FEASIBILITY OF A MICRO-FLUIDIC HEALTH CARE

DEVICE MEASURING CONTENT OF SODIUM CHLORIDE

Toshiyuki Horiuchi and Daichi Shinoda

Tokyo Denki University, 2-2, Kanda-Nishiki-Cho, Chiyoda-Ku, Tokyo, Japan

Keywords: Micro-fluidic device, Health care device, Body fluid, Spectral transmittance, Deep ultra violet, Sodium

chloride, Micro-reservoir, Thick resist.

Abstract: Feasibility of developing a new-type micro-fluidic health care device was investigated. Blood test and

urinalysis are generally used for the health check. However, to check more simply and easily diseases,

utilization of small quantity but easily collected other body fluids such as sputum, sweat, and tears were

taken up. These body fluids contain sodium chloride, and it is considered that the content relates to the

health conditions. Therefore, the method to easily detect the sodium chloride content was investigated, and

it was found that the measurement of spectral transmittance in deep ultra violet light region was effective. It

was clarified that the transmittance at wavelengths of 190-200 nm noticeably decreased relating to sodium

chloride content and the absorption coefficient well corresponded to the content. Although the relationship

between the sodium chloride content and the health condition have to be investigated in detail hereafter, the

new device will be feasible for easily monitoring health conditions.

1 INTRODUCTION

Various bio-devices have been researched and

developed for keeping human health and detecting

illnesses and diseases. Blood test (Almeida, Glesse

and Bonorino, 2011) (Chen, Fang, Qiu, He and

Deng, 2009) (Edward, Kreig and Butler, 2009)

(Noda, Suzuki, Kanno, Hanafusa, Yamamoto, Ijuin,

Hori, Osumi and Kotera, 2010) (Ye and Li, 2011)

and urinalyses (Chen, Fang, Shyu and Lin, 2006)

(Koide, Ito and Karube, 2007) (Mori, Mori and

Yamori, 2011) (Otero, Akinfiev, Palacios and

Presedo, 2011) are generally carried out as a health

examination or a disease check. However, everyone

does not like to be taken the blood using a syringe,

and feel ashamed to offer urine.

For this reason, it was aimed to use other body

fluids which are easily and friendly collected even

though only small quantities are collected. In

concrete, sputum, tear, sweat and snivel were

targeted. If small-size biosensors or devices for

easily diagnosing illnesses were newly developed

using micro-fluidic technology (Horiuchi, Watanabe,

Hayashi and Kitamura, 2010) (Horiuchi, Otsuka,

Ozaki, Ando and Hiraki, 2011), they would be

effective from a view point of not only size saving

and portability but also reduction of sample volume

and painless collection of body fluids.

On the other hand, it is most important to search

how to easily obtain information indicating health

conditions. To conceive a bright idea, measurement

of spectral transmittance in deep ultra violet (UV)

wavelength region was investigated. Spectral

transmittance in infrared wavelength region is often

investigated to know organic materials or molecular

groups contained in specimens. However, the deep

UV region has not sufficiently been investigated.

It was fortunately found that the light

transmittance changed at the wavelength of 190-200

nm, if the object fluid contained sodium chloride

(NaCl). In this paper, how the spectral transmittance

changes in the above deep UV region relating to the

contents of NaCl in aqueous solution is reported. In

addition, although only a few results have been

obtained, it is clarified that similar

spectral

transmittance change is also observed for human

sputum. Accordingly, if the contents of NaCl in

some body fluids relate to the health, it will be

feasible to develop a new health check device.

297

Horiuchi T. and Shinoda D..

FEASIBILITY OF A MICRO-FLUIDIC HEALTH CARE DEVICE MEASURING CONTENT OF SODIUM CHLORIDE.

DOI: 10.5220/0003704102970301

In Proceedings of the International Conference on Biomedical Electronics and Devices (BIODEVICES-2012), pages 297-301

ISBN: 978-989-8425-91-1

 2012 SCITEPRESS (Science and Technology Publications, Lda.)

Wavelength (nm)



Transmittance

2 SPECTRUM TRANSMITTANCE

MEASURING DEVICE

To measure the spectrum transmittance in UV

wavelength region using small quantities of aqueous

solutions of NaCl or body fluids, a micro-reservoir

of resist was fabricated on a quartz plate using

optical lithography, as shown in Fig. 1. Negative

resist SU-8 (MicroChem) composed of an epoxy

resin was coated in 100-μm thick. The SU-8 is

almost transparent for visible light but opaque for

UV light, as shown in Fig. 2. The spectral

transmittance was measured using a

spectrophotometer (JASCO Corp., V-630) of which

the measurable wavelength range was 190-1100 nm.

1 mm

SU-8

Micro-vessel

Quartz plate

50 mm

Figure 1: Device components for investigating spectral

transmittances of body fluids.

-0.2

0.2

0.4

0.6

0.8

0 200 400 600 800 1000

Figure 2: Spectral transmittance of SU-8.

Because SU-8 is a negative resist, exposed parts are

hardened. Accordingly, if the resist is exposed

except the masked central rectangular region, a

concave reservoir is fabricated at the centre of the

quartz plate. On the other hand, hardened SU-8

surrounding the concave reservoir is almost opaque

for UV light. Accordingly, only the place where the

concave reservoir is made becomes almost

transparent for the deep UV light through the quartz

substrate. Therefore, if the measurement light is

widely irradiated including the micro-reservoir, only

the light passing through the reservoir is

distinguishably detected.

Light transmittance depends on the thickness of

the fluids. However, if the fluids to be examined is

infused in the reservoir and capped by another

quartz plate, the thickness becomes almost equal to

the SU-8 thickness coated on the former quartz

plate. Therefore, the fluid thickness is controlled by

adjusting the coated SU-8 thickness.

Two quartz plates with the fluid fused in the SU-

8 reservoir were inserted in a specially prepared

plastic case, and pressed each other by packing

gauze so as the infused fluid did not leak out and

kept the constant thickness. The spectral

transmittance was measured comparing with the

reference set which had the same-size micro-

reservoir without infusing the fluid.

Because the irradiated light beam to specimens

had a slim rectangular shape with a horizontal width

of approximately 2 mm and a vertical length of

approximately 10 mm, a horizontal slim rectangular

micro-reservoir with a size of 2 by 15 mm was

fabricated, as shown in Fig. 3. Accordingly, the light

beam certainly crossed the micro-reservoir. Because

the vertical width of the reservoir was 2 mm,

effective size of the light detected by the photo

sensor in the spectrophotometer was kept 2 mm

square constant. Therefore, the fluid volume

substantially used for the measurement of spectral

transmittance was kept as little as approximately

only 400 μℓ.

SU-8

Micro-reservoir

Quartz plate

Photo senso

Sensing light

Figure 3: Shape of light beam passing through the micro-

vessel fabricated by SU-8.

3 SPECTRAL TRANSMITTANCE

MEASUREMENT OF SODIUM

CHLORIDE

Using the devices, spectral transmittance of the

aqueous solution of NaCl was evaluated, as shown

(b) Cap plate (a) Vessel plate

BIODEVICES 2012 - International Conference on Biomedical Electronics and Devices

298

in Fig. 4. The transmittance values for the

wavelengths of 190-200 nm were largely changed

depending on the contents of NaCl. On the other

hand, when the wavelength was fixed at 190 and 195

nm, for example, the transmittance changed as

shown in Fig.5.

Figure 4: Spectral transmittances of aqueous solution of

NaCl.

Figure 5: Change of light transmittance depending on the

wavelength and concentration ratio of NaCl. Depth of the

micro- reservoir was 100 μm.

It was found in the experiments there was

another merit in this micro-reservoir that the infused

fluids can clearly be observed by eyes, because SU-8

is transparent for visible light. Even if some air

bubbles are occasionally mixed in the fluids infused

in the reservoir, they can easily been detected and

the specimen was omitted or infused again.

In the above experiment, the contents of NaCl

were changed between the ranges of 0.1-0.9%.

Because the weight percentage of physiological

aqueous solution of NaCl is 0.9%, the transmittance

changed for far thinner solutions. For this reason, the

sensitivity would be sufficient to detect the slight

change of NaCl content in the body fluids.

Influence of the fluid thickness or the depth of

micro-reservoir was also investigated. Figure 6

shows the transmittance change depending on the

micro-reservoir depth.

When a light beam passes through the fluid with

a thickness of t, transmittance T and absorption

coefficient α are calculated by eq. (1) and (2).

100

0 0.2 0.4 0.6 0.8 1 1.2

100 μm

130 μm

150 μm

Thickness

Concentration ratio of NaCl

(

)

Figure 6: Change of light transmittance at the wavelength

of 195 nm depending on the micro-reservoir depth and

concentration ratio of NaCl.

−

= . (1)

−=

(2)

Using these equations, absorption coefficient α

was estimated. T and α depend on the wavelength

and the weight percentage of NaCl. When the

wavelength was fixed at 195 nm, relationship

between lnT and t was obtained as shown in Fig. 7.

Figure 7: Relationship between transmittance T and micro-

reservoir depth or the SU-8 thickness t at the wavelength

of 195 nm.

Transmittance Ln T

-1.4

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0 50 100 150 200

0.7 %

NaCl:

0.3 %

0.5 %

1.0%

100

120

180 190 200 210 220 230 240

Pure wate

NaCl 0.1%

NaCl 0.3 %

NaCl 0.5 %

NaCl 1.0%

Wavelength (nm)

1.2

1.0

0.8

0.6

0.4

0.2

Relative transmittance

100

120

0 0.2 0.4 0.6 0.8 1 1.2

195 nm

190 nm

Concentration ratio of NaCl

Wavelen

1.2

1.0

0.8

0.6

0.4

0.2

Relative transmittance

Thickness of SU-8

(

)

FEASIBILITY OF A MICRO-FLUIDIC HEALTH CARE DEVICE MEASURING CONTENT OF SODIUM CHLORIDE

299

Absorption coefficient α (μm

)

Although the transmittance degraded much more

at the wavelength of 190 nm, it was considered that

the transmittance value should be appropriate to

judge its change caused by the health conditions.

The NaCl content of physiological aqueous

solution is 0.9%, and because almost half of the light

with the wavelength of 195 nm transmits through it,

transmittance change is most conspicuously detected

using this wavelength.

Referring to the data shown in Fig. 7, α at the

wavelength of 195 nm was calculated, as shown in

Table 1.

Table 1: Calculated absorption coefficients for various

concentrations of NaCl.

Concentration SU-8 α α

of NaCl thickness (average)

(wt%) (μm)

100 0.001335

0.1 130 0.000596 0.000935

150 0.000876

100 0.00255

0.3 130 0.00221 0.00258

150 0.00297

100 0.00347

0.5 130 0.00419 0.00395

150 0.00419

100 0.00466

0.7 130 0.00527 0.00524

150 0.00580

100 0.00618

0.9 130 0.00657 0.00659

150 0.00703

100 0.00674

1.0 130 0.00685 0.00712

150 0.00776

0.002

0.004

0.006

0.008

0 0.2 0.4 0.6 0.8 1 1.2

Concentration ratio of NaCl

(

)

Figure 8: Relationship between absorption coefficient α

and concentration ratio of sodium chloride. The error bars

show each deviation range of three data shown in Table 1.

The average values of α is plotted, as shown in Fig.

8. Although the absorption coefficient α became

almost linear, the inclination gradually decreased as

the contents of NaCl increased.

4 SPECTRAL TRANSMITTANCE

MEASUREMENT OF SPUTUM

Because it was verified that the spectral

transmittance typically changed caused by the

content of NaCl at wavelengths of deep UV region,

spectral transmittance of sputum was investigated

next. The same tools were used for the experiments,

and micro-reservoirs of SU-8 with a thickness of

100 μm were prepared. Although the curvature

tendency of the spectral transmittance curve slightly

differed from that of NaCl aqueous solution, it was

clarified that the transmittance also decreased in UV

region for sputum, as shown in Fig. 9.

Figure 9: Spectral transmittance of sputum measured using

the newly fabricated devices.

In the case of sputum, the transmittance

decreased for a wider wavelength range comparing

with that of the aqueous solution of NaCl. In other

word, the transmittance decreased at the

wavelengths of 190-230 nm. It probably depends on

the fact that other materials are also contained in the

sputum except NaCl.

However, the transmittance did not almost

decrease in the wavelength region of 190-200 nm for

potassium chloride (KCl). Although various contents

in sputum may influence the transmittance change, it

is supposed that the main content causing the

transmittance decrease at the wavelength range of

190-200 nm is NaCl.

It was clarified that the spectral transmittances of

100

180 190 200 210 220 230 240

1.0

0.8

0.6

0.4

0.2

Relative transmittance

Wavelength (nm)

BIODEVICES 2012 - International Conference on Biomedical Electronics and Devices

300

NaCl and sputum for deep UV light conspicuously

decreased. Because the transmittance or the

absorption depends on the concentration ratios of

components, the variations of the transmittance

curves or the absorption coefficients will become the

detectors of the health. It will be feasible to obtain

some health information from the transmittance

curves or the absorption coefficient values, if a lot of

practices are heaped up.

5 CONCLUSIONS

Fundamental research for developing a new micro-

fluidic health care device was presented. It was

clarified that the spectral transmittance for deep UV

light with wavelengths of 190-200 nm noticeably

changed depending on the content of NaCl. Utilizing

these characteristics, health check or disease finding

will be feasible using small quantity body fluids

such as sputum. To obtain reliable spectral

transmittance data, micro-reservoirs of thick resist

SU-8 were fabricated on quartz plates using optical

lithography, and test fluids were infused in the

reservoirs. Because the infused fluids were capped

by another quartz plate, and the fluid thickness was

decided by the depth of the reservoir, the spectral

transmittances were measured with very good

repeatability. The transmittance became appropriate

values when the micro-reservoir depth was 100-150

μm.

It is an important subject to clarify how the

spectral transmittance curves and the absorption

coefficients of body fluids change depending on

health conditions, and it should be investigated

hereafter. Accordingly, the distance to the goal is

very long. However, a lead to develop a new micro-

fluidic health care device was obtained.

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