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

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pla

sma

volu

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[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