This work was supported by the Ministry of Science and Technology, Taiwan, R.O.C., under Grant NSC 103-2112-M-002-008-MY3.

1. Fabrication of the Microchip
<ol>
	<li>Preparation of the ITO electrode
	<ol>
		<li>Use commercial illustration software to draw a cross pattern. Set the distance between the diagonal electrodes to 160 &#181;m and make the arms of the cross pattern 30 mm wide and 55 mm long, as shown in Figure 1. Save the illustration file as a DXF file.</li>
		<li>Use a glass cutter to trim the ITO glass to a size of 25 mm x 50 mm (width x length). Use 75% ethanol and DI water to rinse the ITO glass several times.</li>
		<li>Put the ITO glass onto the pulsed-fiber laser marking machine. Focus the laser on the surface of the ITO glass by adjusting the distance between the ITO glass and the laser to 279.5 mm. 
		NOTE: The laser used here has the following specifications: 1,064 nm, 20 W, 90 to 120 ns pulse width, and 20 to 80-kHz pulse repetition frequency, with a pulsed-light intensity at about 5 x 105 W/cm2).</li>
		<li>Directly input the illustration file (DXF file) onto the computer of the laser marking machine. Click the &#34;Mark Parameter&#34; button and input the following parameters: speed, &#34;800 mm/s;&#34; power, &#34;60%;&#34; and frequency, &#34;40 kHz.&#34; Tick the &#34;Frame,&#34; &#34;Fill,&#34; and &#34;Fill First&#34; terms.
		<ol>
			<li>Click the &#34;Preview&#34; button position the pattern at the ITO glass center. Click the &#34;Mark Sample&#34; button to pattern the ITO glass (Figure 1A).</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Setting up a four-phase generator and connecting the experimental microchip
	<ol>
		<li>Build the circuits of the invertors, as shown in Figure 2A.</li>
		<li>Connect the 4 wires on the four-phase electrode by direct contact with tape, as shown in Figure 2C. Divide the &#34;Channel 1&#34; of the function generator into two branches using a double BNC connector.
		<ol>
			<li>Connect one branch to the wire (#1) attached to the ITO electrode and the other to the input of the invertor. Connect the output of the invertor to the wire (#3), as shown in Figure 2B.</li>
		</ol>
		</li>
		<li>Connect &#34;Channel 2&#34; with the same procedure as in step 1.2.2, but connect to the wires (#2 and #4) as shown in Figure 2B.</li>
		<li>For the EROT experiments, set the phase shift between the two channels to 90&#176;, directly on the function generator. Apply a sine wave at 0.5-4 Vpp voltage amplitude and a frequency ranging from 100 Hz to 5 MHz during the experiments, as shown in Figure 2D.</li>
		<li>For the DEP experiments, connect one branch of Channel 1 to the wire (#1) attached to the ITO electrode and the other to the input of the invertor. Connect the output of the invertor to the wire (#2). Connect Channel 2 using the same procedure, but connect to the wires (#3 and #4).</li>
		<li>Set the phase shift between the 2 channels at 0&#176;, directly on the function generator. Apply a sine wave at 0.5-4 Vpp voltage amplitude and a frequency ranging from 100 Hz to 5 MHz during the experiments, as shown in Figure 2D.</li>
	</ol>
	</li>
</ol>
2. Preparation of the Samples
<ol>
	<li>Preparation of Janus particles
	<ol>
		<li>Centrifuge the 2 &#181;m silica particle aqueous suspension (10% w/w) at 2,200 x g for 1 min.</li>
		<li>Pipette 2 &#181;L of sedimentary silica particles into a 1.5 mL microcentrifuge tube and add 500 &#181;L of ethanol (99.5% v/v). 
		NOTE: The supernatant does not need to discarded; just save it in the refrigerator at 4 &#176;C. It does not need to be resuspended before pipetting.</li>
		<li>Sonicate the ethanol-silica particle suspension using an ultrasonicator (43 kHz, 50 W) for 1 min and then centrifuge it at 2,200 x g for 3 min.</li>
		<li>Substitute the supernatant with 500 &#181;L of ethanol and repeat step 2.1.3 three times.</li>
		<li>Substitute the supernatant with 8 &#181;L of ethanol and sonicate the ethanol-silica particle suspension using an ultrasonicator (43 kHz, 50 W) for 3 min. 
		NOTE: About 10 &#181;L of ethanol-silica particle suspension should remain in the tube at this step.</li>
		<li>Pipette 2 &#181;L of ethanol-silica particle suspension and drop it on a normal glass slide (width: 25 mm, length: 75 mm, and thickness: 1.2 mm) to form a droplet. 
		Note: This quantity of particle suspension is enough to prepare the monolayers for 5-6 slides (2 &#181;L for each slide).</li>
		<li>Slowly drag the ethanol-silica particle droplet slightly with a cover glass to form a monolayer of silica particles (Figure 3A).</li>
		<li>Put the slide with the monolayer of silica particles into a sputtering device to be coated with Au.
		<ol>
			<li>Remove the air from the sputter chamber at 100 mTorr and inject argon for 10 min (replace the air with argon). Stop injecting argon and then remove the argon from the chamber at 70 mTorr.</li>
			<li>Set the current to 15 mA for 200 s. (Figure 3B); Janus particles are already prepared at this step.</li>
		</ol>
		</li>
		<li>Drop 20 &#181;L of DI water on the sputtered slide and scrape the Janus particles from the monolayer using a normal 200 &#181;L pipette tip. 
		NOTE: The Janus particles scraped from the monolayer suspend in the DI water droplet at this step.</li>
		<li>Pipette the Janus particle suspension droplet and drop it into another 1.5-mL centrifuge tube.</li>
		<li>Use the Janus particle suspension to prepare the sample by diluting it with DI water to a suitable concentration for experiments. 
		NOTE: The concentration of the particle suspension in the experiments described here is about 2,000 counts/&#181;L.</li>
	</ol>
	</li>
	<li>Preparation of fully coated metallic particles14
	<ol>
		<li>Mix the PDMS polymer base and the curing agent at a 10:1 weight ratio.</li>
		<li>Tape around the glass slide to form the lateral walls of the container. Pour the mixture of PDMS onto a taped slide to achieve a PDMS layer of 2-3 mm, as shown in Figure 4A.</li>
		<li>Put the taped slide (container) with the PDMS mixture in an airtight chamber and run the vacuum pump for 30 min to remove the bubbles in the PDMS mixture.</li>
		<li>Put the taped slide (container) with the PDMS mixture (step 2.2.3) into the oven. Cure the PDMS mixture at 70 &#176;C for 2 h to form a PDMS stamp.</li>
		<li>After the PDMS stamp is cured, remove the slide and tape to get the PDMS stamp, the surface of which attached originally to the glass slide, forming a flat surface, as shown in Figure 4B.</li>
		<li>Follow the steps from 2.1.1-2.1.8 to prepare a monolayer of Janus particles on a slide.</li>
		<li>Use the flat surface of the PDMS stamp to stamp the monolayer with uniform pressure.</li>
		<li>Put the PDMS stamp with the monolayer of Janus particles, which is inverted from the glass slide made in step 2.1.8, into the sputtering device to be coated with Au.
		<ol>
			<li>Remove air from the sputter chamber at 100 mTorr and inject argon for 10 min (replace the air with argon). Stop injecting argon and then remove the argon from the chamber at 70 mTorr.</li>
			<li>Set the current to 15 mA for 200 s (Figure 4C); the fully coated metallic particles are already prepared at this step.</li>
		</ol>
		</li>
		<li>Follow the steps from 2.1.9-2.1.11 to prepare the sample for experiments.</li>
	</ol>
	</li>
</ol>
3. Experiments for AC Electrokinetic Measurement
<ol>
	<li>Wrap 5 pieces of paraffin film to prepare a spacer. Combine the ITO electrode array with the film spacer of 500-&#181;m thickness using a heat gun and place the electrode on the microscope stage.
	<ol>
		<li>Drop 8 &#181;L of particle suspension, which was prepared in steps 2.1 and 2.2, onto the center of the cross electrode array. Place a cover glass on the spacer.</li>
	</ol>
	</li>
	<li>For the EROT experiments, on the function generator, set the phase shift between the 2 channels to 90&#176;. Apply a sine wave at 0.5-4 Vpp voltage amplitude and a frequency ranging from 100 Hz to 5 MHz during the experiments (based on the connection in steps 1.2.2-1.2.3).
	<ol>
		<li>Choose the wave form by clicking the &#34;waveform&#34; button on the function generator. Input the voltage and frequency value using the numbered buttons on the function generator and then turn on the AC signal by clicking &#34;output&#34; button.</li>
	</ol>
	</li>
	<li>For the DEP experiments, set the phase shift between the 2 channels to 0&#176;. Apply a sine wave at 0.5-4 Vpp voltage amplitude and a frequency of 100 Hz to 5 MHz during the experiments (based on the connections in step 1.2.5) by setting up the function generator as in step 3.2.1.</li>
	<li>Turn on the AC signal by clicking the &#34;output&#34; button and capture the images of particle motion and rotation under an inverted optical microscope with a 40X, NA 0.6 objective using a camera.</li>
	<li>Input the images of particle motion and rotation to the software and analyze the trajectory of particles by particle tracking to obtain the particle and angular velocities. 
	Note: The &#34;Image J&#34; software and its &#34;MultiTracker&#34; plugin were used here for image binarization and particle tracking.</li>
</ol>

<ol>
	<li>Walther, A., M&#252;ller, A. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Janus+particles.">Janus particles.</a> Soft Matter. 4 (4), 663-668 (2008).</li><li>Chen, Y. -. L., Jiang, H. -. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrorotation+of+a+metallic+coated+Janus+particle+under+AC+electric+fields.">Electrorotation of a metallic coated Janus particle under AC electric fields.</a> Appl Phys Lett. 109 (19), 191605 (2016).</li><li>Zhang, L., Zhu, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Directed+assembly+of+janus+particles+under+high+frequency+ac-electric+fields:+Effects+of+medium+conductivity+and+colloidal+surface+chemistry.">Directed assembly of janus particles under high frequency ac-electric fields: Effects of medium conductivity and colloidal surface chemistry.</a> Langmuir. 28 (37), 13201-13207 (2012).</li><li>Gangwal, S., Cayre, O. J., Velev, O. 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The authors have nothing to disclose.

Fabricating ITO electrode arrays using the fiber laser marking machine provides a rapid method to prepare electrodes with arbitrary patterns. However, there are still some disadvantages to this method, such as fewer charge carriers and the lower fabrication accuracy of ITO electrodes compared to metal electrodes created by traditional methods. These disadvantages could limit some experiments. For example, fewer charges carriers could affect the distribution of the electric field when there is a large distance between electrodes. In addition, the adjustment of the patterning parameters is a critical step in this method, which directly affects the quality of the ITO electrode arrays. For example, the laser power affects the removal of the ITO conductive layer from the glass substrate. The frequency and speed of the laser determine the smoothness of the ITO electrode edges. Usually, appropriate patterning parameters are found by trial and error. In short, this method is capable of rapidly and efficiently producing electrodes on ITO glass in arbitrary patterns, which can to applied to many kinds of electrical experiments, for research and other applications.
Preparing the Janus particles and metallic particles with the drying process is a simple and convenient method. In contrast to other methods, such as the Pickering emulsion method10, the electrohydrodynamic co-jetting method11, the microfluidic photopolymerization method12, and the chemical synthesis method15, this method is capable of preparing a large number of particles in a short time. However, the limitation of this method is that the metal deposition on the surfaces of the particles could be non-uniform, which could slightly change the particle shape. Although the drying process method has this limitation, it is still a useful method to prepare Janus particles and metallic particles.
In summary, this article provides functional methods to rapidly prepare electrode arrays in arbitrary patterns, as well as a large number of fully or partially coated metallic particles. This can facilitate the development and application of electrokinetics, including for the manipulation and characterization of particles in microfluidic devices.

Janus particles, named after the Roman god with a double face, are asymmetric particles whose two sides have physically or chemically different surface properties1,2. Due to this asymmetric feature, Janus particles exhibit special responses under electric fields, such as DEP3,4,5,6, EROT2, and induced-charge electrophoresis (ICEP)7,8,9. Recently, several methods to prepare Janus particles have been reported, including the Pickering emulsion method10, the electrohydrodynamic co-jetting method11, and the microfluidic photopolymerization method12. However, these methods require a series of complicated apparatus and procedures. This article introduces a simple method to prepare Janus particles and fully coated metallic particles. A monolayer of micro-scaled silica particles is prepared in a drying process and is put into a sputtering device to be coated with Au. One hemisphere of the particle is shaded, and only the other hemisphere is coated with Au2,13. The monolayer of the Janus particle is stamped with a polydimethylsiloxane (PDMS) stamp and then treated with a second coating process to prepare fully coated metallic particles14.
To characterize the electrical properties of a Janus particle, different AC electrokinetic responses, such as DEP, EROT, and electro-orientation, are widely used9,15,16,17,18,19. For example, EROT is the steady-state rotational response of a particle under an externally imposed rotating electric field2,9,15,16. By measuring the EROT, the interaction between the induced dipole of the particles and the electric fields can be obtained. DEP, which arises from the interaction between the induced dipoles and a non-uniform electric field, is capable of leading to particle movement3,4,5,9,15. Different kinds of particles can be attracted to (positive DEP) or repelled from (negative DEP) the electrode edges, which serves as a general method for manipulating and characterizing particles in the microfluidic device. The translational (DEP) and rotational (EROT) characteristics of the particle under the electric field are dominated by the real and imaginary part of the Clausius-Mossotti (CM) factor, respectively. The CM factor depends on the electrical properties of the particles and the surrounding liquid, which are revealed from the characteristic frequency, &#969;c = 2&#963; / aCDL, of DEP and EROT, where &#963; is the liquid conductivity, a is the particle radius, and CDL is the capacitance of the electrical double layer15,16. To measure the EROT and DEP of particles, specially designed electrode array patterns are needed. Traditionally, a photolithographic technique is used to create electrode arrays and requires a series of complicated procedures, including photoresist spin-coating, mask alignment, exposure, and development15,18,19,20.
In this article, the rapid fabrication of electrode arrays is demonstrated by direct optical patterning. A transparent thin-film ITO layer, which is coated on the glass substrate, is partially removed by a fiber laser marking machine (1,064 nm, 20 W, 90 to 120 ns pulse width, and 20 to 80 kHz pulse repetition frequency) to form a four-phase electrode array. The distance between the diagonal electrodes is 150-800 &#181;m, which can be adjusted to suit the experiments. The four-phase electrode array can be used to characterize and concentrate particles in different microfluidic devices15,16,18. To generate the four-phase electric field, the electrode array is connected to a 2-channel function generator and to two invertors. The phase shift between the adjacent electrodes is set at either 90&#176; (for EROT) or 180&#176; (for DEP)15. The AC signal is applied at a 0.5 to 4 Vpp voltage amplitude, and the frequency ranges from 100 Hz to 5 MHz during the operation process. Janus particles, metallic particles, and silica particles are used as samples to measure their AC electrokinetic properties. Suspensions of the particles are placed on the center region of the electrode array and are observed under an inverted optical microscope with a 40X, NA 0.6 objective. Particle motion and rotation are recorded with a digital camera. The DEP movement is recorded at the annular region, between 40 and 65 &#181;m radially away from the array center, and EROT is recorded at the circular region, 65 &#181;m radially away from the array center. Particle velocity and angular velocity are measured by the particle-tracking method. The particle centroids are distinguished by gray scale or geometry of particles using software. The particle velocity and angular velocity are obtained by measuring the movements of the particle centroids.
This article provides a simple method to rapidly fabricate arbitrarily patterned electrode arrays. It introduces the preparation of fully or partially coated metallic particles, which can be used in different fields, with uses ranging from biology to industry applications.

<table border="0" cellpadding="0" cellspacing="0" width="768">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:287px;">Silica Microsphere-2.34 &#181;m</td>
			<td style="width:187px;">Bangs Laboratories</td>
			<td style="width:129px;">SS04N</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:287px;">Ethyl Alcohol (99.5%)</td>
			<td style="width:187px;">KATAYAMA CHEMICAL</td>
			<td style="width:129px;">E-0105</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:287px;">SYLGARD 184 A&#38;B Silicone Elastomer(PDMS)</td>
			<td>DOW CORNING</td>
			<td style="width:129px;"></td>
			<td>PDMS&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:287px;">&#160;ITO glass</td>
			<td style="width:187px;">Luminescence Technology</td>
			<td style="width:129px;">LT-G001</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:287px;">Fiber laser marking machine</td>
			<td style="width:187px;">Taiwan 3Axle Technology</td>
			<td style="width:129px;">TAFB-R-20W</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:287px;">&#160;2-channel function generator</td>
			<td style="width:187px;">Gwinsek</td>
			<td style="width:129px;">AFG-2225</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:287px;">CMOS camera</td>
			<td style="width:187px;">Point Grey</td>
			<td style="width:129px;">GS3-U3-32S4M-C</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:287px;">Sputter</td>
			<td style="width:187px;">JEOL</td>
			<td style="width:129px;">JFC-1100E</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:287px;">Operational Amplifiers</td>
			<td style="width:187px;">Texas Instruments</td>
			<td style="width:129px;">LM6361N</td>
			<td>OP invertor&#160;</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:287px;">Ultrasonic Cleaner</td>
			<td style="width:187px;">Gui Lin Yiyuan Ultrasonic Machinery Co.</td>
			<td style="width:129px;">DG-1</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:287px;">Microcentrifuge</td>
			<td style="width:187px;">Scientific Specialties, Inc.</td>
			<td style="width:129px;"></td>
			<td>1.5ml</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:287px;">Mini Centrifuge</td>
			<td style="width:187px;">LMS</td>
			<td style="width:129px;">MC-MCF-2360</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:287px;">Microscope cover glass</td>
			<td style="width:187px;">Marienfeld-Superior</td>
			<td style="width:129px;"></td>
			<td>18*18mm</td>
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			<td height="21" style="height:21px;width:287px;">Inverted optical microscope</td>
			<td style="width:187px;">Olympus</td>
			<td style="width:129px;">OX-71&#160;</td>
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		<tr height="21">
			<td height="21" style="height:21px;width:287px;">Parafilm</td>
			<td style="width:187px;">bemis</td>
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preparation of janus particles and alternating current electrokinetic measurements with a rapidly fabricated indium tin oxide electrode array

This article provides a simple method to prepare partially or fully coated metallic particles and to perform the rapid fabrication of electrode arrays, which can facilitate electrical experiments in microfluidic devices. Janus particles are asymmetric particles that contain two different surface properties on their two sides. To prepare Janus particles, a monolayer of silica particles is prepared by a drying process. Gold (Au) is deposited on one side of each particle using a sputtering device. The fully coated metallic particles are completed after the second coating process. To analyze the electrical surface properties of Janus particles, alternating current (AC) electrokinetic measurements, such as dielectrophoresis (DEP) and electrorotation (EROT)- which require specifically designed electrode arrays in the experimental device- are performed. However, traditional methods to fabricate electrode arrays, such as the photolithographic technique, require a series of complicated procedures. Here, we introduce a flexible method to fabricate a designed electrode array. An indium tin oxide (ITO) glass is patterned by a fiber laser marking machine (1,064 nm, 20 W, 90 to 120 ns pulse-width, and 20 to 80 kHz pulse repetition frequency) to create a four-phase electrode array. To generate the four-phase electric field, the electrodes are connected to a 2-channel function generator and to two invertors. The phase shift between the adjacent electrodes is set at either 90&#176; (for EROT) or 180&#176; (for DEP). Representative results of AC electrokinetic measurements with a four-phase ITO electrode array are presented.

The four-phase electrode array is created by a fiber laser marking machine. The ITO conductive layer coated on the glass is removed by a focus laser to form a cross pattern with a gap of 160 &#181;m, as shown in Figure 1B.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/55950/55950fig1.jpg" /> 
Figure 1: Preparation of the ITO Electrode. (A) Schematics of creating a four-phase ITO electrode with a fiber laser marking machine (1,064 nm, 20 W, 90- to 120 ns pulse-width, and 20 to 80 kHz pulse repetition frequency). (B) Bright-field image of the cross electrode array under a microscope. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55950/55950fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
The circuit diagram of the invertor is shown in Figure 2A. To create the four-phase electric field, the electrode array is connected to a 2-channel function generator and to two invertors, as shown in Figure 2B.
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/55950/55950fig2.jpg" /> 
Figure 2: Setup of a Four-phase Generator and the Connection of the Experimental Microchip. (A) The circuit diagram of the invertor. (B) Schematics of the experimental microchip. (C) Connect the 4 wires on the four-phase electrode through direct contact with tape. (D) The phase shift between the adjacent electrodes is set at either 90&#176; (for EROT) or 180&#176; (for DEP). <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55950/55950fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
A monolayer of silica particles is prepared by slowly dragging the ethanol-silica particle droplet slightly using a cover glass, as shown in Figure 3A. The monolayer of silica particles is put into the sputtering device to be coated with Au. Finally, the Janus particles are prepared, as shown in Figure 3C.
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/55950/55950fig3.jpg" /> 
Figure 3: Preparation Procedures of Janus Particles. (A) The monolayer of silica particles under a microscope. (B) Schematic drawing of coating a thin layer of Au onto a monolayer of silica particles. (C) Bright-field image of a Janus particle under a microscope. The dark side of the particle is the Au coating. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55950/55950fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
The preparation of fully coated metallic particles is shown in Figure 4. The container, which consists of a slide and tape, is loaded with the PDMS mixture to a 2 to 3 mm height, as shown in Figure 4A. The PDMS mixture is put into the oven at 70 &#176;C for 2 h to form a PDMS stamp. The PDMS stamp, with a flat surface, is shown in Figure 4B. The preparation procedure of fully coated metallic particles is shown in Figure 4C. The fully coated metallic particle is shown in Figure 4D.
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/55950/55950fig4.jpg" /> 
Figure 4: Preparation of Fully Coated Metallic Particles. (A) The PDMS mixture in the slide-tape container. (B) The PDMS stamp with a flat surface. (C) Preparation procedures of fully coated metallic particles. (D) Bright-field image of a fully coated metallic particle under a microscope. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55950/55950fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
The representative results of particle EROT and DEP are shown in Figure 5. The EROT of Janus particles is generally in the opposite direction of the electric field (counter-field), with a maximum angular speed at a characteristic frequency, as shown in Figure 5A. The EROT of Janus particles at a low frequency reverses to the co-filed direction, which could be because of the more complicated polarization mechanism and the induced-charge electroosmotic flow around the metallic surface hemisphere15,16. The EROT of silica particles is co-field in all testing frequency ranges, and its characteristic frequency is at the lowest testing frequency (~500 Hz), as shown in Figure 5B. The EROT of metallic particles is counter-field in all testing frequency ranges, and its characteristic frequency is lower than that of Janus particles, as shown in Figure 5C. From Figure 5A-5C, we can see the change in the imaginary part of the CM factors, with the electric field frequencies between different kinds of particles. Besides, we can see that the EROT characteristic frequency of the Janus particles is higher than in fully coated metallic particles. This result suggests that the polarization of Janus particles cannot be directly explained by a simple superposition model of two-hemisphere structures. There is a more complicated mechanism for the polarization of Janus particles2. The DEP measurements of metallic particles are shown in Figure 5D.The results show that the DEP response of metallic particles is n-DEP at lower frequencies, but p-DEP at higher frequencies, with a crossover frequency that agrees with the characteristic frequency in the EROT measurement.
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/55950/55950fig5.jpg" /> 
Figure 5: The Representative Results of Particle EROT and DEP. (A) EROT spectrum of Janus particles. (B) EROT spectrum of silica particles. (C) EROT spectrum of fully coated metallic particles. (D) DEP spectrum of fully coated metallic particles. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55950/55950fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Preparation of Janus Particles and Alternating Current Electrokinetic Measurements with a Rapidly Fabricated Indium Tin Oxide Electrode Array at JoVE.com

Preparation of Janus Particles and Alternating Current Electrokinetic Measurements with a Rapidly Fabricated Indium Tin Oxide Electrode Array

In this article, a simple method to prepare partially or fully coated metallic particles and to perform AC electrokinetic property measurements with a rapidly fabricated indium tin oxide (ITO) electrode array is demonstrated.

This article provides a simple method to prepare partially or fully coated metallic particles and to perform the rapid fabrication of electrode arrays, ...

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8.1K Views.  National Taiwan University. In this article, a simple method to prepare partially or fully coated metallic particles and to perform AC electrokinetic property measurements with a rapidly fabricated indium tin oxide (ITO) electrode array is demonstrated.

Video: Preparation of Janus Particles and Alternating Current Electrokinetic Measurements with a Rapidly Fabricated Indium Tin Oxide Electrode Array

Probing and Mapping Electrode Surfaces in Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) are potentially the most efficient and cost-effective solution to utilization of a wide variety of fuels beyond hydrogen 1-7. The performance of SOFCs and the rates of many chemical and energy transformation processes in energy storage and conversion devices in general are limited primarily by charge and mass transfer along electrode surfaces and across interfaces. Unfortunately, the mechanistic understanding of these processes is still lacking, due largely to the difficulty of characterizing these processes under in situ conditions. This knowledge gap is a chief obstacle to SOFC commercialization. The development of tools for probing and mapping surface chemistries relevant to electrode reactions is vital to unraveling the mechanisms of surface processes and to achieving rational design of new electrode materials for more efficient energy storage and conversion2. Among the relatively few in situ surface analysis methods, Raman spectroscopy can be performed even with high temperatures and harsh atmospheres, making it ideal for characterizing chemical processes relevant to SOFC anode performance and degradation8-12. It can also be used alongside electrochemical measurements, potentially allowing direct correlation of electrochemistry to surface chemistry in an operating cell. Proper in situ Raman mapping measurements would be useful for pin-pointing important anode reaction mechanisms because of its sensitivity to the relevant species, including anode performance degradation through carbon deposition8, 10, 13, 14 ("coking") and sulfur poisoning11, 15 and the manner in which surface modifications stave off this degradation16. The current work demonstrates significant progress towards this capability. In addition, the family of scanning probe microscopy (SPM) techniques provides a special approach to interrogate the electrode surface with nanoscale resolution. Besides the surface topography that is routinely collected by AFM and STM, other properties such as local electronic states, ion diffusion coefficient and surface potential can also be investigated17-22. In this work, electrochemical measurements, Raman spectroscopy, and SPM were used in conjunction with a novel test electrode platform that consists of a Ni mesh electrode embedded in an yttria-stabilized zirconia (YSZ) electrolyte. Cell performance testing and impedance spectroscopy under fuel containing H2S was characterized, and Raman mapping was used to further elucidate the nature of sulfur poisoning. In situ Raman monitoring was used to investigate coking behavior. Finally, atomic force microscopy (AFM) and electrostatic force microscopy (EFM) were used to further visualize carbon deposition on the nanoscale. From this research, we desire to produce a more complete picture of the SOFC anode.

We present a unique platform for characterizing electrode surfaces in solid oxide fuel cells (SOFCs) that allows simultaneous performance of multiple characterization techniques (e.g. in situ Raman spectroscopy and scanning probe microscopy alongside electrochemical measurements). Complementary information from these analyses may help to advance toward a more profound understanding of electrode reaction and degradation mechanisms, providing insights into rational design of better materials for SOFCs.

Solid oxide fuel cells (SOFCs) are potentially the most efficient and cost-effective solution to utilization of a wide variety of fuels beyond hydrogen ...

Characterization of Electrode Materials for Lithium Ion and Sodium Ion Batteries Using Synchrotron Radiation Techniques

Intercalation compounds such as transition metal oxides or phosphates are the most commonly used electrode materials in Li-ion and Na-ion batteries. During insertion or removal of alkali metal ions, the redox states of transition metals in the compounds change and structural transformations such as phase transitions and/or lattice parameter increases or decreases occur. These behaviors in turn determine important characteristics of the batteries such as the potential profiles, rate capabilities, and cycle lives. The extremely bright and tunable x-rays produced by synchrotron radiation allow rapid acquisition of high-resolution data that provide information about these processes. Transformations in the bulk materials, such as phase transitions, can be directly observed using X-ray diffraction (XRD), while X-ray absorption spectroscopy (XAS) gives information about the local electronic and geometric structures (e.g.&#160;changes in redox states and bond lengths). In situ experiments carried out on operating cells are particularly useful because they allow direct correlation between the electrochemical and structural properties of the materials. These experiments are time-consuming and can be challenging to design due to the reactivity and air-sensitivity of the alkali metal anodes used in the half-cell configurations, and/or the possibility of signal interference from other cell components and hardware. For these reasons, it is appropriate to carry out ex situ experiments (e.g.&#160;on electrodes harvested from partially charged or cycled cells) in some cases. Here, we present detailed protocols for the preparation of both ex situ and in situ samples for experiments involving synchrotron radiation and demonstrate how these experiments are done.

We describe the use of synchrotron X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) techniques to probe details of intercalation/deintercalation processes in electrode materials for Li-ion and Na-ion batteries. Both in situ and ex situ experiments are used to understand structural behavior relevant to the operation of devices

Intercalation compounds such as transition metal oxides or phosphates are the most commonly used electrode materials in Li-ion and Na-ion batteries. ...

Development of a 3D Graphene Electrode Dielectrophoretic Device

The design and fabrication of a novel 3D electrode microdevice using 50 &#181;m thick graphene paper and 100 &#181;m double sided tape is described. The protocol details the procedures to construct a versatile, reusable, multiple layer, laminated dielectrophoresis chamber. Specifically, six layers of 50 &#181;m x&#160;0.7 cm x&#160;2 cm graphene paper and five layers of double sided tape were alternately stacked together, then clamped to a glass slide. Then a 700 &#956;m diameter micro-well was drilled through the laminated structure using a computer-controlled micro drilling machine. Insulating properties of the tape layer between adjacent graphene layers were assured by resistance tests. Silver conductive epoxy connected alternate layers of graphene paper and formed stable connections between the graphene paper and external copper wire electrodes. The finished device was then clamped and sealed to a glass slide. The electric field gradient was modeled within the multi-layer device. Dielectrophoretic behaviors of 6 &#956;m polystyrene beads were demonstrated in the 1 mm deep micro-well, with medium conductivities ranging from 0.0001 S/m to 1.3 S/m, and applied signal frequencies from 100 Hz to 10 MHz. Negative dielectrophoretic responses were observed in three dimensions over most of the conductivity-frequency space and cross-over frequency values are consistent with previously reported literature values. The device did not prevent AC electroosmosis and electrothermal flows, which occurred in the low and high frequency regions, respectively. The graphene paper utilized in this device is versatile and could subsequently function as a biosensor after dielectrophoretic characterizations are complete.

A microdevice with high throughput potential is used to demonstrate three-dimensional (3D) dielectrophoresis (DEP) with novel materials. Graphene nanoplatelet paper and double sided tape were alternately stacked; a 700 &#956;m micro-well was drilled transverse to the layers. DEP behavior of polystyrene beads was demonstrated in the micro-well.

The design and fabrication of a novel 3D electrode microdevice using 50 &#181;m thick graphene paper and 100 &#181;m double sided tape is described. The ...

Writing and Low-Temperature Characterization of Oxide Nanostructures

Oxide nanoelectronics is a rapidly growing field which seeks to develop novel materials with multifunctional behavior at nanoscale dimensions. Oxide interfaces exhibit a wide range of properties that can be controlled include conduction, piezoelectric behavior, ferromagnetism, superconductivity and nonlinear optical properties. Recently, methods for controlling these properties at extreme nanoscale dimensions have been discovered and developed. Here are described explicit step-by-step procedures for creating LaAlO3/SrTiO3 nanostructures using a reversible conductive atomic force microscopy technique. The processing steps for creating electrical contacts to the LaAlO3/SrTiO3 interface are first described. Conductive nanostructures are created by applying voltages to a conductive atomic force microscope tip and locally switching the LaAlO3/SrTiO3 interface to a conductive state. A versatile nanolithography toolkit has been developed expressly for the purpose of controlling the atomic force microscope (AFM) tip path and voltage. Then, these nanostructures are placed in a cryostat and transport measurements are performed. The procedures described here should be useful to others wishing to conduct research in oxide nanoelectronics.

Oxide nanostructures provide new opportunities for science and technology. The interfacial conductivity between LaAlO3 and SrTiO3 can be controlled with near-atomic precision using a conductive atomic force microscopy technique. The protocol for creating and measuring conductive nanostructures at LaAlO3/SrTiO3 interfaces is demonstrated.

Oxide nanoelectronics is a rapidly growing field which seeks to develop novel materials with multifunctional behavior at nanoscale dimensions.  Oxide ...

Preparation and Friction Force Microscopy Measurements of Immiscible, Opposing Polymer Brushes

Solvated polymer brushes are well known to lubricate high-pressure contacts, because they can sustain a positive normal load while maintaining low friction at the interface. Nevertheless, these systems can be sensitive to wear due to interdigitation of the opposing brushes. In a recent publication, we have shown via molecular dynamics simulations and atomic force microscopy experiments, that using an immiscible polymer brush system terminating the substrate and the slider surfaces, respectively, can eliminate such interdigitation. As a consequence, wear in the contacts is reduced. Moreover, the friction force is two orders of magnitude lower compared to traditional miscible polymer brush systems. This newly proposed system therefore holds great potential for application in industry. Here, the methodology to construct an immiscible polymer brush system of two different brushes each solvated by their own preferred solvent is presented. The procedure how to graft poly(N-isopropylacrylamide) (PNIPAM) from a flat surface and poly(methyl methacrylate) (PMMA) from an atomic force microscopy (AFM) colloidal probe is described. PNIPAM is solvated in water and PMMA in acetophenone. Via friction force AFM measurements, it is shown that the friction for this system is indeed reduced by two orders of magnitude compared to the miscible system of PMMA on PMMA solvated in acetophenone.

The methodology to perform friction force microscopy experiments for contacting brushes is presented: Two polymer brushes that are grafted from (a) substrates and (b) colloidal probes are slid to show that, by using two contacting immiscible brush systems, friction in sliding contacts is reduced compared to miscible brush systems.

Solvated polymer brushes are well known to lubricate high-pressure contacts, because they can sustain a positive normal load while maintaining low ...

Ultrasound Velocity Measurement in a Liquid Metal Electrode

A growing number of electrochemical technologies depend on fluid flow, and often that fluid is opaque. Measuring the flow of an opaque fluid is inherently more difficult than measuring the flow of a transparent fluid, since optical methods are not applicable. Ultrasound can be used to measure the velocity of an opaque fluid, not only at isolated points, but at hundreds or thousands of points arrayed along lines, with good temporal resolution. When applied to a liquid metal electrode, ultrasound velocimetry involves additional challenges: high temperature, chemical activity, and electrical conductivity. Here we describe the experimental apparatus and methods that overcome these challenges and allow the measurement of flow in a liquid metal electrode, as it conducts current, at operating temperature. Temperature is regulated within &#177;2 &#176;C using a Proportional-Integral-Derivative (PID) controller that powers a custom-built furnace. Chemical activity is managed by choosing vessel materials carefully and enclosing the experimental setup in an argon-filled glovebox. Finally, unintended electrical paths are carefully prevented. An automated system logs control settings and experimental measurements, using hardware trigger signals to synchronize devices. This apparatus and these methods can produce measurements that are impossible with other techniques, and allow optimization and control of electrochemical technologies like liquid metal batteries.

Ultrasound velocimetry is used to study mixing by fluid flow in liquid metal electrodes. The focus of this manuscript is to illustrate the methods used for making precise, spatially-resolved ultrasound measurements while limiting oxidation and controlling and monitoring temperature, applied current, and the heater power being supplied.

A growing number of electrochemical technologies depend on fluid flow, and often that fluid is opaque. Measuring the flow of an opaque fluid is inherently ...

Surface Enhanced Raman Spectroscopy Detection of Biomolecules Using EBL Fabricated Nanostructured Substrates

Fabrication and characterization of conjugate nano-biological systems interfacing metallic nanostructures on solid supports with immobilized biomolecules is reported. The entire sequence of relevant experimental steps is described, involving the fabrication of nanostructured substrates using electron beam lithography, immobilization of biomolecules on the substrates, and their characterization utilizing surface-enhanced Raman spectroscopy (SERS). Three different designs of nano-biological systems are employed, including protein A, glucose binding protein, and a dopamine binding DNA aptamer. In the latter two cases, the binding of respective ligands, D-glucose and dopamine, is also included. The three kinds of biomolecules are immobilized on nanostructured substrates by different methods, and the results of SERS imaging are reported. The capabilities of SERS to detect vibrational modes from surface-immobilized proteins, as well as to capture the protein-ligand and aptamer-ligand binding are demonstrated. The results also illustrate the influence of the surface nanostructure geometry, biomolecules immobilization strategy, Raman activity of the molecules and presence or absence of the ligand binding on the SERS spectra acquired.

We describe the fabrication and characterization of nano-biological systems interfacing nanostructured substrates with immobilized proteins and aptamers. The relevant experimental steps involving lithographic fabrication of nanostructured substrates, bio-functionalization, and surface-enhanced Raman spectroscopy (SERS) characterization, are reported. SERS detection of surface-immobilized proteins, and probing of protein-ligand and aptamer-ligand binding is demonstrated.

Fabrication and characterization of conjugate nano-biological systems interfacing metallic nanostructures on solid supports with immobilized biomolecules ...

Iridium Oxide-reduced Graphene Oxide Nanohybrid Thin Film Modified Screen-printed Electrodes as Disposable Electrochemical Paper Microfluidic pH Sensors

A facile, controllable, inexpensive and green electrochemical synthesis of IrO2-graphene nanohybrid thin films is developed to fabricate an easy-to-use integrated paper microfluidic electrochemical pH sensor for resource-limited settings. Taking advantages from both pH meters and strips, the pH sensing platform is composed of hydrophobic barrier-patterned paper micropad (&#181;PAD) using polydimethylsiloxane (PDMS), screen-printed electrode (SPE) modified with IrO2-graphene films and molded acrylonitrile butadiene styrene (ABS) plastic holder. Repetitive cathodic potential cycling was employed for graphene oxide (GO) reduction which can completely remove electrochemically unstable oxygenated groups and generate a 2D defect-free homogeneous graphene thin film with excellent stability and electronic properties. A uniform and smooth IrO2 film in nanoscale grain size is anodically electrodeposited onto the graphene film, without any observable cracks. The resulting IrO2-RGO electrode showed slightly super-Nernstian responses from pH 2-12 in Britton-Robinson (B-R) buffers with good linearity, small hysteresis, low response time and reproducibility in different buffers, as well as low sensitivities to different interfering ionic species and dissolved oxygen. A simple portable digital pH meter is fabricated, whose signal is measured with a multimeter, using high input-impedance operational amplifier and consumer batteries. The pH values measured with the portable electrochemical paper-microfluidic pH sensors were consistent with those measured using a commercial laboratory pH meter with a glass electrode.

The study demonstrates the growth of iridium oxide-reduced graphene oxide (IrO2-RGO) nanohybrid thin films on irregular and rough screen-printed carbon substrate through a green electrochemical synthesis, and their implementation as a pH sensor with a patterned paper-fluidic platform.

A facile, controllable, inexpensive and green electrochemical synthesis of IrO2-graphene nanohybrid thin films is developed to fabricate an easy-to-use ...

Non-aqueous Electrode Processing and Construction of Lithium-ion Coin Cells

Research into new and improved materials to be utilized in lithium-ion batteries (LIB) necessitates an experimental counterpart to any computational analysis. Testing of lithium-ion batteries in an academic setting has taken on several forms, but at the most basic level lies the coin cell construction. In traditional LIB electrode preparation, a multi-phase slurry composed of active material, binder, and conductive additive is cast out onto a substrate. An electrode disc can then be punched from the dried sheet and used in the construction of a coin cell for electrochemical evaluation. Utilization of the potential of the active material in a battery is critically dependent on the microstructure of the electrode, as an appropriate distribution of the primary components are crucial to ensuring optimal electrical conductivity, porosity, and tortuosity, such that electrochemical and transport interaction is optimized. Processing steps ranging from the combination of dry powder, wet mixing, and drying can all critically affect multi-phase interactions that influence the microstructure formation. Electrochemical probing necessitates the construction of electrodes and coin cells with the utmost care and precision. This paper aims at providing a step-by-step guide of non-aqueous electrode processing and coin cell construction for lithium-ion batteries within an academic setting and with emphasis on deciphering the influence of drying and calendaring.

Non-aqueous electrode processing is central to the construction of coin cells and the evaluation of new electrode chemistries for lithium-ion batteries. A step-by-step guide to the basic practices needed as an electrochemical engineer working with batteries in an academic experimental setting is furnished.

Research into new and improved materials to be utilized in lithium-ion batteries (LIB) necessitates an experimental counterpart to any computational ...

Methods for Measuring the Orientation and Rotation Rate of 3D-printed Particles in Turbulence

Experimental methods are presented for measuring the rotational and translational motion of anisotropic particles in turbulent fluid flows. 3D printing technology is used to fabricate particles with slender arms connected at a common center. Shapes explored are crosses (two perpendicular rods), jacks (three perpendicular rods), triads (three rods in triangular planar symmetry), and tetrads (four arms in tetrahedral symmetry). Methods for producing on the order of 10,000 fluorescently dyed particles are described. Time-resolved measurements of their orientation and solid-body rotation rate are obtained from four synchronized videos of their motion in a turbulent flow between oscillating grids with R&#955; = 91. In this relatively low-Reynolds number flow, the advected particles are small enough that they approximate ellipsoidal tracer particles. We present results of time-resolved 3D trajectories of position and orientation of the particles as well as measurements of their rotation rates.

We use 3D printing to fabricate anisotropic particles in the shapes of jacks, crosses, tetrads, and triads, whose alignments and rotations in turbulent fluid flow can be measured from multiple simultaneous video images.

Experimental methods are presented for measuring the rotational and translational motion of anisotropic particles in turbulent fluid flows. 3D printing ...