Transport of Colloidal Cargo by Catalytic PtAu Nanomotors

1
Pt
Au
Transport of Colloidal Cargo by Catalytic PtAu
Nanomotors Shakuntala Sundararajan1, Andrew
Zudans1, Paul Lammert2, Vincent H. Crespi2 and
Ayusman Sen1 1Department of Chemistry,
Pennsylvania State University 2 Department of
Physics, Pennsylvania State University
Chemotaxis and Phototaxis of Catalytic PtAu
Nanorods 3 Yiying Hong1, Darrell Velegol2 and
Ayusman Sen1 1Department of Chemistry,
Pennsylvania State University 2Department of
Chemical Engineering, Pennsylvania State
University
Control of Catalytically Generated Electroosmotic
Fluid Flow Using Surface Zeta Potential
Engineering 1Jeffrey M. Catchmark1 and
Shyamala Subramanian21Agricultural and
Biological Engineering, Pennsylvania State
University 2Engineering Science and Mechanics,
Pennsylvania State University

• Objective Control the direction of
  nano/micro-sized motors movement, by either
  chemotaxis or phototaxis.
• New photo-responsive micromotor has been
  designed. UV stimulates the movement of the
  functionalized colloidal particles, and induces
  reversible pattern formation.
• Mechanism of phototaxis will be investigated in
  more detail and a mathematical model developed.
• Principle of chemotaxis could be generalized and
  extended to broader applications.

PtAu/H2O2 system as a prototype. Applications
for self-propelled nano/microscale motors
include self-assembly of superstructures, roving
sensors, and site-directed delivery of
materials. Objective Studying the effect of
cargo size on motor motion.
Steering motor-cargo doublets using magnetic
fields and chemotaxis Future Directions Loading
and Unloading of cargo.

• Objective Engineering structures which align
  the electroosmotic and electrophoretic forces
  using surface patterning techniques

PtAu nanorods chemotax toward higher
concentration of H2O2
Chemotaxis is observed outside living systems for
the first time, by using the catalytic PtAu
nanorods with hydrogen peroxide (H2O2) in gel as
an attractant. By combining the Brownian rotation
(tumbling) and the powered diffusion (straight
swimming), the rods migrate toward higher H2O2
region, while maintaining randomness. An
alternative mechanism is suggested, in which
memory is not required, as compared to bacterial
chemotaxis. With this concept, we can direct the
movement of nanomotors by chemical gradient.
Colloid-Ag micromotor phototaxes toward UV light
Ag reacts with H2O2 under the illumination of UV
light and generates chemical concentration
gradient, which is able to power the movement of
a colloidal particle. This movement is
controllable by adjusting the UV intensity.

• Surface potential tailored by patterning
  carboxyl (-60mV) and amine (50mV) terminated SAMs
• Colloidal tracers used to observe switching in
  the direction of the fluid flow
• Future Creation of fluidic and molecular
  sorting devices.

Cantilever Sensor Based on Catalytically Produced
Electrokinetic Forces 2Jeffrey M. Catchmark1
and Shyamala Subramanian2

• Colloid-Ag particles agglomerate at UV spot

• Sensor for H2O2 based on electrokinetic
  decomposition by catalytic Au/Ag micro
  cantilever.
• Ag - Au junction patterned selectively on the
  free standing edge of a silicon microcantilever.
• Cantilever experiences forces resulting from
  electroosmotic fluid flow due to H2O2
  decomposition.
• Sensor response quantified Changes in catalytic
  forces vs. concentration of H2O2

• Req Equivalent sphere radius of a rod or a
  rod-sphere doublet is the radius of a sphere
  which has the same drag coefficient.
• The lower (higher) values correspond to rods of
  2.5 (3.2) µm length. (Metal segments 1.2 µm
  each, PPy length 0.1 µm to 0.8 µm).
• Experimentally observed doublet speeds,
  normalized to the speeds of bare rods, closely
  track the ratio of the corresponding equivalent
  sphere sizes, except for a larger than expected
  mobility of the doublets with the largest cargo.
  

• Colloid-Ag agglomeration follows UV

References 1 Subramanian, S Catchmark, J.M.
J. Phys. Chem. C 2007, 111, 11959-11964. 2
Subramanian, S Catchmark, J.M. Small 2007, 3,
1934-1940. 3 Hong, Y. Blackman, N.M.K. Kopp,
N.D. Sen, A. Velegol, D. Phys. Rev. Lett. 2007,
99, 178103-178106.