JPH0850093A - Spectroscopic measurement of glucose concentration - Google Patents

Abstract

PURPOSE:To optically measure the concn. of glucose with good accuracy by using a light wave having a shorter wavelength within a near infrared region. CONSTITUTION:A sample 15 is irradiated with the measuring light from a light source 2 and the absorption spectrum of glucose in the sample is calculated from the reflected light from the sample 15 and the concn. of glucose is measured from the absorption spectrum. In this method, a plurality of wavelengths are used as the wavelengths to be used of the absorption spectrum and a plurality of the selected wavelengths are set to ones selected from either one of wavelength bands of 950-1150nm and 1150-1300nm. Since the selected wavelengths are extremely near to a visible region, they penetrate into the deep part of the tissue of a living body and, since the effect of water absorption is low, an accurate measuring result is obtained. Since a plurality of the selected wavelengths are near mutually, measuring accuracy is also enhanced from this point of view.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for spectroscopically separating and measuring the concentration of glucose, which is one of saccharides, from the concentrations of other saccharides having a similar molecular structure, such as sucrose. , Non-destructively the sugar content of food, agricultural products, fruits, or biological fluids of humans, animals, etc.
In other words, without taking out the liquid to be measured from the object to the outside,
Regarding how to measure.

[0002]

2. Description of the Related Art The above-mentioned non-destructive measuring method is extremely useful because the step of taking out the biological fluid to be measured from the measuring object can be omitted.

In this nondestructive measuring method, it is insufficient that the measurable range is only the skin layer of the object to be measured. For example, if the measurement target is fruit,
The epidermis, which is the epidermis layer, differs from those of the inner flesh in terms of tissue structure, composition and distribution of chemical components. In order to measure the sugar content of pulp, it is necessary to measure a part deeper than the epidermis layer.

As a prior art, Japanese Patent Laid-Open No. 60-23663
No. 1 discloses a method for non-destructively measuring sugars, particularly glucose, in human serum. This measurement method is called an incident angle modulation method. Basically, a sample is irradiated with a light wave (measurement light) from the outside, and the light wave diffused and reflected from the inside of the sample is spectrally analyzed. It is a spectroscopic method. In this method, the incident angle of the light wave on the sample is changed. If this incident angle is small, that is, if it is close to normal incidence, light penetrates deep into the epidermis, and if this incident angle is large, the penetration depth of light becomes shallow. In this way, if the subdermal penetration depth of light is changed and the spectral signal is extracted and the difference signal is taken, it is possible to separate and extract the information of the deeper depth, that is, the sugar content.

[0005]

However, in the above-mentioned conventional method, there is a problem that the mechanism for modulating the incident angle becomes complicated, and when the incident angle of the light wave is changed, the reflection characteristic of the epidermis surface is changed. As a result, there is a problem that the reproducibility deteriorates.

Further, in the above conventional method, the measurement wavelength of the light wave is 2270 ± 15 nm, 210 in the near infrared region.
0 ± 15 nm, 1765 ± 15 nm, 1575 ± 15 nm are used, and a wavelength of 1000 to 2700 nm is used as a reference wavelength. However, in order to realize better measurement accuracy, the measurement wavelength is in the near infrared range. Shorter wavelengths should be used. This is because, in particular, biological fluids such as agricultural products and fruits contain a large amount of water, so that the permeability of the used light wave to water becomes a problem, and this permeability becomes greater on the shorter wavelength side.

Incidentally, wavelengths in the mid-infrared region, particularly 7500 to 1
The infrared region of 5000 nm is called the fingerprint region, which is an effective wavelength region for spectral analysis and has been used for a long time for identifying and quantifying organic compounds. However, in this region, the absorption of background water is extremely large, so
It is considered impossible to quantify specific components including water. Further, although visible light has good water permeability, it is difficult to quantify by light color because there are many colorless saccharides in the visible region, and there is no spectrum of a specific absorption band in the visible region.

The inventor of the present invention has developed a spectroscopic measuring method which can simplify the measuring apparatus.

This spectroscopic measurement method is as follows.

That is, the light intensity of the light source is measured by irradiating the sample with the measuring light from the light source, calculating the absorption spectrum of glucose in the sample from the reflected light from the sample, and measuring the glucose concentration from the absorption spectrum. Is set to a first predetermined value to calculate a glucose absorption spectrum at a first depth of the sample, and the light intensity of the light source is set to a second predetermined value to absorb a glucose absorption spectrum at a second depth of the sample. The second step of calculating the absorption spectrum of glucose in the deep portion between the first and second depths of the sample is calculated from the difference between the absorption spectra calculated in the first step and the second step, and the sample is calculated based on the absorption spectrum. And a third step of measuring the glucose concentration in the deep part of the glucose concentration, the method for spectroscopically measuring the glucose concentration.

According to the above-mentioned measuring method, the background noise of the epidermis layer of the sample is removed by adopting the technique of changing the light intensity of the light source to measure the glucose concentration in the deep portion which is the desired measurement site. Therefore,
A complicated device such as a light wave incident angle modulator required for the conventional method is not required, and the first problem can be solved.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned second problem and to obtain a more accurate measurement result by using a light wave having a shorter wavelength in the near infrared region. The object of the present invention is to provide a spectroscopic measurement method capable of obtaining the above.

[0013]

Means for Solving the Problems and Actions / Effects The measuring method according to the present invention for achieving the above object is as follows.

That is, the present invention provides a method of irradiating a sample with a measuring light from a light source, calculating an absorption spectrum of glucose in the sample from reflected light from the sample, and measuring a glucose concentration from the absorption spectrum. The absorption spectrum has a plurality of selection wavelengths to be used, and the plurality of selection wavelengths have wavelength bands of 950 to 1150 nm or 1
It is a method for spectroscopically measuring glucose concentration, which is characterized in that the wavelength is selected from any one wavelength band of 150 to 1300 nm.

According to the above-mentioned method, these selected wavelengths of the absorption spectrum are shorter than the conventional measurement wavelength and are closer to the visible region, so that they penetrate deeper into the living tissue.
Therefore, the degree of freedom of the measurement site of the biological tissue is expanded as compared with the conventional one. In particular, if you want to measure the concentration of glucose in blood flowing through the blood vessels of a person, if the light wave of the selected wavelength is used, the light wave reaches the dermis where the capillaries are distributed, or a portion close to it, Non-destructively,
That is, it becomes possible to measure without taking out blood. In addition, since the light wave of the selected wavelength, that is, a short wavelength close to the visible region is used, the influence of water absorption is small and the spectral brightness of the light source used is high, that is,
Since the N ratio becomes large, there is an advantage that the device performance is improved and a more accurate measurement result can be obtained. Furthermore, since the plurality of selected wavelengths are selected to be close to each other, the measurement accuracy is improved also from this point.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below with reference to the accompanying drawings.

FIG. 1 shows an apparatus used to carry out a measuring method according to an embodiment of the present invention. First, this device will be described.

In the figure, MI is a well-known Michelson interference optical system, and includes a light source 2, a slit 7a for transmitting light from the light source 2, and a fixed mirror 3 and a moving mirror 5 for transmitting the light passing through the slit 7a. Two light waves R1, which are orthogonal to each other
A beam splitter 4 for splitting and projecting to R2, each mirror 3,
A slit 7b for transmitting the light reflected by the beam 5 and re-superimposed on the beam splitter 4 and a moving mirror driving device 6 for moving the moving mirror 5 to a predetermined position are provided. The moving mirror driving device 6 is connected to the computer 12 and controlled by a signal from the computer. The light intensity of the light source 2 can be adjusted by the light source intensity controller 1. The light source intensity controller 1 is connected to the computer 12 and is controlled by a signal from the computer 12.

In the figure, reference numeral 8 is a reflecting mirror, which reflects the light wave emitted from the condenser plate 7b of the Michelson interference optical system MI toward the integrating sphere 9. A bandpass filter 13 is interposed between the reflecting mirror 8 and the integrating sphere 9. The light wave in the wavelength band selected by passing through the bandpass filter 13, that is, the measurement light enters the integrating sphere 9 through its entrance, and irradiates the sample 15 installed in the sample window of the integrating sphere. The light wave that has penetrated into the sample is diffusely reflected by the subepithelial internal tissue of the sample and comes out again on the sample surface. These diffusely reflected lights are integrated sphere 9
The light is collected by and is detected by the detector 10, that is, the photoelectric converter, installed in the other window of the integrating sphere. Detector 10
The electric signal photoelectrically converted by is amplified by the amplifier 11,
Then, it is converted into a digital signal by the A / D converter, and the digital signal is input to the computer 12.

Next, the measurement wavelength region selected by the bandpass filter 13 will be described.

As described above, the water content of foods, agricultural products, fruits or biological fluids such as humans and animals, which are the objects of measurement of the present invention, is high. Therefore, it is important to consider the light absorption of water.

FIG. 2 shows the absorption coefficient of water in the near infrared region. The horizontal axis represents wavelength, and the vertical axis represents extinction coefficient. As is clear from the figure, the absorption peak of pure water is 1.
It is in the bands of 93 μm, 1.43 μm, 1.15 μm, and 0.96 μm. The light transmittance is higher on the shorter wavelength side.
Comparing the absorbance of water at wavelengths of 1.93 μm and 0.96 μm, they differ by 3 to 4 digits. Therefore, in the near-infrared region which is closer to the visible region than the conventional measurement wavelength band, if there is a quantifiable wavelength band of the target chemical component, that is, saccharide, the penetration of light into biological tissues including water. This means that the depth becomes deeper, and the region having a concentration representative of the component concentration of the target region is reached sufficiently deep. In addition, the fact that a wavelength range close to the visible range can be used has an advantage that the performance of the measuring apparatus improves because the spectral brightness of the light source used also increases.

Therefore, the present inventors have taken up glucose and saccharose, which have practically significant meanings and have very similar molecular structures, as saccharide samples, and examined their separation and quantitative properties in the near infrared region. . As a result, the near-infrared spectra of glucose and saccharose are very similar, so that the spectra overlap and interfere with each other in the mixed system, but the wavelength is shorter than the conventional measurement wavelength and has a significantly different wavelength. I found that there is a band of.
The bandpass filter 13 has a function of transmitting only light waves in this wavelength band.

The light wave or spectrum in this significant band will be described in detail below.

In the case of the aqueous solution type sample, as shown in FIG. 3, it is difficult to visually discriminate a significant difference in the spectra of the sucrose aqueous solution and the glucose aqueous solution with respect to pure water. Therefore, the difference spectrum between the glucose solution and pure water
(Figure 4) and difference spectrum between sucrose aqueous solution and pure water
I checked (Fig. 5). This difference spectrum is a spectrum obtained by subtracting the spectrum of pure water with the water content thereof from the spectrum of the glucose aqueous solution or the sucrose aqueous solution.
(Hereinafter, this is referred to as pseudo pure glucose or pseudo pure sucrose). In FIGS. 4 and 5, the numbers in each graph indicate the molar concentrations of glucose and sucrose. That is, No1: 2.0 Mol / liter No2: 1.0 Mol / liter No3: 0.5 Mol / liter No4: 0.25 Mol / liter No5: 0.125 Mol / liter Next, in order to check the difference between the spectra of glucose and sucrose. When the pseudo pure glucose spectrum and the pseudo pure saccharose spectrum are compared, the result is as shown in FIG. 6, and the difference spectrum (pseudo pure glucose spectrum-pseudo pure saccharose spectrum) is as shown in FIG. As described above, glucose and saccharose are very similar in molecular structure, which is reflected in the spectrum (FIG. 6). However, even if the molecular structure is similar, the band of 1150 to 1300 nm and the wavelength of 950 to
A significant difference is observed in the 1150 nm band.

3 of glucose / sucrose mixed aqueous solution
1150 to 1 in which the above-mentioned significant difference is recognized in the component system
Three typical wavelengths in the band of 300 m, that is, a typical wavelength of the relatively dominant absorbance of glucose (123
0 nm), the relative dominant absorption wavelength of saccharose (1205 nm), and the base wavelength (1285 nm) that does not depend on the concentrations of glucose and sucrose. it can. The results of testing unknown samples based on the results are shown in FIGS. FIG. 8 is a test concentration (vertical axis) obtained by the following glucose concentration application model formula (linear linear equation including constants) in a glucose / sucrose mixed aqueous solution.
And the actual concentration (known concentration / horizontal axis).

Test-applied model formula Cg = Pg ₀ + Pg ₁ A (λ ₁ ) + Pg ₂ A (λ ₂ ) + Pg ₃ A (λ ₃ ) Cg: Glucose test concentration A (λ ₁ ), A (λ ₂ ), A (λ ₃ ): Each selected wavelength (λ ₁ = 1205n
Absorbance at m, λ ₂ = 1230 nm, λ ₃ = 1285 nm) Pg ₀ , Pg ₁ , Pg ₂ , Pg ₃ : Coefficients The coefficients of the above model formulas are obtained by conducting tests on a required number of standard samples. The straight line in the figure shows the relationship in which the measured concentration and the assay concentration have a one-to-one correspondence. In the figure, the “.” Mark is a plot of the results obtained for a certain number of samples, and it is clear that all the results are along a straight line, which allows glucose to be separated using the selected wavelength. It turns out that it can be quantified.

Although the above description is about glucose,
Saccharose can also be separated and quantified by using three selection wavelengths (1205 nm, 1230 nm, 1285 nm) as in the above. FIG. 9 shows the relationship between the test concentration (vertical axis) obtained by the sucrose concentration test application model equation in the glucose / sucrose mixed aqueous solution and the actually measured concentration (known concentration / horizontal axis). In this case as well, it is clear that the results obtained for the sample are along a one-to-one correspondence straight line.

Similarly, one significant difference band 950-1
Typical wavelength at 150 nm (950 nm, 980 nm, 1
It is possible to separate and quantify the three components of glucose, saccharose and pure water using 107 nm).

Further, significant differences in glucose and saccharose spectra are also observed in the band from 1300 to 1450 nm (only partially shown in FIG. 7). Therefore, three typical wavelengths in this band (1349 nm,
The components can be separated using 1385 nm, 1400 nm).
A calibration curve was obtained using a mathematical formula in the same manner as in the above example, and the results of assaying unknown samples are shown in FIG. 10 (glucose concentration is shown) and FIG. 11 (saccharose concentration). As is clear in each figure, all of the "." Marks indicating the test results are along a straight line corresponding to one to one.

The selected wavelengths of the light waves used in the measuring apparatus shown in FIG. 1 are, as described above, three wavelength bands 950 to 1
150nm, 1150-1300nm, 1300-1450nm
Is a wavelength selected from any of the above.

Next, referring to FIG.
A method for measuring the saccharide concentration of the tissue in the deep part b, specifically, the glucose concentration will be specifically described as an example.

First, as a first step, in order to examine the spectrum of the tissue of the epidermis layer a of the sample, the light source intensity controller 1 sets the light from the light source 2 to a predetermined light intensity. That is, it is adjusted so that the light wave emitted from the integrating sphere 9 toward the sample 15 is incident only on the skin layer a and is reflected again to the outside. In this way, sample 15
The spectrum of the skin layer a of is measured. In this case, the bandpass filter 13 transmits only a light wave of a required wavelength band, for example, 1150 to 1300 nm. The computer 12 calculates an interferogram (interference waveform) from the input signal, and then Fourier transforms the interferogram to calculate a normal absorption spectrum.
Then, as a second step, the light source intensity controller 1
The light intensity on the light source is increased so that the light wave from the integrating sphere 9 penetrates to the deep portion b of the sample 15. In this way, the spectra of both the skin layer a and the deep portion b of the sample 15 are calculated. In this case as well, the computer 12 executes the same program as in the case of measuring the skin layer a. Then, as a third step, the computer 12 calculates the difference spectrum between the two spectra obtained in the first step and the second step, and then measures the concentration of the target component, that is, glucose from the wavelength bands 1150 to 1300 nm. Several wavelengths required for, eg 1205n
Three wavelengths, m, 1230 nm and 1285 nm, are selected and then these selected wavelengths are applied to the predetermined mathematical formula given above to determine the glucose concentration.

By carrying out the above spectrum, the background noise of the epidermal layer a, which does not contain glucose at all or meaningfully, is removed, and the concentration of glucose in the tissue at the depth b is measured. You can get the value.

[Brief description of drawings]

FIG. 1 is a schematic view of a measuring apparatus for carrying out the measuring method of the present invention.

FIG. 2 is a graph showing an absorption coefficient of water in a near infrared band.

FIG. 3 is a graph showing absorbance spectra of pure water, an aqueous glucose solution and an aqueous saccharose solution.

FIG. 4 is a graph showing a difference spectrum between an aqueous glucose solution and pure water.

FIG. 5 is a graph showing a difference in absorbance between difference spectra of a sucrose aqueous solution and pure water.

FIG. 6 is a graph showing a difference in absorbance between a pseudo pure glucose spectrum and a pseudo pure saccharose spectrum.

FIG. 7 is a graph showing a difference in absorbance between a difference spectrum between a pseudo pure glucose spectrum and a pseudo pure saccharose spectrum.

FIG. 8 is a graph showing a relationship between a test concentration and an actually measured concentration obtained by applying a specific selection wavelength by a glucose concentration test application model formula according to an embodiment of the present invention in a glucose / sucrose mixed aqueous solution.

FIG. 9 is a graph showing the relationship between the test concentration and the actually measured concentration in the glucose / saccharose mixed aqueous solution obtained by the sucrose concentration test application model formula according to the example of the present invention.

FIG. 10 is a diagram when applying another specific selected wavelength.
Is a graph similar to.

FIG. 11 is a diagram when another specific selected wavelength is applied.
Is a graph similar to.

[Explanation of symbols]

 1 Light Source Intensity Controller 2 Light Source 3 Fixed Mirror 4 Beam Splitter 5 Moving Mirror 6 Moving Mirror Drive 7a, 7b Slit 8 Reflecting Mirror 9 Integrating Sphere 10 Detector 11 Amplifier 12 Computer 13 Bandpass Filter 14 A / D Converter 15 Sample MI Michelson interference optics

Claims (1)

[Claims] 1. A sample is irradiated with measurement light from a light source,
Calculating the absorption spectrum of glucose in the sample from the reflected light from the sample, in the method of measuring the glucose concentration from the absorption spectrum, the selection wavelength to be used of the absorption spectrum is a plurality, the plurality of selection wavelengths, A method for spectroscopically measuring glucose concentration, which has a wavelength selected from any one of wavelength bands 950 to 1150 nm or 1150 to 1300 nm.