sulfonate) derived carbon and its air oxidized counterpart were studied. The carbons were used to fabricate chips-like devices that were further used for electrical resistance measurements when exposed to various concentrations of dry ammonia. The sulfur-containing carbon after oxidation had a nine times greater response to ammonia than before oxidation. This response was evaluated from the point of view of reactive adsorption and physisorption. The initial reactions of ammonia with the sulfonic groups on the non-oxidized carbon led to an irreversible increase in resistance, while on the oxidized carbon, deprived of sulfonic groups, physisorption caused an opposite effect. After equilibration and reactive adsorption, a reversible decrease in resistance upon exposure to ammonia was found on both samples. The extensive characterization of the carbons’ surfaces, and their performance as ammonia adsorbents, suggest that the sensing mechanism is governed by the physical adsorption of ammonia inside the micropores. Higher concentration of ammonia in air results in more pores being filled and thus, in the stronger response of the sensor.     

Ag nanocrystal as a promoter for carbon nanotube-based room-temperature gas sensors

We have investigated the room-temperature sensing enhancement of Ag nanoparticles (NPs) for multiwalled carbon nanotube (MWCNT)-based gas sensors using electrical measurements, in situ infrared (IR) microspectroscopy, and density functional theory (DFT) calculations. Multiple hybrid nanosensors with structures of MWCNTs/SnO(2)/Ag and MWCNTs/Ag have been synthesized using a process that combines a simple mini-arc plasma with electrostatic force directed assembly, and characterized by electron microscopy techniques. Ag NPs were found to enhance the sensing behavior through the "electronic sensitization" mechanism. In contrast to sensors based on bare MWCNTs and MWCNTs/SnO(2), sensors with Ag NPs show not only higher sensitivity and faster response to NO(2) but also significantly enhanced sensitivity to NH(3). Our DFT calculations indicate that the increased sensitivity to NO(2) is attributed to the formation of a NO(3) complex with oxygen on the Ag surface accompanying a charge rearrangement and a net electron transfer from the hybrid to NO(2). The significant response to NH(3) is predicted to arise because NH(3) is attracted to hollow sites on the oxidized Ag surface with the H atoms pointing towards Ag atoms and electron donation from H to the hybrid sensor.     

New fluorescent hyperbranched polymeric sensors as probes for monitoring photopolymerization reactions

Two polychromophoric dansyl hyperbranched fluorescent probes (HBPs) have been used as fluorescent sensors to follow photopolymerization reactions of acrylic monomers through fluorescence monitoring. Simultaneously, photo-DSC measurements were conducted. The combined data obtained by both techniques allowed to measure precise and adequately the kinetics of the systems. Differences are found depending on the composition of the formulation, but no depending on the probe inserted in the systems. The behavior and sensitivity of the functional HBP's have been compared with their low molecular weight monochromophoric reference compounds. Hyperbranched polychromophoric probes showed the same sensitivity towards the process than the monochromophoric probes, confirming the high sensitivity of the hyperbranched probes. Also, the data obtained by fluorescence allow distinguishing the different steps involved in the mechanism of a radical crosslinking polymerization, which could not be observed only with calorimetric measurements. The advantages of the functional HBP fluorescent probes towards their low molecular weight homologues are discussed.     

Synthesis and application of novel tricyanofuran hydrazone dyes as sensors for detection of microbes

Acknowledging the need to develop rapid and sensitive bacterial recognition approaches, we functionalised the tricyanofuran hydrazone molecular switch. Of significant interest in relation to the synthesised hydrazones is the formation of two different conjugated structures upon exposure to different pH values. Many bacteria release ammonia gas, which alkalises environments. Herein we report the synthesis of a tricyanofuran hydrazone having the function of a colorimetric pH sensor. The UV‐visible absorption and fluorescence spectra exhibit reversible colour changes of the tricyanofuran hydrazone solution in acetonitrile under acid–base conditions. Our results indicate that the tricyanofuran hydrazone probe can identify the bacterial targets quickly with high sensitivity. The infected samples exhibit a significant colour change from orange to blue and in the mean time there is a decrease in fluorescence emission as a function of ammonia and volatile amines released from bacterial metabolites. This tricyanofuran hydrazone chromophore is proposed for use in food packaging with a pH‐sensing capability.     

Copolymers from oligosiloxane methacrylates as a plasticizer-free membrane matrix for ion-selective sensors

Cross-linked copolymers have been prepared by free-radical photoinitiated polymerization of dimethacryloxypropyl oligodimethylsiloxane with monomethacryloxypropyl oligodimethylsiloxane and the polar comonomers cyanomethyl methacrylate, cyanoethyl methacrylate, trifluoroethyl methacrylate and hexafluoroisopropyl acrylate, respectively, for use as a plasticizer-free membrane matrix for ion-selective sensors. The polymerization course in dependence on the composition of the monomer mixture and on the presence of ionophore and ion conducting salt as well as chloroform as solvating agent was studied by means of differential scanning calorimetry. The resulting copolymer membranes were characterized concerning the content of residual CC double bonds and sol as well as their thermo-mechanical and electroanalytical properties. The thermal and mechanical properties of these copolymer membranes exhibiting a heterogeneous network structure are adjustable in a wide range by variation of the ratio of the monomers used. In comparison with the most widely used poly(vinyl chloride) based membranes containing a plasticizer, the K⁺ and Ca²⁺ selective sensor membranes based on the new copolymers exhibit analogous or even better electro-analytical properties and above all, a distinctly longer lifetime.     

Ultra-thin nanocrystalline diamond detectors

In this work, we present the results of investigations into the possibility of using the radio frequency chemical vapor deposition (RF CVD)-manufactured nanocrystalline diamond (NCD) layers as a material for detectors of ionizing radiation. The 0.2-μm-thick NCD layers were deposited on n- and p-type silicon substrates. The obtained Si–NCD–metal detector structures have been characterized electrically (I–V and C–V characteristics) and spectrally (spectral response to highly energetic ²⁵²Cf fission fragments). The measured results have been compared with some theoretical predictions.     

In-Silico Selection of Aptamer Targeting SARS-CoV-2 Spike Protein

Aptamers are single-stranded, short DNA or RNA oligonucleotides that can specifically bind to various target molecules. To diagnose the infected cases of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in time, numerous conventional methods are applied for viral detection via the amplification and quantification of DNA or antibodies specific to antigens on the virus. Herein, we generated a large number of mutated aptamer sequences, derived from a known sequence of receptor-binding domain (RBD)-1C aptamer, specific to the RBD of SARS-CoV-2 spike protein (S protein). Structural similarity, molecular docking, and molecular dynamics (MD) were utilized to screen aptamers and characterize the detailed interactions between the selected aptamers and the S protein. We identified two mutated aptamers, namely, RBD-1CM1 and RBD-1CM2, which presented better docking results against the S protein compared with the RBD-1C aptamer. Through the MD simulation, we further confirmed that the RBD-1CM1 aptamer can form the most stable complex with the S protein based on the number of hydrogen bonds formed between the two biomolecules. Based on the experimental data of quartz crystal microbalance (QCM), the RBD-1CM1 aptamer could produce larger signals in mass change and exhibit an improved binding affinity to the S protein. Therefore, the RBD-1CM1 aptamer, which was selected from 1431 mutants, was the best potential candidate for the detection of SARS-CoV-2. The RBD-1CM1 aptamer can be an alternative biological element for the development of SARS-CoV-2 diagnostic testing.