Mouthguard-Type Wearable Sensor for Monitoring Salivary Turbidity to Assess Oral Hygiene.

Salivary turbidity is a promising indicator for evaluating oral hygiene. This study proposed a wearable mouthguard-type sensor for continuous and unconstrained measurement of salivary turbidity. The sensor evaluated turbidity by measuring the light transmittance of saliva with an LED and a phototransistor sealed inside a double-layered mouthguard. The sensor was also embedded with a Bluetooth wireless module, enabling the wireless measurement of turbidity. The mouthguard materials (polyethylene terephthalate-glycol and ethylene-vinyl acetate) and the wavelength of the LED (405 nm) were experimentally determined to achieve high sensitivity in salivary turbidity measurement. The turbidity quantification characteristic of the proposed sensor was evaluated using a turbidity standard solution, and the sensor was capable of turbidity quantification over a wide dynamic range of 1-4000 FTU (formazine turbidity unit), including reported salivary turbidity (400-800 FTU). In vitro turbidity measurement using a saliva sample showed 553 FTU, which is equivalent to the same sample measured with a spectrophotometer (576 FTU). Moreover, in vivo experiments also showed results equivalent to that measured with a spectrophotometer, and wireless measurement of salivary turbidity was realized using the mouthguard-type sensor. Based on these results, the proposed mouthguard-type sensor has promising potential for the unconstrained continuous evaluation of oral hygiene.

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.

Real-Time Continuous Monitoring of Oral Soft Tissue Pressure with a Wireless Mouthguard Device for Assessing Tongue Thrusting Habits.

In orthodontics, understanding the pressure of oral soft tissues on teeth is important to elucidate the cause and establish treatment methods. We developed a small wireless mouthguard (MG)-type device that continuously and unrestrainedly measures pressure, which had previously been unachieved, and evaluated its feasibility in human subjects. First, the optimal device components were considered. Next, the devices were compared with wired-type systems. Subsequently, the devices were fabricated for human testing to measure tongue pressure during swallowing. The highest sensitivity (51-510 g/cm2) with minimum error (CV < 5%) was obtained using an MG device with polyethylene terephthalate glycol and ethylene vinyl acetate for the lower and upper layers, respectively, and with a 4 mm PMMA plate. A high correlation coefficient (0.969) was observed between the wired and wireless devices. In the measurements of tongue pressure on teeth during swallowing, 132.14 ± 21.37 g/cm2 for normal and 201.17 ± 38.12 g/cm2 for simulated tongue thrust were found to be significantly different using a t-test (n = 50, p = 6.2 × 10-19), which is consistent with the results of a previous study. This device can contribute to assessing tongue thrusting habits. In the future, this device is expected to measure changes in the pressure exerted on teeth during daily life.

Long-range surface plasmon aptasensor for label-free monitoring of vancomycin.

Vancomycin (VCM) causes poisoning symptoms at high concentrations; thus, therapeutic drug monitoring is recommended to measure and control blood levels regularly. However, blood analysis at regular intervals does not allow knowing the detailed temporal change in concentration. To address this challenge, we developed a long-range surface plasmon (LRSP) aptasensor for measuring VCM label-free and real-time by combining a sensitive LRSP sensor and a peptide aptamer with a VCM recognition site. First, three different biosensors for VCM were compared. One was prepared by immobilizing the peptide aptamer directly on (Direct-Apt) or via a self-assembled monolayer (SAM) on a gold surface (SAM-Apt). The other used anti-VCM antibodies immobilized on a gold surface via the SAM (SAM-Ab). The Direct-Apt showed larger sensor output to VCM than the other biosensors. The dynamic range for VCM was 0.78-100 µM, including the therapeutic range (6.9-13.8 µM). The Direct-Apt also showed the sensor output only from VCM among four different antibiotics, demonstrating the high selectivity for VCM. The VCM captured by the aptamer could be removed by rinsing with phosphate-buffered saline. The measurement was rapid, with 72- and 77-sec response and recovery times, allowing not only repeated but also real-time measurements. Finally, the Direct-Apt in 20% serum solutions showed comparable sensitivity to VCM in the buffer solution, indicating high capability for real-sample.

Blood sorbitol measurement in diabetic rats treated with an aldose reductase inhibitor using an improved fiber-optic sorbitol biosensor.

Sorbitol is known as a biomarker for the evaluation of the progress of diabetic complications. We have developed a sorbitol biosensor using an optical fiber for rapid diagnosis and pathological evaluation of diabetic complications. In this paper, we measured blood sorbitol in diabetic rats using an improved biosensor, and discussed the effectiveness of the developed biosensor and the significance of sorbitol measurement. In order to investigate the effectiveness of the developed biosensor, the blood sorbitol level of type II diabetic rats prepared by streptozotocin administration was measured with the developed sensor. The values of sorbitol were highly correlated with the values measured by the F-kit of food analysis and that we confirmed the sorbitol concentration could be quantified using the developed biosensor. Furthermore, the aldose reductase inhibitor "eparlrestat", which is a therapeutic drug that suppresses the accumulation of sorbitol, was administered to diabetic rats, and the blood sorbitol level was measured with the developed biosensor. As a result, the blood glucose level was high in both the treated group and the non-treated group, but the blood sorbitol level in the treated group decreased. The results suggest that the measurement of the sorbitol level with the developed biosensor in addition to the blood glucose level enables evaluation of complications like diabetic neuropathy. In the future, we expected that the developed sorbitol biosensor will be miniaturized, the pretreatment method for blood samples will be simplified, and it will be applied to the development of therapeutic agents for diabetic complications and personalized medicine.

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.

Biochemical Methanol Gas Sensor (MeOH Bio-Sniffer) for Non-Invasive Assessment of Intestinal Flora from Breath Methanol.

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 ß-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.

External ears for non-invasive and stable monitoring of volatile organic compounds in human blood.

Volatile organic compounds (VOCs) released through skin (transcutaneous gas) has been increasing in importance for the continuous and real-time assessment of diseases or metabolisms. For stable monitoring of transcutaneous gas, finding a body part with little interference on the measurement is essential. In this study, we have investigated the possibility of external ears for stable and real-time measurement of ethanol vapour by developing a monitoring system that consisted with an over-ear gas collection cell and a biochemical gas sensor (bio-sniffer). The high sensitivity with the broad dynamic range (26 ppb-554 ppm), the high selectivity to ethanol, and the capability of the continuous measurement of the monitoring system uncovered three important characteristics of external ear-derived ethanol with alcohol intake for the first time: there is little interference from sweat glands to a sensor signal at the external ear; similar temporal change in ethanol concentration to that of breath with delayed peak time (avg. 13 min); relatively high concentration of ethanol relative to other parts of a body (external ear-derived ethanol:breath ethanol = 1:590). These features indicated the suitability of external ears for non-invasive monitoring of blood VOCs.

Sensitive and selective methanol biosensor using two-enzyme cascade reaction and fluorometry for non-invasive assessment of intestinal bacteria activity.

For understanding the status of intestinal flora non-invasively, methanol (MeOH) has been attracting the attention. In this study, we have developed and compared two different liquid-phase methanol biosensors. One, referred to as the AOD electrosensor, utilized alcohol oxidase (AOD) and an oxygen electrode. It electrochemically measured the decrease in oxygen through AOD-catalyzed oxidation of MeOH. The other, referred to as the AOD-FALDH fluorosensor, exploited a cascade reaction of AOD and formaldehyde dehydrogenase (FALDH) in conjunction with a fiber-optic sensor. It measured increase in the fluorescence from reduced form of ß-nicotinamide adenine dinucleotide (NADH) that was a final product of the two-enzyme cascade reaction. Due to the cascade reaction, the AOD-FALDH fluorosensor showed 3 times better sensitivity along with 335 times wider dynamic range (494 nM-100 mM) than those of the AOD electrosensor (1.5-300 µM). The selectivity to MeOH was also improved by the cascade reaction with AOD-FALDH as no sensor output was observed from other aliphatic alcohols than MeOH in contrast to the AOD electrosensor. Although the use of FALDH resulted in the increase in the sensor output from aldehydes, such as acetaldehyde and formaldehyde, considering their concentrations in body fluids, the influence on the sensor output is limited. These results indicate that incorporating the cascade reaction into fluorometry enables enhanced biosensing of MeOH that will be useful for assessment of intestinal flora with little burden.

Ultra-Sensitive Isopropanol Biochemical Gas Sensor (Bio-Sniffer) for Monitoring of Human Volatiles.

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.

Skin ethanol gas measurement system with a biochemical gas sensor and gas concentrator toward monitoring of blood volatile compounds.

We developed a biochemical gas sensor (bio-sniffer) using the enzymatic reaction of alcohol dehydrogenase (ADH) to target ethanol in skin gas. By introducing a gas concentrator using liquid nitrogen, we constructed a highly sensitive system for skin gas measurements. The ethanol bio-sniffer was built from an optical-fiber probe employing an ADH enzyme membrane, an UV-LED light source for excitation, and a photomultiplier tube. Ethanol was measured by detecting the autofluorescence of the coenzyme NADH due to the enzymatic reaction of ADH. We established a system for measuring concentrated gases by connecting the sensor with a gas concentrator and introducing concentrated skin gas to the sensing surface. This suppressed diffusion of the concentrated gases to achieve maximum fluorescence intensity by optimizing the measurement system. The calibration curve from obtained peak values showed ethanol gas can be measured over 1-3100 ppb, which included skin gas concentrations during alcohol consumption. Finally, when applied to measurements of ethanol in skin gas following alcohol consumption, the output was found to be dependent on concentration, similarly to using standard gases. Consecutive measurements were possible using periodic sampling with 6-min intervals for 180 min of monitoring. Skin ethanol concentrations rose from 20 min after consuming the alcohol, exhibited a peak value of 25 ppb skin gas ethanol at around 60 min, and gradually declined. Thus, the system can be used for non-invasive percutaneous evaluation of human volatile organic chemicals in blood.

A Wearable Cellulose Acetate-Coated Mouthguard Biosensor for In Vivo Salivary Glucose Measurement.

In this study, a cellulose acetate (CA) membrane is formed as an interference rejection membrane on a glucose sensor to measure glucose in saliva. Glucose in saliva is successfully measured in vivo without any pretreatment of human saliva. A mouthguard (MG) glucose sensor is developed to monitor salivary glucose, which is reported to be correlated with the blood glucose level. Salivary components of ascorbic acid (AA) and uric acid (UA) hinder the accurate measurement of the glucose concentration of human saliva. CA-coated electrodes are prepared to investigate the interference rejection membrane. To measure hydrogen peroxide, which is a reaction product of glucose oxidase, effects of AA and UA are examined. Characteristics of the fabricated biosensor are examined on the basis of artificial saliva. The as-developed MG sensor can quantify the glucose concentration in the range of 1.75-10 000 µmol/L, which includes a salivary sugar concentration of 20-200 µmol/L. For the measurement of saliva samples collected from healthy subjects, the output corresponding to the concentration is confirmed; this suggests the possibility of glucose measurement. This MG glucose sensor can provide a useful method for the unrestricted and noninvasive monitoring of saliva glucose for the management of diabetes patients.

Evaluation for regional difference of skin-gas ethanol and sweat rate using alcohol dehydrogenase-mediated fluorometric gas-imaging system (sniff-cam).

Skin gas that contains volatile metabolites (volatilome) is emanated continuously and is thus expected to be suitable for non-invasive monitoring. The aim of this study was to investigate the relationship between the regional difference of sweat rate and skin volatilome distribution to identify the suitable site to monitor metabolisms. In this study, we developed a biofluorometric gas-imaging system (sniff-cam) based on nicotinamide adenine dinucleotide (NAD)-dependent alcohol dehydrogenase (ADH) to visualize transcutaneous ethanol (EtOH) distribution. The EtOH distribution was converted to a fluorescence distribution of reduced NAD with autofluorescence property. First, we optimized the solution volume and concentration of the oxidized NAD, which was a coenzyme of ADH. Owing to the optimization, a two-dimensional distribution of EtOH could be visualized from 0.05-10 ppm with good sensitivity and selectivity. Subsequently, transcutaneous EtOH imaging and measurement of sweat rate were performed at the palm, dorsum of hand, and wrist of participants who consumed alcohol. Transcutaneous EtOH from all skin parts was imaged using the sniff-cam; the concentrations initially increased until 30 min after drinking, followed by a gradual decrease. Although the determined peak EtOH concentrations of typical subjects were approximately 1100 ± 35 ppb (palm), which were higher than 720 ± 18 ppb (dorsum) and 620 ± 13 ppb (wrist), the results of sweat rate suggested that the dorsum of hand and the wrist were appropriate sites. Finally, the sniff-cam could visualize the individual difference of alcohol metabolism capacity originating from aldehyde dehydrogenase phenotype by imaging transcutaneous EtOH.

Convenience biosensing approach of lactic acid in stratum corneum for skin care assessment.

BACKGROUND: Lactic acid in the stratum corneum contributes to skin flexibility, making it a useful indicator of skin conditions. It is this useful to devise a simple technique to measure the lactic acid in the stratum corneum. To this aim, a printed chip biosensor was developed to analyze lactic acid in tape stripped (TS) stratum corneum samples. MATERIALS AND METHODS: Lactic acid was extracted from TS stratum corneum samples. A normal lactic acid sensor was prepared by applying lactate oxidase (LOD) to a printed chip. Another lactic acid sensor was prepared using LOD and a mediator osmium polymer immobilized on a printed chip. The amount of lactic acid in the extracted solutions was quantified using either the prepared biosensors or an existing analysis method. RESULTS: The results measured using the normal lactic acid sensor show low correlation with the results measured using an existing analytical method as a comparison, but those of the mediator osmium lactic acid sensor show high correlation. CONCLUSIONS: The amount of lactic acid in samples extracted from the stratum corneum using a simple TS technique can be simply analyzed with high accuracy using a printed chip biosensor.

Transcutaneous Blood VOC Imaging System (Skin-Gas Cam) with Real-Time Bio-Fluorometric Device on Rounded Skin Surface.

A skin-gas cam that allows continuous imaging of transcutaneous blood volatile organic compounds (VOCs) emanated from human skin was developed. The skin-gas cam is able to reveal the relationship between the local skin conditions and transcutaneous blood VOCs in the field of volatile metabolomics (volatolomics). A ring-type ultraviolet (UV) light-emitting diode was mounted around a camera lens as an excitation light source, which enabled the simultaneous excitation and imaging of fluorescence. A nicotinamide adenine dinucleotide (NAD)-dependent alcohol dehydrogenase (ADH) was used to detect ethanol as a model sample. When gaseous ethanol was applied to an ADH-immobilized mesh that was wetted with an oxidized NAD solution placed in front of the camera, a reduced form of NAD (NADH) was produced through an ADH-mediated reaction. NADH emits fluorescence by UV excitation, and thus, the concentration distribution of ethanol was visualized by measuring the distribution of the fluorescence light intensity from NADH on the ADH-immobilized mesh surface. In this study, a new gas application method that mimicked the release mechanism of transcutaneous gas for quantification of the transcutaneous gas concentration was evaluated. Also, spatiotemporal changes of transcutaneous ethanol for various body parts were measured. As a result, we revealed a relationship between local skin conditions and VOCs that could not be observed previously. In particular, we demonstrated the facile measurement of transdermal gases from around the ear where capillaries are densely distributed below a thin stratum corneum.

Ultrasensitive Sniff-Cam for Biofluorometric-Imaging of Breath Ethanol Caused by Metabolism of Intestinal Flora.

We developed a gas-imaging system (sniff-cam) for gaseous ethanol (EtOH) with improved sensitivity. The sniff-cam was applied to measure the extremely low concentration distribution of breath EtOH without the consumption of alcohol, which is related to the activity of the oral or gut bacterial flora. A ring-type ultraviolet-light-emitting diode was mounted around a camera lens as an excitation light source, which enabled simultaneous excitation and imaging of the fluorescence. In the EtOH sniff-cam, a nicotinamide adenine dinucleotide (NAD)-dependent alcohol dehydrogenase (ADH) was used to catalyze the redox reaction between EtOH and the oxidized form of NAD (NAD+). Upon application of gaseous EtOH to the ADH-immobilized mesh that was soaked in an NAD+ solution and placed in front of the camera, NADH was produced through an ADH-mediated reaction. NADH expresses fluorescence at an emission wavelength of 490 nm and excitation wavelength of 340 nm. Thus, the concentration distribution of EtOH was visualized by measuring the distribution of the fluorescence light intensity from NADH on the ADH-immobilized mesh surface. First, a comparison of image analysis methods based on the red-green-blue color (RGB) images and the optimization of the buffer pH and NAD+ solution concentration was performed. The new sniff-cam showed a 25-fold greater sensitivity and broader dynamic range (20.6-300000 ppb) in comparison to those of the previously fabricated sniff-cam. Finally, we measured the concentration distribution of breath EtOH without alcohol consumption using the improved sniff-cam and obtained a value of 116.2 ± 35.7 ppb (n = 10).

Repeated immunosensing by a dithiobis(succinimidyl propionate)-modified SAW device.

The possibility of dithiobis(succinimidyl propionate) (DSP) for repeated immunoassay with a surface acoustic wave (SAW) immunosensor was explored. In the sensor, DSP was used to modify a gold-coated quartz sensing area of a SAW device by forming a self-assembled monolayer on the gold surface. In a model sandwich assay using mouse (mIgG) and anti-mouse (a-mIgG) antibodies, the primary antibody, mIgG, firstly reacted with N-hydroxysuccinimide ester groups of DSP and was immobilized on the SAW device to fabricate the SAW immunosensor. Optimization of adsorption time of mIgG revealed that both degrees of adsorption and immobilization of mIgG reached a saturation at 30 min although the immobilization was more dependent on the adsorption time. Through characterization of the DSP-modified SAW immunosensor, a high selectivity, with which no sensor output was observed from various kinds of secondary antibodies except for a-mIgG, along with 8-fold shorter measurement time (15 min) than that of enzyme-linked immunosorbent assay were obtained. Furthermore, 10 repeated measurement of a-mIgG demonstrated a high reproducibility of the sensor output (coefficient of variation of 7.0%). These validate the utility of DSP in the SAW immunosensor for rapid and repeated measurement of antigens.

Switchable sniff-cam (gas-imaging system) based on redox reactions of alcohol dehydrogenase for ethanol and acetaldehyde in exhaled breath.

Measuring the volatile organic compounds (VOCs) released from a human is a promising method for noninvasive disease screening and metabolism assessment. Selectively imaging multiple VOCs derived from human breath and skin gas is expected to improve current gas analysis techniques. In this study, a gas-imaging system (sniff-cam) that can be used to simultaneously image the concentration distribution of multiple VOCs, namely, ethanol (EtOH) and acetaldehyde (AcH), was developed. The sniff-cam was based on the pH-dependent redox reactions of nicotinamide adenine dinucleotide (NAD)-dependent alcohol dehydrogenase (ADH). The sniff-cam was constructed with a camera, two ADH-immobilized meshes, and a UV-LED array sheet. The ADH-immobilized mesh containing a solution of the oxidized form of NAD (NAD+) or reduced form (NADH) was used as an EtOH-imaging mesh and an AcH-imaging mesh, respectively. The distributions of the EtOH and AcH concentrations were visualized through the fluorescence of NADH (the excitation wavelength was 340 nm; the emission wavelength was 490 nm) occurring by the ADH-mediated redox reaction. First, the influence of pH on the activity of the redox reaction of ADH was measured, and then the quantitativeness and selectivity of the sniff-cam were evaluated. The ADH-mediated reactions of EtOH and AcH showed maximum activities at pH 9.0 and pH 6.5, respectively. The sniff-cam demonstrated not only a dynamic range (0.1-1000 ppm for EtOH and 0.2-10 ppm for AcH) for measuring EtOH and AcH in breath after drinking alcohol, but also displayed a high selectivity against other breath VOCs. Finally, EtOH and AcH in breath after drinking alcohol were measured simultaneously. A group with high activity of aldehyde dehydrogenase type 2 (EtOH = 143.3 ±â€¯13.5 ppm, AcH = 1.7 ±â€¯0.2 ppm) and a group with low activity (EtOH = 163.3 ±â€¯28.0 ppm, AcH = 8.4 ±â€¯0.5 ppm) displayed differences in the concentrations of EtOH and AcH contained in their breath samples, and the effectiveness of the developed method was confirmed and compared with previous results. It is suggested that the multiplexed sniff-cam in the future may be capable of selectively and simultaneously imaging various VOCs in human breath and skin gas by using multiple NADH-dependent enzymes.

Optical and Electrochemical Sensors and Biosensors for the Detection of Quinolones.

One major concern associated with food safety is related to residual effects of antibiotics that are widely used to treat animals and result in antimicrobial resistance. Among different groups of antibiotic, the use of quinolones in livestock is of major concern due to the significance of these antimicrobial drugs for the treatment of a range of infectious diseases in humans. Therefore, it is desirable to develop reliable methods for the rapid, sensitive, and on-site detection of quinolone residue levels in animal-derived foods to ensure food safety. Sensors and biosensors are promising future platforms for rapid and on-site monitoring of antibiotic residues. In this review, we focus on recent advancements and modern approaches in quinolone sensors and biosensors.