1. Transport of Colloidal Cargo by Catalytic PtAu Nanomotors Shakuntala Sundararajan 1, Andrew Zudans 1, Paul Lammert 2, Vincent H. Crespi 2 and Ayusman Sen 1 1 Department of Chemistry, Pennsylvania State University 2 Department of Physics, Pennsylvania State University Nanoscale Motors Powered by Catalytic Reactions (CTS-0506967); PI: Ayusman Sen (asen@psu.edu) Control of Catalytically Generated Electroosmotic Fluid Flow Using Surface Zeta Potential Engineering [1] Jeffrey M. Catchmark 1 and Shyamala Subramanian 2 1 Agricultural and Biological Engineering, Pennsylvania State University 2 Engineering Science and Mechanics, Pennsylvania State University Objective: Engineering structures which align the electroosmotic and electrophoretic forces using surface patterning techniques Chemotaxis and Phototaxis of Catalytic PtAu Nanorods [3] Yiying Hong 1, Darrell Velegol 2 and Ayusman Sen 1 1 Department of Chemistry, Pennsylvania State University 2 Department of Chemical Engineering, Pennsylvania State University PtAu nanorods chemotax toward higher concentration of H 2 O 2 GEL 25 microns GEL 24 microns GEL 24 microns 110hr38hr 0.7hr 30%H 2 O 2 0%H 2 O 2 Chemotaxis is observed outside living systems for the first time, by using the catalytic PtAu nanorods with hydrogen peroxide (H 2 O 2 ) in gel as an attractant. By combining the Brownian rotation (tumbling) and the powered diffusion (straight swimming), the rods migrate toward higher H 2 O 2 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 0 h 4 h 8 h (UV stopped) 50x 20x 24 h (agglomeration relaxed) 24 h (UV shifted 0.5mm)25.5 h48 h old spot new UV spot new spot 50x 5x Ag reacts with H 2 O 2 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. UV colloid Ag H2O2H2O2 Ag + +OOH - overall movement Colloid-Ag particles agglomerate at UV spot Colloid-Ag agglomeration follows UV 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. 1%2% Air Water Amplitude/V 0,0 0.05 0.1 0.15 0.2 0.25 0.3 2550 v/kHz 75100125150175 Sensor for H 2 O 2 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 H 2 O 2 decomposition. Sensor response quantified: Changes in catalytic forces vs. concentration of H 2 O 2 Cantilever Sensor Based on Catalytically Produced Electrokinetic Forces [2] Jeffrey M. Catchmark 1 and Shyamala Subramanian 2 Pt-Au/ H 2 O 2 system : Spatially localized catalytic reactions can produce ion gradients driving electroosmotic and electrophoretic forces Electrokinetic effects drive autonomous nano/micro-sized motors and fluid pumps Current research gains control over motor/fluid-pumping direction, transport and steering of colloidal cargo, optimizing motor design for enhanced performance e-e- H+H+ 2H 2 O 2 O 2 + 2H + + 2e - 2H 2 O H 2 O 2 + 2H + + 2e - R eq : 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. 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. Table 2: Experimentally observed doublet speeds versus theoretical expectations based on completed double-layer boundary-integral equation (CDL-BIEM) calculations Table 1: Cargo Radius vs. Motor Speed PtAu/H 2 O 2 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. a) Electrostatic Interaction Modes of Cargo Attachment b) Biotin-Streptavidin Based Interaction Biotin terminated disulfide Pt-Au cargo PS- + + + + + Amidine cargo + - - - - - - PPy Pt- Au - - - - - - - - - - - - Streptavidin Steering Cargo Bearing Motors Using Magnetic Fields FIELD OFF FIELD ON 0sec 4 sec 4sec 0 sec 5 µm Transmission Optical Microscopy images of a Pt-Au-Ni-Au-Ni-Au–PPy rods bearing a 1.05 µm amidine cargo (top) in absence of magnetic field and (bottom) presence of field 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. PtAu