Sensor for ethanol

It is difficult to incorporate dehydrogenases that are coupled with NAD(P) into amperometric enzyme sensors owing to the irreversible electrochemical reaction of NAD. We have developed an amperometric dehydrogenase sensor for ethanol in which NAD is electrochemically regenerated within a membrane matrix. 

The amperometric dehydrogenase sensor for ethanol consists of a platinum electrode on the surface of which alcohol dehydrogenase (ADH), Meldra blue (MB) and NAD are immobilized with a conductive polypyrrole membrane as schematically illustrated in Fig.24. 

Xu et al. reported the cataluminescence and catalysis studies of ethanol on nanosized Cei-j Zrj.02 materials. The ceria-rich solid solutions x = 0.05-0.25) showed high cataluminescence activity at 220 °C and were supposed to be efficient low temperature CTL sensors for ethanol (Ye et al., 2006). Lv et al. (Xuan et al., 2009) reported the cataluminescence studies of CS2 on ceria NRs, nanocubes, and nanospheres. The chemiluminescence is used as a sensitive gas sensor for the determination of CS2 and a high selectivity over a number of organic gases was demonstrated. 

AOD has been coimmobilized with alcohol dehydrogenase in order to increase the sensitivity of alcohol determination (Hopkins, 1985). In the presence of oxygen and NADH ethanol is recycled between the two enzymes. Thus more H2O2 is formed than substrate is present in the enzyme membrane, i.e., the sensitivity is enhanced (see also Section 3.2.4). A further advantage of this system is that this recycling is restricted to ethanol, because methanol is converted only by AOD but notbyADH. Conversely, isopropanol is oxidized by ADH but not by AOD. Thus, by combination of the two enzymes the selectivity of the sensor for ethanol is improved. 

Lina W. U.,Mclntosh M., Xueji Z., Huangxian J. U., Amperometric sensor for ethanol based on one-step electropolymerization of thionine-carbon nanofiber nanocomposite containing alcohol oxidase, Talanta, 74, 387-392, 2007. 

Rao, B. B. (2000) Zinc oxide ceramic semi-conductor gas sensor for ethanol vapour) Materials Chemistry and Physics, 64(1), 62-65. 

Figure 26. Humidity effect on a conduclomeiric polymer gas sensor for ethanol.

Gataluminescence (GTL) is the chemiluminescence produced during catalytic oxidation reactions. Ye et al studied GTL and the catalytic oxidation reactions of ethanol on nanosized Gei r,02 materials. The ceria-rich solid solutions (x= 0.05-0.25) showed high GTL activity at 220°G and were considered to be efficient low-temperature GTL sensors for ethanol. The GTL intensity of ethanol oxidation was closely related to the steady-state activity of the Gei jZr 02 catalysts in the oxidative dehydrogenation of ethanol. Xuan et al studied the GTL of GS2 on the surface of ceria nanorods, nanocubes, and... 

Tsang SC, Bulpitt C. Rare earth oxide sensors for ethanol analysis. Sens. Actuators, B Chemical. 1998 52 226-235. DOI 10.1016/S0925-4005(98)00233-0. 

Alcohol oxidase was used to generate H202 followed by its reaction with luminol in the presence of K3[Fe(CN)6] as a catalyst [53], The luminescence was transmitted from the flow cell to the detector via optical fibers. Ethanol can be determined in the 3-750-pmol/L concentration range, with a detection limit of 3 pmol/L. Also, using an immobilized alcohol dehydrogenase reactor in glass beads, a FIA sensor for a reduced form of NADH was constructed by the ECL using the above-mentioned ruthenium tris(2,2 -biryridine) complex. The sensor was satisfactorily applied to the determination of ethanol concentration [54],... 

An electron transfer type of enzyme sensor was thus fabricated by a electrochemical process. Although no appreciable leakage of ADH and MB from the membrane matrix was detected, NAD leaked slightly. To prevent this leakage, the ADH-MB-NAD/polypyrrole electrode was coated with Nation. A calibration curve is presented in Fig.25 for ethanol determination in an aquous solution with the enzyme sensor. Ethanol is selectively and sensitively determined in the concentration range from 0.1 nM to 10 mM. 

In a further development, an ADH-MB-NAD/polypyrrole electrode, a platinum counter electrode and an Ag/AgCl reference electrode were assembled and covered with a gas-permeable polymer membrane to form an gaseous ethanol sensor. This appears to be the first time that a complete enzyme sensor for gaseous ethanol has been fabricated in such a manner with NAD incorporated in immobilized form. 

Figure 3.11 — (A) Immobilized peroxidase sensor. Glass-immobilized peroxidase is packed in the flow-cell shown. The plastic support plate fits the top surface of the photomultiplier chamber of the immunometer so as to support the vertically held flow-cell in front of the photomultiplier itself. (B) Flow system for hydrogen peroxide/ethanol determinations. For ethanol determinations, the immobilized alcohol oxidase column is inserted immediately after the injection valve (shown by the arrows). Luminol (62 /zM) and 4-iodophenoI (0.4 M) are dissolved in 200 mM borate buffer (pH 8.9) and pumped at a flow-rate of 0.8 mL/min. Phosphate buffer (10 mM, pH 7.0) is pumped at 1.6 ml/min. (Reproduced from [78] with permission of Elsevier Science Publishers).

Furthermore, the use of Ralstonia eutropha JMP134-containing sensors for the determination of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) has been described [118,121]. This sensor was sensitive to 2,4-D and 2,4,5-T (2,4,5-trichlorophenoxyacetic acid) with a detection Emit of 40 mg 1 with a response time of 15 s. Moreover, catechol, benzoic acid, and sahcylaldehyde caused higher signals, but no or very little signal was obtained for phenol, biphenyl, and the usual substrates such as glucose, fructose, ethanol, and acetate. 

The present authors and coworkers observed intense CTL emission during the catalytic oxidation of ethanol or acetone vapor on a heated aluminum oxide powder [8]. This phenomenon was applied to the consumption-free CTL-based sensor for detecting combustible vapors. The CTL response was fast and reproducible for a change in concentration of a sample vapor in air. CTL emission has three distinct features ... 

PEROXIDASE-MIMETIC SENSOR FOR DETECTION OF ETHANOL IN LOW CONCENTRATIONS IN AQUEOUS SOLUTIONS... 

A software sensor for on-line determination of substrate was developed based on a model for fed-batch alcoholic fermentation process and on-line measured signals of ethanol, biomass, and feed flow. The ethanol and biomass signals were obtained using a colorimetric biosensor and an optical sensor developed in previous works that permitted determination of ethanol at a concentration of 0-40 g/L and biomass of 0-60 g/L. The volume in the fermentor could be continuously calculated using the total measured signal of the feed flow. The results obtained show that the model used is adequate for the proposed software sensor and determines continuously the substrate concentration with efficiency and security during the fermentation process. 

This article presents the design and implementation of a software sensor for the continuous determination of substrate concentration based on a simple model of a fed-batch fermentation process and the available signals of two other sensors—one for on-line biomass determination (7) and the other for on-line ethanol determination (8)—developed in previous works. The software sensor proposed provides a continuous signal that can be used in a control loop to manipulate the substrate feed flow in order to maintain almost constant substrate concentration and obtain an excellent level of productivity and yield during all of the process, as shown in experimental control strategy studies in previous works (9). 

Figure 3 shows the experimental results of tests 1 and 2 obtained for the substrate concentration calculated using the software sensor and the filtered sensor measurements for ethanol and biomass. The differences between the two experiments are the initial biomass concentration and concentration of substrate in the feed, as shown in Table 1. 

Alcohol oxidase. We have chosen to use alcohol oxidase from Hansenula polv-morpha (2) in our research. The enzyme has eight sub-units, all of which must be associated for the enzyme to exhibit activity. It is a large enzyme Mn 600,000 and has poor stability upon freeze drying. This factor combined with an almost flat activity response to pH between 6 and 10 and a maximum temperature activity at 40-50°C made the enzyme an ideal candidate for the study of enzyme stabilization in the dry state, especially as we wished to prepare diagnostic kits for ethanol and solid phase enzyme based sensors. 

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