Optoelectronic tweezers (OET) or light patterned dielectrophoresis (DEP) has been proved to be an effective micromanipulation technology for cell sorting, cell separation and cell communications. Apart from being useful for cell biology experiments, the capability of moving small objects accurately also makes OET an attractive technology for other micromanipulation applications. In this work, we demonstrated the use of OET to manipulate conductive silver-coated Poly(methyl methacrylate) (PMMA) microspheres into different patterns. The silver-coated PMMA microspheres were suspended in deionized water and manipulated by positive DEP force generated by an OET device. It is found that the microspheres can be moved at a max speed of over 3000 µm/s, corresponding to around 4 nano-newton (10-9 N) DEP force, which is at least an order of magnitude stronger than the DEP force imposed on widely-reported glass and PMMA microspheres. Simulations were carried out to clarify the underlying mechanism and it is found that the strong DEP force is caused by the significant increase of the gradient of electric field due to the silver shells of the microspheres. The strong DEP force makes it possible to manipulate these metallic microspheres efficiently with high reliability, which is important for applications on electronic component assembling and circuit construction

Cooper, Jonathan

Juvert, Joan

Neale, Steven

Zhang, Shuailong

English

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Assembling and manipulating metallic beads using optoelectronic tweezer
Shuailong Zhang, Joan Juvert, and Steven Neale*
School of Engineering, University of Glasgow, Glasgow, G12 8LT, UK
*Steven.Neale@glasgow.ac.uk
Introduction: The aim of this work is to develop a new method with the potential to revolutionise the process of assembling micron/nanoscale electronic
components into circuits. This will be accomplished by developing a radically new assembly strategy based on a touch-less opto-electro-fluidic manipulation
technique known as optoelectronic tweezers (OET). In this work, we demonstrated the use of OET to manipulate conductive silver-coated Poly(methyl
methacrylate) (PMMA) microspheres (50 micron diameter) into different patterns. It is found that the microspheres can be moved at a max velocity of 3200 µm/s,
corresponding to 4.18 nano-newton (10-9 N) DEP force, and also be positioned with high accuracy due to this high DEP force.
References
[1] A. Zarowna-Dabrowska, et al., “Miniaturized optoelectronic tweezers controlled by GaN micro-pixel light emitting diode arrays,” Opt. Express, vol
19, no. 3, pp. 2720-2728, 2012.
[2] A. H. Jeorrett, et al., “Optoelectronic tweezers system for single cell manipulation and fluorescence imaging of live immune cells,” Opt. Express, vol
22, no. 2, pp. 1372-1380, 2014.
Acknowledgement
Background
What are optoelectronic tweezers?
Optoelectronic tweezers (OET) is a technology using a light-patterned
photoconductive electrode to provide real time control over the positioning
of electric fields, thus achieving particle trapping and manipulation [1].
The structure of an OET device
An OET device, shown in Fig.1 (a), typically consists of an upper and a
lower glass slide coated with a transparent conductor (typically indium tin
oxide, ITO) with the lower slide coated with an additional photoconductive
layer (typically amorphous silicon (a-Si:H)).
How does an OET device work?
A light pattern is projected onto the device which creates non-uniform
distribution of electric field around the area which has been illuminated. In
this case, ‘virtual electrodes’ are generated, which can be used to corral
polystyrene microbeads via dielectrophoresis (DEP), as shown in Fig.1 (b).
Aims
Fig.1 (a): Schematic of a typical OET device; (b) polystyrene microbeads
manipulation  and trapping using OET [2].
Moving Electronic Components
The main aim of this work is to assemble electronic components into
circuits using OET, producing a step change in the size of the smallest
components that can be assembled using the current surface mount
technology. We expect to fabricate high-performance micron-sized (or even
nano-sized) circuits using OET. A schematic and an microscope image of
using OET to move a resistor are shown in Fig.2 (a) and (b).
Moving Metallic beads to Create Conductive Path
Another aim is to use OET device to manipulate and pattern lines of
conductive microbeads to form metal conductive paths acting as electrical
contacts for the circuit, essentially as a form of mask-less lithography.
Experimental results will be shown in the following part.
Fig.2 (a): Schematic of using OET device to move a resistor ; (b) a microscope image of
using OET device to move a resistor (400×200 µm).
Experimental results
• Scanning electron microscope (SEM) image of silver-
coated PMMA microspheres is shown in Fig.3
• Schematic experimental setup is shown in Fig.4 (a).
The metallic microspheres were attracted to the
illumination region due to positive DEP force, as
shown in Fig.4 (b) and (c).
Fig.3: SEM image of silver-coated PMMA microspheres with 700
magnification times.
• Fig.5 (a)-(f) shows the microscope images of metallic
microspheres trapped by 200 µm diameter and 60 µm
diameter circular light patterns at different velocities. As
shown, the centre-to-centre distance between the
microsphere and the light pattern increases as the velocity
increases.
• By measuring the centre-to-centre distance between the
trapped microsphere and circular light pattern at varying
velocities, a trap profile can be plotted, which shows the
DEP force experienced by a microsphere at different
locations within the trap, as shown in Fig.6.`
• The metallic microspheres can be moved at a max
velocity of 3200 µm/s by traps created by light patterns
with 200 µm and 150 µm diameters, corresponding to a
DEP force of 4.18 nN, and a max velocity of 3000 µm/s
by traps created by light patterns with 100 µm and 50 µm
diameters, corresponding to a DEP force of 3.9 nN.
Conclusion: We have demonstrated the use of OET to manipulate conductive silver microspheres into different patterns. It is found that the microspheres can be
exerted with strong DEP force (10-9 N) and also be positioned with high accuracy. The aim of this work is to develop a new method to assemble micron/nanoscale
electronic components into circuits.
(a)
Fig.4 (a):Schematic experimental setup; microscope images of a
metallic microsphere (b) before and (c) after being trapped by a 200
µm circular light pattern.
Fig.5 Microscope images of metallic microspheres trapped by 200 µm
diameter circular light pattern at (a) 600 µm/s, (b) 1600 µm/s and (c)
3200 µm/s; microscope images of metallic microspheres trapped by 60
µm diameter circular light pattern at (d) 600 µm/s, (e) 1400 µm/s and (f)
3000 µm/s.
Fig.7:Microscope images of metallic microsphere and reference
bubble with varied spacing: (a) 1.39 µm, (b) 2.5 µm, (c) 3.3 µm, (d)
5.3 µm, (e) 8.4 µm, (f) 10.6 µm and (g) 20.7 µm. An example of the
measurement lines (red coloured) fitted to the microsphere and
bubble boundaries to estimate the spacing, is shown in (a).
Microscope images of (h) ‘O’, (i) ‘E’, (j) ‘T’ formed by assembling
the metallic microspheres in parallel via the OET device.
• Due to the strong DEP force, the metallic microspheres
can be positioned with high accuracy, as shown in Fig.7
(a)-(j). The targeted separations between the bubble and
bead are 1 µm, followed by 2 µm, 3 µm, 5 µm, 8 µm, 10
µm and 20 µm.
Fig.6: Trap profiles of metallic microspheres created by 200 µm,
150 µm, 100 µm and 60 µm diameter light pattern.


Assembling and Manipulating Metallic Beads Using Optoelectronic Tweezers

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Assembling and manipulating metallic beads using optoelectronic tweezerShuailong Zhang, Joan Juvert, and Steven Neale*School of Engineering, University of Glasgow, Glasgow, G12 8LT, UK*Steven.Neale@glasgow.ac.ukIntroduction: The aim of this work is to develop a new method with the potential to revolutionise the process of assembling micron/nanoscale electroniccomponents into circuits. This will be accomplished by developing a radically new assembly strategy based on a touch-less opto-electro-fluidic manipulationtechnique known as optoelectronic tweezers (OET). In this work, we demonstrated the use of OET to manipulate conductive silver-coated Poly(methylmethacrylate) (PMMA) microspheres (50 micron diameter) into different patterns. It is found that the microspheres can be moved at a max velocity of 3200 µm/s,corresponding to 4.18 nano-newton (10-9 N) DEP force, and also be positioned with high accuracy due to this high DEP force.References[1] A. Zarowna-Dabrowska, et al., “Miniaturized optoelectronic tweezers controlled by GaN micro-pixel light emitting diode arrays,” Opt. Express, vol19, no. 3, pp. 2720-2728, 2012.[2] A. H. Jeorrett, et al., “Optoelectronic tweezers system for single cell manipulation and fluorescence imaging of live immune cells,” Opt. Express, vol22, no. 2, pp. 1372-1380, 2014.AcknowledgementBackgroundWhat are optoelectronic tweezers?Optoelectronic tweezers (OET) is a technology using a light-patternedphotoconductive electrode to provide real time control over the positioningof electric fields, thus achieving particle trapping and manipulation [1].The structure of an OET deviceAn OET device, shown in Fig.1 (a), typically consists of an upper and alower glass slide coated with a transparent conductor (typically indium tinoxide, ITO) with the lower slide coated with an additional photoconductivelayer (typically amorphous silicon (a-Si:H)).How does an OET device work?A light pattern is projected onto the device which creates non-uniformdistribution of electric field around the area which has been illuminated. Inthis case, ‘virtual electrodes’ are generated, which can be used to corralpolystyrene microbeads via dielectrophoresis (DEP), as shown in Fig.1 (b).AimsFig.1 (a): Schematic of a typical OET device; (b) polystyrene microbeadsmanipulation  and trapping using OET [2].Moving Electronic ComponentsThe main aim of this work is to assemble electronic components intocircuits using OET, producing a step change in the size of the smallestcomponents that can be assembled using the current surface mounttechnology. We expect to fabricate high-performance micron-sized (or evennano-sized) circuits using OET. A schematic and an microscope image ofusing OET to move a resistor are shown in Fig.2 (a) and (b).Moving Metallic beads to Create Conductive PathAnother aim is to use OET device to manipulate and pattern lines ofconductive microbeads to form metal conductive paths acting as electricalcontacts for the circuit, essentially as a form of mask-less lithography.Experimental results will be shown in the following part.Fig.2 (a): Schematic of using OET device to move a resistor ; (b) a microscope image ofusing OET device to move a resistor (400×200 µm).Experimental results• Scanning electron microscope (SEM) image of silver-coated PMMA microspheres is shown in Fig.3• Schematic experimental setup is shown in Fig.4 (a).The metallic microspheres were attracted to theillumination region due to positive DEP force, asshown in Fig.4 (b) and (c).Fig.3: SEM image of silver-coated PMMA microspheres with 700magnification times.• Fig.5 (a)-(f) shows the microscope images of metallicmicrospheres trapped by 200 µm diameter and 60 µmdiameter circular light patterns at different velocities. Asshown, the centre-to-centre distance between themicrosphere and the light pattern increases as the velocityincreases.• By measuring the centre-to-centre distance between thetrapped microsphere and circular light pattern at varyingvelocities, a trap profile can be plotted, which shows theDEP force experienced by a microsphere at differentlocations within the trap, as shown in Fig.6.`• The metallic microspheres can be moved at a maxvelocity of 3200 µm/s by traps created by light patternswith 200 µm and 150 µm diameters, corresponding to aDEP force of 4.18 nN, and a max velocity of 3000 µm/sby traps created by light patterns with 100 µm and 50 µmdiameters, corresponding to a DEP force of 3.9 nN.Conclusion: We have demonstrated the use of OET to manipulate conductive silver microspheres into different patterns. It is found that the microspheres can beexerted with strong DEP force (10-9 N) and also be positioned with high accuracy. The aim of this work is to develop a new method to assemble micron/nanoscaleelectronic components into circuits.(a)Fig.4 (a):Schematic experimental setup; microscope images of ametallic microsphere (b) before and (c) after being trapped by a 200µm circular light pattern.Fig.5 Microscope images of metallic microspheres trapped by 200 µmdiameter circular light pattern at (a) 600 µm/s, (b) 1600 µm/s and (c)3200 µm/s; microscope images of metallic microspheres trapped by 60µm diameter circular light pattern at (d) 600 µm/s, (e) 1400 µm/s and (f)3000 µm/s.Fig.7:Microscope images of metallic microsphere and referencebubble with varied spacing: (a) 1.39 µm, (b) 2.5 µm, (c) 3.3 µm, (d)5.3 µm, (e) 8.4 µm, (f) 10.6 µm and (g) 20.7 µm. An example of themeasurement lines (red coloured) fitted to the microsphere andbubble boundaries to estimate the spacing, is shown in (a).Microscope images of (h) ‘O’, (i) ‘E’, (j) ‘T’ formed by assemblingthe metallic microspheres in parallel via the OET device.• Due to the strong DEP force, the metallic microspherescan be positioned with high accuracy, as shown in Fig.7(a)-(j). The targeted separations between the bubble andbead are 1 µm, followed by 2 µm, 3 µm, 5 µm, 8 µm, 10µm and 20 µm.Fig.6: Trap profiles of metallic microspheres created by 200 µm,150 µm, 100 µm and 60 µm diameter light pattern.

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Assembling and Manipulating Metallic Beads Using Optoelectronic Tweezers

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