Application of microbiological sensors in fermentation processes

A review is presented of microbiological sensors which are composed of micro-organisms immobilized in a membrane and coupled to a sensing element. Conventional microbiological sensors such as those for biochemical oxygen demand (BOD), ethanol and acetic acid are discussed briefly. Novel sensors are then described. The sensor for carbon dioxide is based on a chemoautotrophic bacterium, that for alcohol on cell membranes of the acetic acid bacteria, Gluoconabacter suboxydans. Sensors for BOD carbon dioxide are based on thermophilic bacteria. Finally, a microbial field effect transistor sensor (FET) for alcohol sensor is described. For all the sensors, the ranges of linear response and their long-term stabilities are reported.     

Monitoring liquid transport and chemical composition in lab on a chip systems using ion sensitive FET devices

A novel single silicon thin film field-effect-transistor (FET) is developed for use as a sensor to monitor transport and chemical properties of liquids in microfluidic systems. The sensor elements which are compatible with existing (bio-)chemical sensor schemes based on ion-sensitive-field-effect-transistors (ISFET) can detect capillary filling speed and level in aqueous solutions. Using a transitor based detection scheme, this approach has the potential to enable high speed flow detection on large scales with high spatial resolution. The prototype devices presented in the present study have been fabricated by using a simple cost-efficient route for circuit board lithography. The thin film FET device characteristics are discussed and a theoretical model for liquid transport detection based on FETs is developed. Typical experimental data are also presented.     

Reference field effect transistors based on chemically modified ISFETs

Different hydrophobic polymers were used for chemical modification of ion-sensitive field effect transistors (ISFETs) in order to prepare a reference FET (REFET). Chemical attachment of the polymer to the ISFET gate results in a long lifetime of the device. Properties of polyacrylate (polyACE) REFETs are described in detail. The polyACE-REFET is superior to other polymer modified REFETs, showing an excellent pH insensitivity (?1 mV pH^?1), a long lifetime and an electrically identical behaviour as an unmodified pH ISFET or a cation-selective PVC-MEMFET (membrane FET). The cation permeselectivity of the polymer can be significantly reduced by addition of immobile cations. The applicability of a polyACE-REFET in differential measurements with a pH ISFET and a K⁺ MEMFET is demonstrated.     

Fluorimetric sensor for the determination of fluoride at the nanograms per millilitre level

A rapid, sensitive and selective method is described for the determination of traces of fluoride in real samples based on the integration of retention and fluorescence detection (λ_ex = 335 nm, λ_em 405 nm) of a ternary complex [zirconium(IV)-Calcein Blue-fluoride) using a conventional flow cell packed with an anion-exchange resin. A study of a large number of experimental variables (flow-injection configuration, type of support, eluting carrier, sample pH, etc.) allowed the development of an optimized, highly selective determination of fluoride with an analytical concentration range of 1–40 ng ml^?1 (r.s.d. 1%) with a sampling frequency of 30 h^?1. A critical comparison with a probe sensor using the same chemical system showed the described flow-through sensor to be clearly superior.     

A lactate electrode with lactate oxidase immobilized on nylon net for blood serum samples in flow systems

Commercially available lactate oxidase from Mycobacterium smegmatis is immobilized on a nylon net which is fixed on an oxygen probe to provide a simple l-lactate sensor. A citrate buffer, pH 6.0, is the only reagent required. The high activity of the enzyme obtained with this immobilization process permits the use of only 20–100 μl of plasma; diluted with citrate buffer to 2 ml, the sample is pumped through a flow cell. The high dilution offsets inhibitory effects of some anions present in blood such as oxalate, hydrogencarbonate and chloride. The response of the sensor is linear over the range 0.2– 2 × 10^?4 M l-acetate. The lifetime is about two months. Effects of pH, temperature and different buffers are described and results on serum samples are reported.     

Flow through FTIR sensor based on solid phase spectroscopy (SPS) on conventional octadecyl (C18) silica

The concept of a novel FTIR flow through sensor based on rigid silica C18 particles placed in a mid-IR flow cell is presented applied to the example of caffeine determination in soft drinks. The system is based on a standard flow cell equipped with two polyethylene spacers of different size that yield a gap inside the assembled flow cell. Particles of appropriate size (<25 μm diameter) suspended in methanol are pumped into the assembled flow cell where the particles are retained at the gap formed by the two spacers. Using an automated sequential injection system, pre-conditioning, sample–sensor interaction and sorbent regeneration can be performed in a highly reproducible way. The characterization and validation results clearly demonstrate the capability of the developed flow through FTIR sensor to determine non-polar molecules, such as caffeine, at the parts per million level, with a linear range from 1.8 to 115 mg L⁻¹, a precision expressed as R.S.D. of 4.1% and a sample throughput of approximately 10 samples/h. Furthermore, the sensor has the potential to be easily adapted to the analysis of polar, non-polar, cationic and anionic molecules by changing the solid support, providing interesting possibilities for the development of new applications in the trace analysis of organic molecules.     

Fabrication of a non-enzymatic glucose sensor field-effect transistor based on vertically-oriented ZnO nanorods modified with Fe2O3

Herein, we report a non-enzymatic glucose sensor field-effect transistor (FET) based on vertically-oriented zinc oxide nanorods modified with iron oxide (Fe₂O₃-ZNRs). Compared with ZnO-based non-enzymatic glucose sensors, which show poor sensing performances, modification of ZnO with Fe₂O₃ dramatically enhances the sensing behavior of the fabricated non-enzymatic FET glucose sensor due to the excellent electrocatalytic nature of Fe₂O₃. The fabricated non-enzymatic FET sensor showed excellent catalytic activity for glucose detection under optimized conditions with a linear range up to 18 mM, detection limits down to ~ 12 μM, excellent selectivity, good reproducibility and long-term stability. Moreover, the fabricated FET sensor detected glucose in freshly drawn mouse whole blood and serum samples. The developed FET sensor has practical applications in real samples and the solution-based synthesis process is cost effective.     

Enzyme Immunoassay Using a Reusable Extended-gate Field-Effect-Transistor Sensor with a Ferrocenylalkanethiol-modified Gold Electrode

A reusable extended-gate field-effect transistor (FET) sensor with an 11-ferrocenyl-1-undecanethiol (11-FUT) modified gold electrode was developed for applying to enzyme immunoassay. It was found that the 11-FUT modified FET sensor detected a thiol compound 50 times or more repeatedly after a treatment with a 5% hydrogen peroxide solution. The gate-voltage shift of the FET sensor showed a fairly good linearity (R(2) = 0.998) within a range from 10(-2) to 10(-6) M on the concentration of 6-hydroxyl-1-hexanethiol, which is a thiol compound, at a Nernstian response of 58.5 mV/decade. The FET-based immunoassay was constructed by combining the 11-FUT modified-FET sensor with the enzyme-linked immunosorbent assay (ELISA), in which the enzyme chemistry of acetylcholinesterase (AChE) was used to generate a thiol compound. The 11-FUT modified FET sensor with an AC voltage at 1 MHz superimposed onto the reference electrode detected the AChE-catalyzed product corresponding to a serum concentration of interleukin 1beta from 10 to 5000 pg/mL. In addition, all measurements were successfully performed by using the same FET-sensor chip after a treatment with a 5% hydrogen peroxide solution.     

Determination of ammonia in air and aqueous samples with a gas-sensitive semiconductor capacitor

The properties of a new type of ammonia gas-sensitive semiconductor capacitor are described. The sensor is based on a palladium MOS field-effect capacitor with a thin layer (3 nm) of iridium surrounding the palladium gate. The lower limit of detection for ammonia in air is 1 ppm (0.59 mg kg^?1). The analytical characteristics and temperature-dependence of the sensor in measurements of ammonia in air are evaluated. Ammonia in aqueous solutions is determined by the use of a continuous flow system utilizing a gaspermeable membrane in combination with the sensor. The calibration plot of the voltage drop of the capacitor vs. ammonia concentration in 150-μl samples is linear in the concentration range 0.2 × 10^?6–5 × 10^?5 M. Ammonia is determined in rain and river water as well as in whole blood and blood serum; 15 samples per hour can be assayed. Analytical recovery studies and the selectivity properties of the system are described and discussed. Finally, the properties of the flow-through system in continuous monitoring are described.     

Flow-through tubular PVC matrix membrane electrode without inner reference solution for flow injection analysis

A simply constructed tubular PVC matrix membrane electrode without inner reference solution suitable for flow injection analysis is described. The nitrate-selective electrode developed allows simple replacement of an exhausted membrane, or change of function with a new sensor membrane. The compact design ensures mechanical stability and the tubular configuration minimizes distortion of the hydrodynamic flow in the detector. Nitrate can be determined in the range 10^?1–10^?5 M, under different flow conditions, with a sampling frequency of about 120 h^?1.     

Glucose-sensitive field-effect transistor with a membrane containing co-immobilized gluconolactonase and glucose oxidase

A glucose-sensitive field-effect transistor (FET) with a two-enzyme membrane containing gluconolactonase and glucose oxidase is investigated. The two-enzyme membrane (ca. 1 μm thick) is formed on the ion-sensitive gate of the FET by photopolymerization. The gluconolactonase used was a partially purified product prepared from crude glucose oxidase by gel filtration. A glucose sensor with only purified glucose oxidase has little response for glucose, but the co-immobilization of gluconolactonase and glucose oxidase considerably enhanced the response amplitude of the glucose sensor. The composition of the two-enzyme/photopolymer solution is optimized; gluconolactonase with an activity at least twice that of glucose oxidase is necessary. The linear calibration graph extends from 0.2 to 2 mM glucose.     

A New Validated Potentiometric Method for Batch and Continuous Quality Control Monitoring of Oseltamivir Phosphate (Taminil) in Drug Formulations and Biological Fluids

A new validated potentiometric method is described for batch and continuous quality control monitoring of the drug oseltamivir phosphate (Taminil) (OST). The method involves the development of a potentiometric sensor responsive to the drug based on the use of the ion‐association complex of (OST⁺) cation with phosphomolybdate anion (PMA^?) as an electroactive material in a poly(vinyl chloride) matrix membrane plasticized with o‐nitrophenyloctyl ether (o‐NPOE). Optimization of the performance characteristics of the sensor is described. A membrane incorporating the OST‐PMA‐NPOE complex in a tubular flow through detector is used in a two channel flow injection set up for continuous monitoring of the drug at a frequency of ～30 samples h^?1. The sensor shows fast near‐Nernstian response for OST over the concentration range 5.2×10^?5–0.8×10^?2 M (21.34 µg mL^?1–3.23 mg mL^?1) with a detection limit of 9.1×10^?6 M (3.73 µg mL^?1) over the pH range 4.6–6.1. The sensor displays good selectivity for OST drug over some basic drugs, inorganic cations, excipients and diluents commonly used in the drug formulations. Validation of the assay method is tested by measuring the lower detection limit, range, linearity, bias, trueness, accuracy, precision, and between‐day‐variability, within day reproducibility, selectivity and ruggedness (robustness). The results reveal good potentiometric performance of the proposed sensor for determination of OST in pharmaceutical capsules and in biological fluid matrices as well as for testing the dissolution profile of the drug and drug homogeneity.     

Development of an optical chemical sensor based on 2-(5-bromo-2-pyridylazo)-5-(diethylamino)phenol in Nafion for determination of nickel ion

An optical chemical sensor based on immobilization of 2-(5-bromo-2-pyridylazo)-5-(diethylamino)phenol (Br-PADAP) in Nafion membrane is described. The membranes were cast onto glass substrates and were used for the determination of nickel in aqueous solutions by spectrophotometry. The sensor system is highly transparent, mechanically stable and showed no evidence of reagent leaching. The influence of several parameters such as pH, ligand concentration, and type and concentration of regenerating solution were optimized. The sensor system showed good sensitivity in the range 0.5-20 μg ml⁻¹ with a detection limit of 0.3 μg ml⁻¹ Ni(II). The sensor has been incorporated into a home-made flow-through cell for determination of nickel in flowing streams with improved sensitivity, precision and detection limit. The calibration curve in the flow system was linear in the range 0.1-16 μg ml⁻¹ with a detection limit of 0.07 μg ml⁻¹. The sensor is easily regenerated by dilute nitric acid solution. The proposed method was successfully applied to the determination of nickel content in vegetable oil and chocolate samples and the results were compared with those obtained using atomic absorption spectrometry.     

Use of a solid sensing zone implemented with unsegmented flow analysis for simultaneous determination of thiabendazole and warfarin

For the first time, a solid sensing zone implemented with unsegmented flow analysis is described for the simultaneous determination of two pesticides, thiabendazole and warfarin. The system works as a simple and rapid spectrofluorimetric biparameter sensor. The sensor is based on the retention of the analytes on the sensing solid zone (octadecyl silane C₁₈ gel) placed in the detection zone itself into a quartz flow-cell. A temporary sequentiation in the arrival of the analytes to the sensing zone is achieved by on line separation using a pre-column of the same gel placed just before the flow cell. Thiabendazole is determined the first (using methanol 30% (v/v) as carrier/elution solution) because it passes through the pre-column while warfarin is strongly retained in it. Then, warfarin is conveniently eluted from the pre-column (using methanol 50% (v/v) as carrier/elution solution) the intrinsic fluorescence peak height measured at an excitation wavelength of 309 nm and an emission wavelength of 368 nm is used as analytical signal. Using a low sample volume (40 μl), the analytical signal showed a very good linearity in the range 10-800 ng ml⁻¹ and 2-40 μg ml⁻¹ with detection limits of 2.35 ng ml⁻¹ and 0.54 μg ml⁻¹ for thiabendazole and warfarin, respectively. The sensor was satisfactorily applied to the determination of these two analytes in pesticides and pharmaceutical preparations.     

Bio-field-effect transistors as detectors in flow-injection analysis

The development of enzyme-modified bio-field-effect transistors (BioFETs) for the determination of glucose, urea, penicillin G, penicillin V and cephalosporin C is reported. BioFETs are produced by covering the pH-sensitive gate areas of ion-selective field-effect transistors with enzyme membranes. The characteristics of the resulting BioFETs and the influence of several parameters, e.g., pH and buffer capacity, are described. The measuring range covers 1–2 orders of magnitude of substrate concentration, and the BioFETs are applicable for 3–12 weeks, depending on the enzyme. They show a short response time and are well suited for detection in flow systems. The frequency of determination with BioFETs in flow systems is high (15–20 measurements per hour). The application of a BioFET in on-line bioprocess control is described. A glucose oxidase FET monitors the glucose concentration during cultivation of Escherichia coli. The results correspond well with off-line liquid chromatographic determinations.     

A New Poly (Vinyl Chloride) Matrix Membrane Electrode for Manual and Flow Injection Determination of Pilocarpine in Some Pharmaceutical Preparations

Abstract

A novel pilocarpinium ion selective membrane electrode is prepared, characterized and used in pharmaceutical analysis. The electrode system incorporates a PVC membrane with pilocarpine-reineckatc ion pair complex as an electroactive material. The electrode exhibits a fast near-Nernstian response for 10^?1-4x10^?5M pilocarpine over the pH range 4-6.5. The electrode displays a good selectivity for pilocarpine with respect to a number of foreign cations. Pilocarpine in various pharmaccutical preparations is determined either by direct potentiometry or potentiometric titration with NaTPB using the proposed sensor. Pilocarpinereineckate membrane is also used in a flow through sandwich cell as a detector for flow injection determination of pilocarpine. Results with an average recovery of 99% and a relative standard deviation of ± 0.3% are obtained. The data compare favorably with those obtained by the standard US Pharmacopeia method.     

A miniature flow-through cell with a four-function chemfet integrated circuit for simultaneous measurements of potassium,hydrogen, calcium and sodium ions

A miniature, flow-through cell with a four-functin ChemFET integrated-circuit is described for the simultaneous measurement of K⁺, H⁺, Ca²⁺ and Na⁺ in aqueous solutions. Depletion-mode field-effect devices with ion-implanted n^? channels are used, in conjunction with ionophore-doped, polymeric electroactive gates. A polyimide/photopolymer-based technique is employed for selective encapsulation of the devices, and an efficient, V-type flow-through cell cap, suitable for application in blood analysis, is described. The ChemFET cell has a dead-space of 30 μl and a 100% response time of 20 s ata sample flow rate of 24.3 μl s^?1, hence the effective dead space is approximately 486 μl. the useful lifetime of the cell is typically 4–12 weeks. Electronic circuitry is described for multiplexing the individual channels rapidly and accurately, and for linearizing the resultant analogue output signal.     

Renewable Drops Electrochemical Sensor for Sulfide Ions Detection

The design and characteristics of a novel electrochemical system, which uses a drop as a renewable electroanalytical sensor, are described. This article describes the performance of the electrochemical system, the coupling of the experimental arrangement with flow injection technique and a demonstration of its applicability for the measurement of sulfide. The method is based on renewable drops of ferricyanide ions, buffered by borate. The ferrocyanide ions, product of the reaction between ferricyanide and sulfide ions, are oxidized on a platinum microelectrode and the current measured is related to sulfide concentration. The measurements can be done in continuous or static flow mode. In continuous mode, the detection limit is 5.0×10^?5 mol L^?1.     

Flow and batch systems for copper(II) potentiometric sensing

A new carbon paste electrode modified with tetramethyl thiuram disulfide is prepared to use as copper potentiometric sensor in batch and flow analysis. The influence of pH and carbon paste composition on the potentiometric response is studied. The principal parameters of the flow system are optimized and the detection limits and the selectivity coefficients of the potentiometric sensor are calculated for static and flow mode. In both cases, the sensor shows high selectivity to copper ions but in flow analysis this selectivity is higher. The obtained detection limits are 4.6 × 10⁻⁸ M for batch measurements and 2.0 × 10⁻⁷ M for on-line analysis. The potentiometric sensor is applied to copper(II) determination in real samples in static and flow measurements. In both analysis modes, successful results are obtained.     

A Novel Thin‐Film Copper Array Based on an Organic/Inorganic Sensor Hybrid: Microfabrication,Potentiometric Characterization,and Flow‐Injection Analysis Application

A first step towards the microfabrication of a thin‐film array based on an organic/inorganic sensor hybrid has been realized. The inorganic microsensor part incorporates a sensor membrane based on a chalcogenide glass material (Cu‐Ag‐As‐Se) prepared by pulsed laser deposition technique (PLD) combined with an PVC organic membrane‐based organic microsensor part that includes an o‐xylyene bis(N,N‐diisobutyl‐dithiocarbamate) ionophore. Both types of materials have been electrochemically evaluated as sensing materials for copper(II) ions. The integrated hybrid sensor array based on these sensing materials provides a linear Nernstian response covering the range 1×10^?6–1×10^?1 mol L^?1 of copper(II) ion concentration with a fast, reliable and reproducible response. The merit offered by the new type of thin‐film hybrid array includes the high selectivity feature of the organic membrane‐based thin‐film microsensor part in addition to the high stability of the inorganic thin‐film microsensor part. Moreover, the thin‐film sensor hybrid has been successfully applied in flow‐injection analysis (FIA) for the determination of copper(II) ions using a miniaturized home‐made flow‐through cell. Realization of the organic/inorganic thin‐film sensor hybrid array facilitates the development of a promising sophisticated electronic tongue for recognition and classification of various liquid media.