In machine olfaction, the response pattern of multiple sensors with different characteristics is recognized. In this paper, various types of sensors for machine olfaction and pattern recognition methods are explained. Then, sensing methods robust against disturbances of, for example, the concentration, temperature and humidity are described. Those robust sensing systems include the relative measurement method and frequency analysis method. Moreover, we show a higher-order sensing and an elimination method of humidity influence using a pre-concentrator with a variable temperature as well as a pre-concentrator device using a surface acoustic wave device, which improves the robustness and performance of machine olfaction.

TG-protein coupled receptors (GPCRs) are known to possess two different conformations, active and inactive, and spontaneously alternate between the two in the absence of ligands. Here, we analyzed the agonist-independent GPCR activity for its possible role in receptor-instructed axonal projection. We generated transgenic mice expressing activity mutants of the β2-adrenergic receptor. We found that mutants with altered agonist-independent activity changed the transcription levels of axon targeting molecules, thus, causing shifts in target sites of olfactory sensory neurons. We conclude that the equilibrium of conformational transitions set by each odorant receptor is the major determinant of expression levels of axon targeting molecules.

Some parts of metabolic chemicals in the body are exhaled into the breath. The exhaled breath may express metabolic conditions. In an earlier age, a doctor's nose diagnosed several human diseases. Cancer screening tests have been developed using odor material with canine scent detection. This news strongly suggested that breath diagnosis is not a dream. The collaboration of analytical engineers and clinicians for breath research will realize breath diagnoses in the near future.

Novel biochemical gas sensors “Bio-sniffers” with metabolizing enzymes have been developed for monitoring odorous chemicals (i.e. trimethylamine, methyl mercaptan, etc.). Their combination with an optical technique made it possible to convert odorous chemical-information into optical-information. A highly sensitive fluorometric sniffer for formaldehyde vapor was also demonstrated by means of a UV-LED and a photomultiplier tube. In addition, a spatiotemporal gas visualization system was developed with an electron multiplying CCD camera, which detects biochemical luminescence at the enzyme immobilized mesh, thereby providing two-dimensional images of ethanol vapor (i.e. exhaled breath after drinking, etc.).

Existing odorant sensors are mainly fabricated based on metal-oxide semiconductor devices or quartz crystal microbalances. These sensors have been used for practical odorant-detection applications, because of their long-term stability and physicochemical principles. However, the performance of these sensors is still inferior to that of the olfactory systems of living organisms in terms of selectivity, sensitivity, and response time. Living organisms, especially insects, are equipped with sophisticated molecular mechanisms, starting with odorant receptors, which enable sensitive real-time detection of various types of odorants present in the environment.

Therefore, focusing on the olfactory mechanisms of insects, we have developed two odorant sensor elements based on cultured cell lines and transgenic silkmoths, in other words, insect odorant receptor genes are inserted into their genome with genetic engineering techniques. One sensor element using an insect cultured cell line, the Sf21 cell line, is able to sensitively detect odorants by increasing its fluorescent intensity over at least 2 months. The other sensor element using the transgenic silkmoth, Bombyx mori, not only has sensitive odorant detection but also odor source orientation. These results show that our proposed sensor elements can be applied to detect various kinds of odorants with high sensitivity and selectivity, and provide an innovative platform to develop odorant sensors with high performance.

In olfaction, the repertoire of receptors that detect sensory stimuli as sensors, is more than 100-fold higher than in color vision. The large variation in olfactory receptors may be attributable to both the structural variation of odorants and the difficulty in odorant discrimination based on a specific binding of a given odorant to its most sensitive receptor, due to the intermolecular interaction between the odorant and the receptor being weaker than that of neurotransmitters. Signal summation among multiple receptors may be required to extract the elemental information characteristic of a given stimulus, because a concentration range where only a single type of receptor detects the odorant is usually very narrow. In the olfactory neural pathway, there should be a hierarchical information processing system to automatically enhance characteristic signals from the most sensitive and specific receptors for odor representation with signals from greatly overlapping receptors. We introduce our recent research regarding the receptor codes for odors.

The flavor and fragrance analyzer (FFAh) developed by the author is explained. Electronic noses are important because they do not have to separate the odors from the chemical elements. Therefore, the masking or pairing effects between odors will be able to be analyzed in the future by FFAs because these effects are considered interaction effects between odor chemicals. The FFA has already achieved the expression of an odor with an odor strength as an odor index and odor character by its similarity to reference odors. The odor character is depicted by using multiple discrimination thresholds from a reference odor. The author also recommends the use of this easy sensory test apparatus that uses a dilution and mixing device by which detection thresholds and discrimination thresholds can be easily obtained by following the directions for the apparatus with a nose within a short period of time.

Smart anti-cancer nanofiber meshes with dynamically and reversibly tunable properties demonstrate the ability to generate heat and release anti-cancer drugs in response to a simple on and off switching of an alternating magnetic field. This smart nanofiber mesh effectively induced the apoptosis of cancer cells by a synergistic effect of the anti-cancer drug and hyperthermia.

The advancement of laser technology allows us to use various different optical phenomena for material analysis. This benefit of the laser has also expanded the application of laser microscopy to various research fields. Not only observing the shape of the sample, laser microscopy can visualize the interiors of the sample noninvasively and also analyze the sample material with a combination of a spectroscopic techniques. In this article, I introduce the principles of laser microscopy, the imaging properties and the applications.