Manipulation of Nanoparticles and Nanotubes by Dieletrophoresis ME 395 March 16, 2004 Ned Cameron, Christine Darve, Christina Freyman, and Li Sun

Outline Techniques for Separation Electrodes Stern Layer Applications of DEP Activities Results

Separation Techniques Electrophoresis - migration of charged molecules in an electrical field Electroosmosis - the movement of liquid through a bed of particles by applying an electric field Dielectrophoresis (DEP) - the manipulation of polarizable particles by non-uniform AC fields. Non-invasive, non-destructive, alternating pulses, at controllable frequency

Dielectrophoretic Force DEP Force on the particle –r = radius of particle –ε m = permittivity of medium –Re[K(ω)]-real part of the Clausius-Mossotti factor –  E - gradient of electric field

Clausius-Mossotti Factor ε * m = complex permittivities of the medium ε * p = complex permittivities of the particle σ the conductivity; ε the permittivity; ω the angular frequency of the applied electric field; j=  -1,  p  surface conductance of particle/radius of particle If K(ω) > 0, then particles move to regions of highest field strength - positive DEP If K(ω) < 0, then particles move to regions of lowest field strength - negative DEP

Activity 1 - Plotting Re[K(ω)] vs ω for 500 and 200 nm beads A plot of the Clausius- Mossotti factor versus frequency for 216-nm- (dashed) and 557-nm- diameter (solid) latex particles with a particle permittivity  p = 2.55 and a medium conductivity  m = 1 mSm -1. The surface conductance was set at 2.32 nS for both sizes of particles. Morgan, Hywel et al. “Separation of Submicron Bioparticles by Dielectrophoresis.” Biophys J, July 1999, p , Vol. 77, No. 1

Electrode Arrays and Electric Field Analysis The Scaling Law V ~ the applied voltage and Le ~the characteristic length of the electrodes

Deposit gold electrodes Si Substrate Electrode Fabrication & Electrode Configuration

Parallel / Tip-to-tip electrode array N G Green and H Morgan, Dielectrophoretic investigations of sub-micrometre latex spheres, J. Phys. D: Appl. Phys. 30 (1997) 2626–2633.

Castellated electrode array N G Green and H Morgan, Dielectrophoretic separation of nano-particles, J. Phys. D: Appl. Phys. 30 (1997)

Polynomial electrode array (1) N G Green and H Morgan, Dielectrophoretic investigations of sub-micrometre latex spheres, J. Phys. D: Appl. Phys. 30 (1997) 2626–2633.

Michael Pycraft Hughes, AC Electrokinetics: Applications for Nanotechnology Polynomial electrode array (2)

Stern Model & Interfacial Effects on Electrode surface charges bound ions (Stern layer) diffuse double layer Double layer or Stern layer Electro-osmosis

Combination of DEP and EHD forces

Applications of DEP

100 kHz, positive DEP Chains of beads at the electrodes 1 MHz, negative DEP Beads trapped at the center Electrode array for DEP Electric field map Positive and negative DEP Digitized images of 282 nm latex spheres in a fluorescence microscopes Suspending buffer: 10 mM potassium phosphate, conductivity  =0.17 S/m

Complications of negative DEP High frequency (MHz) needed to achieve negative DEP Particles are trapped in the electric cage Brownian motion Dielectric potential well where particles are trapped in negative DEP Potential barrier preventing particles from entering the well  E 2 map electrode

Example of electrode configurations for electric cages.

DEP applications - 1 Separation of metallic and semi-conducting nano-tubes (for nano-scale electronics research and applications) –Suspension of Carbon nano-tubes subjected to a inhomogeneous AC field –Metallic nanotubes (and bundles containing at least one metallic nano-tube dominating the dielectric properties) are attracted at the electrodes –The nano-tubes remaining in the suspension are semi conducting Suspension drop electrodes SWNT experimental set-up R. Krupke, F. Hennrich, H. Lohneysen, M. Kappes, Universitat Karlsruhe, D, Science, 301, pp (2003).

DEP applications - 2 Trapping of human viruses (detection, research of viral properties) –250 nm diameter enveloped human virus and viral capsid of Herpes simplex (HSV-1) –Gold electrodes on glass slides, 1 Hz to 20 MHz AC excitation –Stable levitation of a single viral capsid in the potential well electrodes virus envelope Herpes Simplex Virion (HSV-1), virus and its envelope M. Hughes and H. Morgan, University of Glasgow, UK, J. of D: appl. Phys., 31, pp (1998).

DEP applications - 3 Concentration of colloids from solution –Useful, e.g., to collect single parts for nano-machines on the “assembly site” using negative DEP. Examples: two or more interlocking molecules, normally in a highly dilute solution, concentrated by DEP into a confined space where they assemble; collecting "fuel" for a nano- machine from solution. Self- assembly reaction takes place at the collection point; bringing together "stacking" particles of different types, which bind on contact etc. Example of manipulation of nano-particles: –14 nm diameter fluorescently labeled latex spheres precipitated from an aqueous solution (  =2.5 mSm -1 ) by positive (a) and negative (b) DEP. –micro spheres and colloidal gold particles fictionalized using antibodies, used to construct microscopic biosensors (1) 8 Vpp, 2 MHz 10 Vpp, 10 MHz (1) Velev OD, Kaler EW, In situ assembly of colloidal particles into miniaturized biosensors

DEP applications - 4 Dielectrophoretic separation and transportation of cells on micro fabricated chips –microchip with a suitable array of electrodes produces controlled transport and switching electric fields –The electric field pattern is switched so that human blood cells are transported from the top of the chip to the left side (see next slide) J. Xu, L. Wu, M. Huang, W. Yang, J. Cheng, X-B Wang, AVIVA Bioscences Corp, CA & Dept. of Biological Sciences and Biotechnolog, Tsinghua University, Beijing, China Particle switch with 4- phase signals applied to the electrodes Transportation chip (bottom) and guide chip (top) separated by 80  m Fluid chamber comprising a DEP chip

DEP applications - 4 J. Xu, L. Wu, M. Huang, W. Yang, J. Cheng, X-B Wang, AVIVA Bioscences Corp, CA & Dept. of Biological Sciences and Biotechnolog, Tsinghua University, Beijing, China Blood cell Transport along top channel Three-way switching to left channel Transport along left channel Transport electrode Three- way switch White blood cells retained by sinusoidal electrodes human blood Application of AC voltages caused carbon beads to be collected along electrode edges and polystyrene beads to be levitated.

DEP applications - 5 Dielectrophoretic size-sensitive particle filter for micro-fluidics applications –The dielectrophoretic force, and the cross-over frequency from positive to negative DEP, depends on the particle radius –At given frequency, particles with smaller radius tend to experience positive DEP, particle with larger radius experience negative DEP –By proper geometry arrangement of electrodes and operating frequency selection it is possible to trap particles selectively based on their size J. Auerswald, H.F. Knapp, Micro Center Central Switzerland trapped free

DEP applications - 6 DEP of 557 nm diameter latex spheres (a) Negative DEP with polynomial electrode array. (b) Negative DEP with castellated electrode array. (c) Positive DEP with polynomial electrode array. (d) Positive DEP with castellated electrode array. N.G. Green, A. Ramos, H. Morgan, J. Phys. D: Appl. Phys., 33, pp (2000)

DEP applications - 6 (a) Schematic of fluid flow observed in polynomial arrays at high frequencies. (b) Schematic of fluid flow observed at low frequencies and low potentials. (c) Experimental image (12 Volts peak-to-peak, 6 MHz). (d) Experimental image (5 Volts peak-to-peak, 3 MHz). N.G. Green, A. Ramos, H. Morgan, J. Phys. D: Appl. Phys., 33, pp (2000)

DEP applications - 6 Diagrams and experimental images of AC electro-osmosis for two designs of electrodes. (a) Schematic diagrams for polynomial electrode arrays. (b) Schematic diagrams for castellated electrode arrays. (c) Experimental image for polynomial electrode arrays. (d) Experimental image for castellated electrode arrays. N.G. Green, A. Ramos, H. Morgan, J. Phys. D: Appl. Phys., 33, pp (2000)

DEP applications - 6 Experimental images of 557 nm diameter latex spheres over three decades of frequency on castellated electrode arrays at an applied potential of 8 Volts peak-to-peak and a solution conductivity of 2 mSm -1. N.G. Green, A. Ramos, H. Morgan, J. Phys. D: Appl. Phys., 33, pp (2000)

The Experiment The Equipment:

Activity 2: Positive DEP Movies –posfork.avi –posstick.avi –possquare.avi

Activity 3: Negative DEP Movie –negstick.avi

Activity 4: Carbon Nanotube Manipulation Positive –cntpos.avi Negative –negcnt.avi

Side view of traveling wave device Buffer – 10 mM potassium phosphate Conductivity 0.17 Sm-1 Latex sphere diameter: 557 nm 1 Hz to 20 MHz AC Negative DEP: 5 V 5 MHz Positive DEP: 5 V 500 kHz Top view of device design Y1 = A · sin(  t) Y2 = A · sin(  t +  /2) Y3 = A · sin(  t +  ) Y4 = A · sin(  t +3  /2) Inspired from John Zelena (Mechanical Engineering) – Wilkes University, NSF Summer Undergraduate Fellowship in Sensor Technologies, technical report (2004). Future Activity: Four Electrode Manipulation

Acknowledgements Thanks to: –Dr. Moldova –Prof. Espinosa –Dr. Espinosa’s graduate students that had to keep logging us back on to the server when we would crash the computer