Angular Orientation of Nanorods using. Nanophotonic Tweezers

Transcription

1 Angular Orientation of Nanorods using Nanophotonic Tweezers Pilgyu Kang, Xavier Serey, Yih-Fan Chen, David Erickson *, Sibley School of Mechanical and Aerospace Engineering, School of Applied and Engineering Physics, Cornell University, Ithaca, New York United States, and Department of Biomedical Engineering and Medical Device Innovation Center, National Cheng Kung University, Tainan 701, Taiwan Supporting Information Materials and Methods Preparation of microtubules For the orientation experiment with microtubules, porcine brain tubulin protein is used to form the microtubule. The tubulin protein is labeled with TRITC rhodamin. The TRITC rhodamine labeled tubulin protein (Cat. # TL590M) is supplied from Cytoskeleton Inc. Denver, CO. USA. The microtubules were re-incubated with Paclitaxel (Cat. # TXD01) between 30 minutes to an hour prior to the experiments. Preparation of the multiwalled carbon nanotube Carbon nanotubes suspensions were prepared by ultrasonification of 0.01% MWCNT powder (7-15 nm OD, Sigma-Aldrich product # , and nm OD, Sigma-Aldrich product # ) and 0.5 % Tween-20 (Sigma-Aldrich Product # P1379) in heavy water. 1

2 Fabrication of the Silicon Nitride and Silicon PhC resonator 15 The fabrication of the silicon photonic crystals and silicon nitride photonic crystals was performed with standard E-Beam lithography in the CNF. Additional information is available in references 13 and 14. The design of the resonators followed the method developed by Quan et al 29 ) Flow Cell Preparation To flow the nanorods, the flow compartment is made on the fabricated device. 127 µm-thick parafilm spacer that has 2 mm-width flow channel is placed on the device such that the flow channel is placed on the resonator. Inlet and outlet holes were made on a coverslip using the Universal Laser Systems, VersaLaser VLS3.50. PDMS pieces to fix Tygon tubuing in the holes were attached on the coverslip. The coverslip is then placed on the top of the parafilm spacer. The entire sandwiched components were briefly heated on hotplates at 80 C to make sealed compartment. The flow compartment was estimated to be approximately 2 mm 100 µm as the cross-section. In orientation experiments, the sample is injected into the compartment through Tygon tubing by a syringe pump. Prior to experiments, washing buffer solution of PBS, Tween20 (0.05% w/w), and Casein (0.05% w/w) was incubated for 30 minutes to wash the surface of the resonator and prevent nonspecific binding. Orientation Experiments For a light source a 1064 nm fiber coupled high power diode laser (LU1064M400 Lumics, EL Segundo, CA) was used to achieve optical orientation and optical trapping. A laser power was controlled by a laser diode controller, THORLABS ITC 502 combined with a temperature control. The temperature of a laser diode was adjusted to tune the center wavelength of the laser diode such that slightly dissimilar resonance wavelength of resonators resulted from fabrication is compensated. The Laser light was coupled into silicon nitride waveguides through a lensed fiber. The power coupled to the resonator was measured by a detector of a power meter aligned with output of waveguides. Polarization of a laser light was 2

3 controlled to be transverse electric (TE) mode with a polarizer and a manual fiber polarization controller through which a fiber passes. The measured power was to reach maximum during control. Images were captured and recorded with an upright fluorescent microscope, Olympus BXFM system equipped with a Hamamastu ORCA-ERCCD camera. To excite the fluorescence of TRITC labeled microtubules, a mercury arc lamp was used with a TRITC filter set. Image processing and Data analysis Image analysis of the orientation and the Brownian motion of nanorods were performed using ImageJ 12. OrientationJ 22 was used to measure the orientation angle quantitatively. The standard deviations of the measured orientation angles were affected by imaging quality with a 10-15% error. 3

4 Supplemental Movies Movie 1 The orientation of the microtubule by the optical torque exerted by the silicon nitride photonic crystal resonator. The silicon nitride photonic crystal resonator is located in the center across top and bottom. In the beginning prior to orientation, an approximately 10 µm-length microtubule is angled at π/2 with respect to horizontal direction, which is perpendicular to the resonator. The direction of electric field is across left and right. In hydrodynamic flow imposed with syringe pump (u = 1 µl/hr, where u is flow rate) the microtubule was located as closer to the resonator so that it could interact with electric field. Prior to orientation experiments hydrodynamic flow was relaxed to prevent rotation by flow. After the microtubule had been oriented, the oriented microtubule moved on the right disappearing in the field of view. Movie 2 The constrained rotational Brownian motion with the simultaneous application of the optical torque and the optical trap. An approximately 8 µm-long microtubule was optically oriented, being optically trapped on resonator. The microtubule was slight moved up along resonator by scattering force. Rotational Brownian motion affected by optical force and optical torque simultaneously was observed by epi-fluorescent microscopy. The hydrodynamic flow relaxation was also carried out prior to orientation experiment. From the movie image analysis was conducted to measure orientation angles as a function of time. Based on the results, rotational diffusion coefficient was determined for suppressed rotational Brownian motion. Movie 3 Trapping and orientation of carbon nanotubes. The light travels through the bus waveguide from the bottom of the field of view to the top. The resonator is evanescently coupled at the left of the bus waveguide. At the beginning of the movie, a carbon nanotube is trapped on the resonator. Another carbon nanotube is pushed upwards by the light in the bus waveguide towards the resonator. Upon arriving on the resonator, the carbon nanotube remains there trapped 4

5 and oriented. A third carbon nanotube diffuses to the resonator but is not trapped but pushed upwards by the bus waveguide. Movie 4 Flow orientation of trapped carbon nanotube aggregates. Carbon nanotube aggregates are trapped on a photonic crystal resonator and on a waveguide. The flow is controlled externally with a syringe pump. The direction of the flow is changed, as a result, the carbon nanotubes reorient themselves to point towards the direction of the flow. 5