Highly sensitive chemiluminescence flow sensor for ascorbic acid

A highly sensitive chemiluminescence(CL) flow sensor is proposed for the determination of ascorbic acid. The analytical reagents luminol and iron(II) are immobilized on anion-exchange and cation-exchange resins, respectively, and can be eluted by sodium sulphate. The calibration graphs are linear in the range 1 × 10^–9 to 1 × 10^–6 g mL^–1 and the detection limit is 4.0 × 10^–10 g mL^–1. The sensor has been applied successfully to the determination of ascorbic acid in vegetables.     

An extremely sensitive monoboronic acid based fluorescent sensor for glucose

An extremely sensitive monoboronic acid based fluorescent sensor for glucose was developed. This was carried out by assembling a fluorescent monoboronic acid, 3-aminophenylboronic acid (PBA) indirectly onto gold surface via its electrostatic interaction with cysteine (Cys) that was directly assembled on the gold surface. The formation of self-assembled bilayers (SAB) was confirmed and primarily characterized by cyclic voltammetry and X-ray photoelectron spectra (XPS). The SAB containing PBA was found fluorescent and its fluorescence showed an extremely high sensitivity to the presence of glucose and other monosaccharides such as galactose and fructose with quenching constants at 10⁸ M⁻¹ order of magnitude compared to those at 10² M⁻¹ in bulk solutions. The quenching constants were found to vary in the order of that is different from that in bulk solution which shows the highest binding affinity toward d-fructose and very low sensitivity toward glucose. The reported monoboronic acid based SAB fluorescent sensor showed the highest sensitivity towards glucose with the capacity of detecting saccharides of concentration down to nanomolar level. It was also demonstrated that the fluorescence from PBA/Cys/Au can be easily recovered after each measurement event and therefore also represents a new reusable method for immobilizing reagent in fabricating chemosensors.     

Platinum electrode modified with polyterthiophene doped with metallic nanoparticles,as sensitive sensor for the electroanalysis of ascorbic acid (AA)

A novel electrochemical sensor for ascorbic acid (AA) detection based on platinum electrode modified with polyterthiophene (P3T) and doped with metallic particles (Cu, Co, Ag, Au, Pd) was constructed. The electrocatalytic performances of the modified electrode with polyterthiophene-metallic particles related to the detection of AA, showed a better catalytic activity compared to the modified electrode with polyterthiophene film. The obtained results demonstrate also that the use of P3T–Ag nanocomposite allows a good sensitivity; which gives a high response in oxidation peak of AA. In order to have a good performance using this sensor, several parameters such as polymerization time of the film and immersion time of the film in AgNO₃ solution were optimized.     

Nanoparticle assembled microcapsules for application as pH and ammonia sensor

The encapsulation of molecular probes in a suitable nanostructured matrix can be exploited to alter their optical properties and robustness for fabricating efficient chemical sensors. Despite high sensitivity, simplicity, selectivity and cost effectiveness, the photo-destruction and photo-bleaching are the serious concerns while utilizing molecular probes. Herein we demonstrate that hydroxy pyrene trisulfonate (HPTS), a pH sensitive molecular probe, when encapsulated in a microcapsule structure prepared via the assembly of silica nanoparticles mediated by poly-L-lysine and trisodium citrate, provides a robust sensing material for pH sensing under the physiological conditions. The temporal evolution under continuous irradiation indicates that the fluorophore inside the silica microcapsule is extraordinarily photostable. The fluorescence intensity alternation at dual excitation facilitates for a ratiometic sensing of the pH, however, the fluorescence lifetime is insensitive to hydrogen ion concentration. The sensing scheme is found to be robust, fast and simple for the measurement of pH in the range 5.8-8.0, and can be successfully applied for the determination of ammonia in the concentration range 0-1.2 mM, which is important for aquatic life and the environment.     

Fibre-optic fluorescing sensor for ammonia

The fluorescing sensor is based on the change in fluorescence intensity of a buffered pH indicator solution entrapped in silicone rubber. Exposure to ammonia increases the pH of the trapped solution; this increases the fluorescence intensity, which is monitored via an optical fibre bundle. Ammonium chloride in 0.001 M sodium hydroxide, or the indicators themselves, can serve as buffers. Effects of sensor preparation and buffer composition on response time, reversibility and sensitivity are discussed.     

Polypyrrole-based sensor for hydrazine and ammonia

An ultra-thin layer of polypyrrole can be coated on non-conducting substrates, e.g., acrylic, by dip coating into a colloidal suspension of polypyrrole. This thin coating reversibly combines with low concentrations of ammonia or hydrazine with a concomitant reversible increase in resistance; 0.1 μg cm^?3 of ammonia can readily be detected with a 1 cm² area of sensor.     

Carbon nanocone as an ammonia sensor: DFT studies

Adsorption of NH₃ molecule on a carbon nanocone (CNC) was investigated using density functional theory in terms of energetic, structural, and electronic properties. It is mainly demonstrated that (i) the NH₃ molecule preferentially tends to attach to the apex of the CNC through its N atom, releasing energy of 54.28 kcal/mol, (ii) the CNC may be a promising candidate in gas sensor devices in order to detect the NH₃ molecule, and (iii) the field electron emission current may be enhanced from CNC surface upon the adsorption process.     

The bilayer lipid membrane as a basis for a selective sensor for ammonia

The development of an electrochemical method for the selective sensing of ammonia gas, based on a modified bilayer lipid membrane, is described. Membrane selectivity for ammonium ion is achieved through incorporation of the antibiotic nonactin as ion-carrier. The detection limits compare favourably with those for conventional ammonia gas-sensing electrodes, but the selectivity is much superior. Theoretical evaluation of the potential sensitivity of the new gas-sensor with respect to design parameters is described.     

A reflectometric sensor for ammonia and hydrocarbons

Summary Optical reflection measurements in the visible wavelength range may be used for fast analysis of changes in optical thickness of thin polymer layers caused by swelling of the film in contact with various gaseous analytes. Including an absorbing species into the sensitive layer, the applicability of this sensor can be extended to gases with acidic or basic character. The method is demonstrated using bromocresol purple as pH-indicator in a polydimethylsiloxane layer. Principal component analysis is used for qualitative analysis of a two-component gas.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday     

Optical rubbery ormosils sensor for the detection of ammonia

Rubbery ormosil films with immobilized aminofluorescein (AF) were investigated to develop an optochemical sensor for the determination of ammonia in water. The gel precursors with tetramethoxysilane (TMOS) and dimethyldimethoxysilane (DiMeDMOS) were deposited on glass supports, and characterized in terms of response to pH, and to dissolved ammonia at constant pH. After preconditioning the sensing film was stable for 6 months. The detection limit for ammonia in water was 0.2 microg mL(-1) (S/N 2), the response being linearly dependent on concentration in the range of 0.5 to 80 microg mL(-1) ammonia. The response time was less than 5 min. The effects of sodium chloride concentration, temperature, and coexisting metal ions and compounds were investigated.     

Optical rubbery ormosils sensor for the detection of ammonia

Rubbery ormosil films with immobilized aminofluorescein (AF) were investigated to develop an optochemical sensor for the determination of ammonia in water. The gel precursors with tetramethoxysilane (TMOS) and dimethyldimethoxysilane (DiMeDMOS) were deposited on glass supports, and characterized in terms of response to pH, and to dissolved ammonia at constant pH. After preconditioning the sensing film was stable for 6 months. The detection limit for ammonia in water was 0.2 μg mL^–1 (S/N 2), the response being linearly dependent on concentration in the range of 0.5 to 80 μg mL^–1 ammonia. The response time was less than 5 min. The effects of sodium chloride concentration, temperature, and coexisting metal ions and compounds were investigated. Received: 22 December 2000 / Revised: 5 March 2001 / Accepted: 7 March 2001     

Carbon paste electrode modified with a binuclear manganese complex as a sensitive voltammetric sensor for tryptophan

We report on a carbon paste electrode that was modified with a binuclear manganese(II) complex by the drop-coating method. A study on the mechanism of the electro-oxidation of tryptophan (Trp) at this electrode indicated that it enables Trp to be determined with good sensitivity and selectivity. Second-order derivative linear sweep voltammetry at pH 4.1 revealed that a sensitive anodic peak appears at 812?mV (vs. SCE) whose current is proportional to the concentration of Trp in the concentration range from 0.1 to 1.0???mol?L^?1 and 1.0 to 80???mol?L^?1, with a detection limit (S/N?=?3) of 0.08???mol?L^?1 (60?s of accumulation). The method was applied to the determination of Trp in amino acid injection solutions with satisfactory results.

Potentiometric determination of proteins with an ammonia sensor

A flow system is described for the cleavage of proteins with immobilized protease enzyme to L-amino acids which are then converted to ammonia with glass-immobilized L-amino acid oxidase. An ammonia gas electrode is used as detector. Immobilization techniques are discussed, as are optimum conditions for L-phenylalanine. Bovine serum albumin was determined in the range 0.1–100 μg ml^-1. Human blood sera required dilution for analysis.     

High‐sensitive neural network ammonia sensor based on shear horizontal surface acoustic wave devices

In this paper, a shear horizontal surface acoustic wave devices coated with L‐glutamic acid hydrochloride were applied as ammonia sensors. This sensor has shown high sensitivity and fast responses to ppb‐level ammonia. The frequency shift linearly increased as the ammonia concentration increased from 40 to 400 ppb in dry environment. In the humid environment, the frequency shift gradually decreased with ammonia concentration increasing. In order to precisely estimate the ammonia in humid environment, two different neural models, the conventional feedforward neural network and quantum neural network, were used as the identifier and their performances were reported and compared. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis of polypyrrole films for the development of ammonia sensor

In the present investigation, we have synthesized a polypyrrole films by chemical polymerization technique for the development of ammonia sensor. The polypyrrole films were synthesized in an aqueous acidic medium on glass substrate with mild oxidation of ferric chloride at temperature 29°C. The concentrations (molar) of monomer (pyrrole), oxidant (ferric chloride), and dopant (polyvinyl sulfonate) have been optimized for the uniform and porous surface morphology of the synthesized polypyrrole film. The synthesized films were characterized by scanning electron microscopy, ultraviolet‐visible, and Fourier transforms infrared spectroscopy. Ammonia gas sensing behavior of polypyrrole films was studied by using indigenously developed gas sensing chamber. The synthesized polypyrrole film with optimized process parameters shows excellent and reproducible response to low concentration (100 ppm) of ammonia gas. Copyright © 2007 John Wiley & Sons, Ltd.     

Study of the performance of an optochemical sensor for ammonia

An optical sensor for ammonia based on ion pairing has been investigated. A pH-sensitive dye (bromophenol blue) was immobilized as an ion pair with cetyltrimethylammonium in a silicone matrix. The colour of the dye changes reversibly from yellow to blue with increasing concentration of ammonia in the sample. The concentration of ammonia can be determined by measuring the transmittance at a given wavelength. All measurements were performed with a dual-beam, solid state photometer. The measurement range is from 6 × 10⁻⁷ to 1 × 10⁻³ M (0.01 to 17 μg ml⁻¹) in 0.1 M sodium phosphate buffer, pH 8. The 90% and 100% response times at a flow rate of 2.5 ml min⁻¹ are 4 min and 10 min, respectively, for a change from 41.9 to 82.5 μM ammonia, or 12 min and 48 min, respectively, for change from 160 to 0 μM ammonia. A continuous drift in signal baseline and ammonia sensitivity limited the measurement stability. The sensor was useful over a period of a few days. The storage stability is more than 10 months (dry). No interference due to pH was observed in the range from pH 5 to pH 9. Sensor performance is seriously affected by amines and cationic detergents. The sensor could be sterilized with 3% hydrogen peroxide or dry heat (90 °C).     

Cylindrical sensor geometry for absorbance-based fiber-optic ammonia sensors

A novel cylindrical shape geometry is proposed for fiber-optic ammonia sensors based on chromophoric indicator dyes. Sensors are constructed by trapping the internal indicator solution inside a short segment of a gas-permeable tube. Fiber-optic probes are used to supply incident radiation and to collect light that transverses through the internal solution. This cylindrical sensor geometry provides large optical path lengths which permits the use of chromophoric indicator dyes. Unlike the conventional distal tip geometry, the diffusion path is independent of the optical path which results in short response times coupled with high sensitivity and low limits of detection. Our experiments indicate that stray radiation is negligible for this sensor design, and that the optical path length essentially equals the distance between the fiber-optic probes. Sensors constructed with Bromothymol Blue as the indicator dye are evaluated. As part of this evaluation, three different modes of operation are tested. The best analytical performance obtained when a single discrete aliquot of the internal solution is used. Steady-state responses are achieved within 13-16 min for 200 nM levels of ammonia from sensors with limits of detection ranging from 150 to 20 nM.     

The investigation of the behavior of a long period grating sensor with a copper sensitive coating fabricated by layer-by-layer electrostatic adsorption

Sensors based on changes of refractive index in response to sorption of an analyte on the coating or film of a long period grating fiber (LPG) fiber have recently been reported. In most prior work the coating or film swelled during interaction with the analyte. The swelling mechanism produced a kinetic response that slowed both the sensor's time for steady-state measurement and the reversibility of the sensor. Here, the analytical utility of fabricating these nanometer thin films using the layer-by-layer (LBL) electrostatic assembly method is evaluated using Cu^II as the test analyte and Cibacron Blue as the reagent immobilized in the LBL assembly; a generation-4 poly(amidoamine) dendrimer served as the spacer in the assembly. Detection of 1.3 mg Cu^II L⁻¹ was observed when six bilayers comprised the coating. The stable response was achieved with 0.6 mg L⁻¹ in less than 1 min. When 0.1 M HCl was used as the rinsing solution, this LPG sensor was reversible and the signal to similar concentrations of Cu^II reproducible.