Biobased High-Performance Rotary Micromotors ... - ACS Publications

Subscriber access provided by - Access paid by the | UCLA Library

Article

Biobased High-Performance Rotary Micromotors for Individually Reconfigurable Micromachine Arrays and Microfluidic Applications Kwanoh Kim, Zexi Liang, Minliang Liu, and Donglei (Emma) Fan ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b13997 • Publication Date (Web): 29 Dec 2016 Downloaded from http://pubs.acs.org on January 3, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Biobased High-Performance Rotary Micromotors for Individually Reconfigurable Micromachine Arrays and Microfluidic Applications Kwanoh Kim,1 Zexi Liang,2 Minliang Liu,1, 3 and Donglei (Emma) Fan1,2,* 1

2

3

*

Department of Mechanical Engineering, The University of Texas at Austin, Austin, TX 78712, USA Materials Science and Engineering Program, The University of Texas at Austin, Austin, TX 78712, USA Current address: School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA Correspondence can be addressed to: [email protected]

Abstract In this work, we report an innovative type of rotary bio-micromachines by using diatom frustules as integrated active components, including the assembling, operation, and performance characterization. We further investigate and demonstrate unique applications of the biomicromachines in achieving individually reconfigurable micromachine arrays and microfluidic mixing. Diatom frustules are porous cell walls of diatoms made of silica. We assembled rotary micromachines consisting of diatom frustules serving as rotors and patterned magnets serving as bearings in electric fields. Ordered arrays of micromotors can be integrated and rotated with controlled orientation and speed up to ~3000 rpm, one of the highest in biomaterial-based rotary micromachines. Moreover, by exploiting the distinct electro-mechanical properties of diatom frustules and metallic nanowires, we realized the first reconfigurable rotary micro/nanomachine arrays with controllability in individual motors. Finally, the diatom micromachines are successfully integrated in microfluidic channels and operated as mixers. This work demonstrated the high-performance rotary micromachines by using bioinspired diatom frustules and their applications, essential for low-cost bio-MEMS/NEMS devices and relevant to microfluidics. Keywords: biomaterials, diatoms, micromotors, nanomotors, biocompatibility, electric tweezers, microfluidics, nanomanipulation, reconfigurability, micromixers

1 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Introduction Micro/nanomachines are one of the most active research areas due to their high potential in revolutionizing multiple fields including disease diagnosis, drug delivery, microsurgery, and microfluidics.1-4 With rapid advances in nanofabrication, various types of miniaturized machines have been developed. According to the employed energy sources, they can be categorized into electric, magnetic, acoustic, optical, and chemical micro/nanoscale machines/motors.1-6 The demonstrated applications range from drug/biochemical delivery,7-9 micro/nanocargo transport,10-12 biochemical detection,13-15 cell trapping,16 to water purification.17,18 Rotary micro/nanomachines received special interests in the development of micro/nanomachines.5 They not only generate controlled torques that can compel nanoentities and molecules19-23 but also gain thrust for linear propulsion from rotation, resembling screws, for applications including microsurgery and cargo transport.11,24-28 Furthermore, by employing micro/nanoentities of designed structures, dimensions, and chemistry, these rotary micro/nanomachines can be equipped with sensing functions, i.e., for applications in tunable biochemical release and real-time monitoring.8,20 Although the synthesis of nanoparticles for the use in rotary nanomotors have been well established,29 it remains an arduous task to obtain artificial micro/nanostructures with 3-D functional hierarchical features at a low cost.30,31 On the contrary, various biological systems in nature offer intricate 3-D nanostructures ranging from superhydrophobic surfaces of lotus leaves,32 spiral xylem vessels of plants,33 adhesive setae of geckos,34 to the iridescent wings of morpho butterflies.35 Owing to their ordered nanoscale features, these 3-D biological structures often offer unique optical and mechanical properties, which have found many useful applications in nanophotonics, biochemical detection, photocatalysis, nanomaterial synthesis.33,36-39 However,


Page 2 of 24

Page 3 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


up to now, limited works have been done in employing naturally existing 3-D materials in micro/nanomotors (rotary MEMS), which promise many intriguing applications.33 Diatoms are unicellular photosynthetic algae that reside in marine ecosystems in large quantities. They produce silica cell walls called frustules, which have hierarchical micro/nanopores on the surfaces. Diatoms are not only abundant in nature but also have diverse species approximately 100,000.40 This offers a large selection of features and sizes for various purposes, which could be explored in low-cost nanomanufacturing. Moreover, frustules are mechanically strong, chemically stable, biologically benign, environmentally friendly, and even edible, which makes them highly desirable in various biomedical and environmental applications.41-47 In this work, we report the first work on assembling of diatom frustules into rotary biomicromachines in microfluidic systems for mixing applications. The micromotors have the diatom frustules as rotors and patterned magnets as bearings, which can be integrated into ordered arrays and rotated with controlled orientation and speed up to ~3000 revolutions per minute (rpm). Furthermore, by exploiting the unique electro-mechanical properties of diatom frustules and metallic nanorods, we realized reconfigurable rotary micro/nanomotor arrays with controllability in individual motors. Finally, the biomicromachines are successfully operated in microfluidic systems as micromixers. This work could inspire a new type of microelectromechanical system (MEMS) devices made of naturally existing biomaterials that offer high performance, low cost, and bio-friendliness.

Methods Diatom frustules are abundantly available as diatomaceous earth powder. They have been widely used as health supplements for humans and livestock, as well as insecticides for organic 3 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

gardening. We obtained refined diatom frustules by processing inexpensive commercial diatomaceous earth powder (e.g., $10 for 10 lb. Natural Gardener, Austin, TX) via dispersion, sonication, and multistep filtration in deionized (DI) water. Unwanted small particles and broken pieces of frustules are removed via filter papers of a nominal pore size of ~50 µm (Fisher Scientific, Pittsburgh, PA). Those remaining on the filter paper are collected as shown in Fig. 1(a). After sequentially rinsing and vortexing with 2-propanol (IPA), acetone, and DI water each for three times, the frustules are dispersed on a Si substrate and coated with a tri-layer metallic Cr (3 nm)/Ni(40 nm)/Au(40 nm) thin film via electron-beam evaporation as shown in Fig. 1(b). Finally, after another round of sonication and rinsing in IPA and acetone, the metallized diatom frustules are stored in DI water. With one side covered by the Cr/Ni/Au film, the frustules exhibit ferromagnetic responses to external magnetic fields, i.e., they can be facilely aligned in the direction of magnetic fields and transported toward the high field region in a magnetic field gradient [Video S1]. Each layer in the metallic film serves for a purpose: the Cr improves the adhesion of the metallic thin film to the surface of diatom frustules; the Ni provides magnetic force; and the Au works as a passivation layer that prevents magnetic aggregation of the frustules and their undesired attachment to the substrate. Through this processing, pure or magnetic diatom frustules can be facilely obtained with refined sizes and shapes.

Results and Discussion Transport of Diatom Frustules We integrated the diatom frustules as building blocks of rotary MEMS, or micromotors. To assemble the diatom micromotors at designed locations and produce reliable mechanical thrusts from their motion, it is essential to transport these tiny building blocks with high precision and efficiency. We have recently developed an innovative nanoparticle manipulation 4 ACS Paragon Plus Environment

Page 4 of 24

Page 5 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


technique based on strategically combined uniform DC and AC electric fields, the so-called electric tweezers,48-51 where nanoparticles are aligned and transported in the direction of AC field due to the dielectrophoretic (DEP) forces and DC electric fields due to the electrophoretic (EP) forces, respectively. In the center of two orthogonal sets of parallel microelectrodes, or quadrupole electrodes, the AC and DC electric fields can be independently applied in both the X and Y directions to manipulate nanoparticles along arbitrary trajectories in a two-dimensional (2D) space [Fig. 1(c)]. Here, for the first time, we applied the electric tweezers to manipulate diatom frustules with hierarchical porous nanostructures and dimension (~20 µm in length and ~9 µm in diameter). The moving characteristics show similarity and distinction from those of nanowires we tested previously.50 The speed linearly increases with the DC voltage up to 134 µm/sec as shown in Fig. 1(d) after reaching a threshold voltage of ~1.2 V in average, which is not found in the manipulation of nanoparticles such as nanowires. The threshold voltage in the manipulation of diatom frustules could be originated from the much larger hindering force from the substrates compared to those on smaller nanoparticles such as nanowires.49 The hindering force can result from both friction and adhesion, which depend on the surface properties and size of particles. The mechanism requires further investigation. Meanwhile, it can be determined that the EP force (FEP) due to the DC electric field (E) drives the motion, which balances with the viscous (Fƞ) and the hindering forces from the substrate (Fh), given by FEP = Fƞ + Fh. It is known that FEP ∝ E and the viscous force (Fη) is proportional to the moving velocity (v), given by Fη = bƞv, where b and ƞ are the geometric factor and liquid viscous coefficient, respectively. Therefore, it can be determined that the moving velocity (v) is proportional to the applied electric field (E), i.e., v ∝ E. This analysis agrees with the experimental observation, where the moving velocity of diatom



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

frustules linearly increases with the applied voltage [Fig. 1(d)]. From this analysis and the experimental results in Fig. 1(d), we can also determine the average hindering forces from the substrate as ~8.9×10-12 N based on the calculation of the geometry factor (b).52 With the understanding of the transport characteristics by manipulation in one-dimension (1-D), next we transported the diatom frustules in a 2-D space in the center area of quadrupole microelectrodes [Fig. 1(c)]. By sequentially applying electric voltages with controlled intensity and duration in both the X and Y directions, we successfully compelled frustules to move along programmed trajectories and even spell letters, such as “U” and “T” [Fig. 1(e), Video S2 and S3], demonstrating the feasibility in positioning the diatom frustules at any designated locations. The orientation of diatom frustules can be controlled by the AC voltages, particularly for those with coating of metallic thin films in a high AC electric field [Video S4]. However, in microelectrodes with low electric field strength, the AC alignment can be less efficient, which could be due to the low electric polarizability of pure silica frustules and the hindering forces from the substrate.

Rotation of Diatom Frustules Before assembling diatom frustules into micromotors, we need to know if the diatom frustules can be rotated with external AC electric fields [Fig. 2(a)]. A rotating electric field is created by imposing four AC voltages on quadrupole microelectrodes with sequential 90° phase shifts.20,48 By adjusting the intensity, frequency and phase sequence of the AC voltages, we found the diatom frustules, although made of insulating silica, can be efficiently compelled to rotate with highly controlled orientation and speed as shown in Fig. 2(b). Various geometries, such as ovals, rods, and squares, rotate simultaneously [Video S5]. Both the speed and direction


Page 6 of 24

Page 7 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


can be instantly changed without noticeable transition due to the low Reynolds number regime of the suspension.48,53 The rotation speed (Ω), which is the first derivative of the angular position of the frustule as a function of time, increases with the square of the applied AC voltages (V2) up to a certain rotation speed, i.e., step-out frequency [Fig. 2(c)]. The rotation of the diatom frustules can be attributed to the electric torques Te due to the interaction between a particle and the electric fields, given by Te = -2πabcεmE2Im[K], where a, b, c are dimensions in the x, y, z directions, respectively.54 Here, the E2 dependence accounts for the experimentally observed linear increase of rotation speed (Ω) with V2. The rotation characteristics are also determined by the electric properties of both the particle and the suspension medium as well as the geometry of the particle as shown in the imaginary part of the Clausius-Mossotti factor Im[K] [supporting information]:54 Im = −

. Here, f is determined by

(1)

, where ω is the applied AC

frequency, σp and σm are the electric conductivities of the particle and medium, respectively; εp and εm are the permittivity of the particle and the medium, respectively; Li is the depolarization factor of the particle, the value of which highly depends on the shape of the particles orientation and accounts for the different rotation speed observed from diatoms of distinct geometry as shown in Video S5. Note that the value of f is always positive. The rotation of diatom frustules is in the same direction of electric field [Fig. 2(d)], always opposite to that of metallic nanostructures, such as Au nanowires in the tested frequency range. This suggests it can be an important and viable route in obtaining desired rotation behaviors of devices in electric fields by exploiting the electric properties of materials. In the later study, we achieved nanomotor arrays



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

with reconfigurablity in individual nanomotors based on our understanding of material-electricfield interactions and will discuss in details later.

Diatom Frustule Micromotors Although the above study revealed that randomly suspended 3-D porous diatom frustules can be effectively manipulated, in order to employ them as useful components of miniature devices to produce mechanical thrusts with high robustness and controllability, it is of great importance to assemble them at designated locations. It is known that for microscopic particles, even a small liquid agitation can disrupt their positions and manipulation. Here, we assembled a new type of rotary micromotors using Cr/Ni/Au-coated diatom frustules as rotors as shown in Fig. 3(a). We selected frustules of ~20 µm (15 – 25 µm) in length and ~ 10 µm (9 – 15 µm) in diameter and lithographed circular magnetic micropatterns of 1 – 5 µm in diameter consisting of a thin film stack of Cr (5 nm)/Ni (80 nm)/Au (100 nm) for anchoring the diatom rotors. The micromotors can be facilely assembled by transporting the metallized diatoms to the patterned magnets by the electric tweezers [Fig. 1(c)]. When near the vicinity of the bearings, the frustules can be anchored onto the bearing by the magnetic forces rapidly [Fig. 3(a)]. The assembling takes as swift as ten seconds. We sequentially assembled arrays of diatom micromotors in designed patterns, such as 2×2 arrays [Fig. 3(b) and Video S6]. Note that owing to the magnetic Ni layers deposited on the diatom frustules, we also assembled micromotors by magnetic manipulations. Here, the magnetic forces between the rotors and the bearings can integrate the different components of the micromotors with high precision and robustness, while still allowing the rotation. Similar to that of the pure diatom frustules in Fig. 2, in a rotating electric field, the


Page 8 of 24

Page 9 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


diatom micromotors can be compelled to rotate either clockwise or counterclockwise. In a 150 µm-gap quadruple microelectrode, the diatom motors can reach speeds over 2800 rpm at only 17 V (20 kHz), the same level of car engines on highway [Fig. 3(c) and Video S7]. Such motors can continuously rotate for ~11.5 minutes [Fig. 3(d) and Video S8]. Even higher speed and longer lifetime could be expected, i.e., by reducing surface frictions and designing symmetric microrotors.55

Individually Controlled Micromotors in Arrays It is highly essential to achieve micro/nanomotors with reconfigurability for the development of intelligent devices. Reconfigurable collective behaviors of swarming micro/nanoentities and their interactions have been reported recently.6,56 Here, we report the first reconfigurable rotary micromotor array with controls on individual micromotors. It is by leveraging the distinct mechanical responses of different materials in an electric field. Electrically driven rotation was first observed by Arno in 1892 and has been used for the characterization of dielectric properties of biological cells and the separation of biomolecules.54 In our recent studies, we applied this technique and obtained continuous rotation of metallic nanowires48 and semiconducting nanostructures57,58 in AC electric fields. We also found that materials made of semiconductors, insulators, metals and their composites exhibit distinct rotation behaviors in an electric field. Leveraging these finding along with the unique electromechanical properties of diatom frustules, we demonstrated a new approach in obtaining reconfigurable rotary micromotor arrays. We began our study by characterizing the rotation speed and orientation of pure silica diatom frustules and metal-coated diatom frustules at different AC frequencies. It is found that



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

the pure diatom frustules (18 µm (l, length) × 10.5 µm (d, diameter)) always rotate in only one direction in the entire frequency range [Fig. 4(a)]. For metallic Au/Ni/Au nanowires (10 µm (l) × 300 nm (d)), they also only rotate in one orientation, while counter to that of pure diatom frustules. For the metal-coated diatom frustules (11 µm (l) × 6.5 µm (d)), they rotate in the same orientation as that of the metallic Au/Ni/Au nanowires at low frequencies before reversing the direction to that of the pure silica diatom frustules at high frequencies, above ~120 kHz. It could be attributed to different electric torques dominating at distinct AC frequency regimes for the composite metal-coated diatom frustules. Due to the complexity in analytically modeling the core-shell system, we conducted a qualitative analysis assisted with experimental results. For pure insulating diatom frustules, the rotation is determined by Eq. (1) and depends on both the permeability and the electric conductivity of the diatom frustule and the suspension medium given by (εmσp - σmεp). Note that (εmσp - σmεp) = σmσp(τm - τp), where τp and τm are the charge relaxation time of the diatom frustule and the medium, respectively. The overall effect results in τp > τm, where τp = εp/σp and the electric conductivity of diatom frustules σp is low. Therefore, Im[K] < 0 as shown by Eq. (1). Since the electric torque Te ∝ -Im[K], the rotation direction of diatom frustules is in the same orientation of external electrical field in the entire tested frequency range to 1 MHz as shown in Fig. 4(a–b). The rotation of metallic nanowires observed here is prominent at low frequencies, counter to that of the insulating diatom frustules and in the same orientation defined previously.58 It could be attributed to their distinct interactions with external field. However, when the overall structure consists of both metallic films and an insulating diatom frustule, the rotation behaviors of the composite structure shows a transition depending on the AC frequency. Experimentally, we found there is no rotation (Ω = 0) at a frequency of ~120 kHz. This could be attributed to the different magnitude of the electric torques


Page 10 of 24

Page 11 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


exerted on the metallic films deposited on the diatom frustules and the insulating body of diatom frustules at different AC frequency regimes. As observed in Fig. 4(a), the electric torques applied on the metallic and the insulating nanostructures have opposite signs and dominate at low and high frequencies, respectively, which results in the observed transition in the rotation direction. With the above experimentation and understanding, we integrated a metal-coated diatom frustule (13 µm (l) × 9 µm (d) or 12 µm (l) × 10 µm (d)) and a Au/Ni/Au nanowire into a single chip [Fig. 4(b–f) and Video S9]. Both of them can be rotated in the same direction in an electric field with low frequency (10 kHz) [Fig. 4(c)]. Near the crossover frequency (45 kHz), the metalcoated diatom frustule cannot receive enough torques to overcome the drag forces and only the nanowire rotates [Fig. 4(d)]. When the frequency is increased higher than the crossover frequency, such as 65 kHz, the frustule rotor rotates again but reversed its orientation, while the metallic nanowire rotor remains rotating in the same direction regardless of the AC frequency. As a result, the two motors rotate in opposite directions [Fig. 4(e)]. As the frequency further increasing, the rotation of the nanowire rotor finally stops while the diatom motor rotates continuously [Fig. 4(f) at 300 kHz]. Therefore, by simply controlling the applied AC frequencies, we achieved reconfigurable nanowire arrays of (a) both motors rotate in the same direction, (b) one motor rotates while the other stops, and (c) both motors rotate while in opposite directions. To the best of our knowledge, such controllability in rotary micro/nanomotors is achieved for the first time, which is by leveraging the distinct electromechanical interactions of different materials with electric fields. This work demonstrates an unprecedented approach in developing sophisticated micro/nanomachines that can be controlled on individuals for complex operations.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Microfluidic applications Finally, the diatom frustule micromotors were integrated in microfluidic channels as micromixers. Mixing of fluids and molecules is a critical issue in microfluidic and lab-on-a-chip devices for analytical chemistry and biomedical diagnostics, which often involve complex biochemical reaction. In microfluidic flow which occurs at a low Reynolds number regime,53 molecular diffusion dominates the mixing and this often makes the total biochemical reaction process slow and inefficient. In this reason, various types of micromixers which can induce flow disturbance and chaotic advection59 have been developed to improve the mixing efficiency and the throughput of biochemical reactions. Among them, rotary active micromixers which are inspired by magnetic bar stirrers employ patterned microstructures or microspheres rotated by additional power sources such as magnetic fields,60-63 motile microorganisms,64 or optical beams65 to agitate fluid flow and enhance the mixing efficiency. Despite their enhanced mixing efficiency, these micromixers require complicated designs, sophisticated fabrication processes, or bulky external power sources. In addition, the magnetic microspheres are vulnerable to fluidic perturbation61-63 and the focused optical beams with high intensity can cause damage of biosamples.65 On the contrary, our diatom frustule micromotors can be facilely assembled even into arrays and stably rotated with precisely controlled speed and direction. Moreover, the sophisticated and relatively taller 3D geometries of the diatom micromotors can be advantageous for more effective liquid agitation in microchannels, which is shown in simulations discussed as below. The microfluidic channels are made of SU-8 (~200 µm wide and 50 – 100 µm deep) with integrated microelectrodes and patterned micromagnets (4 µm diameter) [Fig. 5(a) and (b)]. A polydimethylsiloxane (PDMS) stamp with a circular opening was used to introduce the diatom


Page 12 of 24

Page 13 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


frustule suspension. The microelectrodes with ~150-µm gaps were patterned to accommodate multiple micromotors as an array and narrow enough to generate a strong electric field [Fig. 5(b)]. Next, we assembled multiple diatom frustule motors in the microfluidic channel and rotated them synchronously both clockwise and counter clockwise [Fig. 5(c)]. The flows around the rotating motors were visualized with 1-µm-diameter polystyrene (PS) spheres dispersed in the microchannel [Fig. 5(d)]. As found from their trajectories, the frustule motors produced fluidic motion effectively in the surrounding medium. For instance, in Fig. 5(d) and Video S10, a frustule motor (~20 µm in length and ~10 µm in diameter) rotating at ~57 rpm can drag PS spheres in ~46-µm diameter from its center. By the fact that PS microspheres outside this range show Brownian motions only, it is obvious that the rotary micromotor can actively generate flows even at the low Reynolds number regime (Re) of 6.64 × 10-4 [supporting information]. The velocity distribution of the flow field around the rotating motors is revealed by the velocity contours from a two-dimensional simulation by using COMSOL Laminar Model. The velocity of the flow field in a microchannel (150 µm wide and 500 µm long) is calculated for a diatom frustule micromotors represented by a cylindrical microrod (20 µm in length and 15 µm in diameter) as well as for a commonly studied nanowire (20 µm in length and 300 nm in diameter) rotating at 3000 rpm in a static liquid medium [Fig. 5(e)]. To simplify the simulation, a 2-D cross sectional model is used. It is found that the flow velocity reaches the highest value in the vicinity of the outer half of the rotating diatom motors and the flow extends much beyond the region swiped by the motors. Both the flow spread and the impacted area are much greater than those of nanowire of the same longitudinal dimension as shown in Fig. 5(e). It demonstrates the applications of the diatom frustules for active manipulation of microscale flows, such as mixing due to the naturally existing 3-D structures. We also note that the mixing efficiency and flow



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

manipulation could be further enhanced by placing multiple micromotors in design arrays in a microfluidic device.

Conclusion In summary, we developed micromotors composed of diatom frustule rotors and patterned micromagnets and their applications in microfluidic systems. Both pure and metalcoated diatom frustules can be precisely transported and rotated by electric/magnetic fields, and they can be facilely assembled into arrays of micromotors. The micromotors can be operated with controlled rotation orientation and speed at least 2800 rpm. The rotation can continue for more than 10 min, which is a long lifetime among the reported biomaterials based micro/nanomotors. Leveraging our findings of the distinct electro-mechanical prosperities of diatom frustules and metallic nanowires in electric fields, we designed and achieved the first reconfigurable rotary micro/nanomachine arrays, where each micromotor can be controlled individually. Finally, the diatom frustule micromotors are integrated into microfluidic devices and demonstrated for microfluidic mixing. The robust, high-performance, and reconfigurable bio-micromachines reported in this work could inspire new advances in micromachines and microfluidics for various applications, such as integrated sub-components of complex functional micromachines, reconfigurable microfluidic mixers and pumps, and robotic biochemical release and sensing platforms.8

Acknowledgement This work is supported by Welch Foundation (grant no. F-1734), the National Science Foundation (CAREER award grant no. CMMI 1150767 and ECCS-1446489), and National Institutes of Health (9R42ES024023-02) in part. 14 ACS Paragon Plus Environment

Page 14 of 24

Page 15 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Supporting Information Available: Videos of manipulation and rotation characteristics of diatom frustules and assembled micromotors, demonstration of individually controllable micro/nanomotor array and micromotors in microchannels. Details of calculation of Reynolds number and derivation of imaginary part of the Clausius-Mossotti factor for a prolate spheroid. This material is available free of charge via the Internet at http://pubs.acs.org.

References: (1) (2) (3)

(4) (5) (6)

(7)

(8) (9)

(10) (11)

(12)

Kim, K.; Guo, J.; Xu, X.; Fan, D. L. Recent Progress on Man-Made Inorganic Nanomachines. Small 2015, 11 (33), 4037–4057. Guix, M.; Mayorga-Martinez, C. C.; Merkoçi, A. Nano/Micromotors in (Bio)Chemical Science Applications. Chem. Rev. 2014, 114 (12), 6285–6322. Duan, W.; Wang, W.; Das, S.; Yadav, V.; Mallouk, T. E.; Sen, A. Synthetic Nano- and Micromachines in Analytical Chemistry: Sensing, Migration, Capture, Delivery, and Separation. Annu. Rev. Anal. Chem. 2015, 8 (1), 311–333. Wang, H.; Pumera, M. Fabrication of Micro/Nanoscale Motors. Chem. Rev. 2015, 115 (16), 8704–8735. Kim, K.; Guo, J.; Liang, Z. X.; Zhu, F. Q.; Fan, D. L. Man-Made Rotary Nanomotors: a Review of Recent Developments. Nanoscale 2016, 8 (20), 10471–10490. Wang, W.; Duan, W.; Ahmed, S.; Sen, A.; Mallouk, T. E. From One to Many: Dynamic Assembly and Collective Behavior of Self-Propelled Colloidal Motors. Acc. Chem. Res. 2015, 48 (7), 1938–1946. Fan, D.; Yin, Z.; Cheong, R.; Zhu, F. Q.; Cammarata, R. C.; Chien, C. L.; Levchenko, A. Subcellular-Resolution Delivery of a Cytokine Through Precisely Manipulated Nanowires. Nat. Nanotechnol. 2010, 5 (7), 545–551. Xu, X.; Kim, K.; Fan, D. Tunable Release of Multiplex Biochemicals by Plasmonically Active Rotary Nanomotors. Angew. Chem. Int. Ed. 2015, 54 (8), 2525–2529. Garcia-Gradilla, V.; Orozco, J.; Sattayasamitsathit, S.; Soto, F.; Kuralay, F.; Pourazary, A.; Katzenberg, A.; Gao, W.; Shen, Y.; Wang, J. Functionalized Ultrasound-Propelled Magnetically Guided Nanomotors: Toward Practical Biomedical Applications. ACS Nano 2013, 7 (10), 9232–9240. Sundararajan, S.; Lammert, P.; Zudans, A.; Crespi, V.; Sen, A. Catalytic Motors for Transport of Colloidal Cargo. Nano Lett. 2008, 8 (5), 1271–1276. Gao, W.; Kagan, D.; Pak, O. S.; Clawson, C.; Campuzano, S.; Chuluun-Erdene, E.; Shipton, E.; Fullerton, E. E.; Zhang, L.; Lauga, E.; Wang, J. Cargo-Towing Fuel-Free Magnetic Nanoswimmers for Targeted Drug Delivery. Small 2012, 8 (3), 460–467. Tottori, S.; Zhang, L.; Qiu, F.; Krawczyk, K. K.; Franco-Obregón, A.; Nelson, B. J. Magnetic Helical Micromachines: Fabrication, Controlled Swimming, and Cargo Transport. Adv. Mater. 2012, 24 (6), 811–816. 15 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(13) (14)

(15)

(16) (17) (18) (19) (20)

(21)

(22)

(23)

(24) (25)

(26)

(27) (28) (29)

(30)

Campuzano, S.; Kagan, D.; Orozco, J.; Wang, J. Motion-Driven Sensing and Biosensing Using Electrochemically Propelled Nanomotors. Analyst 2011, 136 (22), 4621–4630. Xu, X.; Kim, K.; Li, H.; Fan, D. L. Ordered Arrays of Raman Nanosensors for Ultrasensitive and Location Predictable Biochemical Detection. Adv. Mater. 2012, 24 (40), 5457–5463. Xu, X.; Li, H.; Hasan, D.; Ruoff, R. S.; Wang, A. X.; Fan, D. L. Near-Field Enhanced Plasmonic-Magnetic Bifunctional Nanotubes for Single Cell Bioanalysis. Adv. Funct. Mater. 2013, 23 (35), 4332–4338. Malachowski, K.; Jamal, M.; Jin, Q.; Polat, B.; Morris, C. J.; Gracias, D. H. Self-Folding Single Cell Grippers. Nano Lett. 2014, 14 (7), 4164–4170. Soler, L.; Magdanz, V.; Fomin, V. M.; Sanchez, S.; Schmidt, O. G. Self-Propelled Micromotors for Cleaning Polluted Water. ACS Nano 2013, 7 (11), 9611–9620. Gao, W.; Wang, J. The Environmental Impact of Micro/Nanomachines: a Review. ACS Nano 2014, 8 (4), 3170–3180. Gore, J.; Bryant, Z.; Nöllmann, M.; Le, M. U.; Cozzarelli, N. R.; Bustamante, C. DNA Overwinds When Stretched. Nature 2006, 442 (7104), 836–839. Kim, K.; Xu, X.; Guo, J.; Fan, D. L. Ultrahigh-Speed Rotating Nanoelectromechanical System Devices Assembled From Nanoscale Building Blocks. Nat. Commun. 2014, 5, 3632. Wang, W.; Li, S.; Mair, L.; Ahmed, S.; Huang, T. J.; Mallouk, T. E. Acoustic Propulsion of Nanorod Motors Inside Living Cells. Angew. Chem. Int. Ed. 2014, 53 (12), 3201– 3204. Balk, A. L.; Mair, L. O.; Mathai, P. P.; Patrone, P. N.; Wang, W.; Ahmed, S.; Mallouk, T. E.; Liddle, J. A.; Stavis, S. M. Kilohertz Rotation of Nanorods Propelled by Ultrasound, Traced by Microvortex Advection of Nanoparticles. ACS Nano 2014, 8 (8), 8300–8309. Kim, K.; Guo, J.; Xu, X.; Fan, D. E. Micromotors with Step-Motor Characteristics by Controlled Magnetic Interactions Among Assembled Components. ACS Nano 2015, 9 (1), 548–554. Solovev, A. A.; Xi, W.; Gracias, D. H.; Harazim, S. M.; Deneke, C.; Sanchez, S.; Schmidt, O. G. Self-Propelled Nanotools. ACS Nano 2012, 6 (2), 1751–1756. Xi, W.; Solovev, A. A.; Ananth, A. N.; Gracias, D. H.; Sanchez, S.; Schmidt, O. G. Rolled-Up Magnetic Microdrillers: Towards Remotely Controlled Minimally Invasive Surgery. Nanoscale 2013, 5 (4), 1294–1297. Srivastava, S. K.; Medina Sánchez, M.; Koch, B.; Schmidt, O. G. Medibots: Dual‐ Action Biogenic Microdaggers for Single‐Cell Surgery and Drug Release. Adv. Mater. 2016, 28 (5), 832–837. Ghosh, A.; Fischer, P. Controlled Propulsion of Artificial Magnetic Nanostructured Propellers. Nano Lett. 2009, 9 (6), 2243–2245. Gibbs, J. G.; Fischer, P. Active Colloidal Microdrills. Chem. Commun. 2015, 51 (20), 4192–4195. Xia, Y.; Yang, P.; Sun, Y.; Wu, Y.; Mayers, B.; Gates, B.; Yin, Y.; Kim, F.; Yan, H. One‐Dimensional Nanostructures: Synthesis, Characterization, and Applications. Adv. Mater. 2003, 15 (5), 353–389. Hawkeye, M. M.; Brett, M. J. Glancing Angle Deposition: Fabrication, Properties, and Applications of Micro- and Nanostructured Thin Films. J. Vac. Sci. Technol. A 2007, 25 16 ACS Paragon Plus Environment

Page 16 of 24

Page 17 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(31) (32) (33) (34)

(35) (36) (37) (38) (39)

(40) (41)

(42)

(43) (44)

(45)

(46)

(47)

(48) (49)

(5), 1317–1335. Gibbs, J. G.; Mark, A. G.; Lee, T.-C.; Eslami, S.; Schamel, D.; Fischer, P. Nanohelices by Shadow Growth. Nanoscale 2014, 6 (16), 9457–9466. Barthlott, W.; Neinhuis, C. Purity of the Sacred Lotus, or Escape From Contamination in Biological Surfaces. Planta 1997, 202 (1), 1–8. Gao, W.; Feng, X.; Pei, A.; Kane, C. R.; Tam, R.; Hennessy, C.; Wang, J. Bioinspired Helical Microswimmers Based on Vascular Plants. Nano Lett. 2014, 14 (1), 305–310. Autumn, K.; Liang, Y. A.; Hsieh, S. T.; Zesch, W.; Chan, W. P.; Kenny, T. W.; Fearing, R.; Full, R. J. Adhesive Force of a Single Gecko Foot-Hair. Nature 2000, 405 (6787), 681–685. Huang, J.; Wang, X.; Wang, Z. L. Controlled Replication of Butterfly Wings for Achieving Tunable Photonic Properties. Nano Lett. 2006, 6 (10), 2325–2331. Parker, A. R.; Townley, H. E. Biomimetics of Photonic Nanostructures. Nat. Nanotechnol. 2007, 2 (6), 347–353. Hall, S. R.; Bolger, H.; Mann, S. Morphosynthesis of Complex Inorganic Forms Using Pollen Grain Templates. Chem. Commun. 2003, No. 22, 2784–2785. Gebeshuber, I. C. Biotribology Inspires New Technologies. Nano Today 2007, 2 (5), 30– 37. Zhao, Y.; Wei, M.; Lu, J.; Wang, Z. L.; Duan, X. Biotemplated Hierarchical Nanostructure of Layered Double Hydroxides with Improved Photocatalysis Performance. ACS Nano 2009, 3 (12), 4009–4016. Round, F. E.; Crawford, R. M.; Maan, D. G. The Diatoms : Biology & Morphology of the Genera; Cambridge University Press: Cambridge; New York, 1990. Townley, H. E.; Parker, A. R.; White-Cooper, H. Exploitation of Diatom Frustules for Nanotechnology: Tethering Active Biomolecules. Adv. Funct. Mater. 2008, 18 (2), 369– 374. Gordon, R.; Losic, D.; Tiffany, M. A.; Nagy, S. S.; Sterrenburg, F. A. S. The Glass Menagerie: Diatoms for Novel Applications in Nanotechnology. Trends Biotechnol. 2009, 27 (2), 116–127. Losic, D.; Mitchell, J. G.; Voelcker, N. H. Diatomaceous Lessons in Nanotechnology and Advanced Materials. Adv. Mater. 2009, 21 (29), 2947–2958. Yang, W.; Lopez, P. J.; Rosengarten, G. Diatoms: Self Assembled Silica Nanostructures, and Templates for Bio/Chemical Sensors and Biomimetic Membranes. Analyst 2011, 136 (1), 42–53. Ren, F.; Campbell, J.; Wang, X.; Rorrer, G. L.; Wang, A. X. Enhancing Surface Plasmon Resonances of Metallic Nanoparticles by Diatom Biosilica. Opt. Express 2013, 21 (13), 15308–15313. Ren, F.; Campbell, J.; Rorrer, G. L.; Wang, A. X. Surface-Enhanced Raman Spectroscopy Sensors From Nanobiosilica with Self-Assembled Plasmonic Nanoparticles. IEEE J. Sel. Top. Quantum Electron. 2014, 20 (3), 127–132. Yang, J.; Zhen, L.; Ren, F.; Campbell, J.; Rorrer, G. L.; Wang, A. X. Ultra-Sensitive Immunoassay Biosensors Using Hybrid Plasmonic-Biosilica Nanostructured Materials. J. Biophotonics 2015, 8 (8), 659–667. Fan, D. L.; Zhu, F. Q.; Cammarata, R. C.; Chien, C. L. Controllable High-Speed Rotation of Nanowires. Phys. Rev. Lett. 2005, 94 (24), 247208. Fan, D. L.; Cammarata, R. C.; Chien, C. L. Precision Transport and Assembling of 17 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(50) (51) (52) (53) (54) (55) (56)

(57)

(58) (59) (60) (61) (62)

(63) (64)

(65)

Nanowires in Suspension by Electric Fields. Appl. Phys. Lett. 2008, 92 (9), 093115. Fan, D. L.; Zhu, F. Q.; Cammarata, R. C.; Chien, C. L. Electric Tweezers. Nano Today 2011, 6 (4), 339–354. Chien, C.-L.; Fan, D.; Cammarata, R. C. System and Method for Precision Transport, Positioning, and Assembling of Longitudinal Nano-Structures. June 2, 2015. Keshoju, K.; Xing, H.; Sun, L. Magnetic Field Driven Nanowire Rotation in Suspension. Appl. Phys. Lett. 2007, 91 (12), 123114. Purcell, E. M. Life at Low Reynolds Number. Am. J. Phys. 1977, 45 (1), 3–11. Jones, T. B. Electromechanics of Particles; Cambridge University Press: Cambridge; New York, 1995. Guo, J.; Kim, K.; Lei, K. W.; Fan, D. L. Ultra-Durable Rotary Micromotors Assembled From Nanoentities by Electric Fields. Nanoscale 2015, 7 (26), 11363–11370. Ahmed, S.; Gentekos, D. T.; Fink, C. A.; Mallouk, T. E. Self-Assembly of Nanorod Motors Into Geometrically Regular Multimers and Their Propulsion by Ultrasound. ACS Nano 2014, 8 (11), 11053–11060. Fan, D. L.; Zhu, F. Q.; Xu, X.; Cammarata, R. C.; Chien, C. L. Electronic Properties of Nanoentities Revealed by Electrically Driven Rotation. Proc. Natl. Acad. Sci. U.S.A. 2012, 109 (24), 9309–9313. Xu, X.; Liu, C.; Kim, K.; Fan, D. L. Electric-Driven Rotation of Silicon Nanowires and Silicon Nanowire Motors. Adv. Funct. Mater. 2014, 24 (30), 4843–4850. Aref, H. Stirring by Chaotic Advection. J. Fluid Mech. 1984, 143, 1–21. Lu, L.-H.; Ryu, K. S.; Liu, C. A Magnetic Microstirrer and Array for Microfluidic Mixing. J. Microelectromech. Syst. 2002, 11 (5), 462–469. Lee, S. H.; van Noort, D.; Lee, J. Y.; Zhang, B.-T.; Park, T. H. Effective Mixing in a Microfluidic Chip Using Magnetic Particles. Lab Chip 2009, 9 (3), 479–482. Kang, T. G.; Hulsen, M. A.; Anderson, P. D.; Toonder, den, J. M. J.; Meijer, H. E. H. Chaotic Mixing Induced by a Magnetic Chain in a Rotating Magnetic Field. Phys. Rev. E 2007, 76 (6), 066303. Rida, A.; Gijs, M. A. M. Manipulation of Self-Assembled Structures of Magnetic Beads for Microfluidic Mixing and Assaying. Anal. Chem. 2004, 76 (21), 6239–6246. Al-Fandi, M.; Jaradat, M. A. K.; Fandi, K.; Beech, J. P.; Tegenfeldt, J. O.; Yih, T. C. Nano-Engineered Living Bacterial Motors for Active Microfluidic Mixing. IET Nanobiotechnol. 2010, 4 (3), 61–71. Ukita, H.; Kanehira, M. A Shuttlecock Optical Rotator-Its Design, Fabrication and Evaluation for a Microfluidic Mixer. IEEE J. Sel. Top. Quantum Electron. 2002, 8 (1), 111–117.


Page 18 of 24

Page 19 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figures

Figure 1. (a and b) Scanning electron microscope (SEM) images of (a) as-obtained and (b) metal-coated diatom frustules. (c) Schematics of the electric tweezers with two orthogonal sets of parallel electrodes for the manipulation of diatom frustules on the substrate with a patterned micromagnet (µ-magnet). (d) Velocity of diatom frustules as a function of DC voltages. (Inset: micrographs of diatom frustules of cylinder and disk shapes. Scale bars: 10 µm). (e) Trajectory of a diatom frustules manipulated by the electric fields to spell letters of “U” and “T.”



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 2. (a) Sequential optical images of a rotating diatom frustule. (b) Accumulative angle of a diatom frustule rotating in clockwise (cw) and counterclockwise (ccw) orientations at different speed depending on the applied AC voltage. (c) Rotation speed of a diatom frustule increases with the square of the applied AC voltage (V2) linearly. (d) Illustration of a diatom frustule rotating in the same direction of the electric field (grey arrow).


Page 20 of 24

Page 21 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3. (a) Overlaid sequential optical images of the assembling of a Cr/Ni/Au-coated diatom frustule on a patterned micromagnet in electric fields. (b) Multiple diatom frustule motors rotate simultaneously in a 2×2 array. (c) Accumulative angle of versus time of a diatom frustule motor rotating at >2800 rpm (inset: sequential snap shots of the micromotor). (d) Diatom frustule motor continuously rotating for ~11.5 minutes.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 4. (a) Rotation speed of metallic Au/Ni/Au nanowires (red diamond), diatom frustules with (turquoise squares) or without (blue dots) coating of the metallic Cr/Ni/Au layers as a function of electric field frequency. In AC electric fields of 5 kHz to 1 MHz, metallic nanowires and diatom frustules rotated in opposite directions through the entire frequency range. While metal-coated diatom frustules rotate in the same orientation as that of the metallic Au/Ni/Au nanowires at low frequencies before reversing the direction to that of the pure silica diatom frustules at high frequencies above ~120 kHz. (b – f) Reconfigurable micromotors arrays in the same rotating electric field (grey arrow): (c) at 15 V/10 kHz, both motors rotate simultaneously in the same direction; (d) at 17 V/45 kHz, only the nanowire motor rotates; (e) at 17 V/65 kHz, both motors rotate simultaneously in opposite directions; and (f) at 15 V/300 kHz, only frustule motor rotates. All the unlabeled scale bars are 10 µm. [(c) – (e) shows one device (f) is a new device]


Page 22 of 24

Page 23 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5. (a) Schematic and (b) optical image of diatom frustule micromotors (µ-motors) integrated in a microchannel (µ-channel). (c) Sequential optical snap shots showing the cw and ccw rotation of the micromotor array in (b). (d) PS spheres dispersed around the assembled frustule motor in a microchannel and the trajectories of the PS spheres dragged by the rotating micromotor. (e) COMSOL simulation of the fluidic field around a rotating diatom frustule micromotor in the microfluidic channel in (d).



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table of Contents (TOC) Graphic


Page 24 of 24

Biobased High-Performance Rotary Micromotors ... - ACS Publications

Recommend Documents