Method and apparatus for monitoring a sample

Abstract: [Object] The present invention has an object of providing a method and apparatus for monitoring a gas or fine particles by means of a living plant. [Constitution] In the method of the present invention for monitoring a gas or fine particles, a carbon dioxide gas is first supplied to a living plant while it is illuminated with excitation light, and fluorescence emitted from the plant is detected; then, a mixture of a carbon dioxide and a gas or fine particles to be monitored is supplied to the living plant while it is illuminated with the excitation light, and fluorescence emitted from the plant is detected, in the same manner as in the above step; and finally, the fluorescence emitted upon illumination with the excitation light during application of the carbon dioxide is detected and compared with the fluorescence emitted upon illumination with the excitation light during application of the mixture of the carbon dioxide and the gas of a small quantity or fine particles. Since the intensity or wavelength of the fluorescence emitted in the above two cases differs with the amount or kind of gas or fine particles, the results of above comparison can be used to monitor the gas or fine particles.

Description: Various techniques have been proposed in which a living organism such as a living plant is used to detect an odour or the like that is present as a small quantity in the form of a gas, a vapour, an aerosol or fine particles that will be referred to subsequently as a sample. A first technique known today is the construction of a high-sensitivity odour sensor using a liposome which is an artificial biomembrane. An example of this technique is described in the issue dated May 11, 1989 of Nikkei Sangyo Shinbun. A second approach is the detection of an odour gas by recording a change in the cell potential of a leaf of a plant when a mixture of an odour gas and a carbon dioxide gas is applied to the plant. An example of this approach is described in "Koryo (Perfumes)", No. 158, June 1988. The prior art techniques described above have suffered from the disadvantage of requiring complicated procedures. For example, the second approach cannot be implemented without connecting electrodes to a leaf of a living plant. According to a first aspect of this invention a method of sample monitoring comprises the steps of: supplying carbon dioxide gas to a living plant while illuminating it with excitation light, and detecting a first fluorescence emitted from the plant; supplying a mixture of carbon dioxide gas and the sample to be monitored to the plant while illuminating it with excitation light, and detecting a second fluorescence emitted from the plant; and, comparing results of the detection of the first and second fluorescence to monitor the sample. According to a second aspect of this invention an apparatus for monitoring a sample, comprises: means for illuminating a living plant with excitation light; means for selectively supplying the plant with a carbon dioxide gas or a mixture of a carbon dioxide gas and the sample to be monitored; and, means for detecting a first fluorescence emitted from the plant upon illumination while the plant is supplied with the carbon dioxide gas, and for detecting a second fluorescence emitted from the plant upon illumination while the plant is supplied with the mixture of the carbon dioxide gas and the sample, a difference between results of the detection of the first and second fluorescence being used to monitor the sample. The present invention provides a method and apparatus that can identify a sample such as an odour or the like that is present only in a very small quantity in an easy and reliable manner with high precision. An embodiment of a method and apparatus in accordance with this invention will now be described with reference to the accompanying drawings; in which:- Fig. 1 is a schematic diagram showing the construction of an odour-monitoring system according to an embodiment of the present invention; Fig. 2(a) is a graph showing an example of temporal intensity variations of fluorescence emitted from a leaf in response to illumination with excitation light; and, Fig. 2(b) is a graph showing an example of wavelength characteristics of the intensity of fluorescence emitted from the leaf in response to illumination with the excitation light. Fig. 1 shows the construction of a monitor system according to an embodiment. As shown, a leaf 1 of a living plant is fixed in position by means of tapes 2. A pure carbon dioxide gas in a container 3 is supplied to the leaf 1 via a pipe 41, a three-way valve 51, a pipe 42, a three-way valve 52 and a pipe 43. Other pipes 44 and 45 are connected to the three-way valves 51 and 52, respectively, and a container 62 of a sample of an odour substance 61 to be identified is provided between these pipes 44 and 45. By controlling the three-way valves 51 and 52, the leaf 1 can selectively be supplied with either a pure carbon dioxide gas or a mixture of a carbon dioxide gas and an odour gas in a desired manner. A light source 7, e.g., a semiconductor laser, is provided for illuminating the leaf 1 with excitation light, and resulting fluorescence is received by a photodiode 81. The output of the photodiode 81 is recorded by a recorder 82. A monitoring procedure of the system described above is described next. First, while the leaf 1 is illuminated with the excitation light from the light source 7 and resulting fluorescence is detected by the photodiode 81, a pure carbon dioxide gas is supplied to the leaf 1 from the container 3 via the pipes 41, 42 and 43. A temporal change in the fluorescence intensity and its wavelength characteristic are measured. After a certain period has passed and generation of the fluorescence has returned to the initial state where there was no supply of a carbon dioxide gas, the three-way valves 51 and 52 are switched so that the odour gas in the container 62 is mixed, by a very small quantity, into the carbon dioxide gas being supplied from the container 3. Again, a temporal change in the intensity of resulting fluorescence and its wavelength characteristic are measured. After passage of a given period, the measurement is stopped, and the both measurement results are compared with each other. Fig. 2(a) shows an example of results of comparison as regards the temporal change in the fluorescence intensity. The solid-line curve represents the case where the pure carbon dioxide gas was supplied, and the dashed-line curve denotes the case of supplying the mixture of the carbon dioxide gas and the odour gas of a very small quantity. In either case, the fluorescence intensity decreases sharply immediately after the supply of a gas, thereafter increases rapidly, and then exhibits a gradual decrease. This intensity variation depends upon whether the odour gas is present or not, and also depends on the amount and kind of odour gas. Further, since the deviation from the case of supplying the pure carbon dioxide gas in the intensity variation curve appears even in the case of supplying a gas of an extremely small quantity (on the ppb order), it is possible to construct a high-sensitivity gas monitor. Fig. 2(b) shows an example of results of comparison as regards the wavelength dependency of the fluorescence intensity. The solid-line curve represents the case where air was supplied, and the dashed-line curve denotes the case of supplying a carbon dioxide gas. As shown, the presence of the carbon dioxide gas contributes to a significant increase in fluorescence intensity in the wavelength range of less than about 500 nm. In the range of 530-560 nm, the fluorescence intensity is higher in the case of supplying air. Again, since such wavelength dependency of the fluorescence intensity varies with the amount and kind of odour gas or fine particles, it is possible to construct a high-sensitivity gas monitor. The present invention enables the detection of a gas of an extremely small quantity and, hence, it can be used for the purpose of identifying gases and fine particles that are deleterious to humans, animals or plants. The invention also enables a subject to check the state of his internal organs and other parts by merely breathing out onto a leaf of a monitor plant. The invention also finds utility in checking whether a plant suffers from a disease or insect pests. As described in the foregoing, in accordance with the present invention, the florescence emitted from a living plant upon illumination with the excitation light while it is supplied with a carbon dioxide gas is detected and compared with the fluorescence emitted from the same living plant upon illumination with the excitation light while it is supplied with a mixture of a carbon dioxide gas and a gas of a very small quantity or fine particles to be monitored. The temporal variation and wavelength characteristic of the fluorescence intensity not only depend on the amount or kind of gas or fine particles to be monitored, but is also responsive to even a gas or fine particles of an extremely small amount. Therefore, results of a comparison between the two cases can be used to monitor the gas or fine particles with high sensitivity, whereby an odour or the like that is present in the form of a gas of a very small quantity or fine particles can be identified in an easy and reliable manner with high precision.

Claims: A method of sample monitoring comprising the steps of: supplying carbon dioxide gas to a living plant while illuminating it with excitation light, and detecting a first fluorescence emitted from the plant; supplying a mixture of carbon dioxide gas and the sample to be monitored to the plant while illuminating it with excitation light, and detecting a second fluorescence emitted from the plant; and, comparing results of the detection of the first and second fluorescence to monitor the sample. A method according to claim 1, wherein the detection results are temporal variations of fluorescence intensities. A method according to claim 1, wherein the detection results are wavelength characteristics of the fluorescence. A method according to any one of the preceding claims, wherein the results of the detection are compared to monitor the identity of the sample. A method according to any one of the preceding claims, wherein the results of the detection are compared to monitor the sample quantitatively. A method according to any one of the preceding claims, wherein a leaf of the plant is illuminated with the excitation light and fluorescence from the leaf is detected. An apparatus for monitoring a sample, comprising: means (7) for illuminating a living plant (1) with excitation light; means (3,41-45,51,52,61,62) for selectively supplying the plant (1) with a carbon dioxide gas or a mixture of a carbon dioxide gas and the sample to be monitored; and, means (81) for detecting a first fluorescence emitted from the plant (1) upon illumination while the plant (1) is supplied with the carbon dioxide gas, and for detecting a second fluorescence emitted from the plant (1) upon illumination while the plant (1) is supplied with the mixture of the carbon dioxide gas and the sample, a difference between results of the detection of the first and second fluorescence being used to monitor the sample. An apparatus according to claim 7, further comprising means (82) for recording the detection results. An apparatus according to claim 7 or 8, wherein the means for detecting (81) detects temporal variations of fluorescence intensities or the wavelength characteristics of the fluorescence. An apparatus according to any one of claims 6 to 9, which also includes a plant (1) arranged so that the illuminating means (7) illuminates a leaf of the plant (1) and so that the detecting means (81) detects fluorescence from the plant (1) leaf.

Inventors: ITOH HIROYASU C O HAMAMATSU PH, ITOH, HIROYASU, C/O HAMAMATSU PHOTONICS K.K.
Applicants: HAMAMATSU PHOTONICS KK, HAMAMATSU PHOTONICS K.K.
Application year: 1991
Main classification: G01N33
IPC codes: G01N21, G01N33