Membrane oscillator as chemical sensor

A rhythmic, sustained, stable potential oscillation was reproducibly observed for a lipid membrane supported by a micropore of a thin membrane tip micropipet. Amplitude and period of the oscillation voltage were controlled by changing the pore diameter. The smaller the hole diameter, the smaller the amplitude and the period became. We call this relationship “size effect.” We observed with an optical microscope dynamic behavior of lipids across the oil/water interface, which are formed at a micropore of 2 μm in diameter during self-excited potential oscillation. Periodical movement of a dome-shaped body on the interface is observed, and its expansion and shrinkage are quite synchronous with the potential oscillation. We also applied this self-excited potential oscillation device as a chemical sensor, and reported the effect of chemical substance added into the water phase as a model for the biological chemoreceptive membrane. The experimental results of microscopic observation show that the sensing system using the micropore can distinguish different chemical substances as well as their concentrations, suggesting its application as a chemical sensor.     

Boron-doped carbon nanotubes serving as a novel chemical sensor for formaldehyde

To search for a novel sensor to detect the presence of formaldehyde (HCOH), we investigate reactivities of the intrinsic and boron-doped (B-doped) single-walled (8, 0) carbon nanotube (SWCNT) with HCOH using density functional theory calculations. Compared with the intrinsic SWCNT, the B-doped SWCNT presents high sensitivity to HCOH. This is attributed to the strongly chemical interaction between the electron-rich oxygen atom of HCOH and the electron-scarce boron atom of the doped SWCNT. B-doped SWCNTs are expected to be a potential candidate for detecting the presence of HCOH.     

A double-barreled chemical oscillator

A chemical system, based on the Briggs–Rauscher reaction, which unperturbed undergoes rhythmic activity followed by a long period of iodine production–consumption prior to return of the rhythmic activity, is described. The effect of the various variables on the system is reported.     

Entrainment in a chemical oscillator chain with a pacemaker

Entrainment by a pacemaker was investigated experimentally and numerically in a chain of chemical oscillators using coupled discrete Belousov-Zhabotinsky reaction oscillators. The spontaneous frequency of each oscillator depended on the concentration of catalyst ions. The coupling strengths among the nearest neighbor oscillators were controlled by changing the spacing distance (d) between beads. When the coupling strength was sufficiently strong, the pacemaker entrained other oscillators in the chain. Subsequently, the trigger waves propagating from a pacemaker were observed. The range of trigger wave propagation area, i.e., the number of entrained oscillators, depended on d. Numerical simulation for the system described the experimental results well. Furthermore, photic noise maximized the strength of entrainment at an optimal noise intensity.     

Air electrode of chemical power cell as oxygen sensor

The possibility of using the air electrode of a chemical power cell as an electrochemical oxygen sensor was studied.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 10, 2004, pp. 1663–1666.Original Russian Text Copyright © 2004 by Danilov, Kolbasov, Vyunova.     

Aluminum electrode modified with manganese hexacyanoferrate as a chemical sensor for hydrogen peroxide

A chemically modified electrode was fabricated based on manganese hexacyanoferrate (MnHCF) film. The MnHCF was used as a modifier immobilized onto an aluminum electrode. Stability of the electroactive film formed on the Al electrode surface indicated that MnHCF is a suitable material for the preparation of modified electrodes. The analytical applicability of the modified electrode for the determination of hydrogen peroxide was examined. A linear response in concentration range of 6.0x10(-7)-7.4x10(-3) M (r=0.9997) was obtained with detection limit of 2.0x10(-7) M for the determination of hydrogen peroxide. The modified electrode exhibited a good selectivity for H(2)O(2) in real samples. The mentioned electrode has advantages of being highly stable, sensitive, inexpensive, ease of construction and use.     

Time evolution of the activation energy in a batch chemical oscillator

The batch-operated bromate/phosphate/acetone/dual catalyst system was studied at four temperatures between 5 and 35 degrees C. The dynamics was simultaneously followed by potential measurements with platinum and bromide selective electrodes, and spectroscopically at two different wavelengths. By simultaneously recording these four time series it was possible to characterize the dynamics of the sequential oscillations that evolve in time. The existence of three sequential oscillatory patterns at each temperature allowed estimating the activation energies in each case. Along with the activation energy of the induction period, it was possible to trace the time evolution of the overall activation energy at four different stages as the reaction proceeds. The study was carried out for two different sets of initial concentrations and it was observed that the overall activation energy increases as reactants turn into products. This finding was propounded as a result of the decrease in the driving force, or the system's affinity, of the catalytic oxidative bromination of acetone with acidic bromate, as the closed system evolves toward the thermodynamic equilibrium.     

Fast chromatographic separation techniques as competitors to chemical and biochemical sensor systems

Fast chromatographic methods, e.g. chromatography with supercritical fluids, ion chromatography and especially capillary electrophoresis, are important competitors of chemical sensors in environmental monitoring and process control. These methods show high selectivity and low interferences and it is possible to determine several parameters within a single chromatographic run. In order to show the potential and limitation of sensor systems and chromatographic separation methods in environmental analysis this review is limited to applications in this field.With regard to practical problems a comparison of ion chromatography (IC), capillary electrophoresis (CE) and electrochemical sensors is given for a special example, the ion analysis in waste water. Authentic water samples with a high surfactant content from a car-wash are examined, proving the suitability of IC, CE and electrochemical sensors in terms of specifity, sensitivity, reproducibility, analysis time and calibration linearity. The results show that the chromatographic methods are useful techniques in water analysis, yielding good sensitivity, high resolution and short analysis times. In comparison the chemical sensor also shows short analysis times, good sensitivity and a simple instrumental set-up. The disadvantage is the lack of selectivity and the instability of the sensor signal, when the sensor is exposed to the extremely complex matrix. Good results could only be achieved by pretreatment of the sample solution.     

Conjugated carbazole dimer as fluorescence carrier for preparation of iodine-sensitive chemical sensor

The carbazole derivative, 9-ethyl-3-carbazylidene carbazole hydrazone (ECCH) with two conjugated carbazole rings have been applied as a fluorescence carrier for preparation of an iodine sensitive optical chemical sensor. The response of the sensor is based on quenching of the fluorescence of ECCH by iodine. The conjugated carbazole dimer based sensor shows a linear response toward iodine in the concentration range 1.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol L⁻¹, with a detection limit of 8.0 × 10⁻⁷ mol L⁻¹ at pH of 7.0. The effect of composition of the sensor membrane was studied, and the experimental conditions were optimized. Most commonly coexisting ions do not interfer with the iodine assay. The sensor shows sufficient repeatability, selectivity, operational lifetime of two months and a fast response of less then 50 s. The sensor has been used for determination of iodine in water samples.     

Miniaturized chemical multiplexed sensor array

Miniaturized tin oxide semiconductor sensors are fabricated directly by site-specific dip-pen nanopatterning using precursor inks derived from the sol-gel method. The good flow characteristics and strong affinity of the sols to measurement electrodes enable intimate contact. The measurable, reproducible, and proportionate changes in the resistance of the sensors when exposed to trace quantities of oxidative and reducing gases constitute the basis for such sensors. These sensors show rapid response and ultrafast recovery for the detection of nitrogen dioxide and acetic acid. Furthermore, an array of eight miniaturized sensors is created by doping the pristine tin-based sol ink with different metal ions; the different responses of each sensor to certain gases constitute a reference response spectrum that can be used to recognize the gas. Such recognition ability, instant response and rapid recovery, compact size, and integration with the current microelectronics platform make the miniaturized sensor array a significant development for the on-site and real-time detection of life-threatening gases.     

Preparation of Au nanoparticles modified TiO2 nanotube array sensor and its application as chemical oxygen demand sensor

Au nanoparticles (AuNPs) were electrodeposited at the highly ordered anatase TiO₂ nanotube array (TiO₂NA) electrode to prepare the AuNP-TiO₂NA sensor. The as-prepared sensor can be used for the determination of chemical oxygen demand (COD) in real samples.     

Determination of hydrogen peroxide by utilizing a cobalt(II)hexacyanoferrate-modified glassy carbon electrode as a chemical sensor

A mixed-valence cluster of cobalt(II)hexacyanoferrate possesses an electron transfer property and is suitable for the development of an effective hydrogen peroxide detection scheme. The characteristics of cobalt(II)hexacyanoferrate have been studied using both elemental analysis and infrared spectra, confirming the structure is Co[Fe^II(CN)₆]. The cobalt(II)hexacyanoferrate-modified electrode exhibits a rapid response (t_95% - 6.5 s) to the injection of 5.0 × 10⁻⁵ M hydrogen peroxide. The linearity of the response is up to 1.1 × 10⁻³ M (correlation coefficients is 0.999). The sensitivity of this modified electrode is 11.8 μA/mM-mm². The detection limit of cobalt(II)hexacyanoferrate-modified electrode to hydrogen peroxide is 6.25 × 10⁻⁸ M. The current chemical sensor modified with Co[Fe^II(CN)₆] has better sensitivity than previous ones. The modified glassy carbon electrode shows no interference from ascorbic acid, uric acid, acetaminophen, 1,4-dihydroxyquinone, dopamine at the 2.0 × 10⁻⁴ M level and polyamines at 5.0 × 10⁻⁵ M level.     

A beta-cyclodextrin based fiber-optic chemical sensor: a fractal analysis

A fractal analysis is presented for the binding of pyrene in solution to beta-cyclodextrin attached to a fiber-optic chemical sensor. The specific (k(l)) and non-specific binding rate coefficients and the fractal dimension (D(f)) (specific binding case only) both tend to increase as the pyrene concentration in solution increases from 12.4 to 124 ng ml(-1). Predictive relations for the binding rate coefficient (specific as well as non-specific binding) and for D(f) (specific binding case only) as a function of pyrene concentration are provided. These relations fit the calculated k(l) and D(f) values in the pyrene concentration range reasonably well. Fractal analysis data seem to indicate that an increase in the pyrene concentration in solution increases the "ruggedness" or inhomogeneity on the fiber-optic biosensor surface. The fractal analysis provides novel physical insights into the reactions occuring on the fiber-optic chemical surface and should assist in the design of fiber-optic chemical sensors.     

Methoxyquinoline-diethylenetriamine conjugate as a fluorescent zinc sensor

A 6-methoxyquinoline conjugated diethylenetriamine derivative, N,N'-bis(6-methoxy-2-quinolylmethyl)diethylenetriamine (6-MeOBQDIEN) has been synthesized and its fluorescent response toward zinc ion was investigated. In the presence of zinc ion, 6-MeOBQDIEN exhibits fluorescence (λ(ex) = 329 nm, λ(em) = 418 nm, φ = 0.039). The fluorescent intensity of the zinc complex of the compound is two times higher than the parent BQDIEN (φ = 0.021) under the same conditions. The crystal structure of 6-MeOBQDIEN-Zn complex shows that all five nitrogen atoms participate to the metal coordination in a distorted square-pyramidal geometry (τ = 0.145) with the aliphatic nitrogen in an apical position. Fluorescent microscopic analysis using 6-MeOBQDIEN reveals the zinc ion concentration change in living cells.     

Optical nitrite sensor based on chemical modification of a polymer film

A new, low-cost nitrite sensor was developed by immobilizing a direct indicator dye in an optical sensing film for food and environmental monitoring. This sensor was fabricated by binding gallocyanine to a cellulose acetate film that had previously been subjected to an exhaustive base hydrolysis. The membrane has good durability (>6 months) and a short response time (<7 s). Nitrite can be determined for the range 0.008-1.50 microg/ml with 3delta detection limits of 1 ng/ml. The method is easy to perform and uses acetylcellulose as a carrier. The reagents used for activating the cellulose support are inexpensive, non-toxic and widely available.     

Development of a surface acoustic wave gas sensor for organophosphorus nerve agents employing lanthanide compounds as the chemical interface

The results of a study dealing with surface acoustic wave gas sensors for organophosphorus compounds such as nerve agents are described. Several lanthanum coordination compounds were applied as the chemical interface. The various sensors prepared were challenged with both the nerve agent sarin and the simulant dimethyl methylphosphonate. Many aspects were studied, such as sensitivity, selectivity, reversibility and response rate as well as the effect of temperature and structural features. Detection limits down to 0.1 ppm were found. Response rates require further improvement. Degradation phenomena were observed which in some cases yielded irreversible responses. The selectivity for organophosphorus compounds was found to be promising.