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Just Published: Spectrochimica Acta Part B: Atomic Spectroscopy

A new issue of this journal has just been published. To see abstracts of the papers it contains (with links through to the full papers) click here:

Spectrochimica Acta Part B: Atomic Spectroscopy
http://rss.sciencedirect.com/publication/science/5287

Selected papers from the latest issue:

Thermodynamic equilibrium states in laser-induced plasmas: From the general case to laser-induced breakdown spectroscopy plasmas

28 October 2013, 09:52:48

Publication date: 1 December 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 90
Author(s): G. Cristoforetti , E. Tognoni , L.A. Gizzi
Applications, present and potential, of laser-induced plasmas are today widespread in a large range of fields and continue to extend each day because of the advancement of laser science and technology. These circumstances call for a better knowledge and characterization of physical and chemical processes occurring in a plasma. The spectrum of the radiation emitted by the plasmas is a mine of information about the plasma state and therefore spectroscopy remains one of the key techniques for its investigation. The interpretation of emission spectra, however, requires a deep knowledge of the elementary processes determining the atomic state population and the fractional ion densities, and of their balance. The transient character of laser-induced plasmas and the presence of spatial gradients introduce time-dependent and non-local effects in the energy level population, and thus increase the complexity of the plasma modeling. The thermodynamic approach, describing the atomic and ionic state population by statistical distributions, is the easiest and the most widely used way to model the plasma state but does not account for non-local and non-steady-state effects. It is therefore in many cases unfit for this purpose. As a consequence, kinetic modeling of the plasma is often needed, which must be in many cases integrated by hydrodynamic modeling of plasma expansion and appropriate equations describing the transport of radiation and charged particles into the plasma. In this complex framework, this paper aims at giving a concise description of theoretical issues, redirecting to the key literature for more details, and to delineate possible scenarios occurring in the wide range of laser-induced plasmas. Examples of different classes of laser-induced plasmas are reported, including some experimental results for completeness. Special attention is devoted to the case of ‘cold’ or thermal plasmas, in particular those produced in laser-induced breakdown spectroscopy. The occurrence of local thermodynamic equilibrium is, in that case, discussed as well as the relevance of phenomena leading the system out of equilibrium, such as radiative, transient and diffusive processes. The most important directions for future work, in particular regarding non-stationary and diffusive effects, are also suggested.

Production of aerosols by optical catapulting: Imaging, performance parameters and laser-induced plasma sampling rate

28 October 2013, 09:52:48

Publication date: 1 November 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 89
Author(s): M. Abdelhamid , F.J. Fortes , A. Fernández-Bravo , M.A. Harith , J.J. Laserna
Optical catapulting (OC) is a sampling and manipulation method that has been extensively studied in applications ranging from single cells in heterogeneous tissue samples to analysis of explosive residues in human fingerprints. Specifically, analysis of the catapulted material by means of laser-induced breakdown spectroscopy (LIBS) offers a promising approach for the inspection of solid particulate matter. In this work, we focus our attention in the experimental parameters to be optimized for a proper aerosol generation while increasing the particle density in the focal region sampled by LIBS. For this purpose we use shadowgraphy visualization as a diagnostic tool. Shadowgraphic images were acquired for studying the evolution and dynamics of solid aerosols produced by OC. Aluminum silicate particles (0.2–8μm) were ejected from the substrate using a Q-switched Nd:YAG laser at 1064nm, while time-resolved images recorded the propagation of the generated aerosol. For LIBS analysis and shadowgraphy visualization, a Q-switched Nd:YAG laser at 1064nm and 532nm was employed, respectively. Several parameters such as the time delay between pulses and the effect of laser fluence on the aerosol production have been also investigated. After optimization, the particle density in the sampling focal volume increases while improving the aerosol sampling rate till ca. 90%.

Use of portable X-ray fluorescence instrument for bulk alloy analysis on low corroded indoor bronzes

28 October 2013, 09:52:48

Publication date: 1 November 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 89
Author(s): D. Šatović , V. Desnica , S. Fazinić
One of the most often used non-destructive methods for elemental analysis when performing field measurements on bronze sculptures is X-ray fluorescence (XRF) analysis based on portable instrumentation. However, when performing routine in-situ XRF analysis on corroded objects obtained results are sometimes considerably influenced by the corrosion surface products. In this work the suitability of portable XRF for bulk analysis of low corroded bronzes, which were initially precisely characterized using sophisticated and reliable laboratory methods, was investigated and some improvements in measuring technique and data processing were given. Artificially corroded bronze samples were analyzed by a portable XRF instrument using the same methodology and procedures as when performing in-situ analysis on real objects. The samples were first investigated using sophisticated complementary laboratory techniques: Scanning Electron Microscopy, Proton-Induced X-ray Emission Spectroscopy and Rutherford Backscattering Spectrometry, in order to gain precise information on the formation of the corrosion product layers and in-depth elemental profile of corrosion layers for different aging parameters. It has been shown that for corrosion layers of up to ca. 25μm a portable XRF can yield very accurate quantification results.

Common analyte internal standardization as a tool for correction for mass discrimination in multi-collector inductively coupled plasma-mass spectrometry

28 October 2013, 09:52:48

Publication date: 1 November 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 89
Author(s): Veerle Devulder , Lara Lobo , Karen Van Hoecke , Patrick Degryse , Frank Vanhaecke
It is well known that to achieve accurate isotope ratio data using multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS), mass discrimination needs to be adequately corrected for. In this work, the capabilities and limitations of common analyte internal standardization (CAIS) as a method for correction for mass discrimination were assessed for two target elements, one in the low mass region (boron) and another in the medium mass region (antimony). CAIS has already been used in the context of element determination and, more recently, also in isotope ratio measurements with quadrupole-based ICP-MS, but it has, to the best of the authors' knowledge, never been applied to isotope ratio determination via MC-ICP-MS so far. Results obtained relying on CAIS were compared with those obtained via more established correction models, i.e. external correction in a standard-sample bracketing approach (SSB) and internal correction based on both the Russell's law (original and empirical) and the revised Russell's law. To the best of the authors' knowledge, such comparison has not been done before, especially not for low mass elements. Also the robustness of these approaches with respect to concomitant matrix elements was assessed using synthetic solutions, containing various concentrations of the matrix elements Be, Cs, Be+Cs or Fe. Whereas for B, the isotope ratio result did not seem to be significantly affected by the matrix, thus suggesting that complete separation of B from a matrix might not be necessary, at least in the cases studied, the mass discrimination observed for Sb was influenced by the presence of Cs. The experiments carried out demonstrate that the CAIS technique can be successfully applied for mass bias correction in MC-ICP-MS, providing data of the same quality as the revised Russell's law, while being more transparent and accessible. While for B, all mass bias correction approaches tested provided similar data quality (external correction with SSB gives slightly better precision), for Sb, CAIS and the revised Russell's law provide better precision and accuracy.

Considerations of particle vaporization and analyte diffusion in single-particle inductively coupled plasma-mass spectrometry

28 October 2013, 09:52:48

Publication date: 1 November 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 89
Author(s): Koon-Sing Ho , Kwok-On Lui , Kin-Ho Lee , Wing-Tat Chan
The intensity of individual gold nanoparticles with nominal diameters of 80, 100, 150, and 200nm was measured using single-particle inductively coupled plasma-mass spectrometry (ICP-MS). Since the particles are not perfectly monodisperse, a distribution of ICP-MS intensity was obtained for each nominal diameter. The distribution of particle mass was determined from the transmission electron microscopy (TEM) image of the particles. The distribution of ICP-MS intensity and the distribution of particle mass for each nominal diameter were correlated to give a calibration curve. The calibration curves are linear, but the slope decreases as the nominal diameter increases. The reduced slope is probably due to a smaller degree of vaporization of the large particles. In addition to the degree of particle vaporization, the rate of analyte diffusion in the ICP is an important factor that determines the measured ICP-MS intensity. Simulated ICP-MS intensity versus particle size was calculated using a simple computer program that accounts for the vaporization rate of the gold nanoparticles and the diffusion rate and degree of ionization of the gold atoms. The curvature of the simulated calibration curves changes with sampling depth because the effects of particle vaporization and analyte diffusion on the ICP-MS intensity are dependent on the residence time of the particle in the ICP. Calibration curves of four hypothetical particles representing the four combinations of high and low boiling points (2000 and 4000K) and high and low analyte diffusion rates (atomic masses of 10 and 200Da) were calculated to further illustrate the relative effects of particle vaporization and analyte diffusion. The simulated calibration curves show that the sensitivity of single-particle ICP-MS is smaller than that of the ICP-MS measurement of continuous flow of standard solutions by a factor of 2 or more. Calibration using continuous flow of standard solution is semi-quantitative at best. An empirical equation is formulated for the estimation of the position of complete vaporization of a particle in the ICP. The equation takes into account the particle properties (diameter, density, boiling point, and molecular weight of the constituents of the particle) and the ICP operating parameters (ICP forward power and central channel gas flow rate). The proportional constant and exponents of the variables in the equation were solved using literature values of ICP operating conditions for single-particle inductively coupled plasma-mass spectrometry (ICP-MS) and inductively coupled plasma-atomic emission spectrometry (ICP-AES) measurements of 6 kinds of particles in 12 studies. The calculated position is a useful guide for the selection of sampling depth or observation height for ICP-MS and ICP-AES measurements of single particles as well as discrete particles in a flow, such as laser-ablated materials and airborne particulates.

Multiple emission line analysis for improved isotopic determination of uranium — a computer simulation study

28 October 2013, 09:52:48

Publication date: 1 November 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 89
Author(s): George C.-Y. Chan , Xianglei Mao , Inhee Choi , Arnab Sarkar , Oanh P. Lam , David K. Shuh , Richard E. Russo
Forty-three atomic emission lines for ²³⁵U and ²³⁸U were compiled for computer simulation of isotopic analysis using laser induced breakdown spectroscopy (LIBS). The spectral line profile was assumed to be Lorentzian in shape and the magnitude of three common types of noises (detector-read, photon-shot and flicker) were experimentally determined and incorporated into the simulation. Precision and root mean square error of prediction (RMSEP) for isotopic analysis of a single U line were simulated, and it was found that analytical performance (precision) primarily depended on the signal-to-background ratio (SBR) and net intensity of the emission line, rather than on the magnitude of isotopic splitting (IS), when partial least squares (PLS) was used for calibration. This is because PLS multivariate calibration can be performed correctly even when the spectra are only partially resolved, which in turn relaxes the requirement on having IS larger than the spectral resolution. The analytical performance was found to improve with multiple-line analysis. Depending on the criteria (e.g., SBR, net intensity, magnitude of IS, or best single-line performance) used in sorting the spectral lines into the multiline pool, improvement factors ranging from 2× to 9× were obtained. The absolute uncertainty of isotopic analysis is practically constant and independent of isotopic abundance, which makes experimental estimation of the detection limit in isotopic analysis straightforward because one can experimentally measure this uncertainty with one arbitrary and conveniently chosen isotopic standard and then estimate the detection limit through simple extrapolation.

Optical emission spectroscopy for quantification of ultraviolet radiations and biocide active species in microwave argon plasma jet at atmospheric pressure

28 October 2013, 09:52:48

Publication date: 1 November 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 89
Author(s): G. Wattieaux , M. Yousfi , N. Merbahi
This work deals with absorption and mainly emission spectrometry of a microwave induced surfatron plasma jet launched in ambient air and using an Argon flow carrier gas. The Ar flow rate varies between 1 and 3L/min and the microwave power between 40 and 60W. The analysis of the various spectra has led to the determination of the ozone and atomic oxygen concentrations, ultraviolet (UV) irradiance separating UVA, UVB and UVC, gas temperature, plasma electron density and excitation temperature. Most of these diagnostics are spatially resolved along the plasma jet axis. It is shown more particularly that rotational temperature obtained from OH(A-X) spectra ranges between 800K to 1000K while the apparent temperature of the plasma jet remains lower than about 325K which is compatible with biocide treatment without significant thermal effect. The electron density reaches 1.2×10¹⁴ cm⁻³, the excitation temperature is about 4000K, the UVC radiation represents only 5% of the UV radiations emitted by the device, the ozone concentration is found to reach 88±27ppm in the downstream part of the plasma jet at a distance of 30mm away from the quartz tube outlet of the surfatron and the atomic oxygen concentration lies between 10 and 80ppm up to a distance of 20mm away from the quartz tube outlet. Ozone is identified as the main germicidal active species produced by the device since its concentration is in accordance with bacteria inactivation durations usually reported using such plasma devices. Human health hazard assessment is carried out all along this study since simple solutions are reminded to respect safety standards for exposures to ozone and microwave leakage. In this study, an air extraction unit is used and a Faraday cage is set around the quartz tube of the surfatron and the plasma jet. These solutions should be adopted by users of microwave induced plasma in open air conditions because according to the literature, this is not often the case.

Vibrational emission analysis of the CN molecules in laser-induced breakdown spectroscopy of organic compounds

28 October 2013, 09:52:48

Publication date: 1 November 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 89
Author(s): Ángel Fernández-Bravo , Tomás Delgado , Patricia Lucena , J. Javier Laserna
Laser-induced breakdown spectroscopy (LIBS) of organic materials is based on the analysis of atomic and ionic emission lines and on a few molecular bands, the most important being the CN violet system and the C2 Swan system. This paper is focused in molecular emission of LIBS plasmas based on the CN (B²Σ–X²Σ) band, one of the strongest emissions appearing in all carbon materials when analyzed in air atmosphere. An analysis of this band with sufficient spectral resolution provides a great deal of information on the molecule, which has revealed that valuable information can be obtained from the plume chemistry and dynamics affecting the excitation mechanisms of the molecules. The vibrational emission of this molecular band has been investigated to establish the dependence of this emission on the molecular structure of the materials. The paper shows that excitation/emission phenomena of molecular species observed in the plume depend strongly on the time interval selected and on the irradiance deposited on the sample surface. Precise time resolved LIBS measurements are needed for the observation of distinctive CN emission. For the organic compounds studied, larger differences in the behavior of the vibrational emission occur at early stages after plasma ignition. Since molecular emission is generally more complex than that involving atomic emission, local plasma conditions as well as plume chemistry may induce changes in vibrational emission of molecules. As a consequence, alterations in the distribution of the emissions occur in terms of relative intensities, being sensitive to the molecular structure of every single material.

Application of laser ablation inductively coupled plasma multicollector mass spectometry in determination of lead isotope ratios in common glass for forensic purposes

28 October 2013, 09:52:48

Publication date: 1 November 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 89
Author(s): Knut-Endre Sjåstad , Tom Andersen , Siri Lene Simonsen
Samples of glass used as trace evidence in criminal cases are commonly small, with particle sizes below a millimeter. To perform chemical analysis suitable for forensic purposes, methods capable of analyzing such small samples are required. In this paper, analyses of lead isotope ratios by means of laser ablation inductively coupled multicollector mass spectrometry (LA-MC-ICP-MS) are presented. Sampling by use of laser ablation allows fragments down to 0.1mg to be analyzed with sufficient precision to discriminate between glasses of different origin. In fact, the use of lead isotopes determined by LA-MC-ICP-MS approaches the discrimination attainable by multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) analysis of dissolved samples of 5mg or more. Further, we have obtained a probability distribution by two dimensional kernel density estimates for the collected data set as an alternative presentation method to the well-established bivariate plot. The underlying information available from kernel density estimates is of importance for forensic scientists involved in probabilistic interpretation of physical evidence.

Atomic emission spectroscopy method for mixing studies in high power thermal plasmas

28 October 2013, 09:52:48

Publication date: 1 November 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 89
Author(s): Jochen Altenberend , Guy Chichignoud , Yves Delannoy
Atomic emission spectrometry was used to measure the distribution of concentration ratios and temperature in thermal plasmas produced by high power torches for process engineering. The spectroscopic method is based on absolute line intensity measurement and Abel inversion. Assuming local thermal equilibrium, the temperature is deduced from the absolute emission of an argon line and the concentration ratio is deduced from the emission ratio of two lines. Using the two dimensions of the camera for spatial and spectral resolution, fast measurements with high resolution can be done. The method has been tested on a 60kW inductively coupled plasma torch at atmospheric pressure. The results show that the concentration ratios n(O)/n(Ar) and n(H)/n(Ar) can be measured with an accuracy of 25% and that errors due to deviations from LTE are small. Demixing occurs in the induction zone. The application of the method showed that hydrogen diffuses much more than oxygen. The main disadvantage of this method is that, using emission, it does not permit to measure the concentration in the “cold” zones in the center and at the edge of the plasma.

In situ atom trapping of Bi on W-coated slotted quartz tube flame atomic absorption spectrometry and interference studies

28 October 2013, 09:52:48

Publication date: 1 November 2013
Source:Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 89
Author(s): Ersin Kılınç , Sezgin Bakırdere , Fırat Aydın , O. Yavuz Ataman
Analytical performances of metal coated slotted quartz tube flame atomic absorption spectrometry (SQT-FAAS) and slotted quartz tube in situ atom trapping flame atomic absorption spectrometry (SQT-AT-FAAS) systems were evaluated for determination of Bi. Non-volatile elements such as Mo, Zr, W and Ta were tried as coating materials. It was observed that W-coated SQT gave the best sensitivity for the determination of Bi for SQT-FAAS and SQT-AT-FAAS. The parameters for W-coated SQT-FAAS and W-coated SQT-AT-FAAS were optimized. Sensitivity of FAAS for Bi was improved as 4.0 fold by W-coated SQT-FAAS while 613 fold enhancement in sensitivity was achieved by W-coated SQT-AT-FAAS using 5.0min trapping with respect to conventional FAAS. MIBK was selected as organic solvent for the re-atomization of Bi from the trapping surface. Limit of detection values for W-coated SQT-FAAS and W-coated SQT-AT-FAAS was obtained as 0.14μgmL⁻¹ and 0.51ngmL⁻¹, respectively. Linear calibration plot was obtained in the range of 2.5–25.0ngmL⁻¹ for W-coated SQT-AT-FAAS. Accuracy of the W-coated SQT-AT-FAAS system was checked by analyzing a standard reference material, NIST 1643e. 

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Just Published: Sensors & Actuators B: Chemical

A new issue of this journal has just been published. To see abstracts of the papers it contains (with links through to the full papers) click here:

Sensors & Actuators B: Chemical
http://rss.sciencedirect.com/publication/science/5283

Selected papers from the latest issue:

Recognition of carbon monoxide with SnO2/Ti thick-film sensor and its gas-sensing mechanism

24 October 2013, 08:58:24

Publication date: February 2014
Source:Sensors and Actuators B: Chemical, Volume 191
Author(s): Wen Zeng , Yanqiong Li , Bin Miao , Liyang Lin , Zhongchang Wang
We have synthesized undoped and Ti-doped SnO2 spheres with a facile yet efficient hydrothermal approach and investigated their microstructures and gas sensing response to carbon monoxide, focusing especially on the impact of Ti doping. We find that gas response of SnO2 is enhanced significantly by doping, the origin of which is clarified in light of a proposed adsorption model. Through a combination of systematic measurements with density-functional-theory calculations, we discuss the enhancement mechanism of the gas-sensing function arising from the doping.

Efficient detection and extraction of cobalt(II) from lithium ion batteries and wastewater by novel composite adsorbent

24 October 2013, 08:58:24

Publication date: February 2014
Source:Sensors and Actuators B: Chemical, Volume 191
Author(s): Md. Rabiul Awual , Mohamed Ismael , Tsuyoshi Yaita
This study developed a novel composite adsorbent for highly selective and sensitive detection and extraction of cobalt (Co(II)) from lithium-ion batteries (LIBs) and wastewater. The composite adsorbent was prepared by indirect immobilization of 6-((2-(2-hydroxy-1-naphthoyl)hydrazono)methyl)benzoic acid (HMBA) onto mesoporous silica monoliths. The composite adsorbent enhanced the color formation by stable complexation as [Co(II)–HMBA] ⁿ⁺ complexes during detection and sorption operations. The data evident the one-step detection of wide range Co(II) concentrations into interior pore surface coverage of the composite adsorbent from solutions without using high tech instruments, which was unique feature of this adsorbent. The influence of different sorption parameters, such as: initial Co(II) concentration, equilibration time, solution pH and the presence of competing ions and reuses were studied and discussed systematically. The effective pH range for Co(II) ions detection and sorption was neutral pH region and the maximum sorption capacity of the adsorbent was as high as 189.37mg/g. The adsorbed Co(II) was eluted with stripping agent (0.3M HCl) and simultaneously regenerated into initial form for the next capturing operations after rinsing with water. The data also clarified that the composite adsorbent was selectively extracted Co(II) from LIBs even in the presence of high concentration diverse ions. Importantly, the composite adsorbent was retaining functionality in spite of many chemical treatments during sorption–elution-recovery/regeneration cycles. Therefore, the present study revealed that such a low-cost material could be used as potential adsorbent for the selective detection and recovery of Co(II) ions from LIBs and wastewater streams.

Enhancement of the sensitivity of magneto-optical fiber sensor by magnifying the birefringence of magnetic fluid film with Loyt-Sagnac interferometer

24 October 2013, 08:58:24

Publication date: February 2014
Source:Sensors and Actuators B: Chemical, Volume 191
Author(s): Peng Zu , Chi Chiu Chan , Guo Wei Koh , Wen Siang Lew , Yongxing Jin , Hwi Fen Liew , Wei Chang Wong , Xinyong Dong
Magnetic field sensor by combing magnetic fluid and optical fiber Loyt-Sagnac interferometer is proposed. The sensor takes advantage of the birefringence effect of magnetic fluid. The relative small birefringence of the magnetic fluid is ‘magnified’ by the properly designed optical fiber Loyt-Sagnac interferometric structure. As compared to the reported MF-based sensors, the achieved sensitivity of the proposed sensor is 592.8pm/Oe, which is enhanced by 1–3 orders of magnitude.

Gas sensors based on multiple-walled carbon nanotubes-polyethylene oxide films for toluene vapor detection

24 October 2013, 08:58:24

Publication date: February 2014
Source:Sensors and Actuators B: Chemical, Volume 191
Author(s): Yong Zhou , Yadong Jiang , Guangzhong Xie , Xiaosong Du , Huiling Tai
Two kinds of toluene vapor sensors with different sensitive film structures, i.e., multi-walled carbon nanotubes (MWCNTs)-polyethylene oxide (PEO) composite film and MWCNTs-PEO bilayer film were fabricated. Both sensors were obtained by airbrushing the sensitive films on interdigitated electrodes (IDE). Response performances of both sensors to toluene vapor at room temperature were investigated. Scanning electron microscope (SEM) was used for morphology analysis of the sensitive films. The experimental results showed that sensors with bilayer films revealed a larger sensitivity than that with the composite films. The response and recovery times of both sensors were within 8s. Moreover, sensors with bilayer films exhibited a modest selectivity to toluene vapor. The sensing mechanisms of both sensors were studied as well.

Silver nanoparticles based selective colorimetric sensor for Cd2+, Hg2+ and Pb2+ ions: Tuning sensitivity and selectivity using co-stabilizing agents

24 October 2013, 08:58:24

Publication date: February 2014
Source:Sensors and Actuators B: Chemical, Volume 191
Author(s): V. Vinod Kumar , Savarimuthu Philip Anthony
N-(2-hydroxybenzyl)-valine (VP) and N-(2-hydroxybenzyl)-isoleucine (ILP) organic ligands have been utilized as reducing and surface functionalizing agents in the synthesis of silver nanoparticles (AgNPs) with metal ion interacting functionality. VP and ILP metal interacting ligands functionalized AgNPs exhibited selective colorimetric sensing of toxic Cd²⁺, Hg²⁺ and Pb²⁺ metal ions in aqueous solution at ppm level. The colorimetric sensitivity and metal ion selectivity of VP- and ILP-AgNPs were modulated by incorporating co-stabilizing agents. Importantly, ILP functionalized AgNPs selectively detected Cd²⁺ ions in the polluted ground water samples also.

LSPR optical fibre sensors based on hollow gold nanostructures

24 October 2013, 08:58:24

Publication date: February 2014
Source:Sensors and Actuators B: Chemical, Volume 191
Author(s): M.H. Tu , T. Sun , K.T.V. Grattan
Compared to solid gold nanoparticles (AuNPs) which have been widely used for the construction of localized surface plasmon resonance (LSPR) sensors, hollow gold nanoparticles have attracted greater attention recently due to the stronger plasmonic effect that they demonstrate. Combining this with the known advantages of the use of fibre optic technology, a portable, reliable and highly sensitive sensor system has been developed and reported in this study and evaluated for various potential sensing applications. In this work, hollow gold nanocages have been designed and the synthesized specifically for the development of a LSPR-based optical fibre sensor, in this case for Refractive Index (RI) measurement. In doing so, different hollow structures of nanogold have been synthesized and characterized and the experimental results obtained show that the sensitivity of the hollow nanostructure-based LSPR sensor, in response to known RI variations, is closely related to the hollowness of the gold nanocages. It was observed that with the decrease of the wall thickness of the nanocages, the sensitivity of the LSPR sensor created increases dramatically and this is due to the strong plasmonic coupling seen between the interior and exterior fields. Compared to the LSPR sensors based on solid-nanoparticles reported earlier by the authors, the nanocage-based sensor created in this work has demonstrated an excellent sensitivity of 1933nm/RIU, thus showing a significant improvement of at least 3 fold in sensitivity from that prior work.

Hydrothermal preparation and gas sensing properties of Zn-doped SnO2 hierarchical architectures

24 October 2013, 08:58:24

Publication date: February 2014
Source:Sensors and Actuators B: Chemical, Volume 191
Author(s): Yue Guan , Dawei Wang , Xin Zhou , Peng Sun , Haiyu Wang , Jian Ma , Geyu Lu
A one-step hydrothermal route was used to synthesize undoped and Zn-doped SnO2 hierarchical architectures. The morphologies and structures of the as-prepared samples were characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). The results clearly revealed that the as-prepared SnO2 hierarchical architectures were composed of many 2 dimensional (2D) nanosheets with the thickness of about 30nm. The gas sensing properties of the as-prepared undoped and Zn-doped SnO2 samples were tested toward various gases. The sensor based on S3 (Zn²⁺/Sn⁴⁺ =0.056) showed excellent selectivity toward ethanol at the operating temperature 213°C, giving a response of about 14.4 to 100ppm, which was about 3.2 times higher than that of sensor based on pure SnO2.

A fluorescent chemosensor for paeonol based on tetramethoxy resorcinarene tetraoxyacetic acid

24 October 2013, 08:58:24

Publication date: February 2014
Source:Sensors and Actuators B: Chemical, Volume 191
Author(s): Qian Yang , Chaoguo Yan , Xiashi Zhu
A fluorescent chemosensor for paeonol based on tetramethoxy resorcinarene tetraoxyacetic acid (TRTA) in hexadecyltrimethylammonium bromide (CTAB) medium was investigated. The fluorescence of TRTA was quenched by paeonol due to the formation of weak fluorescent inclusion complex (Paeonol–TRTA), and the fluorescence quenching (ΔF = F TRTA − F Paeonol–TRTA) was sensitized in CTAB. Under the optimal conditions, the linear range of calibration curve for the determination of paeonol was 0.02–6.40μg/mL. The detection limit estimated and RSD was 12.05ng/mL, 2.57% (n =3, c =1.0μg/mL). The mechanism of determination was discussed by quenching type analysis, absorption spectrum titrations, Benesi–Hildebrand method, fluorescence quantum yield and IR spectra. This method has also been applied for the determination of paeonol in real sample with satisfactory result.

A novel signal-on DNAzyme-based electrochemiluminescence, sensor for Pb2+

24 October 2013, 08:58:24

Publication date: February 2014
Source:Sensors and Actuators B: Chemical, Volume 191
Author(s): Yan-fang Wu , Zhi-min Cai , Geng-huang Wu , Ming-cong Rong , Ya-qi Jiang , Chao-yong James Yang , Xi Chen
A novel signal-on electrochemiluminescence (ECL) biosensor for the determination of lead (Pb²⁺) was developed. Background suppression for the ECL detection of Pb²⁺ and hybridization in the presence of Pb²⁺ were realized using a hairpin probe. The 8–17 DNAzymes, which hybridized with their substrate strands, were immobilized onto the surface of a glassy carbon electrode (GCE) via amino coupling method. In the presence of Pb²⁺, the substrate strands were cleaved and released, while DNAzymes alone remained on the GCE surface. The single-stranded DNAzyme could hybridize with a hairpin probe containing an ECL luminophore resulting in quantitative ECL signals. The sequence of the hairpin probe was designed and optimized for hybridizing with single-stranded DNAzyme but not with DNAzyme-substrate double strands. This signal-on strategy possessed low ECL background signals, high sensitivity and selectivity toward Pb²⁺. The ECL sensing approach presented excellent response to Pb²⁺ from 10pM to 100nM with a detection limit of 6.4pM.

On the application of simple matrix methods for electronic tongue data processing: Case study with black tea samples

24 October 2013, 08:58:24

Publication date: February 2014
Source:Sensors and Actuators B: Chemical, Volume 191
Author(s): Irina Yaroshenko , Dmitry Kirsanov , Liudmila Kartsova , Nabarun Bhattacharyya , Subrata Sarkar , Andrey Legin
The paper is devoted to the application of several simple mathematical methods that can be used for analysis of multisensor system data. RV and modified RV′ matrix correlation coefficients, Tucker's congruency coefficients and canonical correlation analysis can be effectively employed to reveal the similarity degree shared between two different data sets obtained for the same samples. This approach can be particularly useful when the number of available samples is too small to construct and validate quantitative regression models, but still the researcher is interested in getting some numerical estimate of the data quality to judge on electronic tongue applicability for particular analytical tasks. As a case study for this work we analyzed the data from potentiometric and voltammetric electronic tongues acquired during the analysis of black tea samples. These samples were also assessed with standard physicochemical methods and professional sensory panel. The relationships between these four data sets were studied with various matrix correlation techniques.

Development of a continuous-flow polymerase chain reaction device utilizing a polymer disk with a spiral microchannel of gradually varying width

24 October 2013, 08:58:24

Publication date: February 2014
Source:Sensors and Actuators B: Chemical, Volume 191
Author(s): Kwang Hyo Chung , Yo Han Choi , Seho Park
This paper describes a continuous-flow polymerase chain reaction (CF-PCR) device utilizing a polymer disk, which is equipped with a long spiral microchannel. In the literature, some CF-PCR devices employing a spiral microchannel have been presented to overcome an inherent deployment problem of heaters in CF-PCR of a serpentine microchannel, however, the spiral arrangement also made a problem of non-constant PCR cycle time, which would reduce the PCR efficiency. As a novel solution in this paper, we made the width of the spiral channel decrease gradually in the radial direction in order to keep the cycle time of one round same independent of radial positions and the PCR speed. In the spiral channel of 5.4-m long, through which the PCR reactant is pumped at a constant flow rate, a cycling zone made of thirty spiral rounds corresponding to 30 PCR cycles was placed between a pre-denaturation zone and a post-extension zone, and each zone was designed to have a fixed flow residence time ratio against to the total PCR time. We developed a fast thermal bonding technique minimizing the destruction of the microchannel in the wide polymer disk of 66-mm diameter. A compact heating apparatus was fabricated in order to impose different temperatures at three heating sectors deployed circumferentially in the disk. As a novel trial, the disk is sandwiched by isolated metal plates of constant temperature for stable thermal maintenance. We conducted numerical simulations for the heat transfer to PCR mixture depending on the PCR speed, and discussed on its effect on PCR result. A successful amplification of a human-genome DNA was obtained in less than 10min. The unique architecture used in this CF-PCR device is understood to be well applied to a field-applicable fast PCR.

CuO nanowires based sensitive and selective non-enzymatic glucose detection

24 October 2013, 08:58:24

Publication date: February 2014
Source:Sensors and Actuators B: Chemical, Volume 191
Author(s): Yuchan Zhang , Yixin Liu , Liang Su , Zhonghua Zhang , Danqun Huo , Changjun Hou , Yu Lei
Copper oxide nanowires (CuO NWs) were prepared by a facile two-step procedure consisting of wet-chemistry synthesis and subsequent direct calcination. The morphology, surface property, and crystal structure of the as-prepared CuO NWs were characterized by SEM, TEM, and XRD. The CuO NWs were further employed to construct a non-enzymatic glucose sensor with excellent performance toward glucose detection in 50mM NaOH solution. The as-developed non-enzymatic glucose sensor showed a fast response time (less than 5s) and a wide dynamic range with excellent sensitivity of 648.2μAcm⁻² mM⁻¹ and 119.9μAcm⁻² mM⁻¹ toward glucose detection at an applied potential of +0.55V and +0.3V (vs. Ag/AgCl), respectively. The Langmuir isothermal theory was employed to fit the obtained calibration curves with high correlation coefficient and the mechanisms for the glucose oxidation promoted by CuO NWs were also discussed. The good selectivity of the CuO NWs based non-enzymatic glucose sensor against electroactive compounds such as ascorbic acid, uric acid, and acetaminophen, and other sugars such as fructose and sucrose at their physiological concentrations were also demonstrated. Furthermore, good accuracy and high precision for the quantification of glucose concentration in human serum samples was attested. These good features indicate that CuO NWs have a great potential in the development of sensitive and selective non-enzymatic glucose sensor.

Sensitive square wave anodic stripping voltammetric determination of Cd2+ and Pb2+ ions at Bi/Nafion/overoxidized 2-mercaptoethanesulfonate-tethered polypyrrole/glassy carbon electrode

24 October 2013, 08:58:24

Publication date: February 2014
Source:Sensors and Actuators B: Chemical, Volume 191
Author(s): Li Chen , Zou Li , Yue Meng , Pei Zhang , Zhaohong Su , Ying Liu , Yi Huang , Yaping Zhou , Qingji Xie , Shouzhuo Yao
Square wave anodic stripping voltammetry was applied to detect Pb²⁺ and Cd²⁺ ions at a glassy carbon electrode modified with overoxidized 2-mercaptoethanesulfonate (MES)-tethered polypyrrole, Nafion and Bi. The PPy–MES interaction was examined by quartz crystal microbalance. Under optimum conditions (5-min preconcentration at −1.2V vs. SCE in pH 4.0 acetate buffer containing 300μgL⁻¹ Bi³⁺), the linear calibration curves ranged from 0.05 to 35μgL⁻¹ for Pb²⁺ and 0.1 to 25μgL⁻¹ for Cd²⁺, respectively, and the limits of detection (S/N =3, S is the signal and N is the noise level) were 0.03μgL⁻¹ for Pb²⁺ and 0.04μgL⁻¹ for Cd²⁺. This method was successfully applied for Pb²⁺ and Cd²⁺ analysis in real water samples.

Graphical abstract

AMSBIO & Sanguine Biosciences Announce Distribution Agreement

AMSBIO has announced that it has reached agreement with Sanguine BioSciences, a biotechnology company enabling personalized medicine research, to distribute and support its products and services throughout Europe.

Commenting on the new agreement Phillip Pridham-Field of AMSBIO said "Sanguine's approach to biospecimen collection and their high patient retention allow researchers to collect the data they need with better turnaround time and with the potential for longitudinal studies. We believe their extensive biospecimen library will be an excellent addition to our current product offerings for researchers in life sciences." 

Sanguine collects and de-identifies biospecimen, medical history and other data from patients diagnosed with severe and chronic diseases for use in biomarker research. Researchers traditionally obtain biospecimen through hospitals, but this process often proves inefficient as the focus for physicians and staff is on diagnosis and treatment, not facilitating research efforts. By connecting directly with patients, Sanguine is able to meet the needs of researchers  and offer timely turnaround of biospecimen and medical data with diverse ranges  for age, race, disease state, gender and treatments underway.  The patient engagement tactics used by the company have led to a 95 percent retention rate,  which also allow for follow-up draws for longitudinal studies. 

"There is no denying that personalized medicine has become a significant area of interest for drug discovery, but there exists a gap between researchers who require biospecimen respective medical data, and patients who want to be a part of research efforts," said Brian Neman, founder and chief executive officer of Sanguine. "We have engaged hundreds of patient subjects, and built a library of  specimen and data that can effectively bridge this gap. We look forward to partnering with AMSBIO to make this service accessible to researchers around the world working in different therapeutic areas."

Sanguine is able to meet, review disclosures and collect blood samples in a  patient's home with its own phlebotomists in multiple major U.S. cities.  Patients are also able to track how their de-identified biospecimen and data are used through the donor web-portal. The company is able to collect and process blood from patients with any disease and has already built large libraries in  multiple chronic and severe conditions, including Huntington's disease,  rheumatoid arthritis, systemic lupus erythematosus, Crohn's disease, ulcerative  colitis and others. In order to maintain appropriate confidentiality, all samples are  de-identified immediately upon collection. Sanguine maintains and reviews  internal ethical guidelines for the procedures under high scrutiny from an  independent review board.

Founded in 1987, AMS Biotechnology (AMSBIO) is recognized today as a leading  company contributing to the acceleration of discovery through the provision of  cutting-edge life science technology products and services for research and  development in the medical, nutrition, cosmetics and energy industries. With a  range of molecular detection reagents and a significant Biorepository AMSBIO  offers tissues, DNA, RNA, protein and tissue microarray products. Key research  areas for AMSBIO include: Oncology, Regenerative Medicine, Environmental  Analysis, Cytotoxicity Screening, Glycomics and Stem Cell Biology.

Sanguine BioSciences is a biotechnology company bridging the gap between  patients and researchers developing personalized medicine. The company engages  patients in biomedical research by delivering transparency throughout the  research process. Sanguine collects and de-identifies patient-derived data in  the form of biospecimen, and physician and self-reported information. These data  are generated and then made available to researchers involved in drug and  biomarker research and discovery with leading academic laboratories and  companies, such as Vertex.

Just Published: Sensors & Actuators A: Physical

A new issue of this journal has just been published. To see abstracts of the papers it contains (with links through to the full papers) click here:

Sensors & Actuators A: Physical
http://rss.sciencedirect.com/publication/science/5282

Selected papers from the latest issue:

Design and calibration of a new compact radiative heat-flux gauge (RHFG) for combustion applications

23 October 2013, 09:20:49

Publication date: 1 December 2013
Source:Sensors and Actuators A: Physical, Volume 203
Author(s): V. Mahendra Reddy , S. Sudheer , S.V. Prabhu , Sudarshan Kumar
It is important to develop an inexpensive and robust gauge for measuring the contribution of radiation heat-flux component while operating in high temperature conditions without the need of cooling water supply. This work presents a new compact radiative heat-flux gauge (RHFG) for measuring the radiative heat-flux from combustion systems operating at high operating temperatures (∼1200K). Various types of total heat-flux meters (convective and radiative) are available for measuring heat-flux. In this study, pure radiative heat-flux measuring gauge (RHFG) is developed. Quartz plate is used as a window of RHFG acting as media to transfer pure radiative heat from the heat source. Copper plate is used as the heat sensing element. A thermocouple is brazed to the copper plate to measure the rate of heat transfer to the sensing element. The mathematical modeling, numerical analysis and construction methodology of RHFG is discussed. Initially, a large sized gauge (G1) is fabricated and calibrated with cone calorimeter. The measured response time of 670s is observed for G1. Numerical analysis is carried out to optimize the size of RHFG and reduce the response time. Four different gauges with various dimensions (G2, G3, G4 and G5) are analyzed numerically and a response time of 208, 17, 14 and 12s respectively is observed. The gauge, G5 is manufactured and calibrated with cone calorimeter with known radiative heat-flux and the experimental response time of 13s is observed. This RHFG is of low cost, simple to manufacture, rugged and requires no water cooling even for high temperature combustion applications.

Design and fabrication of SAW pressure, temperature and impedance sensors using novel multiphysics simulation models

23 October 2013, 09:20:49

Publication date: 1 December 2013
Source:Sensors and Actuators A: Physical, Volume 203
Author(s): G.A. Borrero , J.P. Bravo , S.F. Mora , S. Velásquez , F.E. Segura-Quijano
Surface acoustic wave (SAW) devices have been shown to be suitable for many applications. Some of these applications are temperature, pressure and impedance-based sensors. In this study, we investigate the performance of a SAW resonator as temperature and pressure sensors, and a reflective differential delay line (RDDL) structure as an impedance sensor. The SAW sensors were designed using a proposed FEM-based multiphysics model on COMSOL^® and fabricated using photolitography over a 128° YX LiNbO3 substrate for an operation frequency of 65MHz. Using a vector network analyzer (VNA), the devices were characterized; frequency shifts on the S 11 parameter of resonators were observed depending on the applied external pressure and temperature changes, and amplitude variations for impedance changes in the case of RDDL. The experimental results were compared with simulation data. The evaluated sensitivities were 87.81 ppm/°C, 0.9 ppm/kPa and 0.0023 dB/Ω.

A new design method for a strain sensor using the cross-section modification of a coaxial cable

23 October 2013, 09:20:49

Publication date: 1 December 2013
Source:Sensors and Actuators A: Physical, Volume 203
Author(s): Pengfei Shi , Renjing Gao , Shutian Liu , Jian Zhao
Strain sensors have been used extensively in structural condition monitoring. In this paper, based upon microwave network theory, a novel design method for a real-time strain monitoring sensor is proposed by using the variable cross section of a coaxial cable to detect the strain-induced frequency shift of the peak frequency at which the S parameter exhibits a peak value. With this method, a dual variable-cross-section sensor is designed and fabricated using coaxial cable as the fabrication element. The S-parameters of the sensor obtained analytically by transmission theory are almost consistent with those obtained by numerical simulation. In experiments, the sensitivity of the sensor achieved 5MHz/mɛ with the original segment length of 10.345mm and peak frequency of 5.0GHz, and the resolution achieved is 140.25μɛ. The relative small deviation of nearly 3.2% from the theoretical results to the experimental results adequately validated the feasibility of the design method. Adjusting the diameter of the dielectric layer, the length and cascaded periods of the variable cross-section, the quality factor and sensitivity of the sensor can be optimized. Due to the simplicity and ruggedness of the cable based sensor it has great potential application in structural condition monitoring compared to existing sensors.

Study of the influence of temperature on the optical response of interferometric detector systems

23 October 2013, 09:20:49

Publication date: 1 December 2013
Source:Sensors and Actuators A: Physical, Volume 203
Author(s): Thomas Wood , Judikaël Le Rouzo , François Flory , Raphael K. Kribich , Geoffrey Maulion , Philippe Signoret , Paul Coudray , Thomas Mazingue
In this paper, we will demonstrate a theoretical approach to determining the optical response of interferometric detector systems to external stimuli. The wavelength dispersion of the refractive index and the thermo-optic coefficient of transparent polymer blend waveguide materials are inserted into modeling software in order to simulate the optical response of both Multimode Interferometer (MMI) and Bragg grating (BG) architectures. The optical output of such devices is very sensitive to variations in the refractive index of the constituent materials, and they may be used to detect phenomena such as local temperature changes or relative humidity variations [1]. When the input intensity of the sensor system is normalized to unity, we demonstrate theoretical thermal sensitivities of 2×10⁻⁴/K for BG architectures and 3×10⁻⁵/K for MMI devices. A differential measurement system for BG or MMI components is discussed and simulated. We shall also discuss the use of such systems as gas detectors when a catalyst capable of accelerating the exothermic oxidation of combustible gasses is deposited onto the optical circuit.

Laser profilometer using a Fabry–Perot etalon and an objective

23 October 2013, 09:20:49

Publication date: 1 December 2013
Source:Sensors and Actuators A: Physical, Volume 203
Author(s): Shyh-Tsong Lin , Sheng-Lih Yeh , Yi-Chun Wang , Meng-Zhu Chen
This paper introduces an innovative laser profilometer using a Fabry–Perot etalon and an objective. Following the derivation of the measurement theory, an experimental setup constructed to realize the profilometer is demonstrated, and the experimental results from the uses of this setup are then presented. The experimental setup has a sensitivity, vertical resolution, and stability of 1.62/μm, 2.2nm, and 6.6nm, respectively, and the experimental results agree not only the validity but also the feasibility of the proposed profilometer.

Synthesis of mesoporous polypyrrole nanowires/nanoparticles for ammonia gas sensing application

23 October 2013, 09:20:49

Publication date: 1 December 2013
Source:Sensors and Actuators A: Physical, Volume 203
Author(s): Ishpal Rawal , Amarjeet Kaur
Nanostructured polypyrrole (PPy) has been synthesized in the presence of anionic azo dye {sodium 4-[4-(dimethyl-amino)-phenyldiazo] phenylsulfonate} (MO) and cationic surfactant {cetyltrimethyl ammonium bromide} (CTAB). The synthesis of the prepared PPy samples was confirmed by Fourier transform infrared spectroscopy and structural analysis was carried out using X-ray diffraction technique. Scanning electron microscopy and high resolution transmission electron microscopy investigations confirm the formation of nanostructured PPy. Both the samples have different shapes and dimensions. The sample prepared in the presence of MO has the higher doping level, bipolaron concentration and electrical conductivity (4Scm⁻¹) as compared to the sample prepared in the presence of CTAB (1.69×10⁻⁴ Scm⁻¹). The prepared samples were tested for porosity through BET measurements. It has been found that the PPy nanowires (S1) have larger surface area (156,056.0cm²/g) as compared PPy nanoparticles (S2) (11,259.0cm²/g). Moreover, PPy nanowires have shown better gas sensitivity (∼6%) as compared to PPy nanoparticles (∼4%) and well corroborated with porosity, surface morphology, and the Raman investigations carried out under ammonia environment.

All fiber curvature sensor based on modal interferometer with waist enlarge splicing

23 October 2013, 09:20:49

Publication date: 1 December 2013
Source:Sensors and Actuators A: Physical, Volume 203
Author(s): Haifeng Song , Huaping Gong , Kai Ni , Xinyong Dong
A novel fiber curvature sensor based on modal interferometer with waist-enlarge splicing is proposed. A section of 30mm polarization maintaining fiber (PMF) is spliced with waist enlarge between two conventional single mode fibers (SMFs) to construct an all fiber curvature sensor. The results show that the transmission spectrum has a blue and red shift, corresponding to the opposite curvature directions. The sensitivity coefficient of −10.634nm/m⁻¹ and 10.152nm/m⁻¹ were acquired by concave and convex bending with the range from 0m⁻¹ to 2.054m⁻¹, and the corresponding resolution were 9.4×10⁻⁴ m⁻¹ and 9.85×10⁻⁴ m⁻¹, respectively. And the influence of different lengths of PMF on the sensitivity was also discussed.

A fast response intrinsic humidity sensor based on an etched singlemode polymer fiber Bragg grating

23 October 2013, 09:20:49

Publication date: 1 December 2013
Source:Sensors and Actuators A: Physical, Volume 203
Author(s): Ginu Rajan , Yusof Mohd Noor , Bing Liu , Eliathamby Ambikairaja , David J. Webb , Gang-Ding Peng
A simple, low cost and fast response time intrinsic relative humidity sensor system based on an etched singlemode polymer fiber Bragg (POFBG) is presented in this paper. A macro-bend linear edge filter which converts the humidity induced wavelength shift into an intensity change is used as the interrogation technique. The singlemode POFBG is etched to micro-meters in diameter to improve the response time of the humidity sensor. A response time of 4.5s is observed for a polymer FBG with a cladding diameter of 25μm. The overall sensor system sensitivity was 0.23mV/%RH. The etched POFBG humidity sensor shows anexponential decrease in response time with a decrease in fiber diameter. The developed sensor might have potential applications in a wide range of applications where fast and accurate real time humidity control is required.

Capacitive contact lens sensor for continuous non-invasive intraocular pressure monitoring

23 October 2013, 09:20:49

Publication date: 1 December 2013
Source:Sensors and Actuators A: Physical, Volume 203
Author(s): Guo-Zhen Chen , Ion-Seng Chan , David C.C. Lam
Intraocular pressure (IOP) is a primary indicative factor in the diagnosis and treatment monitoring of glaucoma. Measurement of IOP during conventional single office consultation is insufficient for determination of the pressure peak, and IOP profile is needed for peak determination. A capacitive wearable contact lens sensor for monitoring of the IOP is developed in this study. A curvature-sensitive inductor–capacitor sensor is fabricated and embedded inside a silicone rubber contact lens, such that the curvature of the lens is correlated with the resonance frequency of the sensor. The curvature of the lens is mechanically related to the IOP in the underlying eye such that the IOP can be determined from the resonance frequency of the sensor. To fit human eyes, the sensor was designed to have an outer diameter of 14mm, radius of curvature of 8.5mm, and operates in human IOP range between 5 and 40mmHg. The frequency responses and the ability of the sensor to track IOP cycles were tested. Tests on model silicone eyes and enucleated porcine eyes showed that the sensors have a linearity R >0.997 and a sensitivity >200ppm/mmHg for IOP monitoring. Together with wireless reading circuitry taped around the eye socket, the new contact lens sensor can be used for continuous IOP monitoring in clinics and at home for determination of the peak IOP for use in glaucoma diagnosis and monitoring.

Stress relaxation measurement of viscoelastic materials using a polymer-based microfluidic device

23 October 2013, 09:20:49

Publication date: 1 December 2013
Source:Sensors and Actuators A: Physical, Volume 203
Author(s): Jiayue Shen , Peng Cheng , Wenting Gu , Zhili Hao
This paper presents the stress relaxation measurement of viscoelastic materials using a polymer-based microfluidic device. Comprised of a single polymer rectangular microstructure and a set of electrolyte-enabled distributed resistive transducers, this device is capable of detecting continuous distributed dynamic loads. In a measurement, a rigid cylinder probe is utilized to apply a precisely controlled step displacement input to a material specimen on the device, and consequently the spatially varying stress relaxation behavior of the specimen is translated to time-dependent continuous distributed loads acting on the device, where such loads give rise to time-dependent continuous deflection of the polymer microstructure and register as discrete resistance changes at the locations of the transducers. To account for device-to-device fabrication variations, performance characterization is first conducted on a device as a control experiment, and then a specimen is placed on a characterized device for measurement. Several homogeneous and heterogeneous specimens are measured, and the associated data analysis is conducted for extracting the spatially varying Young's relaxation modulus, which is expressed as the Maxwell model with two relaxation times. The results demonstrate the feasibility of using a single polymer-based microfluidic device to map out the spatially varying stress relaxation behavior of viscoelastic materials.

Laser synthesized gold nanoparticles for high sensitive strain gauges

23 October 2013, 09:20:49

Publication date: 1 December 2013
Source:Sensors and Actuators A: Physical, Volume 203
Author(s): Salamat Burzhuev , Aykutlu Dâna , Bülend Ortaç
We demonstrate high strain sensitivity property of gold nanoparticle (Au-NP) thin films fabricated on flexible polydimethylsiloxane (PDMS) substrates. This behavior is attributed to quantum tunneling effect that is highly dependent on nanoparticle separation. Au-NPs were synthesized in water by nanosecond laser ablation method. The clean surface providing high tunneling decay constant, size of the Au-NPs and Au-NPs aggregate clusters offer advantages for high sensitivity strain sensor. We prepared Au-NPs films on flexible PDMS substrate by using hands-on drop-cast method. To obtain high gauge factor (g factor), we investigated the nanoparticles concentration on the substrate. Laser-generated Au-NPs films demonstrated g factor of ∼300 for higher than 0.22% strain and ∼80 for the strain lower than 0.22% strain, which is favorably comparable to reported sensitivities for strain sensors based on Au-NPs. Mechanical characterizations for the prolonged working durations suggest long term stability of the strain sensors. We discuss several models describing conductance of films in low and high strain regimes.

Improving the stability and reproducibility of the carbon nanotube gas ionization sensor by Co–Ti/Ti co-deposited catalyst layer

23 October 2013, 09:20:49

Publication date: 1 December 2013
Source:Sensors and Actuators A: Physical, Volume 203
Author(s): Chia-Tsung Chang , Chun-Yu Huang , Yu-Ren Li , Huang-Chung Cheng
A novel gas ionization sensor (GIS) of the carbon nanotube (CNT) film using the Co–Ti/Ti co-deposited catalyst layer had been proposed for the first time to exhibit higher stability and better reproducibility with respect to the CNT film ones with the single catalyst layer. For the proposed CNT GIS, the variation of the breakdown voltage (V br ) was less than 25% for the ten devices with the same structure measurement since the lengths of the CNT synthesized were uniform and aligned. Besides, the fluctuation of the V br was about 14% during 1000 operation times in nitrogen at the pressure of 0.035Torr. It was attributed to the adhesion between CNTs and the substrate could be improved since the co-deposited catalyst layer and Ti adhesion layer would be coalesced so that the Co nanoparticles would be partially immersed into Ti layer after hydrogen pretreatment. Such a CNT GIS with the co-deposited catalyst layer also exhibited high sensitivity and selectivity for different kinds of gases detection as well as the good linearity for detecting the gas mixture.

Design and analysis of functional multiwalled carbon nanotubes for infrared sensors

23 October 2013, 09:20:49

Publication date: 1 December 2013
Source:Sensors and Actuators A: Physical, Volume 203
Author(s): R. Afrin , N.A. Shah , M. Abbas , M. Amin , A.S. Bhatti
In this paper, we report the comparison of infrared detection based on buckypapers of chemically modified multiwalled carbon nanotubes by carboxyl and thiol groups. We observed that functionalized carbon nanotube buckypapers had a significant impact on radiation sensing at room temperature. Nanotubes buckypapers were formed by successively increasing cross-linker reagent in carbon nanotubes. It was observed that infrared sensitivity of resistively read-out of carboxylated and thiolated buckypapers increased by increasing the cross-linker reagent up to certain limit. Further increase in cross-linker reagent results in brittleness of buckypaper. The maximum sensitivity of carboxylated and thiolated buckypapers was 3.4% and 16.07% while minimum response time of carboxylated and thiolated buckypapers was 1.29s and 6.09s, respectively. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and Fourier transform infrared spectroscopy were used for analysis of presences of nanotubes, structural morphology and defect density to evaluate all the modifications of the nanotubes structure and the nature of the compounds added to the nanotubes surface by functionalization treatment.

Analysis of a concentric coplanar capacitor for epidermal hydration sensing

23 October 2013, 09:20:49

Publication date: 1 December 2013
Source:Sensors and Actuators A: Physical, Volume 203
Author(s): Huanyu Cheng , Yihui Zhang , Xian Huang , John A. Rogers , Yonggang Huang
Without conformal contact between hydration sensors and skin, measured signals (either capacitance or impedance) can be susceptible to artifacts associated with motion-induced changes and irreproducibility in contact. Devices with mechanical properties matched to the skin enable conformal contact and adhesion via the action of van der Waals forces alone, thereby facilitating accurate, reproducible measurements. Theoretical investigations of concentric coplanar capacitors in this type of ‘epidermal’ format yield analytic expressions of the impedance for single- and double-layer capacitors. The calculated dependence of impedance on material and geometric parameters agree well with finite element analysis and experiments, thereby providing important insights into the design of epidermal systems for hydration sensing.

Real-time 1D hyperspectral imaging of porous silicon-based photonic crystals with one-dimensional chemical composition gradients undergoing pore-filling-induced spectral shifts

23 October 2013, 09:20:49

Publication date: 1 December 2013
Source:Sensors and Actuators A: Physical, Volume 203
Author(s): Adam Leacock-Johnson , Adrian Garcia Sega , Adnan Sharief , Michael J. Sailor , Gordon M. Miskelly
A line-scan hyperspectral imager can provide real-time spectral information at many points along a transect of a gradient-modified material. This is demonstrated by monitoring the optical reflectance spectrum of a porous silicon photonic crystal with a hydrophobic/hydrophilic pore-wall surface composition gradient while it is immersed in water to which ethanol is added. The combination of the hyperspectral imager and the pore-wall composition gradient allows a detailed study of the pore filling process. It is observed that even the most hydrophobic pores fill to a small extent when only a small amount of ethanol has been added. This gradient of filling is in contrast to visible observation of the porous silicon samples, which can suggest a step change in pore filling. The pore-filling process can take many minutes when the solution composition allows pores at a given position along the gradient to be about 50% filled. These observations demonstrate the utility of aligning a line-scan hyperspectral imager with a gradient material.