Gas-phase Biosensor Research Articles

Gas-Phase Biosensors (Bio-Sniffers) for Measurement of 2-Nonenal, the Causative Volatile Molecule of Human Aging-Related Body Odor.

The molecule 2-nonenal is renowned as the origin of unpleasant human aging-related body odor that can potentially indicate age-related metabolic changes. Most 2-nonenal measurements rely on chromatographic analytical systems, which pose challenges in terms of daily usage and the ability to track changes in concentration over time. In this study, we have developed liquid- and gas-phase biosensors (bio-sniffers) with the aim of enabling facile and continuous measurement of trans-2-nonenal vapor. Initially, we compared two types of nicotinamide adenine dinucleotide (phosphate) [NAD(P)]-dependent enzymes that have the catalytic ability of trans-2-nonenal: aldehyde dehydrogenase (ALDH) and enone reductase 1 (ER1). The developed sensor quantified the trans-2-nonanal concentration by measuring fluorescence (excitation: 340 nm, emission: 490 nm) emitted from NAD(P)H that was generated or consumed by ALDH or ER1. The ALDH biosensor reacted to a variety of aldehydes including trans-2-nonenal, whereas the ER1 biosensor showed high selectivity. In contrast, the ALDH bio-sniffer showed quantitative characteristics for trans-2-nonenal vapor at a concentration range of 0.4-7.5 ppm (with a theoretical limit of detection (LOD) and limit of quantification (LOQ) of 0.23 and 0.26 ppm, respectively), including a reported concentration (0.85-4.35 ppm), whereas the ER1 bio-sniffer detected only 0.4 and 0.8 ppm. Based on these findings, headspace gas of skin-wiped alcohol-absorbed cotton collected from study participants in their 20s and 50s was measured by the ALDH bio-sniffer. Consequently, age-related differences in signals were observed, suggesting the potential for measuring trans-2-nonenal vapor.

Enzyme-embedded electrospun fiber sensor of hydrophilic polymer for fluorometric ethanol gas imaging in vapor phase

Non-invasive measurement of volatile organic compounds (VOCs) emitted from living organisms is a powerful technique for diagnosing health conditions or diseases in humans. Bio-based gas sensors are suitable for the sensitive and selective measurement of a target VOC from a complex mixture of VOCs. Conventional bio-based sensors are normally prepared as wet-type probes to maintain proteins such as enzymes in a stable state, resulting in limitations in the commercialization of sensors, their operating environment, and performance. In this study, we present an enzyme-based fluorometric electrospun fiber sensor (eFES) mesh as a gas-phase biosensor in dry form. The eFES mesh targeting ethanol was fabricated by simple one-step electrospinning of polyvinyl alcohol with an alcohol dehydrogenase and an oxidized form of nicotinamide adenine dinucleotide. The enzyme embedded in the eFES mesh worked actively in a dry state without pretreatment. Substrate specificity was also maintained, and the sensor responded well to ethanol with a sufficient dynamic range. Adjustment of the pH and coenzyme quantity in the eFES mesh also affected enzyme activity. The dry-form biosensor—eFES mesh—will open a new direction for gas-phase biosensors because of its remarkable performance and simple fabrication, which is advantageous for commercialization.

Gas-phase biosensors: A review

In this review, we describe advances in biosensors and bioimaging techniques for gas-phase biochemical molecules. These techniques exploit the high specificity of biorecognition elements for the selective sensing of volatile biochemicals. The review begins with a discussion of gas-phase biosensors using enzymes as recognition elements, in which redox reactions of volatile biochemicals provide detectable products such as fluorescent molecules. Then, biosensors using other biorecognition elements, including antibodies, molecularly imprinted polymers, olfactory receptors, and cells, are introduced. Combinations of these elements with optical, electrochemical, and acoustic wave transducers are also described. A unique and powerful feature of biosensors is that they are little influenced by humidity because biorecognition elements are used in the liquid phase. This notable advantage makes it possible for biosensors to measure volatile biochemicals in the breath and other humid environments. We also discuss progress in capturing the spatiotemporal distribution of volatile biochemicals with improved continuity and the use of imaging technologies. These new technologies are expected to be utilized for determining the relationship between spatiotemporal changes in volatile biochemicals in the breath or skin gas and health, which has not been explored, and for high-precision monitoring of volatile biochemicals in the environment.

(Invited) Bio-Sniffers & Sniff-Cam: Biofluorometirc Gas Sensor and Imaging System for Human Volatile Chemicals

Introduction Various volatile organic compounds exist, such as those the transpired by humans, breath, body odor and smell of the living environment. The human body emits various volatile molecules, depending on a person’s genetics, disease and metabolic condition. In this contribution, novel gas-phase biosensors (bio-sniffer and sniff-cam) using bio-fluorometric techniques for human volatiles will be introduced as a future biosensing approach for preemptive medicine and healthcare. Bio-sniffer for breath acetone as early screening approach of diabetes mellitus. Secondary alcohol dehydrogenase (S-ADH) catalyzes the reduction of acetone and the oxidation of nicotinamide adenine dinucleotide (NADH to NAD+) in a weak acid environment (Fig.1). NADH is excited by 340 nm excitation lights and subsequently emit 490 nm fluorescence. Therefore, acetone can be measured by the decrease in NADH fluorescence intensity. A bio-fluorometric acetone sniffer was constructed by incorporating an optic-probe into a gas/liquid flow cell with S-ADH immobilized diaphragm (Fig.2) [1,2]. The developed biosniffer show rapid response, highly sensitivity and selectivity to acetone. The breath acetone analysis in healthy subjects shows that the mean values were 750.0 ± 434.4 ppb. The breath acetone did not show a statistical difference among different genders and ages. The breath acetone analysis for diabetic patients under medical treatment shows a mean value of 1207.7 ± 689.5 ppb, which was higher than that of healthy subjects (p < 1 × 10−6). In particularly, type-1 diabetic (T1D) patients exhaled a much higher concentration of acetone than type-2 diabetic (T2D) patients (p < 0.01) (Fig.3). These findings are worthwhile in the study of breath biomarkers for early screening of diabetes mellitus. Additionally, the developed bio-sniffers provide a new technique for volatolomics research. Sniff-cam with biofluorometric technique for spatiotemporal gas imaging A decade ago, a chemiluminescence sniff-cam system was developed and applied successfully for distribution imaging of high concentration ethanol vapor (ppm-level) such as breath ethanol after drinking (Fig.4) [3] and wine aroma from wine glass (Fig.5) [4]. In order to improve the performance, we applied the bio-fluorometric technique for highly sensitive sniff-cam system (ppb-level). The sniff-cam with ADH (alcohol dehydrogenase) redox reactions can show a spatiotemporal change of gaseous ethanol (EtOH) or acetaldehyde (AcH) in real-time [5,6]. The sniff-cam was composed of a highly sensitive camera, a UV-LED array sheet, and an ADH-immobilized mesh. The both redox reactions of ADH were employed for detection of gaseous EtOH and AcH where a relationship between fluorescence intensity from nicotinamide adenine dinucleotide. Moreover, the image differentiation method that calculated a fluorescence change rate was employed to visualize a real-time change in the concentration distribution of EtOH and AcH. The dynamic ranges of the sniff-cam for EtOH and AcH were 20ppb-300ppm and 100 ppb-10 ppm. As the physiological application, the sniff-cam successfully achieved the imaging of the concentration distribution of EtOH and AcH in breath and skin gas (Fig. 6). Future potential of the gas-phase biosensors (bio-sniffer and sniff-cam) The future potential of the bio-sniffer and sniff-cam for body volatiles includes the early disease screening, the identification of those locations, the real time evaluation of metabolic condition as a Bio-IoT monitoring.

Dual-target gas-phase biosensor (bio-sniffer) for assessment of lipid metabolism from breath acetone and isopropanol

Volatile organic compounds (VOCs) in breath and skin gas are promising samples for non-invasive and simple disease screening and metabolism assessment. In addition, simultaneous measurement of multiple VOCs helps to improve the examination quality and allows for more reliable disease screening and investigation of detailed metabolic pathways. In this study, we have developed a dual-target gas-phase biosensor (bio-sniffer) that allows for measurement of isopropanol (IPA) and acetone vapours, relevant VOCs for lipid metabolisms, by simply exchanging coenzyme solutions. The measurement exploited a reversible redox reaction that was catalysed by secondary alcohol dehydrogenase (S-ADH). IPA/acetone was oxidised/reduced together with reduction/oxidation of a coenzyme, oxidised (NAD+)/reduced (NADH) form of β-nicotinamide adenine dinucleotide, depending on surrounding pH (8.5/7.5). This reaction resulted in producing/consuming NADH which exhibited autofluorescence (λex = 340 nm, λfl = 490 nm), by which IPA/acetone was measured. The characterization of the dual-target bio-sniffer showed the dynamic ranges for IPA and acetone vapour were 3.3–1000 ppb and 13.0–3000 ppb, respectively, which encompasses those in the breath of healthy people (IPA, 10–30 ppb; acetone, 200–900 ppb). Finally, the dual-target bio-sniffer was applied for measurement of IPA and acetone in the breath of healthy people. As with the standard IPA and acetone vapour, intermittent and repeated measurement of both VOCs in the breath was demonstrated. These results indicated that the dual-target bio-sniffer would be a useful tool to assess the lipid metabolism in detail by measuring temporal changes of IPA and acetone concentrations in the breath.

(Invited) Bio-Sniffers & Sniff-Cam: Biofluorometirc Gas Sensor and Imaging System for Human Volatile Chemicals

Introduction Various volatile organic compounds exist, such as those the transpired by humans, breath, body odor and smell of the living environment. The human body emits various volatile molecules, depending on a person’s genetics, disease and metabolic condition. In this contribution, novel gas-phase biosensors (bio-sniffer and sniff-cam) using bio-fluorometric techniques for human volatiles will be introduced as a future biosensing approach for preemptive medicine and healthcare. Bio-sniffer for breath acetone as early screening approach of diabetes mellitus. Secondary alcohol dehydrogenase (S-ADH) catalyzes the reduction of acetone and the oxidation of nicotinamide adenine dinucleotide (NADH to NAD+) in a weak acid environment (Fig.1). NADH is excited by 340 nm excitation lights and subsequently emit 490 nm fluorescence. Therefore, acetone can be measured by the decrease in NADH fluorescence intensity. A bio-fluorometric acetone sniffer was constructed by incorporating an optic-probe into a gas/liquid flow cell with S-ADH immobilized diaphragm (Fig.2) [1,2]. The developed biosniffer show rapid response, highly sensitivity and selectivity to acetone. The breath acetone analysis in healthy subjects shows that the mean values were 750.0 ± 434.4 ppb. The breath acetone did not show a statistical difference among different genders and ages. The breath acetone analysis for diabetic patients under medical treatment shows a mean value of 1207.7 ± 689.5 ppb, which was higher than that of healthy subjects (p < 1 × 10−6). In particularly, type-1 diabetic (T1D) patients exhaled a much higher concentration of acetone than type-2 diabetic (T2D) patients (p < 0.01) (Fig.3). These findings are worthwhile in the study of breath biomarkers for early screening of diabetes mellitus. Additionally, the developed bio-sniffers provide a new technique for volatolomics research. Sniff-cam with biofluorometric technique for spatiotemporal gas imaging A decade ago, a chemiluminescence sniff-cam system was developed and applied successfully for distribution imaging of high concentration ethanol vapor (ppm-level) such as breath ethanol after drinking (Fig.4) [3] and wine aroma from wine glass (Fig.5) [4]. In order to improve the performance, we applied the bio-fluorometric technique for highly sensitive sniff-cam system (ppb-level). The sniff-cam with ADH (alcohol dehydrogenase) redox reactions can show a spatiotemporal change of gaseous ethanol (EtOH) or acetaldehyde (AcH) in real-time [5,6]. The sniff-cam was composed of a highly sensitive camera, a UV-LED array sheet, and an ADH-immobilized mesh. The both redox reactions of ADH were employed for detection of gaseous EtOH and AcH where a relationship between fluorescence intensity from nicotinamide adenine dinucleotide. Moreover, the image differentiation method that calculated a fluorescence change rate was employed to visualize a real-time change in the concentration distribution of EtOH and AcH. The dynamic ranges of the sniff-cam for EtOH and AcH were 20ppb-300ppm and 100 ppb-10 ppm. As the physiological application, the sniff-cam successfully achieved the imaging of the concentration distribution of EtOH and AcH in breath and skin gas (Fig. 6). Future potential of the gas-phase biosensors (bio-sniffer and sniff-cam) The future potential of the bio-sniffer and sniff-cam for body volatiles includes the early disease screening, the identification of those locations, the real time evaluation of metabolic condition as a Bio-IoT monitoring.

Real-time monitoring of skin ethanol gas by a high-sensitivity gas phase biosensor (bio-sniffer) for the non-invasive evaluation of volatile blood compounds

In this study, a highly sensitive and selective biochemical gas sensor (bio-sniffer) and real-time monitoring system with skin gas cell was constructed for the determination of ethanol gas concentration on human skin. This bio-sniffer measured the concentration of ethanol according to the change in fluorescence intensity of nicotinamide adenine dinucleotide (NADH), which is produced in an enzymatic reaction by alcohol dehydrogenase (ADH). The NADH detection system used an ultraviolet light emitting diode (UV–LED) as the excitation light, and a highly sensitive photomultiplier tube as a fluorescence intensity detector. The calibration range of the ethanol bio-sniffer was validated from 25 ppb to 128 ppm. To measure the concentration of ethanol within skin gas, subjects ingested an alcohol beverage, and the sensor output was monitored. We chose the central part of the palm, a back of the hand, and a wrist as targets. The real-time concentration of skin ethanol gas at each target was measured after drinking. The maximum output values were reached at approximately 70 min after drinking and then gradually decreased. We showed that ethanol release kinetics were different depending on the part of the hand measured with the developed monitoring system. Accordingly, this highly sensitive and selective bio-sniffer with a skin gas cell could be used to measure ethanol on the skin surface and could be applied for breath and skin gas research, as well as investigation of volatile blood compounds used as biomarkers for clinical diagnosis.

Bio-sniffer (gas-phase biosensor) with secondary alcohol dehydrogenase (S-ADH) for determination of isopropanol in exhaled air as a potential volatile biomarker

Exhaled breath analysis has attracted lots of researchers attention in the past decades due to its advantages such as its non-invasive property and the possibility of continuous monitoring. In addition, several volatile organic compounds in breath have been identified as biomarkers for some diseases. Particularly, studies have pointed out that concentration of isopropanol (IPA) in exhaled air might relate with certain illnesses such as liver disease, chronic obstructive pulmonary (COPD), and lung cancer. In this study, a highly sensitive and selective biochemical gas sensor (bio-sniffer) for the breath IPA concentration determination was constructed and optimized. This bio-sniffer measures the concentration of IPA according to the fluorescence intensity of oxidized nicotinamide adenine dinucleotide (NADH), which was produced by an enzymatic reaction of secondary alcohol dehydrogenase (S-ADH). The NADH detection system employed an UV–LED as the excitation light, and a highly sensitive photomultiplier tube (PMT) as a fluorescence intensity detector. A gas-sensing region was developed using an optical fiber probe equipped with a flow-cell and enzyme immobilized membrane, and connected to the NADH measurement system. The calibration range of the IPA bio-sniffer was confirmed from 1ppb to 9060ppb that was comparable to other IPA analysis methods. The results of the analysis of breath IPA concentration in healthy subjects using the bio-sniffer showed a mean concentration of 16.0ppb, which was similar to other studies. These results have demonstrated that this highly sensitive and selective bio-sniffer could be used to measure the IPA in exhaled air, and it is expected to apply for breath IPA research and investigation of biomarkers for clinical diagnosis.

Fluorometric Bio-Sniffer (Gas Phase Biosensor) for Breath Acetone as a Volatile Product of Lipid Metabolism

Breath analysis for healthcare and disease monitoring has become popular recently in global. There are hundreds of volatile organic compounds (VOCs) exist in human breath, and some of them can offer medical and biological information as the bloodstream. Particularly,acetone is one of the typical VOCs in exhaled breath, which is related to lipid metabolism in fasting, exercise and diabetes mellitus. The breath acetone concentrations have been previously shown to correlate strongly with blood acetone concentrations as well as with other ketones such as beta-hydroxybutyrate. Besides, there are many studies found the correlation between the breath acetone concentrations and blood glucose concentrations. Previous research indicated that the breath acetone concentration in healthy people shows the range from 200 to 900 ppb and higher concentration was found in breath of diabetic patients. Increase of the acetone concentration is usually a sign that cells cannot effectively use glucose as energy source, which often occurs in starvation, aerobic exercise, lack of insulin or resistance of insulin. Thus, acetone in exhaled breath has a potential to be a biomarker for non-invasive monitoring the progressive of diabetes. Typical quantitation of gaseous acetone usually uses gas chromatography with mass spectrometry (GC/MS) or proton transfer reaction mass spectrometry (PTR-MS). These methods are highly sensitivity but still have disadvantages in cost, measurement time and hard for continuity. Therefore, a rapid, convenient and highly selective method for acetone determination is strongly required. In this study, a highly sensitive acetone bio-sniffer (gas-phase biosensor) was developed and used to assess the acetone from exhale breath for evaluating the lipid metabolism. Nicotinamide adenine dinucleotide (NADH)-dependent secondary alcohol dehydrogenase (S-ADH) is a kind of enzyme that can reduce acetone to be isopropanol and meanwhile oxidase NADH to be NAD+ in acidic condition. It is known that NADH can be excited by UV (ultraviolet) light at central wavelength of 340 nm and release a fluorescent emission at peak of 490 nm simultaneously, while NAD+ do not have similar optical property. Thus, acetone concentration can be measured using the decreasing of NADH fluorescence intensity that is consumed by the enzymatic reaction of S-ADH. The fluorometric acetone bio-sniffer was composed of a NADH fluorescence measurement system, a flow-cell attaching on the fiber probe and an enzyme-immobilized membrane. The NADH measurement system consisted of a UV-LED as the excitation light source, band-pass filters ( λ = 340 ± 10 nm and λ = 490 ± 10 nm) for reducing noise, a photomultiplier tube (PMT) as fluorescence detector and bifurcated optical fibers for assemble. S-ADH was immobilized on the hydrophilic-PTFE membrane and equipped on the top of flow-cell by silicone O-ring. Phosphate buffer, which contained NADH, was circulated in the flow-cell to supply fresh co-enzyme and eliminate isopropanol and NAD+that produced by the enzyme membrane. When bio-sniffer contacted the gaseous acetone, enzymatic reaction that mentioned above occurred immediately and the change of fluorescence would detect by the PMT. This acetone bio-sniffer showed rapid reaction, highly sensitivity and selectivity. When the acetone vapors were supplied to the sensing region, fluorescent intensity decreased immediately and reached to a steady state. Then, the intensity would return to the initial value in short time when the acetone vapor supply was stopped. The relation between the concentration of acetone and the change of fluorescent intensity was investigated and the dynamic range was confirmed from 20 to 5300 ppb of acetone in the gas phase. This range encompasses the concentration of acetone vapors found in breath of healthy people and of those suffering from disorders of carbohydrate metabolism. The selectivity of the S-ADH was also characterized; several different VOCs were employed to compare the responses. The interference of 2-butanol and 2-pentanone were ignorable because they contained in healthy people in very low concentration. Finally, we applied the bio-sniffer to measure breath acetone for evaluation of lipid metabolism during long time fasting and an aerobic exercise test. The results showed that the mean breath acetone concentration of long time fasting healthy volunteers were higher than those who did not have fasting and display significant difference. Furthermore, the concentration of acetone in breath was observed significantly increase during aerobic exercise and it would recover to the initial value after long time rest. This highly sensitivity acetone bio-sniffer provides a new kind of analytical tool for non-invasive evaluation of human lipid metabolism and it is also expected to use for the clinical applications such as monitoring the progression of diabetes mellitus and diagnosis of other metabolism diseases.

Fluorometric Bio-Sniffer (Gas Phase Biosensor) for Breath Acetone as a Volatile Product of Lipid Metabolism

A highly sensitive acetone bio-sniffer (biochemical gas sensor) for assessment of lipid metabolism utilizing reverse reaction of secondary alcohol dehydrogenase was fabricated and demonstrated. This bio-sniffer consisted of a NADH fluorescence detection system, a flow-cell section, and an enzyme-immobilized membrane. This bio-sniffer presented rapid response, highly sensitivity and selectivity. The analyses of breath acetone concentrations during fasting and aerobic exercise were also demonstrated. The results showed that the breath acetone concentration would increase during long-time fasting and aerobic exercise. This acetone bio-sniffer provides a new kind of analytical tool for non-invasive evaluation of human lipid metabolism and it is also expected to use for the clinical applications such as monitoring the progression of diabetes.

An acetone bio-sniffer (gas phase biosensor) enabling assessment of lipid metabolism from exhaled breath.

Several volatile organic compounds (VOCs) are released from human breath or skin. Like chemical substances in blood or urine, some of these vapors can provide valuable information regarding the state of the human body. A highly sensitive acetone biochemical gas sensor (bio-sniffer) was developed and used to measure exhaled breath acetone concentration, and assess lipid metabolism based on breath acetone analysis. A fiber-optic biochemical gas sensing system was constructed by attaching a flow-cell with nicotinamide adenine dinucleotide (NADH)-dependent secondary alcohol dehydrogenase (S-ADH) immobilized membrane onto a fiber-optic NADH measurement system. The NADH measurement system utilizes an ultraviolet-light emitting diode with peak emission of 335 nm as an excitation light source. NADH is consumed by the enzymatic reaction of S-ADH, and the consumption is proportional to the concentration of acetone vapor. Phosphate buffer which contained NADH was circulated into the flow-cell to rinse products and the excessive substrates from the optode. The change of fluorescent emitted from NADH is analyzed by the PMT. Hence, fluorescence intensity decreased as the acetone concentration increased. The relationship between fluorescence intensity and acetone concentration was identified from 20 ppb to 5300 ppb. This interval included the concentration of acetone vapor in the breath of healthy people and those suffering from disorders of carbohydrate metabolism. Finally, the acetone bio-sniffer was used to measure breath acetone during an exercise stress test on an ergometer after a period of fasting. The concentration of acetone in breath was shown to significantly increase after exercise. This biosensor allows rapid, highly sensitive and selective measurement of lipid metabolism.

Analyte induced water adsorbability in gas phase biosensors: the influence of ethinylestradiol on the water binding protein capacity.

An ultra-sensitive gas phase biosensor/tracer/bio-sniffer is an emerging technology platform designed to provide real-time information on air-borne analytes, or those in liquids, through classical headspace analysis. The desired bio-sniffer measures gaseous 17α- ethinylestradiol (ETED) as frequency changes on a quartz crystal microbalance (QCM), which is a result of the interactions of liquid sample components in the headspace (ETED and water) with a biorecognition layer. The latter was constructed by immobilization of polyclonal antiserum against a phenolic A-ring of estrogenic receptors through protein A. The QCM response exhibited stretched exponential kinetics of negative frequency shifts with reversible and "irreversible" components of mass uptake onto the sensor surface in static headspace conditions when exposed to water solutions of ETED over the sensor working range, from 10(-10) to 10(-17) g L(-1). It was shown that the variations in the QCM response characteristics are due to the change of the water-binding capacity of the sensing layer induced by protein transformations initiated by the binding of ETED molecules. This result is well correlated with the natural physiological function of estrogens in controlling the homeostasis of body fluids in living beings.

Verification of a Specific Reaction between an Airborne Antigen and an Immobilized Antibody at a Gas-Solid Interface

With a specific and strong molecular-recognition capability cultivated in humoral acquired immunity, an antibody has been extensively utilized in various applications, such as diagnostics and therapy. However, so far most of its uses have been limited to be in the liquid phase. In view of its potential uses, such as a gas-phase biosensor or a high-performance air filter, we have tried to verify a previously undescribed binding reaction between protein antigens and corresponding antibodies immobilized on a solid surface by using fluorescence resonance energy transfer between the two. Our data showed that the antibody on a solid surface specifically reacted with a protein antigen supplied from the gas phase under the normal ambient condition. Also discovered was that the reaction occurred even faster than that in the liquid phase under several assay conditions.

バイオ・スニファを用いた化学情報システムに関する研究

A novel chemical code system was constructed with gas-phase biosensors (bio-sniffer) and a commercial inkjet printer. Two volatile chemicals, hydrogen peroxide (H2O2) and ethanol, were used for chemical code and printed by the inkjet printer. Each chemicals could be recognized by bio-sniffer fabricated with catalase and alcohol oxidase (AOD), respectively. Each bio-sniffer shoswed high selectivity due to the substrate specificity of the enzyme. Thus the combination of the sniffers was able to discriminate the inkjet printed 2-bit chemical code (4 patterns).

A gas-phase biosensor for environmental monitoring of formic acid: laboratory and field validation.

In order to encourage more exposure measurements to be performed, a formic acid gas-phase biosensor has been developed for this purpose. In the present paper, an enzyme based biosensor has been validated with respect to analyte selectivity and on-site use. To ensure that the sampler developed measures the compound of interest the biosensor was exposed to three near structural homologues to formic acid, i.e. acetic acid, methanol and formaldehyde. These vapours were generated with and without formic acid and the only compound that was found to have an effect on the performance of the biosensor, albeit a small one, was acetic acid. The field test was performed in a factory using formic acid-containing glue for glulam products. In parallel to the measurements with the biosensor a well defined reference method was used for sampling and analysing formic acid. It was found that the biosensor worked satisfactorily in this environment when used in a stationary position. It was also shown that the biosensor could determine formic acid vapour concentrations down to 0.03 mg m(-3).

アンモニア計測用バイオノーズに関する研究

A gas-phase biosensor (bio-nose) for ammonia was fabricated by incorporating an enzyme electrode with flavin-containing monooxygenase into a reaction unit with both liquid- and gas-phase cells separated a porous diaphragm membrane. The bio-nose was calibrated against ammonia vapors from 3.72 to 366ppm.

呼気アルコール計測用簡易型酵素電極に関する研究

A stick-type gas-phase biosensor (bio-nose) for ethanol vapor was constructed using alcohol oxidase (AOD). The calibration range of the bio-nose for ethanol vapor was from 1.0 to 500ppm. The nose device was also possible to assess the concentration of ethanol in breath air after alcohol-drinking.

アルデヒド化合物ガス用バイオセンサの研究

Most of aldehyde chemicals such as acetaldehyde, formaldehyde, etc. are defined as Specified Malodor Chemical Substances by the Environment Agency in Japan. In this research, a gas-phase biosensor for aldehyde chemicals was constructed by incorporating an aldehyde dehydrogenase (ALDH) immobilized electrode into a flow reaction cell. The sensor was used to measure acetaldehyde (0.525-20ppm) and formaldehyde (50-2000ppb) in the gas-phase with high selectivity for aldehyde vapor in the presence of other gas-phase chemicals and gave a negligible response to these chemicals.

Development of a biosensor for gaseous cyanide in solution

A gas-phase biosensor was developed using cyanide degrading bacteria, an oxygen electrode and a gas permeable PTFE membrane. Cyanide degrading bacteria, Pseudomonas fluorescens NCIMB 11764, consume oxygen upon degradation of cyanide. A change in oxygen concentration was detected using a Clark oxygen electrode. A linear relationship was observed between the current decrease and the cyanide ion concentration in the range 0·1–1 mg/l. The optimum working conditions of the sensor were pH 2 and 30°C. The sensor was unaffected by heavy-metal ions and biochemical oxygen demand (glucose, glutamic acid). A good correlation was found between results obtained with the biosensor and those obtained using the Japanese Industrial Standard (JIS) method. The correlation coefficient was 0·995. When the biosensor was stored at 4°C, but operated at 30°C, the sensor was stable for up to 1 month.

Piezoelectric crystal biosensors

The recent development of piezoelectric devices as biosensors is reviewed. Biological materials, like enzymes, lipids, antibodies and antigens, have been used as specific coatings and were utilized for the determination of different substrates. Methods of protein coating and several applications are reported including microgravimetric immunoassays, microbial assays, DNA hybridization, enzyme detections and gas phase biosensors. Although the piezoelectric immunochemical sensor is convenient to use and very promising, a thorough understanding of the different phenomena associated with crystals frequency measurement in biological reactions is still lacking and deserves further investigation.