A cascade reaction catalysed by bovine carbonic anhydrase (BCA) and horseradish peroxidase (HRP) proceeds over two possible pathways, which explains differences in product formation for differently immobilised enzymes in flow-through reactions.

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In order to detect phytoncide or aroma in a natural environment using an odor sensor of quartz crystal resonator (QCR), the authors investigated the most suitable drying agent to eliminate moisture influences. The odor sensor used is a system of QCRs coated with organic sensory films. It was experimentally found that calcium chloride is the most suitable desiccant for odor sensing to eliminate moisture influences and for use in the natural environment. We then measured 6 kinds of roses; Love (red), Star light (yellow), White Christmas (white), Snow white (white), Catherine Deneuve (pinky orange), and First love (pink), to detect the aroma of these naturally cultivated roses in an outside garden. We have successfully detected the aroma of roses by eliminating moisture influences on the odor sensor by using a calcium chloride desiccant tube. It was found that White Christmas, Star light, and Catherine Deneuve indicate a similar pattern and Snow white, First love, and Love indicate another similar pattern. It was concluded that the odor similarity is not corresponding to the color of roses.

Abstract:There is an interest in sensors for the detection of odorant molecules in the gaseous phase, especially those related to the fragrance of fruits, because odorant sensing is useful for on-site quality control of agricultural products. Previously, gas-chromatographic methods requiring bench-top devices were used for odorant-molecule detection. Herein, we report an odorant sensor based on cyclodextrins (CDs) as a stable odorant receptor, using a highly mass-sensitive and quantitative 27-MHz quartz crystal microbalance (QCM) device, which has the advantage of possible incorporation into portable devices. When ethyl butyrate (a model odorant molecule for fruit fragrances) was flowed onto a QCM plate modified with α-, β-, or γ-CD network films, a decrease in frequency was observed (corresponding to an increase in mass), owing to the capture of odorant molecules by CD molecules. The CD films were capable of capturing and releasing odorant molecules, depending on the type of CD (α-, β-, or γ-CD). Thus, these sensors are reusable for odorant-molecule sensing, and are applicable to pattern recognition of odorant molecules. Thus, sensors based on CD films combined with a QCM handheld device could be applied to monitoring the condition of fruits.

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Quartz-crystal microbalance (QCM) is a technique that can measure nanogram-order masses. When a receptor is immobilized on the sensor surface of a QCM device, the device can detect chemical molecules captured by the mass change. Although QCM devices have been applied to biosensors that detect biomolecules without labels for biomolecular interaction analysis, most highly sensitive QCM devices are benchtop devices. We considered the fabrication of an IC card-sized QCM device that is both portable and battery-powered. Its miniaturization was achieved by repurposing electronic components and film batteries from smartphones and wearable devices. To demonstrate the applicability of the card-sized QCM device as a biosensor, DNA-detection experiments were performed. The card-sized QCM device could detect specific 10-mer DNA chains while discerning single-base differences with a sensitivity similar to that of a conventional benchtop device. The card-sized QCM device can be used in laboratories and in various other fields as a mass sensor.

The application of a multienzyme cascade reaction in electrochemical biosensors has the advantage of expanding the target substrates in addition to selectivity combining multiple enzymes on an electrode. However, the multienzyme system has the drawback of inefficient substance conversion because of the time-consuming passing of intermediates between the enzymes and/or diffusional loss of the intermediates. In this study, the optimal construction of a multienzymatic film in an ammonia detection sensor was investigated using a cascade reaction of l -glutamate oxidase and l -glutamate dehydrogenase as a model sensor. Three enzymatic films were prepared: (1) a mixed film designed to have a short diffusional distance between closely located enzymes, (2) a normal-sequential layered film arranged for the correct reaction pathway, and (3) a reverse-sequential layered film as a negative control. This was followed by comparison of the conversion efficiency of ammonia to hydrogen peroxide using time-dependent potentiometric measurements of a Prussian blue electrode determining the hydrogen peroxide amount. The results indicate that the conversion efficiency of the normal-sequential layered film was the highest among the three enzymatic films. The quantitative evaluation of the intermediate conversion efficiency of the cascade reaction showed that compared to the mixed film (34%), a higher conversion efficiency of 92% was obtained in the first enzymatic reaction step. These findings will promote the use of multienzymatic cascade reaction systems not only in biosensors and bioreactors but also in various industrial fields.