Bacterial isolation by lectin-modified microengines

New template-based self-propelled gold/nickel/polyaniline/platinum (Au/Ni/PANI/Pt) microtubular engines, functionalized with the Concanavalin A (ConA) lectin bioreceptor, are shown to be extremely useful for the rapid, real-time isolation of Escherichia coli (E. coli) bacteria from fuel-enhanced environmental, food, and clinical samples. These multifunctional microtube engines combine the selective capture of E. coli with the uptake of polymeric drug-carrier particles to provide an attractive motion-based theranostics strategy. Triggered release of the captured bacteria is demonstrated by movement through a low-pH glycine-based dissociation solution. The smaller size of the new polymer-metal microengines offers convenient, direct, and label-free optical visualization of the captured bacteria and discrimination against nontarget cells.     

Graphene/Silicon Heterojunction Schottky Diode for Vapors Sensing Using Impedance Spectroscopy

A graphene(G)/Silicon(Si) heterojunction Schottky diode and a simple method that evaluates its electrical response to different chemical vapors using electrochemical impedance spectroscopy (EIS) are implemented. To study the impedance response of the device of a given vapor, relative impedance change (RIC) as a function of the frequency is evaluated. The minimum value of RIC for different vapors corresponds to different frequency values (18.7, 12.9 and 10.7 KHz for chloroform, phenol, and methanol vapors respectively). The impedance responses to phenol, beside other gases used as model analytes for different vapor concentrations are studied. The equivalent circuit of the device is obtained and simplified, using data fitting from the extracted values of resistances and capacitances. The resistance corresponding to interphase G/Si is used as a parameter to compare the performance of this device upon different phenol concentrations and a high reproducibility with a 4.4% relative standard deviation is obtained. The efficiency of the device fabrication, its selectivity, reproducibility and easy measurement mode using EIS makes the developed system an interesting alternative for gases detection for environmental monitoring and other industrial applications.     

A nanochannel/nanoparticle-based filtering and sensing platform for direct detection of a cancer biomarker in blood

A rapid nanochannel-based immunoassay capable of the filtering and subsequent detection of proteins in whole blood without any sample preparation is described. This is accomplished by using a nanoporous/nanochannel membrane modified with antibodies, the conductivity of which toward a redox indicator is tuned by primary and secondary immunoreactions with proteins and gold nanoparticles. This interesting nanopore blockage by gold nanoparticles is enhanced by silver deposition that further decreases the diffusion of the signaling indicator through the nanochannel. The efficiency of the nanochannels to act as immunoreaction platforms including the use of nanoparticles is also monitored by microscopic techniques. Successful detection of immunoglobulins including a cancer biomarker is achieved in buffer as well as in whole blood. This system constitutes an efficient immunoassay capable of detecting up to 52 U mL(-1) of CA15-3. The developed nanochannel/nanoparticle-based device can be used for several other proteins and extended also to DNA detection with interest not only for diagnostics but also environmental monitoring, food analysis, safety, and security applications.     

Magnetic Nanoparticles Modified with Carbon Nanotubes for Electrocatalytic Magnetoswitchable Biosensing Applications

A novel biosensor based on magnetic nanoparticles (MNPs) functionalized with tyrosinase in an operational synergy with a multiwalled carbon nanotube (MWCNT) network is developed. An on–off external magnetic field is applied to a screen‐printed electrode (SPE), which is used as a transducing platform. This enables an interesting on‐demand biosensing performance. The effect of each component on the response of the developed device is carefully evaluated; particularly interesting results are presented for the contributions of MNPs and carbon nanotubes. A tyrosinase‐based model biosensing approach is used, while a potential of ?0.15 V versus Ag/AgCl for the electrochemical reduction of the enzyme products (quinone forms) onto the magnetoswitchable SPE/MNP/Tyr/MWCNT system is applied. The response of the biosensor to catechol is also evaluated; a limit of detection (signal to noise ratio (S/N) = 3) for catechol is found to be around 7.61 μM (S/N = 3) with a relative standard deviation (RSD) of 4.91% (n = 3). The developed device could open the door to a wide range of novel electrocatalytic and bioelectrocatalytic applications of magnetocontrolled redox enzymes. Furthermore, it could be used in miniaturized and portable biosensing systems, such as lab‐on‐a‐chip devices, in medical and environmental applications that have a restricted quantity of sample. Further applications could be envisaged for many other fields, such as external control of catalytic transformations in bioreactors, tailoring of reversible amperometric immunosensors, regeneration of enzyme‐biosensor electrodes, and external triggering of biofuel cells.     

Size-dependent direct electrochemical detection of gold nanoparticles: application in magnetoimmunoassays

The effect of the AuNPs size, ranging from 5 nm to 80 nm, on the electrochemical response of screen-printed carbon electrodes (SPCEs) used as electrochemical transducers is investigated for the first time. A simple hydrodynamic modelling and calculation at the nanoscale level is applied so as to find the effect of the size of AuNP upon the electrochemical response. The results show that the best electrochemical response for AuNP suspension for the same concentration of total gold is obtained for the 20 nm sized nanoparticles. It is concluded that the Brownian motions avoid a better response for smaller AuNPs that should in fact be related with the best electrochemical signal due to their higher surface area. Finally, the size effect is studied for AuNPs acting as electroactive labels in an immunosensor that employs magnetic beads as platforms of the bioreactions. The best response for the 5 nm AuNPs in this case is due to the fact that in the immunosensing conditions the Brownian motions are minimized because the AuNPs contact with the electrotransducer surface is induced by the immunoreaction and the fast magnetic collection of the nanoparticles used as antibody labels upon application of a magnetic field.     

Crystal and electrochemical properties of water dispersed CdS nanocrystals obtained via reverse micelles and arrested precipitation

Different methods of synthesis for the production of electroactive nanocrystals (NCs) for use as labels in DNA sensing systems are presented. They are based on two general ways of controlling the formation and growth of the nanoparticles: (a) physical restriction of the volume available for the growth of the individual nanoparticles by using templates such as reverse micelles; (b) arrested precipitation that depends on exhaustion of one of the reactants. The water dispersed nanocrystals thus obtained are then characterized by optical or electrochemical techniques so as to evaluate the quality of the prepared NCs. A novel direct electrochemical stripping detection protocol that involves the use of a bismuth modified graphite epoxy composite electrode is developed and applied so as to quantify the CdS NCs. The electrochemical study revealed a linear dependency of the stripping current upon the concentration of CdS NCs with a detection limit of around 10(15) CdS NCs cm(-3). The obtained NCs are of great interest for future applications in electrochemical genosensors.     

A grounded theory model for analysis of marine accidents

The purpose of this paper was to design a conceptual model for analysis of marine accidents. The model is grounded on large amounts of empirical data, i.e. the Swedish Maritime Administration database, which was thoroughly studied. This database contains marine accidents organized by ship and variable. The majority of variables are non-metric and some have never been analyzed because of the large number of values. Summary statistics were employed in the data analysis. In order to develop a conceptual model, the database variables were clustered into eleven main categories or constructs, which were organized according to their properties and connected with the path diagram of relationships. For demonstration purposes, one non-metric and five metric variables were selected, namely fatality, ship's properties (i.e. age, gross register tonnage, and length), number of people on board, and marine accidents. These were analyzed using the structural equation modeling (SEM) approach. The combined prediction power of the ‘ship's properties’ and ‘number of people on board’ independent variables accounted for 65% of the variance of the fatality. The model development was largely based on the data contained in the Swedish database. However, as this database shares a number of variables in common with other databases in the region and the world, the model presented in this paper could be applied to other datasets. The model has both theoretical and practical values. Recommendations for improvements in the database are also suggested.     

Invariance properties for a class of quasipolynomials

When a time-delay system involves multiple imaginary roots (MIRs), the stability analysis will become much more complicated than that in the case with only simple imaginary roots (SIRs). An MIR may exhibit different splitting behaviors and, to the best of the authors’ knowledge, their properties have not been fully investigated. In this paper, we focus on characterizing the invariance properties for MIRs with any multiplicity. Furthermore, the proposed methodology makes it possible to also cover some degenerate cases already encountered and discussed in the literature. In addition, we propose an easily implemented frequency-sweeping method, making it possible to derive the asymptotic behavior without invoking the Puiseux series.