Ethanol optical sensor

The ethanol optical sensor also uses fluorimetric detection of NADH. Alcohol dehydrogenase (ADH) is fixed to a microporous teflon membrane in the presence of semicarbazide, which displaces the equilibrium by decomposing the aldehyde formed [206] ... 

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. 

Fig. 1. Complete experimental setup for monitoring and control system for fermentor. T, feed tank V, control valve v, valves F, fermentor t, thermocouple c, coils A, dilutions tanks Bm, multichannel pump C, controller Tt, temperature transmitter Tb, biomass transmitter Sb, biomass optical sensor D, equipment to remove air bubbles R, rotammeter Ft, tangential filter Co, computer So, ethanol colorimetric sensor Vi, injection valve d, waste E+R, reagents-enzymes tanks B, pumps.

Abstract Makrolon , a commercially available polycarbonate with a glassy ultramicroporous structure (mean pore-volume 0.1 nm3), was often employed as sensitive layer for optical sensors in recent years. Due to the definite pore volume-distribution, it can be used as a size-selective sensitive layer. The interaction behaviour of Makrolon of different layer-thicknesses under the influence of methanol, ethanol and 1-propanol is characterized by Spectral El-lipsometry (SE), Surface Plasmon Resonance Spectroscopy (SPR)... 

B. Kieser, F. Dieterle, G. Gauglitz, Discrimination of methanol and ethanol vapors by the use of a single optical sensor with a microporous sensitive layer. Anal. Chem. 74, 4781-4787 (2002). 

Wolfbeis, O. S., Posch, H. E., Optical Sensors. Part 20. A Fibre Optic Ethanol Biosensor , Fresenius Z. Anal. Chem. 332 (1988) 255-257. 

With the complex where L = pyridine an optical nanosensor was developed [135-137], the method used to fix the vapochromic material to the optical fiber was the electrostatic self assembling method (ESA) and the light source used was an 850 nm LED. The sensor was tested for two different alcohols (ethanol and methanol) and it was possible to distinguish between different concentrations. It was also possible to discriminate between the two different alcohols. 

Choi J.W., Bae J.Y., Min J., Cho K.S., Lee W.H., Fiber-optic ethanol sensor using alcohol dehydrogenase-immobilized Langmuir-Blodgett film, Sensor Mater. 1996 8 493-504. 

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],... 

If the oxygen sensitive dye is replaced by a pH sensitive dye, optical pH sensors can be produced. Thus miniaturization of these sensors is easy, and multisensing systems can be set up. Different sensor types for biotechnical application are described in the literature (e.g., ethanol and chloride sensors) [23,24]. 

In comparison to equivalent optical detection methods using whole cell biosensors for water toxicity detection, these results proved to be more sensitive and produce faster response time. Concentrations as low as 1% of ethanol and 1.6 ppm of phenol could be detected in less than 10 min of exposure to the toxic chemical, whilst a recent study [11] which utilized bioluminescent E.coli sensor cells, detected 0.4 M (2.35%) ethanol after 220 min. An additional study [1] based on fluorescent reporter system (GFP), enabled detection of 6% ethanol and 295 ppm phenol after more than one hour. Cha et al [12] used optical detection methods of fluorescent GFP proteins, detected 1 g of phenol per liter (1,000 ppm) and 2% ethanol after 6 hours. Other studies [13] could not be directly compared due to different material used however their time scale for chemicals identification is hours. 

Colorimetric and fluorimetric NH3 sensors contain mixtures of pH indicators having suitable dissociation constants at the tip of the fiber bundle. The measuring solution is separated from this indicator layer by an NH3 gas-permeable membrane covered by an immobilized de-aminating enzyme, e.g. urease (Wolfbeis, 1987 Arnold, 1987). The fluorimetric indication of NADH has been used in optical biosensors for lactate, pyruvate, and ethanol, where the respective dehydrogenase is immobilized at the tip of an optical NADH sensor (Arnold, 1987 Wangsa and Arnold, 1988). 

Arnold et al. (1987) described an optoelectronic ethanol sensor based on fluorimetric detection of NADH formed in the reaction catalyzed by ADH. The enzyme was fixed to the inner surface of a membrane permeable to volatile substances, which separated the sample from the internal sensor solution. This solution contained NADH and semicarbazide, so that no reagent had to be added to the sample. The arrangement was named an internal optical enzyme sensor . 

Zeolite membranes and films have been employed to modify the surface of conventional chemical electrodes, or to conform different types of zeolite-based physical sensors [49]. In quartz crystal microbalances, zeolites are used to sense ethanol, NO, SO2 and water. Cantilever-based sensors can also be fabricated with zeolites as humidity sensors. The modification of the dielectric constant of zeolites by gas adsorption is also used in zeolite-coated interdigitaled capacitors for sensing n-butane, NH3, NO and CO. Finally, zeolite films can be used as barriers (for ethanol, alkanes,...) for increasing the selectivity of both semiconductor gas sensors (e.g. to CO, NO2, H2) and optical chemical sensors. 

Optodes provided with non-fluorescent esters of fluorophores have been used for the determination of external enzyme activities. The fluorophores are liberated by the enzymes and then seen by the optical Ober [214], As ecamples of p(02)-modulated optical biosensors, a glucose probe [213] and an ethanol probe [216] can be mentioned sensors based on glucose, alcohol, and other oxidases were reviewed by Opitz and Lttbbers [217]. The advantages of these 02-dependent optical biosensors are that, unlike corresponding amperometric sensors, they do not consume O2 and that they are strictly diffusion limited in their response. Fiber-optical devices are also available for the determination of substrates of dehydrogenases the NADH fluorescence produced by the immobilized enzyme is measured as a function of time [218, 219]. 

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