Sensors, Volume 6, Issue 4 (April 2006) – 23 articles , Pages 260-472

This paper reports a first microbial biosensor for rapid and cost-effectivedetermination of organophosphorus pesticides fenitrothion and EPN. The biosensorconsisted of recombinant PNP-degrading/oxidizing bacteria Pseudomonas putida JS444anchoring and displaying organophosphorus hydrolase (OPH) on its cell surface asbiological sensing element and a dissolved oxygen electrode as the transducer. Surface-expressed OPH catalyzed the hydrolysis of fenitrothion and EPN to release 3-methyl-4-nitrophenol and p-nitrophenol, respectively, which were oxidized by the enzymaticmachinery of Pseudomonas putida JS444 to carbon dioxide while consuming oxygen,which was measured and correlated to the concentration of organophosphates. Under theoptimum operating conditions, the biosensor was able to measure as low as 277 ppb offenitrothion and 1.6 ppm of EPN without interference from phenolic compounds and othercommonly used pesticides such as carbamate pesticides, triazine herbicides andorganophosphate pesticides without nitrophenyl substituent. The applicability of thebiosensor to lake water was also demonstrated. Full article

This paper presents a two-dimensional-in-space mathematical model ofbiosensors based on an array of enzyme microreactors immobilised on a single electrode.The modeling system acts under amperometric conditions. The microreactors were modeledby particles and by strips. The model is based on the diffusion equations containing a non-linear term related to the Michaelis-Menten kinetics of the enzymatic reaction. The modelinvolves three regions: an array of enzyme microreactors where enzyme reaction as well asmass transport by diffusion takes place, a diffusion limiting region where only the diffusiontakes place, and a convective region, where the analyte concentration is maintained constant.Using computer simulation, the influence of the geometry of the microreactors and of thediffusion region on the biosensor response was investigated. The digital simulation wascarried out using the finite difference technique. Full article

The applicability of differential pulse voltammetry (DPV) and adsorptivestripping voltammetry (AdSV) at a non-toxic meniscus-modified silver solid amalgamelectrode (m-AgSAE) for the determination of trace amounts of genotoxic substances wasdemonstrated on the determination of micromolar and submicromolar concentrations of3-nitrofluoranthene using methanol - 0.01 mol L^-1 NaOH (9:1) mixture as a base electrolyteand of Ostazine Orange using 0.01 mol L^-1 NaOH as a base electrolyte. Full article

A first step towards the fabrication and electrochemical evaluation of thin-filmmicrosensors based on organic PVC membranes for the determination of Hg(II), Cd(II),Pb(II) and Cu(II) ions in solutions has been realised. The membrane-coating mixture used inthe preparation of this new type of microsensors is incorporating PVC as supporting matrix,o-nitrophenyloctylether (o-NPOE) as solvent mediator and a recently synthesizedHg[dimethylglyoxime(phene)]²⁺ and Bis-(4-hydroxyacetophenone)-ethylenediamine aselectroactive materials for Hg(II) and Cd(II), respectively. A set of three commercialisedionophores for Cd(II), Pb(II) and Cu(II) has been also used for comparison. Thin-filmmicrosensors based on these membranes showed a Nernstian response of slope(26-30 mV/dec.) for the respective tested cations. The potentiometric responsecharacteristics (linear range, pH range, detection limit and response time) are comparablewith those obtained by conventional membranes as well as coated wire electrodes preparedfrom the same membrane. The realisation of the new organic membrane-based thin-filmmicrosensors overcomes the problem of an insufficient selectivity of solid-state-based thin-film sensors. Full article

In this paper, methods of sample preparation for potentiometric measurement ofphenylalanine are presented. Basing on the spectrophotometric measurements ofphenylalanine, the concentrations of reagents of the enzymatic reaction (10 mM L-Phe,0,4 mM NAD⁺ , 2U L-PheDH) were determined. Then, the absorption spectrum of thereaction product, NADH, was monitored (maximum peak at 340 nm). The results obtainedby the spectrophotometric method were compared with the results obtained by thecolourimetry, using pH indicators. The above-mentioned two methods will be used asreferences for potentiometric measurements of phenylalanine concentration. Full article

Hydrophobic magnetic nanoparticles (NPs) consisting of undecanoate-cappedmagnetite (Fe₃O₄, average diameter ca. 5 nm) are used to control quantized electron transferto surface-confined redox units and metal NPs. A two-phase system consisting of anaqueous electrolyte solution and a toluene phase that includes the suspended undecanoate-capped magnetic NPs is used to control the interfacial properties of the electrode surface.The attracted magnetic NPs form a hydrophobic layer on the electrode surface resulting inthe change of the mechanisms of the surface-confined electrochemical processes. Aquinone-monolayer modified Au electrode demonstrates an aqueous-type of theelectrochemical process (2e^- 2H⁺ redox mechanism) for the quinone units in the absence ofthe hydrophobic magnetic NPs, while the attraction of the magnetic NPs to the surfaceresults in the stepwise single-electron transfer mechanism characteristic of a dry non-aqueous medium. Also, the attraction of the hydrophobic magnetic NPs to the Au electrodesurface modified with Au NPs (ca. 1.4 nm) yields a microenvironment with a low dielectricconstant that results in the single-electron quantum charging of the Au NPs. Full article

Micromachined thermal heater platforms offer low electrical power consumptionand high modulation speed, i.e. properties which are advantageous for realizing non-dispersive infrared (NDIR) gas- and liquid monitoring systems. In this paper, we report oninvestigations on silicon-on-insulator (SOI) based infrared (IR) emitter devices heated byemploying different kinds of metallic and semiconductor heater materials. Our resultsclearly reveal the superior high-temperature performance of semiconductor over metallicheater materials. Long-term stable emitter operation in the vicinity of 1300 K could beattained using heavily antimony-doped tin dioxide (SnO₂:Sb) heater elements. Full article

A wafer-level functionality testing and characterisation system for ISFETs (ion-sensitive field-effect transistor) is realised by means of integration of a specifically designedcapillary electrochemical micro-droplet cell into a commercial wafer prober-station. Thedeveloped system allows the identification and selection of “good” ISFETs at the earlieststage and to avoid expensive bonding, encapsulation and packaging processes for non-functioning ISFETs and thus, to decrease costs, which are wasted for bad dies. Thedeveloped system is also feasible for wafer-level characterisation of ISFETs in terms ofsensitivity, hysteresis and response time. Additionally, the system might be also utilised forwafer-level testing of further electrochemical sensors. Full article

Various planar technologies are employed for developing solid-state sensorshaving low cost, small size and high reproducibility; thin- and thick-film technologies aremost suitable for such productions. Screen-printing is especially suitable due to itssimplicity, low-cost, high reproducibility and efficiency in large-scale production. Thistechnology enables the deposition of a thick layer and allows precise pattern control.Moreover, this is a highly economic technology, saving large amounts of the used inks. Inthe course of repetitions of the film-deposition procedure there is no waste of material dueto additivity of this thick-film technology. Finally, the thick films can be easily and quicklydeposited on inexpensive substrates. In this contribution, thick-film ion-selective electrodesbased on ionophores as well as crystalline ion-selective materials dedicated forpotentiometric measurements are demonstrated. Analytical parameters of these sensors arecomparable with those reported for conventional potentiometric electrodes. All mentionedthick-film strip electrodes have been totally fabricated in only one, fully automated thick-film technology, without any additional manual, chemical or electrochemical steps. In allcases simple, inexpensive, commercially available materials, i.e. flexible, plastic substratesand easily cured polymer-based pastes were used. Full article

In the oil industry, huge saving may be made if suitable multi-interface levelmeasurement systems are employed for effectively monitoring crude oil separators andefficient control of their operation. A number of techniques, e.g. externally mounteddisplacers, differential pressure transmitters and capacitance rod devices, have beendeveloped to measure the separation process with gas, oil, water and other components.Because of the unavailability of suitable multi-interface level measurement systems, oilseparators are currently operated by the trial-and-error approach. In this paper someconventional techniques, which have been used for level measurement in industry, and newdevelopment are discussed. Full article

In this paper, methods of surface modification of different supports, i.e. glass andpolymeric beads for enzyme immobilisation are described. The developed method ofenzyme immobilisation is based on Schiff’s base formation between the amino groups onthe enzyme surface and the aldehyde groups on the chemically modified surface of thesupports. The surface of silicon modified by APTS and GOPS with immobilised enzymewas characterised by atomic force microscopy (AFM), time-of-flight secondary ion massspectroscopy (ToF-SIMS) and infrared spectroscopy (FTIR). The supports withimmobilised enzyme (urease) were also tested in combination with microreactors fabricatedin silicon and Perspex, operating in a flow-through system. For microreactors filled withurease immobilised on glass beads (Sigma) and on polymeric beads (PAN), a very high andstable signal (pH change) was obtained. The developed method of urease immobilisationcan be stated to be very effective. Full article

GaAs-based Gunn diodes with graded AlGaAs hot electron injectorheterostructures have been developed under the special needs in automotive applications.The fabrication of the Gunn diode chips was based on total substrate removal andprocessing of integrated Au heat sinks. Especially, the thermal and RF behavior of thediodes have been analyzed by DC, impedance and S-parameter measurements. Theelectrical investigations have revealed the functionality of the hot electron injector. Anoptimized layer structure could fulfill the requirements in adaptive cruise control (ACC)systems at 77 GHz with typical output power between 50 and 90 mW. Full article

This paper discusses possible methods for on-chip fluorescent imaging forintegrated bio-sensors. The integration of optical and electro-optical accessories, accordingto suggested methods, can improve the performance of fluorescence imaging. It can boostthe signal to background ratio by a few orders of magnitudes in comparison to conventionaldiscrete setups. The methods that are present in this paper are oriented towards buildingreproducible arrays for high-throughput micro total analysis systems (μTAS). The firstmethod relates to side illumination of the fluorescent material placed into micro-compartments of the lab-on-chip. Its significance is in high utilization of excitation energyfor low concentration of fluorescent material. The utilization of a transparent μLED chip,for the second method, allows the placement of the excitation light sources on the sameoptical axis with emission detector, such that the excitation and emission rays are directedcontroversly. The third method presents a spatial filtering of the excitation background. Full article

An array of 50 MHz quartz microbalances (QMBs) coated with a dendronizedpolymer was used to detect small amounts of volatile organic compounds (VOCs) in the gasphase. The results were compared to those obtained with the commonly used 10 MHzQMBs. The 50 MHz QMBs proved to be a powerful tool for the detection of VOCs in thegas phase; therefore, they represent a promising alternative to the much more delicatesurface acoustic wave devices (SAWs). Full article

Quartz crystal nanobalance (QCN) sensors are considered as powerful mass-sensitive sensors to determine materials in the sub-nanogram level. In this study, a singlepiezoelectric quartz crystal nanobalance modified with polystyrene was employed to detectbenzene, toluene, ethylbenzene and xylene (BTEX compounds). The frequency shift of theQCN sensor was found to be linear against the BTEX compound concentrations in the rangeabout 1-45 mg l^-1. The correlation coefficients for benzene, toluene, ethylbenzene, andxylene were 0.991, 0.9977, 0.9946 and 0.9971, respectively. The principal componentanalysis was also utilized to process the frequency response data of the single piezoelectriccrystal at different times, considering to the different adsorption-desorption dynamics ofBTEX compounds. Using principal component analysis, it was found that over 90% of thedata variance could still be explained by use of two principal components (PC1 and PC2).Subsequently, the successful identification of benzene and toluene was possible through theprincipal component analysis of the transient responses of the polystyrene modified QCNsensor. The results showed that the polystyrene-modified QCN had favorable identificationand quantification performances for the BTEX compounds. Full article

We report on the synthesis and CO gas-sensing properties of mesoporoustin(IV) oxides (SnO_²). For the synthesis cetyltrimethylammonium bromide (CTABr) wasused as a structure-directing agent; the resulting SnO₂ powders were applied as films tocommercially available sensor substrates by drop coating. Nitrogen physisorption showsspecific surface areas up to 160 m²·g-1 and mean pore diameters of about 4 nm, as verifiedby TEM. The film conductance was measured in dependence on the CO concentration inhumid synthetic air at a constant temperature of 300 °C. The sensors show a high sensitivityat low CO concentrations and turn out to be largely insensitive towards changes in therelative humidity. We compare the materials with commercially available SnO₂-basedsensors. Full article

An H₂O₂ sensor for the application in industrial sterilisation processes has beendeveloped. Therefore, automated sterilisation equipment at laboratory scale has beenconstructed using parts from industrial sterilisation facilities. In addition, a software tool hasbeen developed for the control of the sterilisation equipment at laboratory scale. Firstmeasurements with the developed sensor set-up as part of the sterilisation equipment havebeen performed and the sensor has been physically characterised by optical microscopy andSEM. Full article

The workflow of a high throughput screening setup for the rapid identification ofnew and improved sensor materials is presented. The polyol method was applied to preparenanoparticular metal oxides as base materials, which were functionalised by surface doping.Using multi-electrode substrates and high throughput impedance spectroscopy (HT-IS) awide range of materials could be screened in a short time. Applying HT-IS in search of newselective gas sensing materials a NO₂-tolerant NO sensing material with reducedsensitivities towards other test gases was identified based on iridium doped zinc oxide.Analogous behaviour was observed for iridium doped indium oxide. Full article

A solid-state amperometric hydrogen sensor based on a protonated Nafionmembrane and catalytic active electrode operating at room temperature was fabricated andtested. Ionic conducting polymer-metal electrode interfaces were prepared chemically byusing the impregnation-reduction method. The polymer membrane was impregnated withtetra-ammine platinum chloride hydrate and the metal ions were subsequently reduced byusing either sodium tetrahydroborate or potassium tetrahydroborate. The hydrogen sensingcharacteristics with air as reference gas is reported. The sensors were capable of detectinghydrogen concentrations from 10 ppm to 10% in nitrogen. The response time was in therange of 10-30 s and a stable linear current output was observed. The thin Pt films werecharacterized by XRD, Infrared Spectroscopy, Optical Microscopy, Atomic ForceMicroscopy, Scanning Electron Microscopy and EDAX. Full article

A multi-sensor system is a chemical sensor system which quantitatively andqualitatively records gases with a combination of cross-sensitive gas sensor arrays andpattern recognition software. This paper addresses the issue of data analysis foridentification of gases in a gas sensor array. We introduce a software tool for gas sensorarray configuration and simulation. It concerns thereby about a modular software packagefor the acquisition of data of different sensors. A signal evaluation algorithm referred to asmatrix method was used specifically for the software tool. This matrix method computes thegas concentrations from the signals of a sensor array. The software tool was used for thesimulation of an array of five sensors to determine gas concentration of CH4, NH3, H2, COand C2H5OH. The results of the present simulated sensor array indicate that the softwaretool is capable of the following: (a) identify a gas independently of its concentration; (b)estimate the concentration of the gas, even if the system was not previously exposed to thisconcentration; (c) tell when a gas concentration exceeds a certain value. A gas sensor database was build for the configuration of the software. With the data base one can create,generate and manage scenarios and source files for the simulation. With the gas sensor database and the simulation software an on-line Web-based version was developed, with whichthe user can configure and simulate sensor arrays on-line. Full article

A polyaniline-based conducting composite was prepared by oxidativepolymerisation of aniline in a polyvinylchloride (PVC) matrix. The coherent free standingthin films of the composite were prepared by a solution casting method. The polyvinylchloride-polyaniline composites exposed to 120 MeV ions of silicon with total ion fluenceranging from 10¹¹ to 10¹³ ions/cm², were observed to be more sensitive towards ammoniagas than the unirradiated composite. The response time of the irradiated composites wasobserved to be comparably shorter. We report for the first time the application of swiftheavy ion modified insulating polymer conducting polymer (IPCP) composites for sensingof ammonia gas. Full article

A new and simple method for nanostructuring using conventionalphotolithography and layer expansion or pattern-size reduction technique is presented, whichcan further be applied for the fabrication of different nanostructures and nano-devices. Themethod is based on the conversion of a photolithographically patterned metal layer to ametal-oxide mask with improved pattern-size resolution using thermal oxidation. With thistechnique, the pattern size can be scaled down to several nanometer dimensions. Theproposed method is experimentally demonstrated by preparing nanostructures with differentconfigurations and layouts, like circles, rectangles, trapezoids, “fluidic-channel”-,“cantilever”- and meander-type structures. Full article