4-Aminophenyl boronic acid modified gold platforms for influenza diagnosis

As a potential pandemic threat to human health, there has been an urgent need for rapid, sensitive, simpler and less expensive detection method for the highly pathogenic influenza A virus. For this purpose, Quartz Crystal Microbalance (QCM) and Surface Plasmon Resonance (SPR) sensors have been developed for the recognition of hemagglutinin (HA) which is a major protein of influenza A virus. 4-Aminophenyl boronic acid (4-APBA) has been synthesized and used as a new ligand for binding of sialic acid (SA) via boronic acid–sugar interaction. SA has an important role in binding of HA. QCM and SPR sensor surfaces have been modified with thiol groups and then 4-APBA and SA have been immobilized on sensor surfaces, respectively. Sensor surfaces have been screened with AFM and used for the determination of HA from aqueous solution. The selective recognition of the QCM and SPR sensors toward Concanavalin A has been reported in this work. Also, the binding capacity and detection limits of QCM and SPR sensors have been calculated and detection limits were found to be 4.7 × 10^? 2 μM, (0.26 μg ml^? 1) and 1.28 × 10^? 1 μM, (0.72 μg ml^? 1) in the 95% confidence interval, respectively.     

A real time detection of the ovarian tumor associated antigen 1 (OVTA 1) in human serum by quartz crystal microbalance immobilized with anti-OVTA 1 polyclonal chicken IgY antibodies

In this study, we developed a sensitive quartz crystal microbalance (QCM) sensor which employs the anti-ovarian tumor associated antigen 1 (OVTA 1) IgY polyclonal chicken antibodies on the crystal surface for the detection of OVTA 1 in human serum. The anti-OVTA 1 IgY antibodies were anchored on the thiol-activated sensor surface using 1-ethyl-3[3-dimethylaminopropyl] carbodiimide hydrochloride/N-hydroxysuccinimide (EDC–NHS) coupling. The responses for different concentrations of anti-OVTA 1 antibody were also studied and 40 μg/mL was favorable for homogenous antibody coverage. The QCM sensor was used to monitor both immobilization and the target binding affinity. The anti-OVTA 1 antibody based QCM has allowed the competent detection of OVTA 1 in a high linear range of 0.5–10 μg/mL. The total time needed to complete the detection was as short as 5–6 h. The regeneration studies demonstrated that the proposed sensor was reusable up to 9 cycles with a slight loss in binding affinity. The detection of OVTA 1 in human serum allows a potential exploitation of the anti-OVTA 1 polyclonal antibody based QCM immunoassay for the screening of OVTA 1 antigen.     

Ligand exchange based paraoxon imprınted QCM sensor

In the present work, a paraoxon imprinted QCM sensor has been developed for the determination of paraoxon based on the modification of paraoxon imprinted film onto a quartz crystal combining the advantages of high selectivity of the piezoelectric microgravimetry using MIP film technique and high sensitivity of QCM detection. The paraoxon selective memories have formed on QCM electrode surface by using a new metal–chelate interaction based on pre-organized monomer and the paraoxon recognition activity of these molecular memories was investigated. Molecular imprinted polymer (MIP) film for the detection of paraoxon was developed and the analytical performance of paraoxon imprinted sensor was studied. The molecular imprinted polymer were characterized by FTIR measurements. Paraoxon imprinted sensor was characterized with AFM and ellipsometer. The study also includes the measurement of binding interaction of paraoxon imprinted quartz crystal microbalance (QCM) sensor, selectivity experiments and analytical performance of QCM electrode. The detection limit and the affinity constant (K_affinity) were found to be 0.06 μM and 2.25 × 10⁴ M^? 1 for paraoxon [MAAP–Cu(II)–paraoxon] based thin film, respectively. Also, it has been observed that the selectivity of the prepared paraoxon imprinted sensor is high compared to a similar chemical structure which is parathion.     

Performance evaluation of ZnO–CuO hetero junction solid state room temperature ethanol sensor

A semiconductor ethanol sensor was developed using ZnO–CuO and its performance was evaluated at room temperature. Hetero-junction sensor was made of ZnO–CuO nanoparticles for sensing alcohol at room temperature. Nanoparticles were prepared by hydrothermal method and optimized with different weight ratios. Sensor characteristics were linear for the concentration range of 150–250 ppm. Composite materials of ZnO–CuO were characterized using X-ray diffraction (XRD), temperature-programmed reduction (TPR) and high-resolution transmission electron microscopy (HR-TEM). ZnO–CuO (1:1) material showed maximum sensor response (S = R_air/R_alcohol) of 3.32 ± 0.1 toward 200 ppm of alcohol vapor at room temperature. The response and recovery times were measured to be 62 and 83 s, respectively. The linearity R² of the sensor response was 0.9026. The sensing materials ZnO–CuO (1:1) provide a simple, rapid and highly sensitive alcohol gas sensor operating at room temperature.     

Electrosynthesis of pinecone-shaped Pt–Pb nanostructures based on the application in glucose detection

The pinecone-shaped Pt–Pb nanostructures were synthesized by electrochemical deposition. The morphology and composition of the pinecone-shaped Pt–Pb nanostructures were characterized by scanning electron microscopy, energy dispersive X-ray detector, transmission electron microscopy and X-ray photoelectron spectroscopy. Cyclic voltammetry and differential pulse voltammetry were used to evaluate the electrocatalytic performance of the pinecone-shaped Pt–Pb nanostructures electrode toward glucose oxidation in neutral media. As a result, the pinecone-shaped Pt–Pb nanostructures electrode exhibited strong current responses to glucose at a negative potential of ? 0.1 V, where the interference from the oxidation of ascorbic acid was effectively avoided. The sensitivity of the sensor was 10.71 μA mM^?1 cm^?2 with a linearity up to 12 mM and a detection limit of 8.4 μM. In addition, the as-prepared nonenzyme glucose sensor exhibited acceptable stability and reproducibility for determination of glucose. The simple preparation method and good analytical performance can potentially pave the way for effective and highly sensitive non-enzyme glucose sensors.     

Solid-state mixed-potential sensor employing tin-doped indium oxide sensing electrode and scandium oxide-stabilised zirconia electrolyte

The sensing properties of the planar mixed-potential CO sensor coupling scandia-stabilized zirconia (ScsZ) as electrolyte and tin-doped indium oxide (ITO) as sensing electrode to different CO concentrations from ～100 ppm to ～500 ppm have been investigated. The monodispersed ITO particles with spherical shape have been obtained by hydrothermally treating the mixture of the coprecipitated gels with urea as an additive. Directly using urea as the mineralizer, the two coexisting morphologies such as rod-like and spherical shapes have been obtained. The sensor coupling spherical 5 at.% tin-doped indium oxide (5ITO) electrode shows better sensitivity than the sensors coupling both spherical 8 at.% tin-doped indium oxide (S8ITO) and 8 at.% tin-doped indium oxide (RS8ITO) containing rod-like particles. The sensor coupling spherical 5 at.% tin-doped indium oxide (5ITO) electrode also exhibits highly reproducible and stable signals to different CO concentrations.     

Highly sensitive and selective ethanol sensor based on micron-sized zinc oxide porous-shell hollow spheres

Zinc oxide (ZnO) porous-shell hollow spheres (PHS) were prepared by thermally oxidizing high-purity zinc powder in an oxygen-containing atmosphere, and its ethanol gas sensing properties were measured in the concentration range of 10–400 ppm. At the optimum operating temperature of 350 °C, a sensitivity of 0.25/ppm was obtained and the response–concentration curve was of high linearity. The response and recovery times were measured to be ～5–12 s and 8–13 s, respectively. The sensor was proved to be highly selective to ethanol. Our results indicate that ZnO PHS might be a promising material for fabricating practical ethanol sensors.     

Facile preparation of a DNA sensor for rapid herpes virus detection

In this paper, a simple DNA sensor platform was developed for rapid herpes virus detection in real samples. The deoxyribonucleic acid (DNA) sequences of the herpes simplex virus (DNA probe) were directly immobilized on the surface of interdigitated electrodes by electrochemical polymerization along with pyrrole monomers. The potential was scanned from ? 0.7 to + 0.6 V, and the scanning rate was 100 mV/s. Fourier transform infrared spectroscopy was employed to verify specific DNA sequence binding and the conducting polymer. The morphology of the conducting polymer doped with DNA strands was characterized using a field emission scanning electron microscope. As-obtained DNA sensor was used to detect the herpes virus DNA in the real samples. The results show that the current DNA sensors detected the lowest DNA concentration of 2 nM. This sensitivity appears to be better than that of the DNA sensors prepared by immobilization of the DNA probe on the 3-aminopropyl-triethoxy-silance (APTS) membrane.     

Miniaturized implantable pressure and oxygen sensors based on polydimethylsiloxane thin films

We demonstrate the application of polydimethylsiloxane (PDMS) thin films in highly sensitive pressure and oxygen sensors, designed for pressure and oxygen content measurements within the heart and blood vessels. PDMS thin film displacement as a result of pressure changes was transduced by a capacitive detection technique to produce quantitative measurement of absolute pressures. Oxygen measurements were obtained by transducing the current change between a Pt and an Ag/AgCl electrode on a glass substrate, with KCl soaked filter paper as the electrolytic media that is separated from the oxygen carrying fluid by a thin PDMS membrane. The best sensitivity for the pressure sensor was ~ 0.1 nA/KPa, with a noise limited resolution of ~ 0.09 KPa. For the oxygen sensor, the best sensitivity was ~ 2.75 µA for 1% change in oxygen content of the surrounding media, with a noise limited resolution of ~ 6.18 ppm oxygen. These experimental results agree with theoretical modeling predictions, and suggest that the semi-permeable and biocompatible PDMS can be successfully adopted as the contacting membrane in an integrated sensor design to quantify pressure and oxygen content in blood.     

Amperometric choline biosensors based on multi-wall carbon nanotubes and layer-by-layer assembly of multilayer films composed of Poly(diallyldimethylammonium chloride) and choline oxidase

A layer-by-layer deposition technique combined with Multi-wall carbon nanotubes (MWCNTs) was employed for fabricating choline sensors. The terminals and side-walls were linked with oxygen-containing groups when MWCNTs were treated with concentrated acid mixtures. A film of MWCNTs was initially prepared on the platinum electrode surface. Based on the electrostatic interaction between positively charged polyallylamine (PAA) and negatively charged MWCNTs and poly(vinyl sulfate) (PVS), a polymer film of (PVS/PAA)₃ was alternately adsorbed on the modified electrode continuously to be used as a permselective layer. Then poly(diallyldimethylammonium) (PDDA) and choline oxidase(ChOx) multilayer films were assembled layer-by-layer on the pretreated electrode, so an amplified biosensor toward choline was constructed. The choline sensor showed a linear response range of 5 × 10^? 7 to 1 × 10^? 4 M with a detection limit of 2 × 10^? 7 M estimated at a signal-to-noise ratio of 3, and a sensitivity of 12.53 μA/mM with a response time of 7.6 s in the presence of MWCNTs. Moreover, it exhibited excellent reproducibility, long-term stability as well as good suppression of interference. This protocol could be used to immobilize other enzymes for biosensor fabrication.     

Multi-walled carbon nanotube modified carbon paste electrode as an electrochemical sensor for the determination of epinephrine in the presence of ascorbic acid and uric acid

A biocompatible electrochemical sensor for selective detection of epinephrine (EP) in the presence of 1000-fold excess of ascorbic acid (AA) and uric acid (UA) was fabricated by modifying the carbon paste electrode (CPE) with multi-walled carbon nanotubes (MWCNTs) using a casting method. The electro-catalytic activity of the modified electrode for the oxidation of EP was investigated. The current sensitivity of EP was enhanced to about five times upon modification. A very minimum amount of modifier was used for modification. The voltammetric response of EP was well resolved from the responses of AA and UA. The electrochemical impedance spectroscopic (EIS) studies reveal the least charge transfer resistance for the modified electrode. The AA peak that is completely resolved from that of EP at higher concentrations of AA and the inability of the sensor to give an electrochemical response for AA below a concentration of 3.0 × 10^? 4 M makes it a unique electrochemical sensor for the detection of EP which is 100% free from the interference of AA. Two linear dynamic ranges of 1.0 × 10^? 4–1.0 × 10^? 5 and 1.0 × 10^? 5–5.0 × 10^? 7 M with a detection limit of 2.9 × 10^? 8 M were observed for EP at modified electrode. The practical utility of this modified electrode was demonstrated by detecting EP in spiked human blood serum and EP injection. The modified electrode is highly reproducible and stable with anti fouling effects.     

Evaluation on corrosively dissolved gold induced by alkanethiol monolayer with atomic absorption spectroscopy

We have monitored a gold corrosive dissolution behavior accompanied in n-alkanethiol like n-dodecanethiol assembled process with in situ quartz crystal microbalance (QCM), and then observed it with atomic force microscopy (AFM) which showed an evident image of corrosive defects or holes produced on gold substrate, corresponding to gold dissolution induced by the alkanethiol molecules in the presence of oxygen. For detection of the dissolved gold defects during alkanethiol assembled process, an atomic absorption spectroscopy (AAS) has been carried out in this paper, and the detection limit for the dissolved gold could be evaluated to be 15.4 ng/mL. The amount of dissolved gold from the substrates of gold plates as functions of immersion time, acid media, solvents and thiol concentration has been examined in the oxygen saturated solutions. In comparison with in situ QCM method, the kinetics behavior of the long-term gold corrosion on the gold plates in 1.0 mmol/L of n-dodecanethiol solution determined with AAS method was a slow process, and its corrosion rate on gold dissolution could be evaluated to be about 4.4 × 10^? 5 ng·cm^? 2·s^? 1, corresponding to 1.3 × 10⁸ Au atoms·cm^? 2·s^? 1, that was much smaller than that of initial rate monitored with in situ QCM. Both kinetics equations obtained with QCM and AAS showed a consistent corrosion behavior on gold surfaces.     

Hierarchical hollow microsphere and flower-like indium oxide: Controllable synthesis and application as H2S cataluminescence sensing materials

In the present work, In₂O₃ hierarchical hollow microsphere and flower-like microstructure were achieved controllably by a hydrothermal process in the sodium dodecyl sulfate (SDS)-N,N-dimethyl-formamide (DMF) system. XRD, SEM, HRTEM and N₂ adsorption measurements were used to characterize the as-prepared indium oxide materials and the possible mechanism for the microstructures formation was briefly discussed. The cataluminescence gas sensor based on the as-prepared In₂O₃ was utilized to detect H₂S concentrations in flowing air. Comparative gas sensing results revealed that the sensor based on hierarchical hollow microsphere exhibited much higher sensing sensitivity in detecting H₂S gas than the sensor based on flower-like microstructure. The present gas sensor had a fast response time of 5 s and a recovery time of less than 25 s, furthermore, the cataluminescence intensity vs. H₂S concentration was linear in range of 2–20 μg mL^?1 with a detection limit of 0.5 μg mL^?1. The present highly sensitive, fast-responding, and low-cost In₂O₃-based gas sensor for H₂S would have many practical applications.     

Electrogenerated chemiluminescence sensor for formaldehyde based on Ru(bpy)32+-doped silica nanoparticles modified Au electrode

A novel and sensitive electrogenerated chemiluminescence (ECL) sensor for formaldehyde was developed with the amine-functionalized Ru(bpy)₃²⁺-doped silica nanoparticles (Ru-DSNPs) as ECL emitter. Ru(bpy)₃²⁺ doped on the silica nanoparticle can maintain its electrochemical activities, which made silica nano-beads a excellent carrier of Ru(bpy)₃²⁺ species. The uniform Ru-DSNPs (about 75 nm) were conjugated with Au electrode using mercaptoacetic acid as the intermediate to fabricate an ECL sensor for formaldehyde. The ECL analytical performances of this ECL sensor for formaldehyde based on its enhancement ECL emission of Ru(bpy)₃²⁺ were investigated in details. Under the optimum condition, the ECL intensity was linear with the formaldehyde concentration in the range of 1.0 × 10^? 8 mol/L to 1.0 × 10^? 6 mol/L. The detection limit was 6.0 × 10^? 9 mol/L (S/N = 3). This approach offered obvious advantages of being simpler, faster, and more stable compared with other sensors, and possessed great potential for formaldehyde detection which could be applied to determine directly the formaldehyde in real samples without pre-separation.     

A novel iron (III)-PVC membrane potentiomeric sensor based on N-(2-hydroxyethyl)ethylenediamine-N,N',N"-triacetic acid

This work introduces a unique ionophore for the selective determination of Fe(III) ions. This ionophore was N-(2-hydroxyethyl)ethylenediamine-N,N′,N″-triacetic acid (NTA), presenting a high affinity towards the trivalent iron cations. The designed sensor exhibited a wide linear response with a slope of 19.5 ± 0.4 mV per decade over the concentration range of 1.0 × 10^− 9–1.0 × 10^− 2 mol L^− 1, while the illustrated detection limit was 3.0 × 10^− 10 mol L^− 1 of the Fe(III) ions concentration. It was concluded that the sensor response was pH independent in the range of 1.8–4.5. The sensor possessed the advantages of short conditioning time, fast response time (10 s) and, especially, good selectivity towards the transition and heavy metal ions as well as some mono, di and trivalent cations. Concerning the electrode lifetime, no considerable potential divergence was noticed for at least 10 weeks. The sensor accuracy was investigated in the potentiometric titration of a Fe(III) solution with EDTA.     

The properties of ethanol gas sensor based on Ti doped ZnO nanotetrapods

An ethanol gas sensor was fabricated based on Ti doped ZnO nanotetrapods which were prepared by chemical vapor deposition (CVD) of ZnO nanotetrapods followed by co-annealing with TiO₂ powder. X-ray diffraction (XRD), Raman spectra and scanning electron microscopy (SEM) were used to characterize the morphology and structure of the as-obtained sample and the ethanol-sensing characteristics of the device were investigated. ZnO:Ti sensors show higher gas response than ZnO counterparts towards 100 ppm ethanol gas at a temperature of 260 °C. The recovery times of the devices are 3.1 min for ZnO:Ti and 10.1 min for ZnO, respectively. The enhancement of sensing properties of ZnO:Ti tetrapods indicates the potential application for fabricating low power and highly sensitive gas sensors.     

Selective determination of sucrose based on electropolymerized molecularly imprinted polymer modified multiwall carbon nanotubes/glassy carbon electrode

A novel and selective electrochemical sensor was successfully developed for the determination of sucrose by integrating electropolymerization of molecularly imprinted polymer with multiwall carbon nanotubes. The sensor was prepared by electropolymerizing of o-phenylenediamine in the presence of template, sucrose, on a multiwall carbon nanotube-modified glassy carbon electrode. The sensor preparation conditions including sucrose concentration, the number of CV cycles in the electropolymerization step, pH of incubation solution, extraction time of template from the imprinted film and the incubation time were optimized using response surface methodology (RSM). A mixture of acetonitrile/acetic acid was used to remove the template. Hexacyanoferrate(II) was used as a probe to characterize the sensor using electrochemical impedance spectroscopy, cyclic voltammetry and differential pulse voltammetry. Capturing of sucrose by the modified electrode causes decreasing the response of the electrode to hexacyanoferrate(II). Calibration curve was obtained in the sucrose concentration range of 0.01–10.0 mmol L^? 1 with a limit of detection 3 μmol L^? 1. This sensor provides an efficient way for eliminating interferences from compounds with similar structures to sucrose. The sensor was successfully used to determine sucrose in sugar beet juices with satisfactory results.     

Electrochemical sensor for selective determination of N-acetylcysteine in the presence of folic acid using a modified carbon nanotube paste electrode

In the present paper, a novel benzoylferrocene (BF) modified carbon nanotube paste electrode (BFCNPE) was prepared. The modified electrode was further used for the successful determination of N-acetylcysteine (NAC), and it showed an excellent electrocatalytic oxidation activity toward NAC with a lower overvoltage, pronounced current response, and good sensitivity. Under the optimized experimental conditions, the proposed electrochemical NAC sensor exhibited a linear calibration plot that ranged from 3.0 × 10^? 7 to 7.0 × 10^? 4 M with a detection limit of 9.0 × 10^? 8 M. Also, Square wave voltammetry (SWV) was used for simultaneous determination of NAC and folic acid (FA) at the modified electrode. Finally, the proposed method was applied to the determination of NAC in NAC tablets.     

Construction of Tm3+-PVC membrane sensor based on 1-(2-thiazolylazo)-2-naphthol as sensing material

In this study, a new thulium(III) membrane sensor was constructed. The proposed membrane sensor was fabricated based on a membrane containing 2% sodium tetraphenyl borate (NaTPB) as an anionic additive, 65% benzyl acetate (BA) as solvent mediator, 3% 1-(2-thiazolylazo)-2-naphthol (TN) as ionophore, and 30% poly(vinyl chloride) (PVC). The proposed Tm³⁺ electrode exhibits a Nernstian response of 19.5 ± 0.2 mV per decade of thulium concentration, and has a lower detection limit of 8.7 × 10^? 7 mol L^? 1. The linear range of the sensors was 1.0 × 10^? 6 to 1.0 × 10^? 2 mol L^? 1. It works well in the pH range of 3.2–9.5. Moreover, the recommended selective sensor revealed a comparatively satisfactory selectivity regarding most of the alkali, alkaline earth, some transition and heavy metal ions. The membrane sensor was applied to the determination of fluoride ions in mouth wash samples.     

Synthesis,processing and characterization of calcia-stabilized zirconia solid electrolytes for oxygen sensing applications

Precursor powders of calcia-stabilized zirconia (CSZ) solid electrolytes have been synthesized by a sol–gel method. The phase evolution of the precursor powders after thermal treatments at different temperatures were analysized by X-ray diffraction technique. Disc-shaped sensor elements were fabricated via uniaxial pressing of the calcined powders and subsequently sintered at 1650 °C. Scanning electron microscopy (SEM) was used to analyze the microstructure of the sintered pellets. Platinum electrodes were applied to the sintered elements to produce potentiometric/electrochemical gas sensors. The electrical response of the gas sensors to oxygen and the complex impedance of the sensors in air were measured at various temperatures. Impedance analyses indicate that the sensor cell with 15 mol% CaO has much lower resistance (the sum of bulk and grain-boundary resistance) than the sensor cell with 22 mol% CaO. This is also reflected by the EMF responses of both sensor cells to various oxygen concentrations in the testing gas. The EMF deviation from the theoretical value of the CSZ sensor cell with 22 mol% CaO was larger than that of the CSZ sensor cell with 15 mol% CaO. The corrrelations between material compositions, microstructures of the sintered pellets and the electrical properties of the sensors are discussed.