*1.2.3 Device operation*

*Current and Future Aspects of Nanomedicine*

focus in this work.

*1.2.1 Cell culture*

**1.2 Experimental works**

*1.2.2 Device fabrication*

4 to 7 μm. The number of cells was 1.3 × 109

electrodes, which consist solution resistor Rm in parallel with solution capacitance Cm. Both impedance in series with a pair of electrodes capacitance double layer Cdl.

<sup>+</sup>*Rm Rp*

where ω is the angular frequency of the electrical signal. As a result, the ZT is changing according the present of cell in the sensing area. The impedance between electrode (microneedle) and electrolyte (solution medium) is our main

In this work, Sacharomycesceresiae cells and microparticle are used as a model for proof of concepts. Sacharomycesceresiae were cultivated in a petri dish containing 10 ml of YPD broth (Yeast extract Peptone Dextrose). The YPD broth contained 1% yeast extract, 2% peptone and 2% glucose. The YPD dishes were incubated at 37°C for 24 hours. The cells were washed with deioinsed (DI) water three times by centrifugation, then they were suspended in sterilized deioinsed water at various dilutions (1:10) concentration. The cells were incubated on agar plates at 37°C for 24 hours for determining the number of cells. The diameter of yeast cells varies from

ml). The conductivity of DI water is 6 mS/m. The non-fluorescent polystyrene (PS) microbeads with diameter 15 and 9 μm (Polysciences. Inc.) suspended in Phosphatebuffered saline (PBS) solution were diluted to a final concentration of 1000 beads per ml. Polystyrene beads have a known size and electrical properties [22] and have

The photolithography technique was utilized to fabricate the microfluidic device.

The fabrication begins by designing the masks using layout editor software. The laser lithography system (μPG501, Heidelberg Instruments, Germany) has been used to write the two masks (top and bottom) on the chromium (Cr) masks. Two-step photolithography using SU-82025 negative photoresist (MicroChem, USA) was utilized to fabricate the top layer mold. The first layer has a thickness of 25 μm and was spin coated onto a silicon substrate. After pre-baking, the top layer of Cr mask was place onto the first layer of photoresist for pattern transfer by using a mask aligner (SussMicroTech MA-6), then post-baking with development. Next, the second layer with 60 μm thickness was spin coated on the first photoresist layer and pre-baking. Then, the second layer of photoresist substrate was exposed with the bottom layer Cr mask by UV light. After exposed, the top mold master was obtaining by post-bake and developed process. Meanwhile the bottom mold master with 60 μm thickness was fabricated by following the SU-8 microchannel photolithography technique. PDMS pre-polymers (SYLGARD184A) was thoroughly mixing with curing agents (SYLGARD 184B) in a ratio of 10:1 by weigh for fabricate the PDMS microfluidic chip. The mixing PDMS was poured on an SU-8 mold master (top and bottom mold master) and left for whole night cured at room temperature to obtain the PDMS microfluidic chip. To increase the bonding strength between the top side and bottom side of PDMS microfluidic chip, they were cleaned with Isopropyl alcohol (IPA) and treated by Oxygen plasma (Plasma Etch PE-25) for 25 seconds [23]. The bonding

constant impedance across the frequency range used in these experiments.

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ *Rm* <sup>+</sup>*Rp* <sup>+</sup> *<sup>j</sup> Rm Rp*(*Cm* <sup>+</sup>*Cp*)

(1)

colony forming units per milliliter (cfu/

ZT is overall impedance of the measurement system given [21]. *ZT* = \_2

*j Cdl*

**104**

The microscope (Olympus Inverted Microscopes IX71) was utilized to monitor the sensing area of microfluidic chip system. The micromanipulator (EB-700, Everbeing) was utilized to insert the two microneedles into microchannel chip through the square hole at right and left side of the chip. For this experiment, the gap between microneedles was fixed at 20 μm. **Figure 2** illustrated the experimental setup of impedance measurement. The two microneedles were connected to impedance analyzer (Hioki IM3570) for input measuring and the result was displayed on the computer. Then, by controlling the syringe pumps (KDS LEGATO 111, KD Scientific, and USA), the 3-ml syringes of the sample solution and yeast concentration was introduced into microfluidic chip via two tygon flexible tubes.
