Abstract

Light induced dielectrophoresis (LIDEP) is a variant of the dielectrophoresis (DEP) mechanism that has been used for some time to manipulate particles in a microfluidic environment. Rather than relying on lithographically created contacts to generate the required electrical fields, the electrical contacts in LIDEP are created through the selective illumination of a photoconductor. The key question we address is how microscopic traps created via LIDEP compare to optical traps based on the gradient force, in terms of power required and trap stiffness achieved, as well as the size resolution of such a trap. We highlight the complex interplay between optical power and resolution with electrical parameters, such as the electrical resistance and applied AC Voltage. We show that for a spotsize of five micrometres and larger, particles can indeed be trapped with low power. We use trap stiffness per mW to compare LIDEP with an optical trap and show that our system is 470± 94 times stiffer per mW than a conventional optical trap, with no loss of resolution. We also discuss the difficulties of achieving trapping at smaller spot sizes, and that the sub-micron resolution possible with gradient force trapping is very difficult to realise with LIDEP.

© 2007 Optical Society of America

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References

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  1. H. A. Pohl, Dielectrophoresis (Cambridge University Press, Cambridge, 1978).
  2. P. Y. Chiou, A. T. Ohta and M. C. Wu, "Massively parallel Manipulation of single cells and microparticles using optical images," Nature 436, 370-372 (2005).
    [CrossRef] [PubMed]
  3. P. Y. Chiou, A. T. Ohta and M. C. Wu, "Toward all optical lab-on-a-chip system: optical manipulation of both microfluid and microscopic particles," Proc. SPIE 5514, 73-81 (2004).
    [CrossRef]
  4. A. T. Ohta, P. Y. Chiou and M. C. Wu, "Optically-controlled manipulation of live cells using optoelectronic t tweezers," Proc. SPIE 6326, 632617 (2006).
    [CrossRef]
  5. K. Dholakia and P Reece, "Optical micromanipulation takes hold," Nano Today 1, 18 (2006).
    [CrossRef]
  6. A. T. Ohta, P. Y. Chiou, H. L. Phan, S. W. Sherwood, J. M. Yang, A. N. K. Lau, H. Y. Hsu, A. Jamshidi, and M. C. Wu, "Optically controlled cell discrimination and trapping using Optoelectronic Tweezers," IEEE J. Sel. Top. Quantum Electron. 13, 235-243 (2007).
    [CrossRef]
  7. Y. S. Lu, Y. P. Huang, J. A. Yeh, C. Lee and Y. H. Chang, "Controllability of non-contact manipulation by image dielectrophoresis," Opt. Quantum Electron. 37, 1385-1395 (2005).
    [CrossRef]
  8. K. Svoboda and S. M. Block, "Biological applications of optical forces," Annu. Rev. Biophys. Biomol. Struct. 23, 247-285 (1994).
    [CrossRef] [PubMed]
  9. M. P. Hughes, Nanoelectromechanics in Engineering and Biology, (CRC Press, 2003).
  10. Particle trapping software developed by Graham Milne based on the pattern matching capabilities built into LabVIEW.

2007

A. T. Ohta, P. Y. Chiou, H. L. Phan, S. W. Sherwood, J. M. Yang, A. N. K. Lau, H. Y. Hsu, A. Jamshidi, and M. C. Wu, "Optically controlled cell discrimination and trapping using Optoelectronic Tweezers," IEEE J. Sel. Top. Quantum Electron. 13, 235-243 (2007).
[CrossRef]

2006

A. T. Ohta, P. Y. Chiou and M. C. Wu, "Optically-controlled manipulation of live cells using optoelectronic t tweezers," Proc. SPIE 6326, 632617 (2006).
[CrossRef]

K. Dholakia and P Reece, "Optical micromanipulation takes hold," Nano Today 1, 18 (2006).
[CrossRef]

2005

P. Y. Chiou, A. T. Ohta and M. C. Wu, "Massively parallel Manipulation of single cells and microparticles using optical images," Nature 436, 370-372 (2005).
[CrossRef] [PubMed]

Y. S. Lu, Y. P. Huang, J. A. Yeh, C. Lee and Y. H. Chang, "Controllability of non-contact manipulation by image dielectrophoresis," Opt. Quantum Electron. 37, 1385-1395 (2005).
[CrossRef]

2004

P. Y. Chiou, A. T. Ohta and M. C. Wu, "Toward all optical lab-on-a-chip system: optical manipulation of both microfluid and microscopic particles," Proc. SPIE 5514, 73-81 (2004).
[CrossRef]

1994

K. Svoboda and S. M. Block, "Biological applications of optical forces," Annu. Rev. Biophys. Biomol. Struct. 23, 247-285 (1994).
[CrossRef] [PubMed]

Block, S. M.

K. Svoboda and S. M. Block, "Biological applications of optical forces," Annu. Rev. Biophys. Biomol. Struct. 23, 247-285 (1994).
[CrossRef] [PubMed]

Chang, Y. H.

Y. S. Lu, Y. P. Huang, J. A. Yeh, C. Lee and Y. H. Chang, "Controllability of non-contact manipulation by image dielectrophoresis," Opt. Quantum Electron. 37, 1385-1395 (2005).
[CrossRef]

Chiou, P. Y.

A. T. Ohta, P. Y. Chiou, H. L. Phan, S. W. Sherwood, J. M. Yang, A. N. K. Lau, H. Y. Hsu, A. Jamshidi, and M. C. Wu, "Optically controlled cell discrimination and trapping using Optoelectronic Tweezers," IEEE J. Sel. Top. Quantum Electron. 13, 235-243 (2007).
[CrossRef]

A. T. Ohta, P. Y. Chiou and M. C. Wu, "Optically-controlled manipulation of live cells using optoelectronic t tweezers," Proc. SPIE 6326, 632617 (2006).
[CrossRef]

P. Y. Chiou, A. T. Ohta and M. C. Wu, "Massively parallel Manipulation of single cells and microparticles using optical images," Nature 436, 370-372 (2005).
[CrossRef] [PubMed]

P. Y. Chiou, A. T. Ohta and M. C. Wu, "Toward all optical lab-on-a-chip system: optical manipulation of both microfluid and microscopic particles," Proc. SPIE 5514, 73-81 (2004).
[CrossRef]

Dholakia, K.

K. Dholakia and P Reece, "Optical micromanipulation takes hold," Nano Today 1, 18 (2006).
[CrossRef]

Hsu, H. Y.

A. T. Ohta, P. Y. Chiou, H. L. Phan, S. W. Sherwood, J. M. Yang, A. N. K. Lau, H. Y. Hsu, A. Jamshidi, and M. C. Wu, "Optically controlled cell discrimination and trapping using Optoelectronic Tweezers," IEEE J. Sel. Top. Quantum Electron. 13, 235-243 (2007).
[CrossRef]

Huang, Y. P.

Y. S. Lu, Y. P. Huang, J. A. Yeh, C. Lee and Y. H. Chang, "Controllability of non-contact manipulation by image dielectrophoresis," Opt. Quantum Electron. 37, 1385-1395 (2005).
[CrossRef]

Jamshidi, A.

A. T. Ohta, P. Y. Chiou, H. L. Phan, S. W. Sherwood, J. M. Yang, A. N. K. Lau, H. Y. Hsu, A. Jamshidi, and M. C. Wu, "Optically controlled cell discrimination and trapping using Optoelectronic Tweezers," IEEE J. Sel. Top. Quantum Electron. 13, 235-243 (2007).
[CrossRef]

Lau, A. N. K.

A. T. Ohta, P. Y. Chiou, H. L. Phan, S. W. Sherwood, J. M. Yang, A. N. K. Lau, H. Y. Hsu, A. Jamshidi, and M. C. Wu, "Optically controlled cell discrimination and trapping using Optoelectronic Tweezers," IEEE J. Sel. Top. Quantum Electron. 13, 235-243 (2007).
[CrossRef]

Lee, C.

Y. S. Lu, Y. P. Huang, J. A. Yeh, C. Lee and Y. H. Chang, "Controllability of non-contact manipulation by image dielectrophoresis," Opt. Quantum Electron. 37, 1385-1395 (2005).
[CrossRef]

Lu, Y. S.

Y. S. Lu, Y. P. Huang, J. A. Yeh, C. Lee and Y. H. Chang, "Controllability of non-contact manipulation by image dielectrophoresis," Opt. Quantum Electron. 37, 1385-1395 (2005).
[CrossRef]

Ohta, A. T.

A. T. Ohta, P. Y. Chiou, H. L. Phan, S. W. Sherwood, J. M. Yang, A. N. K. Lau, H. Y. Hsu, A. Jamshidi, and M. C. Wu, "Optically controlled cell discrimination and trapping using Optoelectronic Tweezers," IEEE J. Sel. Top. Quantum Electron. 13, 235-243 (2007).
[CrossRef]

A. T. Ohta, P. Y. Chiou and M. C. Wu, "Optically-controlled manipulation of live cells using optoelectronic t tweezers," Proc. SPIE 6326, 632617 (2006).
[CrossRef]

P. Y. Chiou, A. T. Ohta and M. C. Wu, "Massively parallel Manipulation of single cells and microparticles using optical images," Nature 436, 370-372 (2005).
[CrossRef] [PubMed]

P. Y. Chiou, A. T. Ohta and M. C. Wu, "Toward all optical lab-on-a-chip system: optical manipulation of both microfluid and microscopic particles," Proc. SPIE 5514, 73-81 (2004).
[CrossRef]

Phan, H. L.

A. T. Ohta, P. Y. Chiou, H. L. Phan, S. W. Sherwood, J. M. Yang, A. N. K. Lau, H. Y. Hsu, A. Jamshidi, and M. C. Wu, "Optically controlled cell discrimination and trapping using Optoelectronic Tweezers," IEEE J. Sel. Top. Quantum Electron. 13, 235-243 (2007).
[CrossRef]

Reece, P

K. Dholakia and P Reece, "Optical micromanipulation takes hold," Nano Today 1, 18 (2006).
[CrossRef]

Sherwood, S. W.

A. T. Ohta, P. Y. Chiou, H. L. Phan, S. W. Sherwood, J. M. Yang, A. N. K. Lau, H. Y. Hsu, A. Jamshidi, and M. C. Wu, "Optically controlled cell discrimination and trapping using Optoelectronic Tweezers," IEEE J. Sel. Top. Quantum Electron. 13, 235-243 (2007).
[CrossRef]

Svoboda, K.

K. Svoboda and S. M. Block, "Biological applications of optical forces," Annu. Rev. Biophys. Biomol. Struct. 23, 247-285 (1994).
[CrossRef] [PubMed]

Wu, M. C.

A. T. Ohta, P. Y. Chiou, H. L. Phan, S. W. Sherwood, J. M. Yang, A. N. K. Lau, H. Y. Hsu, A. Jamshidi, and M. C. Wu, "Optically controlled cell discrimination and trapping using Optoelectronic Tweezers," IEEE J. Sel. Top. Quantum Electron. 13, 235-243 (2007).
[CrossRef]

A. T. Ohta, P. Y. Chiou and M. C. Wu, "Optically-controlled manipulation of live cells using optoelectronic t tweezers," Proc. SPIE 6326, 632617 (2006).
[CrossRef]

P. Y. Chiou, A. T. Ohta and M. C. Wu, "Massively parallel Manipulation of single cells and microparticles using optical images," Nature 436, 370-372 (2005).
[CrossRef] [PubMed]

P. Y. Chiou, A. T. Ohta and M. C. Wu, "Toward all optical lab-on-a-chip system: optical manipulation of both microfluid and microscopic particles," Proc. SPIE 5514, 73-81 (2004).
[CrossRef]

Yang, J. M.

A. T. Ohta, P. Y. Chiou, H. L. Phan, S. W. Sherwood, J. M. Yang, A. N. K. Lau, H. Y. Hsu, A. Jamshidi, and M. C. Wu, "Optically controlled cell discrimination and trapping using Optoelectronic Tweezers," IEEE J. Sel. Top. Quantum Electron. 13, 235-243 (2007).
[CrossRef]

Yeh, J. A.

Y. S. Lu, Y. P. Huang, J. A. Yeh, C. Lee and Y. H. Chang, "Controllability of non-contact manipulation by image dielectrophoresis," Opt. Quantum Electron. 37, 1385-1395 (2005).
[CrossRef]

Annu. Rev. Biophys. Biomol. Struct.

K. Svoboda and S. M. Block, "Biological applications of optical forces," Annu. Rev. Biophys. Biomol. Struct. 23, 247-285 (1994).
[CrossRef] [PubMed]

IEEE J. Sel. Top. Quantum Electron.

A. T. Ohta, P. Y. Chiou, H. L. Phan, S. W. Sherwood, J. M. Yang, A. N. K. Lau, H. Y. Hsu, A. Jamshidi, and M. C. Wu, "Optically controlled cell discrimination and trapping using Optoelectronic Tweezers," IEEE J. Sel. Top. Quantum Electron. 13, 235-243 (2007).
[CrossRef]

Nano Today

K. Dholakia and P Reece, "Optical micromanipulation takes hold," Nano Today 1, 18 (2006).
[CrossRef]

Nature

P. Y. Chiou, A. T. Ohta and M. C. Wu, "Massively parallel Manipulation of single cells and microparticles using optical images," Nature 436, 370-372 (2005).
[CrossRef] [PubMed]

Opt. Quantum Electron.

Y. S. Lu, Y. P. Huang, J. A. Yeh, C. Lee and Y. H. Chang, "Controllability of non-contact manipulation by image dielectrophoresis," Opt. Quantum Electron. 37, 1385-1395 (2005).
[CrossRef]

Proc. SPIE

P. Y. Chiou, A. T. Ohta and M. C. Wu, "Toward all optical lab-on-a-chip system: optical manipulation of both microfluid and microscopic particles," Proc. SPIE 5514, 73-81 (2004).
[CrossRef]

A. T. Ohta, P. Y. Chiou and M. C. Wu, "Optically-controlled manipulation of live cells using optoelectronic t tweezers," Proc. SPIE 6326, 632617 (2006).
[CrossRef]

Other

H. A. Pohl, Dielectrophoresis (Cambridge University Press, Cambridge, 1978).

M. P. Hughes, Nanoelectromechanics in Engineering and Biology, (CRC Press, 2003).

Particle trapping software developed by Graham Milne based on the pattern matching capabilities built into LabVIEW.

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Figures (6)

Fig. 1.
Fig. 1.

(A). Diagram of a LIDEP chamber. The chamber consists of two plates with an AC Voltage applied across them. The arrows show the electric field resulting from the resistivity change caused by the illumination of the photoconductive plate. (B). A still from a movie showing the paths of trapped and non-trapped particles, the trapped particle being in the center. The plates are moved along the x axis with respect to the laser causing any particle not trapped to move horizontally with respect to the camera, indicated by horizontal lines.

Fig. 2.
Fig. 2.

(A). When the chamber is moved with respect to the optical spot, the trapped particle experiences a dynamic equilibrium at a specific position given by the balance of the trapping force and the drag force exerted by the moving liquid. This position follows a Gaussian distribution around a point to the right of the trap center when the chamber is moved to the right and vice versa. The example shown was taken for a chamber velocity of 4.5 μms-1 (B). Each velocity corresponds to a force that is plotted against the center of the Gaussian position distribution (using the sigma value of the Gaussians as a measure of the error in position). This is compared with simulated data. The graph shown in A corresponds to the two extreme points (at≈1.6 μm position) in B.

Fig. 3.
Fig. 3.

(A). The conductivity of the a-Si can be seen to vary in a Gaussian profile in the x direction to account for the profile of the laser beam. B) Shows the gradient of the electric field in the x direction squared, which is proportional to the DEP force.

Fig. 4.
Fig. 4.

(A). The illuminated conductivity is modelled as a Gaussian distribution with maximum conductivities 10-5, 10-4, 10-3 and 10-2 Sm-1. (B). The resistivities this creates. (C). As the position of the peak gradient in the resistivity moves further from the center of the trap, so does the position of the peak force.

Fig. 5.
Fig. 5.

Changing the optical spot size. A) The potential is plotted for case a 1, 5, 10 and 20μm diameter optical spot and case B) The gradient of the square of the electrical field is plotted for the four spots.

Fig. 6.
Fig. 6.

The profile of a standard optical trap is measured in the same way as the LIDEP trap in Fig. 2(B) to allow for a direct comparison.

Equations (6)

Equations on this page are rendered with MathJax. Learn more.

F drag = 6 πrηv
F drag = 6 πrηv ( 1 9 16 ( r h ) + 1 8 ( r h ) 3 45 256 ( r h ) 4 1 16 ( r h ) 5 )
F DEP = 2 π r 3 ε m Re [ K ( ω ) ] E 2
K ( ω ) = ε p * ε m * ε p * + 2 ε m *
ε * = ε j ( σ ω )
σ = σ bulk + 2 K s r

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