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., Müller, A. H. <a target="_blank" href="http://pubs.rsc.org/en/Content/ArticleLanding/2008/SM/b718131k#!divAbstract">Janus particles.</a> Soft Matter. 4 (4), 663-668 (2008).</li>
<li>Chen, Y. -L., Jiang, H. -R. <a target="_blank" href="http://aip.scitation.org/doi/abs/10.1063/1.4967740?journalCode=apl">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="https://www.ncbi.nlm.nih.gov/pubmed/22924894">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. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Dielectrophoretic+assembly+of+metallodielectric+Janus+particles+in+AC+electric+fields%5BTitle%5D)+AND+%22Langmuir%22%5BJournal%5D)">Dielectrophoretic assembly of metallodielectric Janus particles in AC electric fields.</a> Langmuir. 24 (23), 13312-13320 (2008).</li>
<li>Zhang, L., Zhu, Y. <a target="_blank" href="http://aip.scitation.org/doi/abs/10.1063/1.3378687?journalCode=apl">Dielectrophoresis of Janus particles under high frequency ac-electric fields.</a> Appl Phys Lett. 96 (14), 141902(2010).</li>
<li>Chen, J., Zhang, H., Zheng, X., Cui, H. <a target="_blank" href="http://aip.scitation.org/doi/full/10.1063/1.4868373">Janus particle microshuttle: 1D directional self-propulsion modulated by AC electrical field.</a> AIP Adv. 4 (3), 031325(2014).</li>
<li>Gangwal, S., Cayre, O. J., Bazant, M. Z., Velev, O. D. <a target="_blank" href="http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.100.058302">Induced-charge electrophoresis of metallodielectric particles.</a> Phys Rev Lett. 100 (5), 058302(2008).</li>
<li>Peng, C., Lazo, I., Shiyanovskii, S. V., Lavrentovich, O. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Induced-charge+electro-osmosis+around+metal+and+Janus+spheres+in+water%3A+Patterns+of+flow+and+breaking+symmetries%5BTitle%5D)+AND+%22Phys+Rev+E%22%5BJournal%5D)">Induced-charge electro-osmosis around metal and Janus spheres in water: Patterns of flow and breaking symmetries.</a> Phys Rev E. 90 (5), 051002(2014).</li>
<li>Ramos, A., García-Sánchez, P., Morgan, H. <a target="_blank" href="https://www.infona.pl/resource/bwmeta1.element.elsevier-629cc57b-551e-3eca-bc03-4c5aae304080">AC electrokinetics of conducting microparticles: A review.</a> Curr Opin Colloid Interface Sci. 24, 79-90 (2016).</li>
<li>Hong, L., Jiang, S., Granick, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Simple+method+to+produce+Janus+colloidal+particles+in+large+quantity%5BTitle%5D)+AND+%22Langmuir%22%5BJournal%5D)">Simple method to produce Janus colloidal particles in large quantity.</a> Langmuir. 22 (23), 9495-9499 (2006).</li>
<li>Bhaskar, S., Hitt, J., Chang, S. W. L., Lahann, J. <a target="_blank" href="http://onlinelibrary.wiley.com/doi/10.1002/anie.200806241/full#references">Multicompartmental microcylinders.</a> Angewandte Chemie International Edition. 48 (25), 4589-4593 (2009).</li>
<li>Nie, Z., Li, W., Seo, M., Xu, S., Kumacheva, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Janus+and+ternary+particles+generated+by+microfluidic+synthesis%3A+design%2C+synthesis%2C+and+self-assembly%5BTitle%5D)+AND+%22J+Am+Chem+Soc%22%5BJournal%5D)">Janus and ternary particles generated by microfluidic synthesis: design, synthesis, and self-assembly.</a> J Am Chem Soc. 128 (29), 9408-9412 (2006).</li>
<li>Jiang, H. -R., Yoshinaga, N., Sano, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Active+motion+of+a+Janus+particle+by+self-thermophoresis+in+a+defocused+laser+beam%5BTitle%5D)+AND+%22Phys+Rev+Lett%22%5BJournal%5D)">Active motion of a Janus particle by self-thermophoresis in a defocused laser beam.</a> Phys Rev Lett. 105 (26), 268302(2010).</li>
<li>Pawar, A. B., Kretzschmar, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Multifunctional+patchy+particles+by+glancing+angle+deposition%5BTitle%5D)+AND+%22Langmuir%22%5BJournal%5D)">Multifunctional patchy particles by glancing angle deposition.</a> Langmuir. 25 (16), 9057-9063 (2009).</li>
<li>García-Sánchez, P., Ren, Y., Arcenegui, J. J., Morgan, H., Ramos, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Alternating+current+electrokinetic+properties+of+gold-coated+microspheres%5BTitle%5D)+AND+%22Langmuir%22%5BJournal%5D)">Alternating current electrokinetic properties of gold-coated microspheres.</a> Langmuir. 28 (39), 13861-13870 (2012).</li>
<li>Ren, Y. K., Morganti, D., Jiang, H. Y., Ramos, A., Morgan, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Electrorotation+of+metallic+microspheres%5BTitle%5D)+AND+%22Langmuir%22%5BJournal%5D)">Electrorotation of metallic microspheres.</a> Langmuir. 27 (6), 2128-2131 (2011).</li>
<li>Jones, T. B., Jones, T. B. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aJones%2C+TB+%22Electromechanics+of+particles%22">Electromechanics of particles</a>. , Cambridge University Press. Cambridge, UK. (2005).</li>
<li>Morganti, D. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aMorganti%2C+D+%22AC+electrokinetic+analysis+of+chemically+modified+microparticles%22">AC electrokinetic analysis of chemically modified microparticles</a>. , University of Southampton. (2012).</li>
<li>Morgan, H., Hughes, M. P., Green, N. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Separation+of+submicron+bioparticles+by+dielectrophoresis%5BTitle%5D)+AND+%22Biophys+J%22%5BJournal%5D)">Separation of submicron bioparticles by dielectrophoresis.</a> Biophys J. 77 (1), 516-525 (1999).</li>
<li>Ren, Y., et al. <a target="_blank" href="http://pubs.rsc.org/en/Content/ArticleLanding/2015/LC/c5lc00058k#!divAbstract">Induced-charge electroosmotic trapping of particles.</a> Lab Chip. 15 (10), 2181-2191 (2015).</li>
</ol>

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 ele...

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><tbody><tr><td>Silica Microsphere-2.34 &amp;micro;m</td><td>Bangs Laboratories</td><td>SS04N</td><td></td></tr><tr><td>Ethyl Alcohol (99.5%)</td><td>KATAYAMA CHEMICAL</td><td>E-0105</td><td></td></tr><tr><td>SYLGARD 184 A&amp;amp;B Silicone Elastomer(PDMS)</td><td>DOW CORNING</td><td></td><td>PDMS&amp;nbsp;</td></tr><tr><td>&amp;nbsp;ITO glass</td><td>Luminescence Technology</td><td>LT-G001</td><td></td></tr><tr><td>Fiber laser marking machine</td><td>Taiwan 3Axle Technology</td><td>TAFB-R-20W</td><td></td></tr><tr><td>&amp;nbsp;2-channel function generator</td><td>Gwinsek</td><td>AFG-2225</td><td></td></tr><tr><td>CMOS camera</td><td>Point Grey</td><td>GS3-U3-32S4M-C</td><td></td></tr><tr><td>Sputter</td><td>JEOL</td><td>JFC-1100E</td><td></td></tr><tr><td>Operational Amplifiers</td><td>Texas Instruments</td><td>LM6361N</td><td>OP invertor&amp;nbsp;</td></tr><tr><td>Ultrasonic Cleaner</td><td>Gui Lin Yiyuan Ultrasonic Machinery Co.</td><td>DG-1</td><td></td></tr><tr><td>Microcentrifuge</td><td>Scientific Specialties, Inc.</td><td></td><td>1.5ml</td></tr><tr><td>Mini Centrifuge</td><td>LMS</td><td>MC-MCF-2360</td><td></td></tr><tr><td>Microscope cover glass</td><td>Marienfeld-Superior</td><td></td><td>18*18mm</td></tr><tr><td>Inverted optical microscope</td><td>Olympus</td><td>OX-71&amp;nbsp;</td><td></td></tr><tr><td>Parafilm</td><td>bemis</td><td></td><td>spacer</td></tr></tbody></table>

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 El...

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, ...

preparation-janus-particles-alternating-current-electrokinetic

Research

Education

JoVE Core

JoVE Journal

Electrical Engineering

Engineering

Unit 1

AC Circuit Analysis

SCIENTISTS IN ACTION

8.2K Views.  National Taiwan University.  In dit artikel wordt een eenvoudige methode om gedeeltelijk of volledig gecoate metallische deeltjes te bereiden en AC-elektrokinetische eigenschappen te meten met een snel vervaardigde indiumtinoxide (ITO) -elektrode-array aangetoond. 

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

Patterning Cells on Optically Transparent Indium Tin Oxide Electrodes

The ability to exercise precise spatial and temporal control over cell-surface interactions is an important prerequisite to the assembly of multi-cellular constructs serving as in vitro mimics of native tissues.  In this study, photolithography and wet etching techniques were used to fabricate individually addressable indium tin oxide (ITO) electrodes on glass substrates.  The glass substrates containing ITO microelectrodes were modified with poly(ethylene glycol) (PEG) silane to make them protein and cell resistive.  Presence of insulating PEG molecules on the electrode surface was verified by cyclic voltammetry employing potassium ferricyanide as a redox reporter molecule.  Importantly, the application of reductive potential caused desorption of the PEG layer, resulting in regeneration of the conductive electrode surface and appearance of typical ferricyanide redox peaks.    Application of reductive potential also corresponded to switching of ITO electrode properties from cell non-adhesive to cell-adhesive. Electrochemical stripping of PEG-silane layer from ITO microelectrodes allowed for cell adhesion to take place in a spatially defined fashion, with cellular patterns corresponding closely to electrode patterns.  Micropatterning of several cell types was demonstrated on these substrates.   In the future, the control of the biointerfacial properties afforded by this method will allow to engineer cellular microenvironments through the assembly of three or more cell types into a precise geometric configuration on an optically transparent substrate.

Non-fouling PEG silane monolayer was desorbed from individually addressable ITO electrodes on glass by application of a reductive potential. Electrochemical stripping of PEG-silane layer from ITO microelectrodes allowed for cell adhesion to take place in a spatially defined fashion, with cellular patterns corresponding closely to electrode patterns.

The ability to exercise precise spatial and temporal control over cell-surface interactions is an important prerequisite to the assembly of multi-cellular ...

Biology

AC Electrokinetic Phenomena Generated by Microelectrode Structures

The field of AC electrokinetics is rapidly growing due to its ability to perform dynamic fluid and particle manipulation on the micro- and nano-scale, which is essential for Lab-on-a-Chip applications. AC electrokinetic phenomena use electric fields to generate forces that act on fluids or suspended particles (including those made of dielectric or biological material) and cause them to move in astonishing ways1, 2. Within a single channel, AC electrokinetics can accomplish many essential on-chip operations such as active micro-mixing, particle separation, particle positioning and micro-pattering. A single device may accomplish several of those operations by simply adjusting operating parameters such as frequency or amplitude of the applied voltage. Suitable electric fields can be readily created by micro-electrodes integrated into microchannels. It is clear from the tremendous growth in this field that AC electrokinetics will likely have a profound effect on healthcare diagnostics3-5, environmental monitoring6 and homeland security7.

In general, there are three AC Electrokinetic phenomena (AC electroosmosis, dielectrophoresis and AC electrothermal effect) each with unique dependencies on the operating parameters. A change in these operating parameters can cause one phenomena to become dominant over another, thus changing the particle or fluid behavior. 

It is difficult to predict the behavior of particles and fluids due to the complicated physics that underlie AC electrokinetics. It is the goal of this publication to explain the physics and elucidate particle and fluid behavior. Our analysis also covers how to fabricate the electrode structures that generate them, and how to interpret a wide number of experimental observations using several popular device designs. This video article will help scientists and engineers understand these phenomena and may encourage them to start using AC Electrokinetics in their research.

Manipulating fluids and suspended particles in the micro- and nano-scale is becoming more of a reality as enabling technologies, like AC electrokinetics, continue to develop. Here, we discuss the physics behind AC electrokinetics, how to fabricate these devices and how to interpret the experimental observations.

The field of AC electrokinetics is rapidly growing due to its ability to perform dynamic fluid and particle manipulation on the micro- and nano-scale, ...

Characterizing Electron Transport through Living Biofilms

Here we demonstrate the method of electrochemical gating used to characterize electrical conductivity of electrode-grown microbial biofilms under physiologically relevant conditions.1 These measurements are performed on living biofilms in aqueous medium using source and drain electrodes patterned on a glass surface in a specialized configuration referred to as an interdigitated electrode (IDA) array. A biofilm is grown that extends across the gap connecting the source and drain. Potentials are applied to the electrodes (ES and ED) generating a source-drain current (ISD) through the biofilm between the electrodes. The dependency of electrical conductivity on gate potential (the average of the source and drain potentials, EG = [ED + ES]/2) is determined by systematically changing the gate potential and measuring the resulting source-drain current. The dependency of conductivity on gate potential provides mechanistic information about the extracellular electron transport process underlying the electrical conductivity of the specific biofilm under investigation. The electrochemical gating measurement method described here is based directly on that used by M. S. Wrighton2,3 and colleagues and R. W. Murray4,5,6 and colleagues in the 1980&#39;s to investigate thin film conductive polymers.

A protocol for measuring electrical conductivity of living microbial biofilms under physiologically relevant conditions is presented.

Here we demonstrate the method of electrochemical gating used to characterize electrical conductivity of electrode-grown microbial biofilms under ...

Chemistry

A High Performance Impedance-based Platform for Evaporation Rate Detection

This paper describes the method of a novel impedance-based platform for the detection of the evaporation rate. The model compound hyaluronic acid was employed here for demonstration purposes. Multiple evaporation tests on the model compound as a humectant with various concentrations in solutions were conducted for comparison purposes. A conventional weight loss approach is known as the most straightforward, but time-consuming, measurement technique for evaporation rate detection. Yet, a clear disadvantage is that a large volume of sample is required and multiple sample tests cannot be conducted at the same time. For the first time in literature, an electrical impedance sensing chip is successfully applied to a real-time evaporation investigation in a time sharing, continuous and automatic manner. Moreover, as little as 0.5 ml of test samples is required in this impedance-based apparatus, and a large impedance variation is demonstrated among various dilute solutions. The proposed high-sensitivity and fast-response impedance sensing system is found to outperform a conventional weight loss approach in terms of evaporation rate detection.

This paper presents an impedance-based apparatus for evaporation rate detection of solutions. It offers clear advantages over a conventional weight loss approach: a fast response, high-sensitivity detection, a small sample requirement, multiple sample measurements, and easy disassembly for cleaning and reuse purposes.

This paper describes the method of a novel impedance-based platform for the detection of the evaporation rate. The model compound hyaluronic acid was ...

Focused Ion Beam Fabrication of LiPON-based Solid-state Lithium-ion Nanobatteries for In Situ Testing

Solid-state electrolytes are a promising replacement for current organic liquid electrolytes, enabling higher energy densities and improved safety of lithium-ion (Li-ion) batteries. However, a number of setbacks prevent their integration into commercial devices. The main limiting factor is due to nanoscale phenomena occurring at the electrode/electrolyte interfaces, ultimately leading to degradation of battery operation. These key problems are highly challenging to observe and characterize as these batteries contain multiple buried interfaces. One approach for direct observation of interfacial phenomena in thin film batteries is through the fabrication of electrochemically active nanobatteries by a focused ion beam (FIB). As such, a reliable technique to fabricate nanobatteries was developed and demonstrated in recent work. Herein, a detailed protocol with a step-by-step process is presented to enable the reproduction of this nanobattery fabrication process. In particular, this technique was applied to a thin film battery consisting of LiCoO2/LiPON/a-Si, and has further been previously demonstrated by in situ cycling within a transmission electron microscope.

Focused Ion Beam Fabrication of LiPON-based Solid-state Lithium-ion Nanobatteries for In Situ Testing

A protocol for the fabrication of electrochemically active LiPON-based solid-state lithium-ion nanobatteries using a focused ion beam is presented.

Solid-state electrolytes are a promising replacement for current organic liquid electrolytes, enabling higher energy densities and improved safety of ...

In Situ Lithiated Reference Electrode: Four Electrode Design for In-operando Impedance Spectroscopy

Extending operating voltage of Li-ion batteries results in higher energy output from these devices. High voltages, however, may trigger or accelerate multiple processes responsible for long-term performance decay. Given the complexity of physical processes occurring inside the cell, it is often challenging to achieve a full understanding of the root causes of this performance degradation. This difficulty arises in part from the fact that any electrochemical measurement of a battery will return the combined contributions of all components in the cell. Incorporation of a reference electrode can solve part of the problem, as it allows the electrochemical reactions of the cathode and the anode to be individually probed. A variation in the voltage range experienced by the cathode, for example, can indicate alterations in the pool of cyclable lithium ions in the full-cell. The structural evolution of the many interphases existing in the battery can also be monitored, by measuring the contributions of each electrode to the overall cell impedance. Such wealth of information amplifies the reach of diagnostic analysis in Li-ion batteries and provides valuable input to the optimization of individual cell components. In this work, we introduce the design of a test cell able to accommodate multiple reference electrodes, and present reference electrodes that are appropriate for each specific type of measurement, detailing the assembly process in order to maximize the accuracy of the experimental results.

The incorporation of reference electrodes in a Li-ion battery provides valuable information to elucidate degradation mechanisms at high voltages. In this article, we present a cell design that accommodates multiple reference electrodes, along with the assembly steps to assure maximum accuracy of the data obtained in electrochemical measurements.

Extending operating voltage of Li-ion batteries results in higher energy output from these devices. High voltages, however, may trigger or accelerate ...

A Method for Systematic Electrochemical and Electrophysiological Evaluation of Neural Recording Electrodes

New materials and designs for neural implants are typically tested separately, with a demonstration of performance but without reference to other implant characteristics.&#160;This precludes a rational selection of a particular implant as optimal for a particular application and the development of new materials based on the most critical performance parameters.&#160;This article develops a protocol for in vitro and in vivo testing of neural recording electrodes.&#160;Recommended parameters for electrochemical and electrophysiological testing are documented with the key steps and potential issues discussed.&#160;This method eliminates or reduces the impact of many systematic errors present in simpler in vivo testing paradigms, especially variations in electrode/neuron distance and between animal models.&#160;The result is a strong correlation between the critical in vitro and in vivo responses, such as impedance and signal-to-noise ratio.&#160;This protocol can easily be adapted to test other electrode materials and designs.&#160;The in vitro techniques can be expanded to any other nondestructive method to determine further important performance indicators.&#160;The principles used for the surgical approach in the auditory pathway can also be modified to other neural regions or tissue.

Different electrode coatings affect neural recording performance through changes to electrochemical, chemical and mechanical properties. Comparison of electrodes in vitro is relatively simple, however comparison of in vivo response is typically complicated by variations in electrode/neuron distance and between animals. This article provides a robust method to compare neural recording electrodes.

New materials and designs for neural implants are typically tested separately, with a demonstration of performance but without reference to other implant ...

Neuroscience

Performing In Situ Closed-Cell Gas Reactions in the Transmission Electron Microscope

Gas reactions studied by in situ electron microscopy can be used to capture the real-time morphological and microchemical transformations of materials at length scales down to the atomic level. In situ closed-cell gas reaction (CCGR) studies performed using (scanning) transmission electron microscopy (STEM) can separate and identify localized dynamic reactions, which are extremely challenging to capture using other characterization techniques. For these experiments, we used a CCGR holder that utilizes microelectromechanical systems (MEMS)-based heating microchips (hereafter referred to as &#34;E-chips&#34;). The experimental protocol described here details the method for performing in situ gas reactions in dry and wet gases in an aberration-corrected STEM. This method finds relevance in many different materials systems, such as catalysis and high-temperature oxidation of structural materials at atmospheric pressure and in the presence of various gases with or without water vapor. Here, several sample preparation methods are described for various material form factors. During the reaction, mass spectra obtained with a residual gas analyzer (RGA) system with and without water vapor further validates gas exposure conditions during reactions. Integrating an RGA with an in situ CCGR-STEM system can, therefore, provide critical insight to correlate gas composition with the dynamic surface evolution of materials during reactions. In situ/operando studies using this approach allow&#160;for detailed investigation of the fundamental reaction mechanisms and kinetics that occur at specific environmental conditions (time, temperature, gas, pressure), in real-time, and at high spatial resolution.

Performing In Situ Closed-Cell Gas Reactions in the Transmission Electron Microscope

Here, we present a protocol for performing in situ TEM closed-cell gas reaction experiments while detailing several commonly used sample preparation methods.

Gas reactions studied by in situ electron microscopy can be used to capture the real-time morphological and microchemical transformations of materials at ...

Precise Electrochemical Sizing of Individual Electro-Inactive Particles

Nanoimpact electrochemistry enables the time-resolved in situ characterization (e.g., size, catalytic activity) of single nanomaterial units, providing a means of elucidating heterogeneities that would be masked in ensemble studies. To implement this technique with redox inactive particles, a solution-phase redox reaction is used to produce a steady-state background current on a disk ultramicroelectrode. When a particle adsorbs onto the electrode, it produces a stepwise reduction in the exposed electrode area, which produces, in turn, a stepwise decrease in the current commensurate with the size of the adsorbing species. Historically, however, nanoimpact electrochemistry has suffered from &#34;edge effects,&#34; in which the radial diffusion layer formed at the circumference of the ultramicroelectrodes renders the step size dependent not only on the size of the particle but also on where it lands on the electrode. The introduction of electrocatalytic current generation, however, mitigates the heterogeneity caused by edge effects, thus improving the measurement precision. In this approach, termed &#34;electrocatalytic interruption,&#34; a substrate that regenerates the redox probe at the diffusion layer is introduced. This shifts the rate-limiting step of the current generation from diffusion to the homogeneous reaction rate constant, thus reducing flux heterogeneity and increasing the precision of particle sizing by an order of magnitude. The protocol described here explains the set-up and data collection employed in nanoimpact experiments implementing this effect for improved precision in the sizing of redox in-active materials.

As an analytical technique, nanoimpact electrochemistry, an increasingly important approach to counting and characterizing nanometer-scale, electro-inactive particles, suffers from poor precision due to the heterogeneous current distributions that arise from its use of ultramicroelectrodes. Outlined here is a generalized approach, termed "electrocatalytic interruption," that enhances precision in such measurements.

Nanoimpact electrochemistry enables the time-resolved in situ characterization (e.g., size, catalytic activity) of single nanomaterial units, providing a ...

Tools for Surface Treatment of Silicon Planar Intracortical Microelectrodes

Intracortical microelectrodes hold great therapeutic potential. But they are challenged with significant performance reduction after modest implantation durations. A substantial contributor to the observed decline is the damage to the neural tissue proximal to the implant and subsequent neuroinflammatory response. Efforts to improve device longevity include chemical modifications or coating applications to the device surface to improve the tissue response. Development of such surface treatments is typically completed using non-functional "dummy" probes that lack the electrical components required for the intended application. Translation to functional devices requires additional consideration given the fragility of intracortical microelectrode arrays. Handling tools greatly facilitate surface treatments to assembled devices, particularly for modifications that require long procedural times. The handling tools described here are used for surface treatments applied via gas-phase deposition and aqueous solution exposure. Characterization of the coating is performed using ellipsometry and x-ray photoelectron spectroscopy. A comparison of electrical impedance spectroscopy recordings before and after the coating procedure on functional devices confirmed device integrity following modification. The described tools can be readily adapted for alternative electrode devices and treatment methods that maintain chemical compatibility.

The present protocol describes tools for handling silicon planar intracortical microelectrodes during treatments for surface modification via gas deposition and aqueous solution reactions. The assembly of the components used to handle the devices throughout the procedure is explained in detail.

Intracortical microelectrodes hold great therapeutic potential. But they are challenged with significant performance reduction after modest implantation ...

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

Samenvatting

Meer video's verkennen