Detection of Pseudomonas aeruginosa using a wireless magnetoelastic sensing device

This paper describes the real-time quantification of Pseudomonas aeruginosa (P. aeru) concentrations using a wireless magnetoelastic sensing device. The sensor is fabricated by coating a magnetoelastic ribbon with a polyurethane protecting film. In response to an externally applied time varying magnetic field, the magnetoelastic sensor vibrates at a resonance frequency that can be remotely determined by monitoring the magnetic flux emitted by the sensor. The resonance frequency changes in response to properties changes of a liquid culture medium and bacteria adhesion to the sensor as P. aeru consumes nutrients from the culture medium in growth and reproduction. The effects of properties (conductivity, viscosity, mass) are investigated with quartz crystal microbalance (QCM), microscopy imaging, and conductivity measurement. Using the described technique we are able to directly quantify P. aeru concentrations of 10(3) to 10(8)cells/ml, with a detection limit of 10(3)cells/ml at a noise level of approximately 20 Hz. The lack of any physical connections between the sensor and the monitoring electronics facilitates aseptic operation, and makes the sensor platform ideally suited for monitoring bacteria from within, for example, sealed food containers.     

In-situ monitoring of breast cancer cell (MCF-7) growth and quantification of the cytotoxicity of anticancer drugs fluorouracil and cisplatin

A wireless sensing device was developed for the in-situ monitoring of the growth of human breast cancer cells (MCF-7) and evaluation of the cytotoxicity of the anticancer drugs fluorouracil and cisplatin. The sensor is fabricated by coating a magnetoelastic ribbon-like sensor with a layer of polyurethane that protects the iron-rich sensor from oxidation and provides a cell-compatible surface. In response to a time-varying magnetic field, the magnetoelastic sensor longitudinally vibrates, emitting magnetic flux that can be remotely detected by a pick-up coil. No physical connections between the sensor and the detection system are required. The wireless property facilitates aseptic biological operation, especially in cell culture as illustrated in this work. The adhesion of cells on the sensor surface results in a decrease in the resonance amplitude, which is proportional to the cell concentration. A linear response was obtained in cell concentrations of 5x10(4) to 1x10(6)cellsml(-1), with a detection limit of 1.2x10(4)cellsml(-1). The adhesion strength of cells on the sensor is qualitatively evaluated by increasing the amplitude of the magnetic excitation field. And the cytotoxicity of the anticancer drugs fluorouracil and cisplatin is evaluated by the magnetoelastic biosensor. The cytostatic curve is related with the quantity of cytostatic drug. The lethal concentration (LC50) for cells incubated in the presence of drugs for 20h is calculated to be 19.9muM for fluorouracil and 13.1muM for cisplatin.     

Sensitive and selective cataluminescence‐based sensor system for acetone and diethyl ether determination

A three‐dimensional hierarchical CdO nanostructure with a novel bio‐inspired morphology is reported. The field emission scanning electronic microscopy, transmission electron microscopy and X‐ray diffractometer were employed to characterize the as‐prepared samples. In gas‐sensing measurements, acetone and diethyl ether were employed as target gases to investigate cataluminescence (CTL) sensing properties of the CdO nanostructure. The results show that the as‐fabricated CdO nanostructure exhibited outstanding CTL properties such as stable intensity, high signal/noise values, short response and recovery time. The limit of detection of acetone and diethyl ether was ca. 6.5 ppm and 6.7 ppm, respectively, which was below the standard permitted concentrations. Additionally, a principal components analysis method was used to investigate the recognizable ability of the CTL sensor, and it was found that acetone and diethyl ether can be distinguished clearly. The performance of the bio‐inspired CdO nanostructure‐based sensor system suggested the promising application of the CdO nanostructure as a novel highly efficient CTL sensing material. Copyright © 2014 John Wiley & Sons, Ltd.     

Design and performances of immunoassay based on SPR biosensor with magnetic microbeads

A surface plasmon resonance (SPR) biosensor system was developed for immunoassay, based on the conjugates of magnetic microbeads coupling with antibody which could be trapped on the Au film firmly due to the magnetic force. The magnetic microbeads were used as the solid support for the heat shock protein 70 (Hsp 70) antibody and antibody immobilized magnetic microbeads were utilized instead of the single antibody for the determination of Hsp 70. Since the magnetic bead is coated with dextran, the antibodies and some specific biomolecular receptors can be immobilized using a variety of chemical reactions. Compared to traditional antibody immobilization on the sensing film, there is not a covalent link between the Au film and the antibody. There is a great advantage in that sensor can be stripped and reused, and the same chemistry used to derivative dextran-coated SPR sensors can be used for the magnetic bead-coated sensors. The sensing layer was formed well. Different dilution ratios (v/v) of the conjugates result in different detectable ranges. When the dilution ratios of the conjugate are 1:10 and 1:5, the lowest concentrations of Hsp 70 that can be detected are 1.50 and 0.30 microg ml(-1), respectively.     

High efficiency Hall effect micro-biosensor platform for detection of magnetically labeled biomolecules

Detection of magnetically labeled biomolecules using micro-Hall biosensors is a promising method for monitoring biomolecular recognition processes. The measurement efficiency of standard systems is limited by the time taken for magnetic beads to reach the sensing area of the Hall devices. Here, micro-current lines were integrated with Hall effect structures to manipulate the position of magnetic beads via field gradients generated by localized currents flowing in the current lines. Beads were accumulated onto the sensor surface within seconds of passing currents through the current lines. Real-time detection of magnetic beads using current lines integrated with Hall biosensors was achieved. These results are promising in establishing Hall biosensor platforms as efficient and inexpensive means of monitoring biomolecular reactions for medical applications.     

Magnetoresistive-based biosensors and biochips

Over the past five years, magnetoelectronics has emerged as a promising new platform technology for biosensor and biochip development. The techniques are based on the detection of the magnetic fringe field of a magnetically labeled biomolecule interacting with a complementary biomolecule bound to a magnetic-field sensor. Magnetoresistive-based sensors, conventionally used as read heads in hard disk drives, have been used in combination with biologically functionalized magnetic labels to demonstrate the detection of molecular recognition. Real-world bio-applications are now being investigated, enabling tailored device design, based on sensor and label characteristics. This detection platform provides a robust, inexpensive sensing technique with high sensitivity and considerable scope for quantitative signal data, enabling magnetoresistive biochips to meet specific diagnostic needs that are not met by existing technologies.     

Detection of volatile organic compounds released by wood furniture based on a cataluminescence test system

Wood furniture is an important source of indoor air pollution. To date, the detection of harmful substances in wood furniture has relied on the control of a single formaldehyde component, therefore the detection and evaluation of pollutants released by wood furniture are necessary. A novel method based on a cataluminescence (CTL) sensor system generated on the surface of nano‐3TiO₂–2BiVO₄ was proposed for the simultaneous detection of pollutants released by wood furniture. Formaldehyde and benzene were selected as a model to investigate the CTL‐sensing properties of the sensor system. Field emission scanning electronic microscopy (FESEM), transmission electron microscopy (TEM) and X‐ray diffraction (XRD) were employed to characterize the as‐prepared samples. The results showed that the as‐prepared test system exhibited outstanding CTL properties such as stable intensity, a high signal‐to‐noise ratio, and short response and recovery times. In addition, the limit of detection for formaldehyde and benzene was below the standard permitted concentrations. Moreover, the sensor system showed outstanding selectivity for formaldehyde and benzene compared with eight other common volatile organic compounds (VOCs). The performance of the sensor system will enable furniture VOC limit emissions standards to be promulgated as soon as possible. Copyright © 2015 John Wiley & Sons, Ltd.     

The light-addressable potentiometric sensor for multi-ion sensing and imaging

The light-addressable potentiometric sensor (LAPS) is a semiconductor-based chemical sensor with an electrolyte-insulator-semiconductor structure. The LAPS can have many measuring points integrated on the sensing surface, which are individually accessed by a light beam. By modifying the measuring points with different materials, a single sensor plate can be used as a multi-analyte sensor. In this paper, instrumentation and application of LAPS to multi-ion sensing and imaging are described. As a new application of LAPS, potentiometric imaging of a microfluidic channel is proposed.     

Sequential detection of Salmonella typhimurium and Bacillus anthracis spores using magnetoelastic biosensors

Multiple phage-based magnetoelastic (ME) biosensors were simultaneously monitored for the detection of different biological pathogens that were sequentially introduced to the measurement system. The biosensors were formed by immobilizing phage and 1mg/ml BSA (blocking agent) onto the magnetoelastic resonator's surface. The detection system included a reference sensor as a control, an E2 phage-coated sensor specific to S. typhimurium, and a JRB7 phage-coated sensor specific to B. anthracis spores. The sensors were free standing during the test, being held in place by a magnetic field. Upon sequential exposure to single pathogenic solutions, only the biosensor coated with the corresponding specific phage responded. As the cells/spores were captured by the specific phage-coated sensor, the mass of the sensor increased, resulting in a decrease in the sensor's resonance frequency. Additionally, non-specific binding was effectively eliminated by BSA blocking and was verified by the reference sensor, which showed no frequency shift. Scanning electron microscopy was used to visually verify the interaction of each biosensor with its target analyte. The results demonstrate that multiple magnetoelastic sensors may be simultaneously monitored to detect specifically targeted pathogenic species with good selectivity. This research is the first stage of an ongoing effort to simultaneously detect the presence of multiple pathogens in a complex analyte.     

Sensitive and selective system of benzene detection based on a cataluminescence sensor

Au/La₂O₃ nanomaterials were prepared through calcining Au‐modified La(OH)₃ precursors. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X‐ray diffractometry (XRD) were employed to characterize the as‐prepared samples. Benzene, a common volatile organic compound, was selected as a model to investigate the cataluminescence (CTL)‐sensing properties of the Au/La₂O₃ nanomaterials. Results indicated that the as‐prepared Au/La₂O₃ exhibited outstanding CTL properties such as stable intensity, high signal‐to‐noise values, and short response and recovery times. Under optimized conditions, the benzene assay exhibited a broad linear range of 1–4000 ppm, with a limit of detection of 0.7 ppm, which was below the standard permitted concentrations. Furthermore, the gas sensor system showed outstanding selectivity for benzene compared with seven other types of common volatile organic compounds (VOCs). The proposed gas sensor showed good characteristics with high selectivity, fast response time and long lifetime, which suggested the promising application of the Au/La₂O₃ nanomaterials as a novel highly efficient CTL‐sensing material. Copyright © 2013 John Wiley & Sons, Ltd.     

Voltammetric detection of anti-HIV replication drug based on novel nanocomposite gold-nanoparticle–CaCO<Subscript>3</Subscript> hybrid material

A novel bionanocomposite, horse radish peroxidase- gold-nanoparticle–Calcium carbonate (HRP-AuNPs-CaCO₃), hybrid material was encapsulated by silica sol on a glassy carbon electrode (GCE). The fabricated modified electrode was used as a novel voltammetric sensor for electrochemical sensing of anti-HIV replication drug i.e. deferiprone. The surface morphology of the modified electrode was characterized by scanning electron microscopy (SEM). Results obtained from the voltammetric measurements show that HRP-AuNPs-CaCO₃ modified GCE offers a selective and sensitive electrochemical sensor for the determination of deferiprone. Under experimental conditions, the proposed voltammetric sensor has a linear response range from 0.01 to 10,000 μM with a detection limit of 0.01 μM. Furthermore, the fabricated sensor was successfully applied to determine deferiprone level in spiked urine and serum samples.     

gfp-based N-acyl homoserine-lactone sensor systems for detection of bacterial communication

In order to perform single-cell analysis and online studies of N-acyl homoserine lactone (AHL)-mediated communication among bacteria, components of the Vibrio fischeri quorum sensor encoded by luxR-P(luxI) have been fused to modified versions of gfpmut3* genes encoding unstable green fluorescent proteins. Bacterial strains harboring this green fluorescent sensor detected a broad spectrum of AHL molecules and were capable of sensing the presence of 5 nM N-3-oxohexanoyl-L-homoserine lactone in the surroundings. In combination with epifluorescent microscopy, the sensitivity of the sensor enabled AHL detection at the single-cell level and allowed for real-time measurements of fluctuations in AHL concentrations. This green fluorescent AHL sensor provides a state-of-the-art tool for studies of communication between the individuals present in mixed bacterial communities.     

Titanium and iron titanium oxide nanoparticles in antennae of the migratory ant <Emphasis Type="Italic">Pachycondyla marginata</Emphasis>: an alternative magnetic sensor for magnetoreception?

The most accepted hypothesis of magnetoreception for social insects is the ferromagnetic hypothesis which assumes the presence of magnetic material as a sensor coupled to sensitive structures that transmit the geomagnetic field information to the nervous system. As magnetite is the most common magnetic material observed in living beings, it has been suggested as basic constituent of the magnetoreception system. Antennae and head have been pointed as possible magnetosensor organs in social insects as ants, bees and termites. Samples of three antenna joints: head-scape, scape-pedicel and pedicel-third segment joints were embedded in epoxi resin, ultrathin sectioned and analyzed by transmission electron microscopy. Selected area electron diffraction patterns and X-ray energy dispersive spectroscopy were obtained to identify the nanoparticle compound. Besides iron oxides, for the first time, nanoparticles containing titanium have been identified surrounded by tissue in the antennae of ants. Given their dimension and related magnetic characteristics, these nanoparticles are discussed as being part of the magnetosensor system.     

Monitoring the growth and drug susceptibility of individual bacteria using asynchronous magnetic bead rotation sensors

Continuous growth of individual bacteria has been previously studied by direct observation using optical imaging. However, optical microscopy studies are inherently diffraction limited and limited in the number of individual cells that can be continuously monitored. Here we report on the use of the asynchronous magnetic bead rotation (AMBR) sensor, which is not diffraction limited. The AMBR sensor allows for the measurement of nanoscale growth dynamics of individual bacterial cells, over multiple generations. This torque-based magnetic bead sensor monitors variations in drag caused by the attachment and growth of a single bacterial cell. In this manner, we observed the growth and division of individual Escherichia coli, with 80-nm sensitivity to the cell length. Over the life cycle of a cell, we observed up to a 300% increase in the rotational period of the biosensor due to increased cell volume. In addition, we observed single bacterial cell growth response to antibiotics. This work demonstrates the non-microscopy limited AMBR biosensor for monitoring individual cell growth dynamics, including cell elongation, generation time, lag time, and division, as well as their sensitivity to antibiotics.     

Plasmonic Biosensor Based on Triangular Au/Ag and Au/Ag/Au Core/Shell Nanoprisms onto Indium Tin Oxide Glass

Gold–silver core–shell triangular nanoprisms (Au/AgTNPs) were grown onto transparent indium tin oxide (ITO) thin film-coated glass substrate through a seed-mediated growth method without using peculiar binder molecules. The resulting Au/AgTNPs were characterized by scanning electron microscopy, atomic force microscopy, X-ray diffraction, UV–vis spectroscopy, and cyclic voltammograms. The peak of dipolar plasmonic resonance was located at near infrared region of ～700 nm, which showed the refractive index (RI) sensitivity of 248 nm/RIU. Moreover, thin gold shells were electrodeposited onto the surface of Au/AgTNPs in order to stabilize nanoparticles. Compared with the Au/AgTNPs, this peak of localized surface plasmon resonance (LSPR) was a little red-shift and decreased slightly in intensity. The refractive index sensitivity was estimated to be 287 nm/RIU, which showed high sensitivity as a LSPR sensing platform. Those triangular nanoprisms deposited on the ITO substrate could be further functionalized to fabricate LSPR biosensors. Results of this research show a possibility of improving LSPR sensor by using core–shell nanostructures.     

Recent progress on performances and mechanisms of carbon dots for gas sensing

Carbon dots (CDs), as an attractive zero-dimensional carbon nanomaterial with unique photoluminescent merits, have recently exhibited significant application potential in gas sensing as a result of their excellent optical/electronic characteristics, high chemical/thermal stability, and tunable surface states. CDs exhibit strong light absorption in the ultraviolet range and tunable photoluminescence characteristics in the visible range, which makes CDs an effective tool for optical sensing applications. Optical gas sensor based on CDs have been investigated, which generally responds to the target gas by corresponding changes in optical absorption or fluorescence. Moreover, electrical gas sensor and quartz crystal microbalance sensor whose sensing layer involves CDs have also been designed. Electrical gas sensor exhibits an increase or a decrease in electrical current, capacitance, or conductance once exposed to the target gas. Quartz crystal microbalance sensor responds to the target gas with a frequency shift. CDs greatly promote the absorption of the target gas and improve the sensitivity of both sensors. In this review, we aim to summarize different types of gas sensors involving CDs, and sensing performances of these sensors for monitoring diverse gases or vapors, as well as the mechanisms of CDs in different types of sensors. Moreover, this review provides the prospect of the potential development of CDs based gas sensors.     

High-stability non-invasive autoclavable naked optical CO2 sensor

The fabrication and characterization of a high-stability non-invasive autoclavable naked optical CO(2) sensor is described in this report. The sensor was made by using 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) as the fluorescence dye and cetyltrimethylammonium hydroxide (CTMAOH) as the phase transfer agent (the base). A highly hydrophobic two-component silicone film was used as the polymer matrix, which overcame some of the limitations of the existing plastic type CO(2) sensors, such as dye leaching and cross-sensitivity to ions. To improve the stability of the sensor, several affecting factors were investigated. Experimental results showed that sufficient base and a small amount of water in the sensing film were critical factors that affected the stability of the sensor. Although the sensor was more stable when kept in water, the function of the sensor could recover when the sensor kept in air was transferred into water. The sensor has a lifetime of several months. The detection limit of the sensing film was about 0.03%. The average response and recovery times were 0.66 and 1.94 min, respectively. It had no cross-sensitivity to salt concentrations in the range of 0-0.2 M and to pH in the range of 5.6-8.0, so it can be used in processes with changing ion concentration and pH. It was sterilizable and could be autoclaved many times without losing its sensitivity. The applicability of the sensor in real application was successfully tested in the fermentation of Escherichia coli.     

Configurational Statistics of Magnetic Bead Detection with Magnetoresistive Sensors

Magnetic biosensors detect magnetic beads that, mediated by a target, have bound to a functionalized area. This area is often larger than the area of the sensor. Both the sign and magnitude of the average magnetic field experienced by the sensor from a magnetic bead depends on the location of the bead relative to the sensor. Consequently, the signal from multiple beads also depends on their locations. Thus, a given coverage of the functionalized area with magnetic beads does not result in a given detector response, except on the average, over many realizations of the same coverage. We present a systematic theoretical analysis of how this location-dependence affects the sensor response. The analysis is done for beads magnetized by a homogeneous in-plane magnetic field. We determine the expected value and standard deviation of the sensor response for a given coverage, as well as the accuracy and precision with which the coverage can be determined from a single sensor measurement. We show that statistical fluctuations between samples may reduce the sensitivity and dynamic range of a sensor significantly when the functionalized area is larger than the sensor area. Hence, the statistics of sampling is essential to sensor design. For illustration, we analyze three important published cases for which statistical fluctuations are dominant, significant, and insignificant, respectively.     

Pulse-driven magnetoimpedance sensor detection of cardiac magnetic activity

This study sought to establish a convenient method for detecting biomagnetic activity in the heart. Electrical activity of the heart simultaneously induces a magnetic field. Detection of this magnetic activity will enable non-contact, noninvasive evaluation to be made. We improved the sensitivity of a pulse-driven magnetoimpedance (PMI) sensor, which is used as an electric compass in mobile phones and as a motion sensor of the operation handle in computer games, toward a pico-Tesla (pT) level, and measured magnetic fields on the surface of the thoracic wall in humans. The changes in magnetic field detected by this sensor synchronized with the electric activity of the electrocardiogram (ECG). The shape of the magnetic wave was largely altered by shifting the sensor position within 20 mm in parallel and/or perpendicular to the thoracic wall. The magnetic activity was maximal in the 4th intercostals near the center of the sterna. Furthermore, averaging the magnetic activity at 15 mm in the distance between the thoracic wall and the sensor demonstrated magnetic waves mimicking the P wave and QRS complex. The present study shows the application of PMI sensor in detecting cardiac magnetic activity in several healthy subjects, and suggests future applications of this technology in medicine and biology.     

A surface acoustic wave sensor functionalized with a polypyrrole molecularly imprinted polymer for selective dopamine detection

A surface acoustic wave sensor operating at 104 MHz and functionalized with a polypyrrole molecularly imprinted polymer has been designed for selective detection of dopamine (DA). Optimization of pyrrole/DA ratio, polymerization and immersion times permitted to obtain a highly selective sensor, which has a sensitivity of 0.55°/mM (≈550 Hz/mM) and a detection limit of ≈ 10 nM. Morphology and related roughness parameters of molecularly imprinted polymer surfaces, before and after extraction of DA, as well as that of the non imprinted polymer were characterized by atomic force microscopy. The developed chemosensor selectively recognized dopamine over the structurally similar compound 4‐hydroxyphenethylamine (referred as tyramine), or ascorbic acid,which co‐exists with DA in body fluids at a much higher concentration. Selectivity tests were also carried out with dihydroxybenzene, for which an unexpected phase variation of order of 75% of the DA one was observed. Quantum chemical calculations, based on the density functional theory, were carried out to determine the nature of interactions between each analyte and the PPy matrix and the DA imprinted PPy polypyrrole sensing layer in order to account for the important phase variation observed during dihydroxybenzene injection. Copyright © 2015 John Wiley & Sons, Ltd.