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

Summary

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.

Abstract

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° (for EROT) or 180° (for DEP). Representative results of AC electrokinetic measurements with a four-phase ITO electrode array are presented.

Introduction

Janus particles, named after the Roman god with a double face, are asymmetric particles whose two sides have physically or chemically different surface properties^1,2. Due to this asymmetric feature, Janus particles exhibit special responses under electric fields, such as DEP^3,4,5,6, EROT², and induced-charge electrophoresis (ICEP)^7,8,9. Recently, several methods to pr....

Protocol

1. Fabrication of the Microchip

1. Preparation of the ITO electrode
   1. Use commercial illustration software to draw a cross pattern. Set the distance between the diagonal electrodes to 160 µm 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.
   2. 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.
   3. Put the ITO glass onto the pulsed-fiber laser marking machine. Focus the laser on the surface of the ITO glas....

Results

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 µm, as shown in Figure 1B.

Discussion

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.......

Materials

List of materials used in this article

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