Fiber-optic strain-displacement sensor employing nonlinear buckling

A new class of intrinsic fiber-optic strain-displacement sensors based on the precisely controlled nonlinear buckling of optical fibers and the resulting optical bend loss is introduced. A multimode fiber version of the sensor is described that exhibits a sensing range convenient for many structural monitoring applications (<100 nm to several millimeters), linear response over a wide range of displacements, and excellent repeatability. It is extremely simple to fabricate and employs inexpensive optoelectronics. A high-temperature version of the sensor is capable of operation at temperatures as high as 600 degrees C.     

A disposable amperometric sensor screen printed on a nitrocellulose strip: a glucose biosensor employing lead oxide as an interference-removing agent

A new type of disposable amperometric sensor is devised by screen printing thick-film electrodes directly on a porous nitrocellulose (NC) strip. The chromatographic NC strip is then utilized to introduce various sample pretreatment layers. As a preliminary application, a glucose biosensor based on hydrogen peroxide detection is constructed by immobilizing glucose oxidase (GOx) on the NC electrode strip and by formulating a strong oxidation layer (i.e., PbO2) at the sample loading area, placed below the GOx reaction band. The screen-printed PbO2 paste serves as a sample pretreatment layer that removes interference by its strong oxidizing ability. Samples applied are carried chromatographically, via the PbO2 paste, to the GOx layer, and glucose is catalyzed to liberate hydrogen peroxide, which is then detected at the electrode surface. The proposed NC/PbO2 strip sensor is shown to be virtually insusceptible to interfering species such as acetaminophen and ascorbic and uric acids and to exhibit good performance, in terms of the sensor-to-sensor reproducibility (standard deviation, +/-0.026 - +/-0.086 microA), the sensitivity (slope, -0.183 microA/mM), and the linearity (correlation coefficient, 0.994 in the range of 0-10 mM).     

Bioluminescence immunoassay for thyroxine employing genetically engineered mutant aequorins containing unique cysteine residues

Genetically engineered one-to-one conjugates between an analyte and a protein label have been demonstrated to yield assays with better detection limits and performance characteristics than those prepared by conventional chemical conjugation methods. To date, the preparation of these conjugates has been limited to fusion techniques where a peptide analyte is fused in frame to the protein label. To further expand the range of analytes that can be detected by using genetic engineering techniques coupled with bioanalytical methods, we have employed site-directed mutagenesis to prepare one-to-one analyte-label conjugates that include nonpeptidic analytes such as drugs, vitamins, and hormones. Specifically, we have prepared mutants of the photoprotein aequorin containing single cysteine residues suitable for site-specific conjugation. Aequorin is a photoprotein that emits light at 469 nm and has been employed as a highly sensitive bioluminescent label in the development of binding assays for important biomolecules. We have performed polymerase chain reaction-based site-directed mutagenesis on apoaequorin to yield four mutant aequorins containing unique cysteine residues at positions 5, 53, 71, and 84 in the polypeptide chain for the purpose of site-specific conjugation to a model analyte. A maleimide-activated thyroxine was selected as the model analyte and site-specifically conjugated to the mutants through their unique cysteine residues. A heterogeneous assay for thyroxine was then developed by employing the genetically engineered aequorin mutants.     

Extended-range temporal electronic speckle pattern interferometry

In recent years the availability of high-speed digital video cameras has motivated the study of electronic speckle pattern interferometry (ESPI) in the time domain. To this end a properly sampled temporal sequence of N-fringe patterns is used to analyze the temporal experiment. Samples of temporal speckle images must fulfill the Nyquist criteria over the time axis. When the transient phenomena under study are too fast, the required sampling frequency over time may not be fulfilled. In that case one needs to extend the measuring range of the algorithm used to extract the modulating phase. We analyze how to use short laser pulses or short video acquisition times with fairly long temporal separation among them to estimate the modulating phase of a dynamic ESPI experiment. The only requirement is that the modulating phase being estimated be properly sampled in the spatial domain.     

Improved sensitivity of a histamine sensor using an engineered methylamine dehydrogenase

Methylamine dehydrogenase (MADH) may be immobilized in a polypyrrole (PPy) film on an electrode surface and used as an amperometric sensor for the determination of histamine. Using site-directed mutagenesis, phenylalanine 55 on the alpha subunit of MADH was converted to alanine. This alphaF55A MADH exhibits a 400-fold lower Km value for histamine than does native MADH when assayed in solution. An alphaF55A MADH-PPy sensor was constructed, and its properties were compared to that of the native MADH-PPy sensor. The alphaF55A MADH immobilized on the electrode exhibited Michaelis-Menten behavior in response to varied concentrations of histamine with an approximately 3-fold lower Km value than that exhibited by the immobilized native MADH. The detection limit for the native MADH-PPy sensor was approximately 20 microM while the alphaF55A MADH-PPy sensor exhibited a detection limit of approximately 5 microM, a 4-fold increase compared to the native MADH-PPy sensor. This work highlights the potential value of using site-directed mutagenesis to engineer enzymes to alter and improve biosensor performance.     

Interferometric optical sensor for measuring glucose concentration

With a specially designed probe, the phase difference between s andp polarization of light reflected under surface-plasmon resonance is measured by use of a common-path heterodyne interferometer. For specific ratios of phase difference to glucose concentration, the glucose concentration can be estimated as a function of the measured phase data. A prototype was set up to demonstrate the feasibility of this sensor, which was experimentally tested in the range 40-500 mg/dl with a small quantity of solution and had a measurement resolution of 1.41 mg/dl at 25 degrees C.     

Nonenzymatic electrochemical glucose sensor based on nanoporous PtPb networks

Here, we report on a novel nonenzymatic amperometric glucose sensor based on three-dimensional PtPb networks directly grown on Ti substrates using a reproducible one-step hydrothermal method. The surface morphology and bimetallic composition of the synthesized nanoporous PtPb materials were characterized using scanning electron microscopy and energy-dispersive X-ray spectrometry, respectively. Voltammetry and amperometric methods were used to evaluate the electrocatalytic activities of the synthesized electrodes toward nonenzymatic glucose oxidation in neutral media in the absence and in the presence of chloride ions. The synthesized nanoporous PtPb electrodes have strong and sensitive current responses to glucose. Their amperometric sensitivities increase in the order of Pt-Pb (0%) < Pt-Pb (30%) < Pt-Pb (70%) < Pt-Pb (50%). These nanoporous PtPb electrodes are also highly resistant toward poisoning by chloride ions and capable of sensing glucose amperometrically at a very low potential, -80 mV (Ag/AgCl), where the interference from the oxidation of common interfering species such as ascorbic acid, acetamidophenol, and uric acid is effectively avoided.     

Miniature amperometric self-powered continuous glucose sensor with linear response

Continuous glucose measurement has improved the treatment of type 1 diabetes and is typically provided by externally powered transcutaneous amperometric sensors. Self-powered glucose sensors (SPGSs) could provide an improvement over these conventionally powered devices, especially for fully implanted long-term applications where implanted power sources are problematic. Toward this end, we describe a robust SPGS that may be built from four simple components: (1) a low-potential, wired glucose oxidase anode; (2) a Pt/C cathode; (3) an overlying glucose flux-limiting membrane; and (4) a resistor bridging the anode and cathode. In vitro evaluation showed that the sensor output is linear over physiologic glucose concentrations (2-30 mM), even at low O(2) concentrations. Output was independent of the connecting resistor values over the range from 0 to 10 MΩ. The output was also stable over 60 days of continuous in vitro operation at 37 °C in 30 mM glucose. A 5-day trial in a volunteer demonstrated that the performance of the device was virtually identical to that of a conventional amperometric sensor. Thus, this SPGS is an attractive alternative to conventionally powered devices, especially for fully implanted long-term applications.     

Recognition of the interference spiral image in a fiber optical sensor employing optical vortices

Three methods of processing the image of an interference spiral formed in a fiber optical sensor employing optical vortices have been considered. It is established that a method based on recognition of the spiral image is most stable with respect to noises. Using this technique, it is possible to determine the angle of spiral rotation even when the visibility of the interference pattern decreases to 0.2. The passage from intensity measurements to determination of the geometric parameters of the image significantly increases the range of linearity of interferometric devices employing optical vortices.     

Composite transducers for amperometric biosensors. The glucose sensor

A new concept of a composite transducer for amperometric biosensors based on the use of a solid substance with amphiphilic character (called a solid binding matrix, SBM) is presented. The electrochemical properties of the transducers prepared with five different SBMs and the characteristics and performance of SBM-based glucose sensors prepared by three different methods are described. Biosensor stability is evaluated and discussed. The biosensor was used for the determination of glucose in wine, yielding results which were consistent with those obtained with the commercially available Glucose Enzyme Photometric Kit. The average accuracy was 6% for the whole range of analyzed concentrations (0.2-47 g/L) using the same sample dilution in a buffer.     

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.     

Extended-range spectroscopic pH measurement using optimized mixtures of dyes

The spectroscopic technique for pH measurement is a well-established laboratory technique that can give high-accuracy pH values. Recent studies have shown the advantage of this technique over standard potentiometric methods for pH measurements in fresh water and seawater and also at high temperatures and pressures. However, a limitation of the spectroscopic technique is that a single pH dye is sensitive only over a narrow pH range. We have developed optimized dye mixtures that are both sensitive and accurate over a broad pH range. The measurement is robust and simple, requires a minimum of two wavelengths, and is independent of the volume of the dye mixture added. Optimization of the dye mixture formulation to maximize accuracy in a broad range of pH involves varying both the dye type and its mole fraction and also accounting for spectral noise. This technique has been successfully applied for in situ pH measurements of oilfield formation waters.     

A glucose biosensor employing a stable artificial peroxidase based on ruthenium purple anchored cinder

Iron-enriched industrial waste cinder (CFe*) has been recycled for efficient and stable anchoring of Ru(CN)6(4-) to the formation of a hybrid ruthenium purple complex. The cinder/ruthenium purple hybrid-modified carbon paste electrode (designated as CPE/CFe*-RP) was worked out for hydrodynamic analysis of H2O2 at a low detecting potential of 0.0 V versus Ag/AgCl in pH 7 ammonium buffer solution. The highly active, selective, and stable electrocatalytic system with a function similar to peroxidase enzyme shows a linear calibration curve up to 0.8 mM H2O2 at a rotation rate of 3600 rpm with slope and detection limit (S/N = 3) of 0.11 microA/microM and 33 nM, respectively. Interference by direct electrochemical oxidation of easily oxidizable substances can be prevented as a result of the low detecting potential of the working system. A glucose biosensor was further constructed by coating with glucose oxidase and Tosflex on the CPE/CFe*-RP (denoted as CPE/CFe*-RP/GOx/Ts). The proposed CPE/CFe*-RP/GOx/Ts with a two-layer configuration, that is, enzyme and protecting layers, exhibits good operational performance in terms of response time, linearity, detection limit, and lifetime.     

CuO-NSG的制备及其在非酶葡萄糖传感器中的应用

采用氮和硫共掺杂石墨烯(NSG)作为固定CuO纳米颗粒的新型载体材料,并将获得的CuO-NSG作为电催化葡萄糖氧化(EGO)的催化剂应用于非酶葡萄糖传感器,解决EGO催化剂的稀缺性和高成本性。结果表明,NSG赋予CuO-NSG大的表面积,且NSG和CuO之间存在强界面耦合。由于NSG的显著效果和NSG与CuO的协同效应,CuO-NSG显示出比CuO和CuO-还原氧化石墨烯(RGO)更高的EGO活性。基于CuO-NSG的传感器显示出优异的葡萄糖感测性能,表现出1722μA·mmol·L~(-1)·cm~(-2)的高灵敏度和0.07μmmol·L~(-1)的低检测限及在实际样品分析中的选择性、再现性、稳定性和可行性的良好检测性能。     

A prototype portable instrument employing micro-preconcentrator and FBAR sensor for the detection of chemical warfare agents

The presence of chemical warfare agents(CWAs)in the environment is a serious threat to human safety,but there are many prob-lems with the currently available de...     

A fluorescence affinity hollow fiber sensor for continuous transdermal glucose monitoring

A novel concept of a fluorescence affinity hollow fiber sensor for transdermal glucose monitoring is demonstrated. The glucose-sensing principle is based on the competitive reversible binding of a mobile fluorophore-labeled Concanavalin A (Con A) to immobile pendant glucose moites inside of intensely colored Sephadex beads. The highly porous beads (molecular weight cutoff of 200 kDa) were colored with two red dyes, Safranin O and Pararosanilin, selected to block the excitation and spectrum of the fluorophore Alexa488. The sensor consists of the dyed beads and Alexa488-Con A confined inside a sealed, small segment of a hollow fiber dialysis membrane (diameter 0.5 mm, length 0.5 cm, molecular weight cutoff 10 kDa). In the absence of glucose, the majority of Alexa488-Con A resides inside the colored beads bound to fixed glucose. Thus, excitation light at 490 nm impinging on the sensor is strongly absorbed by the dyes, resulting in a drastically reduced fluorescence emission at 520 nm from the Alexa488-Con A residing within the beads. However, when the hollow fiber sensor is exposed to glucose, glucose diffuses through the membrane into the sensor chamber and competitively displaces Alexa 488-Con A molecules from the glucose residues of the Sephadex beads. Thus, Alexa 488-Con A appears in the void space outside of the beads and is fully exposed to the excitation light, and a strong increase in fluorescence emission at 520 nm is measured. At a medium to high loading degree of Sephadex with Alexa488-Con A (10 mg mL(-1) bead suspension), the absolute fluorescence increase due to 20 mM glucose was very large. It exceeded the response of other sensor devices based on FRET by a factor of 50 (Meadows and Schultz Anal. Chim. Acta 1993, 280, 21-30; Russell et al. Anal. Chem. 1999, 71, 3126-3132). The new sensor featured a glucose detection range extending from 0.15 to 100 mM, exhibiting the strongest dynamic signal change from 0.2 to 30 mM. It showed a reasonably fast response time (4-5 min). The combination of all the beneficial sensor features makes this sensor extremely attractive for future in vivo implantation studies for glucose monitoring in subdermal tissue.