Noninvasive Glucose Monitoring by Mid-infrared

Self-emission Method

Yen-Chun Yeh, Sheng Yang, Fan Zhao and Dominik Schmidt

Department of Electrical Engineering, International Technological University, San Jose, CA, U.S.A.

Keywords: Non-invasive Glucose Monitoring, Mid-infrared Self-emission, Skin Glucose, Blood Glucose.

Abstract: In this article we present a non-invasive glucose monitoring technique by measuring human body mid-

infrared self-emission. The human body is a black body radiator that provides a stable temperature and

infrared radiation; thus the human body is considered a continuous radiation energy source in the mid-

infrared range. The fingerprint spectrum of glucose shows strong peaks between 8.5 m to 10.4 m,

therefore, measuring the self-emission form human body in the mid-infrared range allows estimation of

glucose concentration. Using a simple and miniaturizable design with a tunable Fabry-Perot filter (FPF) and

a thermal detector, glucose concentration can be measured through the human skin.

1 INTRODUCTION

It has been decades since blood glucose monitoring

techniques were introduced for diabetes patients to

help them with daily management of diabetes

treatments, including diet control, oral medication

and insulin injection. The traditional measurement of

blood glucose concentration requires the patients to

stab themselves in the finger with a needle to extract

the blood to the skin surface so that the blood can be

collected for enzymatic reaction and analysis.

However, in the past decade, the desire to avoid the

pain resulting from the puncture and to realize

continuous blood glucose monitoring has driven

research in a variety of non-invasive glucose sensing

techniques. The non-invasive glucose monitoring

techniques can be classified into two different types,

transdermal (Rao, 1993; Volden, 1980; Gebhardt,

2001) and optical (Shen, 2003; Nelson, 2006;

Enejder, 2005). The main idea of transdermal

glucose sensing techniques is to extract the glucose

from the interstitial fluid to the outer surface of the

skin, where the glucose will be collected and

analyzed by a traditional glucose sensor. The

popular transdermal techniques include reverse

iontophoresis, sonophoresis and skin suction blister

technique (Kost, 2000.). Essentially, the key point of

these methods lies in the different approaches to

collect the glucose. The technique used to identify

and quantify glucose remains the same, which is

based on enzymes. By contrast, the optical methods

aim at identifying the unique spectral signature of

glucose and exploring the best way to calibrate and

quantify optical measurements. Due to the noise

coming from the skin, both SNR and sensitivity are

affected. A significant advantage of this system is

not requiring an enzyme replacement.

Non-invasive optical glucose monitoring

methods basically include three different techniques

to measure glucose in the infrared region. Of the

three methods, near-infrared (NIR) (Nelson, 2006)

spectroscopy, mid-infrared (MIR) (Shen, 2003)

spectroscopy, Raman spectroscopy (Enejder, 2005),

only MIR spectroscopy can measure glucose without

a light source. Because the human body is an

excellent black body, it will cause heat emission in

the MIR wavelength range. Therefore, self-emission

from the human body can generate good target

glucose spectra, and enable an easy to measure

glucose concentration in the human body. In the

mid-IR, glucose has a stronger absorption than most

other chemicals, and if avoids most of the water

signal peaks. Also, using the MIR method can avoid

the use of high-energy light sources on the skin,

which can cause burns. Furthermore, these

advantages facilitate the implementation of the non-

invasive system on a single microelectromechanical

system (MEMS) chip, which is our long-term goal.

Therefore, we chose to use thermal emission

spectroscopy as our scheme to realize a non-invasive

glucose sensor. The most significant advantage is

107

Yeh Y., Yang S., Zhao F. and Schmidt D..

Noninvasive Glucose Monitoring by Mid-infrared Self-emission Method.

DOI: 10.5220/0004750101070111

In Proceedings of the International Conference on Biomedical Electronics and Devices (BIODEVICES-2014), pages 107-111

ISBN: 978-989-758-013-0

 2014 SCITEPRESS (Science and Technology Publications, Lda.)

the relative simplicity of the system, which does not

require a light and is relative to fabricate.

2 EXPERIMENTAL

The principle of the glucose measurement device is

that the human body emits strong mid-infrared

(MIR) radiation and some of the chemical molecules

in the human body would cause the distinct

absorption at their characteristic peaks (Vonach,

1998). The human body is essentially a black body

that emits MIR radiation. According to Planck’s law

(Planck, 1991), we know the relationship between

temperature and intensity of radiation. Glucose

molecules have strong characteristic peaks in both

near-infrared (NIR) and mid-infrared (MIR)

spectrum (Carl, 2002). However, the glucose

radiation can only be measured by human body self-

emission in the MIR region, at least without a strong

light source. Also, the glucose IR spectra can avoid

the strong water signal from human body in MIR

range rather than NIR range.

The main application of the device is a

measurement of the glucose MIR radiation from the

self-emission of the human body. Due to the

vibration of the glucose chemical bond, the molecule

would cause absorption or emission of radiant

energy. Therefore, a molecule such as glucose would

form several distinct peaks in the MIR spectra

between 8.5 m and 10.5 m. Figure 1 shows that

the IR spectra of D-glucose in a potassium bromide

(KBr) sample, which was measured by FTIR

spectroscopy (Shumadzu FTIR 8900).

Figure 1: D-glucose spectrum that were measured by FTIR

spectroscopy in a KBr sample. The spectra show the

characteristic peaks between 8 m to 10.5 m.

According to Fig 1, we can recognize the

characteristic peaks of glucose at 9.2 m, 9.3 m,

and 9.6 m. By measuring the distinct peaks from

human body self-emission, the relationship between

MIR radiation at the special wavelength and glucose

concentration can be obtained.

The targets were the men whose age ranged

between 25 to 27 years old and no diabetes history.

Blood glucose measurements started before the

target had a meal and continued measuring the

glucose concentration every 20 minutes. After the

target had a meal, the glucose concentration started

to increase, and we measured the glucose

concentration continuously until the glucose

concentration decreased and become stable. Every

measurement test was done by both the non-invasive

self-emission measurement system (Fabry-Perot

filter system) and the invasive blood test. The

Bayer’s Contour Next meter was used to measure

the glucose concentration by stabbing target’s finger

for getting blood and measuring the glucose on the

chemical strip. The results of the blood invasive

measurement were taken as the reference blood

concentrations.

The self-emission detector system was built up

as shown in Fig 2. The detector was a pyro-electric

thermal detector combined with a tunable Fabry-

Figure 2: Schematic of the Fabry- Perot filter with system.

Perot filter (FPF), which was made by InfraTec

(LFP-80105-337). The tunable Fabry-Perot filter is a

microelectromechanical system (MEMS) optical

filter, and the scanning range was from 8 m to 10.1

m. The detectivity and the noise density of the

pyro-electric thermal detector are 3.7x10

cm(sqrt[Hz])/W and 75 V/(sqrt[Hz]), respectively.

The detectivity and the noise density of the whole

sensor are 3x10

cm(sqrt[Hz])/W and 75

V/(sqrt[Hz]), respectively. The electronics are

purchased from InfraTec for processing the signal

8 9 10 11

Intensity [a.u.]

Wavelength [m]

9.2 m

9.3 m

9.6 m

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and transferring to the computer. The schematic is

shown in Fig. 3. The aperture diameter size of the

sensor was 1.9 mm, and there was a hole on the

polycarbonate black box, which is aligned with

fitting finger the aperture of the sensor. This hole is

used for positioning the target’s finger putting

target’s finger and fixes the position of target.

Since the pyro-electric thermal detector is

measuring the temperature difference, the detector

can only measure an absolute temperature change.

To measure stable IR radiation, an optical chopper

(Stanford research system SR 540) was connected

with the pyro-electric thermal detector to measure

the IR radiation continuously.

The background signal was subtracted from the

intensity result before the averaging process. The

intensity results were plotted against the real time

blood test result to establish a relationship.

Figure 3: Schematic of the electronics part (InfraTec,

2013).

3 RESULT AND DISCUSSION

The target had their blood glucose concentration

measured every 20 minutes in 200 minutes and had a

meal during the experiment. After having the meal,

the target’s blood glucose concentration increased,

and then decreased with time as shown in Fig 2. The

main band at 9.3 m was used as the detection

characteristic peak from infrared self-emission

measurement by FPF system. Figure 4 (a) shows the

blood glucose measurement result by detecting the

self-emission from target’s finger skin. The

concentration change had almost the same tendency

as the measurement result by blood test meter (Fig 4

(b)).

The highest blood glucose concentration was

143.2 mg/dl that measured by FPF system, and the

same point related to 140 mg/dl that was measured

by blood glucose meter. The first point and the last

point measured by the FPF system were 125.4 mg/dl

and 114.3 mg/dl, and related to 124 mg/dl and 108

mg/dl in blood glucose test, respectively.

The relationship between the intensity of the

target’s infrared radiation and real blood glucose

concentration is shown in Fig 5. The measurement

took the blood glucose concentration from 108

mg/dl to 187 mg/dl by measuring a target person

who was just having a meal. Figure 5 (a) and (b)

(a)

(b)

Figure 4: Continuous blood glucose concentration test

result by different two methods. (a) Continuous glucose

monitoring by FPF system. Measured the glucose

concentration by detecting the skin of the target’s finger

by the FPF system. (b) Continuous glucose monitoring by

the blood test meter in 200 minutes. Measured the glucose

concentration by stabbing target’s finger to get the blood

and measuring by Bayer’s Contour meter.

shows the measurement of the band at 9.3 m and

8.9 m. The equation of the trend lines was y =

0.171x - 3.8144 and y = 0.1759x - 4.1653, and the

value of the trend line was 0.723 and 0.712

individually, thus it showed the correlation between

infrared radiation and glucose concentration in

human body. However, the accuracy of the FPF

system still needs to be improved. The body

temperature and the ambient temperature caused a

part of the error, and that was because the detected

100

120

140

160

0100200

Glucose concentration [mg/dl]

Time [min]

100

120

140

160

0100200

Glucose concentration [mg/dl]

Time [min]

NoninvasiveGlucoseMonitoringbyMid-infraredSelf-emissionMethod

109

90 140 190

Intensity [a.u.]

Glucose concentration [mg/dl]

90 140 190

Intensity [a.u.]

Glucose concentration [mg/dl]

signal was affected by heat from surrounding

materials.

According to Plank’s law, the infrared radiation

and the temperature are related. One of the

(a)

(b)

Figure 5: Calibration curve of intensity signal versus blood

glucose concentration. (a) Measuring the band at 9.3 m,

and the R

value of the trend line is 0.723. (b) Measuring

the band at 8.9 m, and the R

value of the trend line is

0.712.

Figure 6: Temperature effect. The relation difference value

and the temperature of target’s skin.

conditions that affects the self-emission

measurement is the temperature of the target’s skin.

The more difference between the trend line (trend

line of intensity vs. glucose concentration) and each

measurement point would be located in a lower

temperature region (temperature was measured by a

thermopile). The relationship between the

temperature and the difference value is shown in

Fig. 6, and the R

value is 0.664. The next step for

improving the relationship between the intensity of

the target’s infrared radiation and real blood glucose

concentration is temperature effect elimination

through improved temperature calibration. Also the

materials surrounding the target need to have a low

thermal mass so they don’t affect the target

temperature.

4 CONCLUSIONS

The Fabry-Perot filter (FPF) system can measure the

mid-infrared radiation from the human body without

an external light source. By measuring the distinct

band from the self-emission of the human body, the

blood glucose concentration can be monitored. This

non-invasive glucose measurement system allows

patients to avoid the pain from stabbing their skin

when they monitor their blood glucose

concentration. However, the system still needs to

calibrate several effects, such as the body

temperature and ambient temperature. All the

components in our setup can be fabricated on a little

chip with a microelectromechanical system

(MEMS). Our final goal is to use this concept to

build a complete non-invasive glucose monitor on a

1 x 1 cm chip.

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