microfluidic device for blood plasma extraction using

MICROFLUIDIC DEVICE FOR BLOOD PLASMA EXTRACTION USING DIELECTROPHORETIC

BLOOD CELL REMOVAL Yuta Nakashima and Takashi Yasuda

Kyushu Institute of Technology, JAPAN

ABSTRACT This paper presents a microfluidic device that can separate several microliters of

blood into blood cells and blood plasma, and transport plasma to a reservoir. This device consists of a main-channel, side-channels, a reservoir, and two electrodes. Blood enters the main-channel by capillary force, and blood cells are removed from the inlets of the side-channels by dielectrophoresis. This permits plasma to be in-jected into the side-channels. Experiments using human blood showed that blood cells were removed and plasma was transported to the reservoir. Also, plasma ex-traction and blood cells removal were affected by channel geometry and frequency of applied AC voltage.

KEYWORDS: Dielectrophoresis, Blood, Separation, Extraction

INTRODUCTION

Our purpose is to fabricate microfluidic devices which can extract blood plasma from a minute amount of blood, and to apply them to a point-of-care medical diag-nosis. Previously, we succeeded in blood separation using dielectrophoresis in a mi-crochannel [1]. However, the previous device could not transport blood plasma from the separation channel to another channel or reservoir. To overcome the disadvan-tage of the previous work, we designed an improved device for blood plasma extrac-tion, and evaluated extracted blood plasma volume and blood cell removal efficiency. This device can be applied to the point-of-care diagnostics technology such as health checkup at home.

DESIGN AND FABRICATION

Figure 1 shows the schematic of a blood plasma extraction device. The fabri-cated device consists of a main-channel, many side-channels that were fabricated along the sidewall of the main-channel, a plasma reservoir, and two electrodes. The microchannels and the plasma reservoir were made of PDMS and their mold was fabricated with double layered SU-8 photoresist films. The two electrodes were de-signed like a framed rectangle shape and a pin shape, and fabricated on the glass plate. The main-channel measures 500 μm in width and 100 μm in depth. Each side-channel was designed to have a smaller section size (5 μm in width and 2 μm in depth) than that of a blood cell. This prevents its infiltration into a side-channel. Figure 1 (d, e) shows the blood plasma extraction method. Blood enters the main-channel by capillary force when we drop a blood droplet at the main-channel inlet. When we apply an AC voltage between the two electrodes, blood cells that blocked the inlets of the side-channels are repelled from the pin-electrode and trapped in the

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Twelfth International Conference on Miniaturized Systems for Chemistry and Life SciencesOctober 12 - 16, 2008, San Diego, California, USA

framed-rectangle-electrode by dielectrophoresis, i.e. blood cells are removed from the inlets of the side-channels. This permits blood plasma to be injected into the side-channels by capillary force. A photograph of the fabricated device is shown in Fig. 2.

Figure 1. Schematic of the blood plasma extraction device.

Figure 2. Photograph of the fab-ricated device.

Figure 3. Blood plasma transportation to the reservoir through the side channels.

EXPERIMENTAL RESULTS

The performance of the device was tested using 5 μl human blood that was di-luted by PBS (phosphate buffer solution) by 10 %. Blood plasma extraction, in case of applied AC voltage of 20 V and 1 MHz, is shown in Fig. 3. We succeeded in blood plasma injection to the reservoir by repelling blood cells at the side-channel inlets using dielectrophoresis. We carried out the experiments using various devices that have different channel geometries: different side-channel width, w, and different main-channel depth, d, which is/isn’t terraced near side-channel inlets. Figure 4 shows the blood cell removal efficiency in various devices with different geometries. As a result, we could remove about 97 % of blood cells using the device that has 100

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Twelfth International Conference on Miniaturized Systems for Chemistry and Life SciencesOctober 12 - 16, 2008, San Diego, California, USA

μm main-channel depth and 5 μm side-channel width in case of applied AC voltage of 20 V and 1 MHz. Also, variation in extracted blood plasma volume in four differ-ent conditions is shown in Fig. 5. We succeeded in blood plasma transportation of about 300 nl to the reservoir using the device that has 5 μm side-channel width in case of applied AC voltage of 20 V and 1 MHz. This extracted blood plasma volume was about three times larger than that in case of applied AC voltage of 20 V and 10 MHz.

Extra

cted

pla

sma

volu

me

[nl]

Time [min]

400

300

200

100

02 4 6 8 100

Voltage: AC 20 [V]Frequency: f [MHz]

w = 5 μm, f = 11w = 5 μm, f = 102w = 10 μm, f = 13w = 10 μm, f = 104

wDepth:100μm

Depth: 2μm

Depth:100μm

Figure 4. Blood cell removal efficiency in various devices with different geometries.

Figure 5. Variation in extracted blood plasma volume in four different condi-tions.

CONCLUSIONS

We succeeded in extracting blood plasma of about 300 nl from a 5 μl blood without any external mechanical driving source. In case of applied AC voltage of 20 V and 1MHz, blood cells were removed about 97 % and blood plasma was trans-ported to the reservoir. Blood plasma extraction efficiency will be increased by add-ing side-channels and optimizing arrangement and shape of device components.

ACKNOWLEDGEMENTS

This work was supported by a fund of the Knowledge Cluster Initiative of MEXT (Ministry of Education, Culture, Sports, Science and Technology).

REFERENCES [1] Yuta Nakashima and Takashi Yasuda, Blood Plasma Extraction from a Minute

Amount of Blood Using Dielectrophoresis, Proc. of the Micro Total Analysis Systems 2007, Vol. 1, pp. 706-708 (2007)

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Twelfth International Conference on Miniaturized Systems for Chemistry and Life SciencesOctober 12 - 16, 2008, San Diego, California, USA