Search Results (7)

Bio-sniffers represent a novel detection technology that demonstrates significant potential in medical diagnostics. Specifically, they assess disease conditions and metabolic status through the detection of volatile organic compounds (VOCs) in exhaled breath. Unlike conventional methods such as gas chromatography-mass spectrometry (GC-MS) and gas chromatography time-of-flight mass spectrometry (GC-TOF-MS), bio-sniffers provide rapid, sensitive, and portable detection capabilities. In this review, we examine the metabolic pathways and detection methods of specific VOCs in the human body, and their roles as disease biomarkers, and focus on the detection principles, performance characteristics, and medical applications of two bio-sniffer types: electrical and optical sensors. Finally, we systematically discuss the current challenges facing bio-sniffers in VOC monitoring, outline future development directions, and provide suggestions for improving sensitivity and reducing environmental interference. Full article

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. Full article

Acute toxicity data are a necessary component of the general analysis of gaseous environments and the prediction of the possible consequences of exposure to a chemical substance on living organisms. One of the fastest ways to obtain such information is to use gas-phase chemical sensors with sensitive layers of biological origin. Here we report an experimental study of complex loadings for classical quartz crystal microbalances arising in closely packed protein layers of ovalbumin (OVA) on the surface of polycrystalline silver, silver coated with rigid carbon fullerene C₆₀, or a soft molecular-organic crystal of copper phthalocyanine (CuPc). OVA molecules are similarly immobilized on the silver and fullerene-decorated surfaces, while the response of the OVA-CuPc layer indicates an insignificant amount of protein on the surface. A systematic study of the kinetics of the responses of these layers to saturated vapors of volatile solvents shows that the QCM resonant frequency change correlates well with the toxicity of gaseous analytes. It has been observed that saturated vapors of water, ethanol, and their mixtures are classically adsorbed with a high adsorption capacity. Benzene and isobutanol showed only a non-monotonic anti-Sauerbrey behavior, while acetone and cyclohexane had a 10-fold smaller quasi-classical response. The possibility of a gaseous analyte changing not only the QCM loading but also the mechanical behavior of the protein mass associated with the surface opens up the possibility of observing nonspecific conformational changes in proteins, which can be the cause of general cytotoxicity. This effect, combined with the native conformation of OVA in densely packed protein films, allows the use of ovalbumin in creating sensitive bio-sniffer layers for fast toxicological assays—a new class of express tests for biosafety and environmental control. Full article

Methanol (MeOH) in exhaled breath has potential for non-invasive assessment of intestinal flora. In this study, we have developed a biochemical gas sensor (bio-sniffer) for MeOH in the gas phase using fluorometry and a cascade reaction with two enzymes, alcohol oxidase (AOD) and formaldehyde dehydrogenase (FALDH). In the cascade reaction, oxidation of MeOH was initially catalyzed by AOD to produce formaldehyde, and then this formaldehyde was successively oxidized via FALDH catalysis together with reduction of oxidized form of β-nicotinamide adenine dinucleotide (NAD⁺). As a result of the cascade reaction, reduced form of NAD (NADH) was produced, and MeOH vapor was measured by detecting autofluorescence of NADH. In the development of the MeOH bio-sniffer, three conditions were optimized: selecting a suitable FALDH for better discrimination of MeOH from ethanol in the cascade reaction; buffer pH that maximizes the cascade reaction; and materials and methods to prevent leaking of NAD⁺ solution from an AOD-FALDH membrane. The dynamic range of the constructed MeOH bio-sniffer was 0.32–20 ppm, which encompassed the MeOH concentration in exhaled breath of healthy people. The measurement of exhaled breath of a healthy subject showed a similar sensorgram to the standard MeOH vapor. These results suggest that the MeOH bio-sniffer exploiting the cascade reaction will become a powerful tool for the non-invasive intestinal flora testing. Full article

We developed a highly sensitive acetone bio-sniffer (gas-phase biosensor) based on an enzyme reductive reaction to monitor breath acetone concentration. The acetone bio-sniffer device 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. This system utilizes an ultraviolet light emitting diode as an excitation light source. Acetone vapor was measured as the fluorescence of NADH consumption by the enzymatic reaction of S-ADH. A phosphate buffer that contained oxidized NADH was circulated into the flow-cell to rinse the products and the excessive substrates from the optode; thus, the bio-sniffer enables the real-time monitoring of acetone vapor concentration. A photomultiplier tube detects the change in the fluorescence emitted from NADH. The relationship between the fluorescence intensity and acetone concentration was identified to be from 20 ppb to 5300 ppb. This encompasses the range of concentration of acetone vapor found in the breath of healthy people and of those suffering from disorders of carbohydrate metabolism. Then, the acetone bio-sniffer was used to monitor the exhaled breath acetone concentration change before and after a meal. When the sensing region was exposed to exhaled breath, the fluorescence intensity decreased and reached saturation immediately. Then, it returned to the initial state upon cessation of the exhaled breath flow. We anticipate its future use as a non-invasive analytical tool for the assessment of lipid metabolism in exercise, fasting and diabetes mellitus. Full article

Our groups have previously developed a biochemical gas sensor to measure isopropanol (IPA) in exhaled air and have applied it for breath IPA investigation in healthy subjects and diabetes patients. In this study, the original bio-sniffer was modified with a series of components that improved the limit of detection (LOD). First, the modified IPA bio-sniffer used a C8855-type photomultiplier tube (PMT) that performed well in the photon sensitivity at the peak wavelength of nicotinamide adenine dinucleotide (NADH) fluorescence. Second, the multi-core bifurcated optical fiber, which incorporated 36 fibers to replace the previous dual-core type, enhanced the fluorescence collection. Third, the optical fiber probe was reinforced for greater width, and the flow-cell was redesigned to increase the area of the enzyme-immobilized membrane in contact with the air sample. These modifications lowered the detection limit to 0.5 ppb, a significant increase over the previous 1.0 ppb. Moreover, the modified bio-sniffer successfully analyzed the IPA concentration in exhaled air from a volunteer, which confirmed its capability for real-world sample detection. The modified bio-sniffer is more applicable to breath measurement and the detection of other extremely-low-concentration samples. Full article

Gas sensors have been object of increasing attention by the scientific community in recent years. For the development of the sensing element, two major trends seem to have appeared. On one hand, the possibility of creating complex structures at the nanoscale level has given rise to ever more sensitive sensors based on metal oxides and metal–polymer combinations. On the other hand, gas biosensors have started to be developed, thanks to their intrinsic ability to be selective for the target analyte. In this review, we analyze the recent progress in both areas and underline their strength, current problems, and future perspectives. Full article