A sensing configuration for the real-time monitoring, detection, and quantification of dissolved carbon dioxide (dCO2) was developed for aquaculture and other applications in freshwater and saline water. A chemical sensing membrane, based on a colorimetric indicator, is combined with multimode optical fiber and a dual wavelength light-emitting diode (LED) to measure the dCO2-induced absorbance changes in a self-referenced ratiometric scheme. The detection and processing were achieved with an embeded solution having a mini spectrometer and microcontroller. For optrode calibration, chemical standard solutions using sodium carbonate in acid media were used. Preliminary results in a laboratory environment showed sensitivity for small added amounts of CO2 (0.25 mg·L−1). Accuracy and response time were not affected by the type of solution, while precision was affected by salinity. Calibration in freshwater showed a limit of detection (LOD) and a limit of quantification (LOQ) of 1.23 and 1.87 mg·L−1, respectively. Results in saline water (2.5%) showed a LOD and LOQ of 1.05 and 1.16 mg·L−1, respectively. Generally, performance was improved when moving from fresh to saline water. Studies on the dynamics of dissolved CO2 in a recirculating shallow raceway system (SRS+RAS) prototype showed higher precision than the tested commercial sensor. The new sensor is a compact and robust device, and unlike other sensors used in aquaculture, stirring is not required for correct and fast detection. Tests performed showed that this new sensor has a fast accurate detection as well as a strong potential for assessing dCO2 dynamics in aquaculture applications.

The detection of dissolved carbon dioxide (dCO 2 ) is made possible through a colorimetric effect that occurs in a sensitive membrane. The reaction with dCO 2 changes the pH of the membrane causing a small difference in its colour which results in a characteristic absorbance spectrum band near 435 nm. A sensing platform based on this effect was developed and tested in gaseous and in aqueous environments. It is a combination of a bundle of large core fibre optics (with diameters above 200 μm) with light emission diodes (LEDs) in the visible range of the spectrum, a silicon photodetector and a polymer membrane sensitive to CO 2 . A variation in the absorption of 3 / %VV was obtained in the range from 0 to 1.6 % of gaseous CO2 with an estimated response time below 60 seconds.

A novel optical fiber sensor is presented for measuring dissolved CO2 for water quality monitoring applications, where the optical signal is based either on refractive index changes or on color change. The sensing chemistry is based on the acid-basic equilibrium of 4-nitrophenol, that is converted into the anionic form by addition quaternary ammonium hydroxide. The CO2 sensitive layer was characterized and tested by using simple absorbance/reflectance measurement setups where the sensor was connected to a fiber optic CCD spectrometer. A prototype simulating a real shallow raceway aquaculture system was developed and its hydraulic behavior characterized. A commercially available partial-pressure-NDIR sensor was used as a reference for dissolved CO2 tests with the new optical fiber sensor under development. Preliminary tests allowed verifying the suitability of the new optical sensor for accurately tracking the dissolved carbon dioxide concentration in a suitable operation range. Direct comparison of the new sensor and the reference sensor system allowed to demonstrate the suitability of the new technology but also to identify some fragilities there are presently being addressed.

In this work a novel optical-fiber sensor for carbon dioxide measurement is presented. A polymeric sensitive layer based on the acid-base equilibrium of phenol and of its derivative 4-nitro-phenol is used for carbon dioxide determination. The sensitive material presents changes in color and in its refractive index. Colorimetric and refractometric measurements were performed. The results show the sensor is more sensitive for lower concentrations and a saturation effect occurs for higher levels. For the colorimetric response, a resolution of ±0.15% was estimated and a response time of 30s was measured. For the refractometric measurements, a resolution of ±0.50% could be estimated and a response time of 12s was measured. Reversibility and reproducibility were also demonstrated.

In this work, a polymeric sensitive layer based on the acid-base equilibrium of phenol and of its derivative p-nitro-phenol is presented for carbon dioxide measurements. Thin films casted on glass slides were tested, using a LED source (λc at 410 nm) and an Ocean Optics USB4000 spectrometer, in the 0% to 15.25% CO2 concentrations range, showing a 40% maximum transmittance variation with a 51s response time and a 0.15% resolution. Preliminary results indicate that CO2also induces refractive index changes in the sensitive layer. Using a fiber based interferometric setup, a CO2 dependent refractive index change of ~0.045 RIU was observed, in the 0%-90% CO2 concentration range.

The paper deals with preparation and characterization of layers of optical absorption transducers sensitive to free chlorine in water and based on commercially available chemicals. The electrochemical deposition and chemical approach based on the sol-gel method were employed for the immobilization of the transducers onto ITO-coated planar optical substrates. The transducers, namely methylene blue, o-phenylenediamine, Lu (III) acetate pthalocyanine tetrasulfonate tetrasodium salt (Lu-III-complex), murexid, quercetin, 1,2,3-benzenetriazole, benzopurpurine, thionine, bilirubin and its metal complexes, and 3-methyl-4 nitro-1(4-nitrophenyl) 2-pyriazoline-5-one (picrolonic acid), were tested. Transmission spectra, redox potentials, layer thickness and optical responses of the transducer layers to chlorine were investigated. By using sensitive layers based on o-phenylenediamine and methylene blue it was possible to detect chlorine in a minimum concentration of 0.25 ppm. The best results were obtained with the o-phenylenediamine layers prepared electrochemically. Both these transducer layers are useable for detection of chlorine up to concentration similar to 8 ppm. (c) 2007 Elsevier B.V. All rights reserved.

Three generations of α,γ-diaminobutyric acid modified poly(propyleneimine) dendrimers [DAB(AM)n, n = 4, 8, 16] containing 4, 8, 16 free amino groups were coupled with Boc-protected α,γ-diaminobutyric acid (DABA) moieties in high yields. These modified dendrimers were deprotected and the chiral dendritic amines with 8, 16 and 32 amino groups on the surface were isolated in excellent yields. Dendrimers with cisplatin moieties at the periphery were obtained in the reaction of the free amine dendrimers and potassium tetrachloroplatinate(II). The highly insoluble complexes were isolated as hydrates and characterized by means of IR, TGA and elemental analysis.

Scanning electrochemical microscopy (SECM) with amperometric or potentiometric measuring tips was used to investigate biocatalytic reactions inside the enzyme layer of a biosensor during its operation. The well known glucose oxidase catalyzed oxidation of glucose has been selected for the studies. Local, instantaneous concentration of dissolved oxygen and hydrogen peroxide was studied observing the amperometric current while miniaturized potentiometric tip served for local pH measurements. Liquid enzyme layer immobilized with Cellophane membrane or cross linked polyacrilamide gel membrane containing entrapped enzyme served for biocatalytic media in the SECM imaging. Local maximum of H2O2 and minimum of O2 profiles were found at approximately 200 μm far from the substrate/enzyme layer boundary. From the experimental findings guidelines to design well functioning biocatalytic sensors could be concluded. The concentration profiles obtained with SECM techniques were compared with the results of simple model calculations carried out with the method of finite changes. Most of earlier made SECM studies dealing with enzyme reactions imaged the electrolyte being in contact with the immobilized enzyme. The data in our investigation, however, were collected inside the working catalytic layer.

As the continuation of the work started earlier, this article deals with the scanning electrochemical microscopic (SECM) study of the function of complex enzyme sensors. In this case reaction layer of the sensor is made of two different parts. One is for interference elimination and the other for selective molecular recognition and measurement. As Scheller's group described this sucrose electrode, the inner that is the measuring layer contains three enzymes: invertase, mutarotase and glucose oxidase while the outer, the eliminating one, uses glucose oxidase and catalase. In our work the concentration profiles of oxygen and hydrogen peroxide were recorded inside the two different enzyme layers with the SECM. The dependence of these profiles on the working parameters such as enzyme activity and activity ratios, reaction layer thickness, sucrose and glucose concentration were observed and compared with the results of model calculations. Method of finite differences was used for the model calculations.

An optical biosensor for urea measurements was developed. The operation of the sensor is based on the well-known urease enzyme-catalyzed hydrolysis of urea. The ammonium ions liberated in the reaction are detected with an ion selective optode membrane containing nonactin as ion selective ionophore and ETH 5294 chromoionophore in a thin (1 μm) plasticized poly(vinylchloride) film. The basic sensing element was home made of a microscope glass slide, a HeNe laser light source, photodiode light detector and light in coupling, de-coupling elements. The transducer membrane and the enzyme containing reaction layer were sandwich-cast with spin coating onto the surface of the sensing slide. The attenuation of the laser light propagating inside the glass wave-guide was used as signal for urea measurements. With this arrangement membranes provided good sensitivity (0.05 absorption unit when going from 0.1 to 1 mM urea) and short (16–20 s) response time. Taking advantage on the improved response time, flow injection urea measurements were made in the 0.01–2 mM concentration range. Thirty sample/hour analysis-rate, good peak-to-peak reproducibility (RSD=0.02) and recovery (95–104%) was achieved with buffer diluted urea solutions. Applications for the analysis of real samples are planned to do in the future.

An opto-electrochemical sensor for copper (II) ion was developed. The sensor consists of a planar conductive indium-tin-oxide (ITO) glass support, which was coated by a polymeric copper (II) sensitive membrane. The sensing membrane is made of plasticized polyurethane matrix containing Zincon colorimetric reagent immobilized as ion pair with tetraoctylammonium ion. The instrumentation used commonly for wave-guide sensor development was extended with a potentiostat that made possible the control of the electric potential of the conductive surface. In this way the transport rate of ionic species through the membrane-sample interface could be influenced. In the presence of copper (II) ions the color of the membrane turned from red to blue, which was monitored optically. By applying positive potential to the conductive surface the direction of the ion diffusion at the membrane/sample interface was changed. As a result the sensing layer was regenerated within 2 minutes and was ready for further measurement. The sensor measured Cu(2+) ion in a concentration range of 1-200 microM.

An all-solid-state anionic surfactant electrode type was developed using teflonized graphite rods coated with electrochemically prepared polypyrrole film as electric connector support. The measuring membrane of the electrodes was made of ion-pairs formed with the appropriate anionic and cationic surfactants incorporated into plasticized poly(vinylchloride) film. Preparation procedure for the ion-pair is described briefly in the text. The electrochemical properties of the electrode were studied and the function of the electrode was tested. Due to the well defined charge transfer mechanisms at the graphite–polypyrrole-membrane interfaces the surfactant electrode showed good stability. The lower limit of detection was in the range of 0.5–1μM in case of the different surfactants tested. Due to the relatively fast response time and the good stability of the electrode, a sample rate of 30sample/h in flow-injection determinations could be achieved.

In this article a recently constructed scanning electrochemical microscope with an original automatic target location facility is described and its operation is demonstrated on different targets. The measuring tip positioning device is based on stepper motor driven linear modules with 75 nm linear travel resolution. The home-built electronic unit and the Windows 95 compatible measuring and image-forming program furnish the microscope to operate in both amperometric and potentiometric modes. A novel, simplex algorithm based automatic target location program was developed to substitute the tedious and lengthy manual tip positioning. In this article different strategies are described and the most important results of this investigation are summarized.