Magnetically Characterized Molecular Lubrication between

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Magnetically characterized molecular lubrication between bio-functionalized surfaces Xinghao Hu, Sri Ramulu Torati, Jonghwan Yoon, Byeonghwa Lim, Kunwoo Kim, and CheolGi Kim ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b00903 • Publication Date (Web): 18 Apr 2018 Downloaded from http://pubs.acs.org on April 18, 2018

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ACS Applied Materials & Interfaces

Magnetically Characterized Molecular Lubrication Between BioFunctionalized Surfaces Xinghao Hu1, Sri Ramulu Torati1,2, Jonghwan Yoon1, Byeonghwa Lim1, Kunwoo Kim1, CheolGi Kim1* 1

Department of Emerging Materials Science, DGIST, Daegu, 42988, Republic of Korea.

2

School of Chemical and Biotechnology, SASTRA Deemed University, Thanjavur, 613401,

India

*E-mail: [email protected].

ABSTRACT: We demonstrate an efficient approach for quantifying frictional forces (sub-pN) at nanobio interfaces by controlled magnetic forces, which is based on simultaneous measurements of critical frequencies for streptavidin-coupled magnetic particles. The maximum phase angle, being corresponded with the critical frequency, is formulated in terms of magnetic, frictional and viscous forces of the particles on DNA and SiO2 functionalized micromagnet arrays. The streptavidin/DNA interface shows lower friction as an enhanced lubrication than the streptavidin/SiO2 interface, which is indicated by the lower transition field of quasi-static motion, the larger ratio of dynamic particles, and also the higher velocity of the particles. The friction coefficients at the streptavidin/DNA and streptavidin/SiO2 interfaces are evaluated numerically as 0.07 and 0.11 respectively, regardless of the vertical force and the velocity. The proposed method would open up new possibilities to study mechanical interactions at biological surfaces.

KEYWORDS: superparamagnetic particle, micromagnet, bio-funtionalization, friction, magnetic field

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1. INTRODUCTION The investigation of surface interaction forces at micro/nanoscale has been gaining an increasing interest in bio-micro/nanoelectromechanical systems (bio-MEMS/NEMS),1–3 since the surface forces would dominate over the volume forces when the surface-to-volume ratio increases with the decrease of device sizes. A number of techniques are available to quantify the tiny forces (pN scale) associated with biological molecules, where the most prominent methodologies are optical tweezers, generally utilized in the studies of organelle transport along microtubule such as kinesin and cytoplasmic dynein;4,5 glass microneedles to stretching, unzipping and twisting DNA;6 biomembrane force probe for investigating the strengths of membrane anchor in lipid membranes and receptor-ligand bonds;7,8 atomic force microscopy (AFM) for exploring the interaction between individual ligands and receptors,9 measuring the isoelectric points of different proteins,10 and determining the friction on protein interfaces;11 and magnetic tweezers traditionally utilized in stretching or twisting DNA.12 However, these methods are only available to manipulate a single object for feasible analysis in biological motion, which is insufficient to represent a bulk performance. Physicochemical heterogeneity of molecules leads fluctuations of the surface energy with a similar effect as roughness.13 By molecular dynamics simulations, it was shown that the heterogeneity caused by adsorbed contamination molecules14 or the dangling bond density15 plays a significant role in friction. Therefore, there is an urgent need for a tool to statistically evaluate the friction force of biomolecules at micro/nanoscale. Earlier, an on-chip micromagnet frictionometer was developed to quantify the friction at nano-bio interfaces between bio-functionalized magnetic particles and micromagnet arrays.16 The micromagnet arrays are able to manipulate the particles to obtain reliable statistics of friction forces in subpN scale, by the measurements of the varied phase-locked angles between the particle location and the field direction under the controlled magnetic forces. However, the calibration of device and the measurements of the phase-locked angles require time consuming, and also has a limitation for obtaining ensemble average of massive biological objects related 2


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with the velocity dependence of friction for understanding of lubrication states.17 In this work, we develop an approach to rapidly quantify ensemble average of frictional forces between massive superparamagnetic particles and on-chip micromagnets, which is based on the critical modulation frequency from the phase-locked to -slipping mode under an applied rotating magnetic field. The particles rotate synchronously with the applied field around the periphery of the micromagnets in the phase-locked mode,18 here the maximum phase-locked angle is mathematically formulated in terms of magnetic driving and drag forces. From the balancing forces relationship at the maximum phase-locked angle, the friction properties at streptavidin/DNA and streptavidin/SiO2 interfaces are evaluated for the parameters of varied velocities and loading forces, which affords an efficient and practical method to evaluate the friction of mechanical interactions at biological surfaces. 2. MATERIALS AND METHODS Superparamagnetic

Particles

and

Micromagnets.

The

2.8

µm

diameter

superparamagnetic particles (Dynabeads M-280 Streptavidin, Invitrogen cat. no. 142.03) functionalized with a streptavidin layer were used in this study. The silicon substrates purchased from Wafermart Co. (Seoul, South Korea) was used for patterning the micromagnets. The micromagnets were stenciled on a silicon substrate by conventional photolithography and lift-off techniques. The detail procedure for the fabrication of micromagnets were described elsewhere.14 In briefly, photoresist patterns of 10 µm diameter disks were patterned on the silicon substrate followed by deposition of 100 nm thick Ni83Fe17 layer by direct current (DC) magnetron sputtering to obtain micromagnets. The high purity sputtering target of Ni83Fe17 was obtained from Kojundo Chemical Laboratory Co., LTD, Japan. Coating of Micromagnets. The silicon substrate along with micromagnets were coated with 50 nm thick SiO2 (Using a RF magnetron sputtering system) and 50 nm thick Au (Using DC magnetron sputtering system) to create streptavidin/SiO2 and streptavidin/DNA interface, respectively. The Au coated silicon substrate was immobilized with thiolated single-strand 3



DNA (GeneChemIncs, Korea). The base sequence for the sss-DNA is as follows: ss-DNA: 5'-SH-(CH2)3-TCCGGAGCTGCCCTACGAGGTCAA-3' The immobilization of ss-DNA on micro-magnets was accomplished by dispensing 10 µL of 100 ng/µL DNA in Tris-EDTA buffer on the patterned surface and subsequently kept for 12 h in a humidifying chamber with a suitable environment. After that the micromagnets were was washed with Tris-EDTA buffer to remove any unbound ss-DNA and kept at 4 ºC when not in use. Rotational Field Set-up. The driving forces, rotating magnetic field for the rotation of magnetic beads around the micromagnets were generated by soft magnetic core solenoids arranged along mutually orthogonal axes (x-y) with respect to the substrate surface. The LabView software (National Instruments) was used to control both the current sources to supply sinusoidal waveforms to each solenoid. A rotating magnetic field in the x-y plane was developed by controlling the current sources along orthogonal axes to shifted the phase by

r

r

r

r

90º, i.e. H x = i cos(ωt ) and H y = j sin(ωt ) . The applied magnetic field was monitored by placing a gauss meter (Lakeshore 450) at the center of the rotating field. Magnetic Forces Simulation. The distribution of induced magnetic-field and gradients on the micromagnet disks was obtained by finite element method (FEM) simulations using Maxwell 3D software (Version 16.1, Ansoft). The simulations were based on experimentally measured initial M-H curve of the 100 nm thick (Ni83Fe17) film. The magnetic properties of the film were measured by VSM (Vibrating Sample Magnetometer, Lakeshore 7400). The obtained saturation magnetization of permalloy film is 668 emu/cc. By numerical differentiation of the induced-field components, the components of the magnetic forces acting on the magnetic beads was obtained. 3. RESULTS AND DISCUSSION In order to measure the frictional force from massive particles simultaneously, we fabricate 90,000 micromagnets in 6 × 6 mm area on one silicon substrate. Each 4


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micromagnet traps the particles at N- and S- poles of high induced-field regime randomly (red peak), under an applied magnetic field in the X-axis direction, as shown in Figure 1a. When the field starts to rotate, the trapped particle moves around the periphery of the micromagnets, but the phase is lagged from the field direction. Figure 1b illustrates the governing force components on a moving particle around the micromagnet periphery, with the phase-locked angle φ from the magnetic field (Happ) rotating in the clockwise direction, The drag force is the sum of frictional ( ) and viscous ( ) forces. The scanning electron microscopy (SEM) image of the particles utilized in this study are shown in Figure 1c. Figure 1d shows a schematic of the nano-bio interface between a streptavidin-coupled particle and a DNA functionalized substrate.

The simulated tangential, radial, and vertical forces ( , , and ) in cylindrical

coordinate are given by following equations: χ

∙ = = ∇ ̂ + ̂ + ̂

= 2"

(1) (2)

= # $%2" + &

(3)

= $ $%2" + '

(4)

Here, ( is the volume of the magnetic bead (m3), χ is the magnetic volume susceptibility of the magnetic bead, 0.7 (the magnetization of the surrounding medium is neglected), ) is is the magnetic flux density (T), the angle (") the permeability of vacuum (4π×10-7 N/A2),

dependence of force components, ("), ("), and (") are obtained by the best

fitting of simulated forces, and the best fitting parameters of #, &, $ and ' are −1.66, 0.46, −5.12 and 0.68 respectively; the magnitude is 27.5 pN for the applied field of 5 mT (Figure S1). Figure 2a shows the calculated ratio of drag and tangential magnetic forces. At the small angles less than ", , the drag force is larger than the driving tangential force, that is, particle can not move. When the phase angle is increased, then the tangential force is

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increased to be balanced with the drag force at 12° angle (curve-Ⅰ). The trapped particle starts to move synchronously around the periphery of the micromagnets at the fixed phase angle from the field, so called phase-locked mode. In this mode, the tangential force is balanced by drag force as following:

= = +

(5)

When the rotating field frequency increases, then the drag force, , being proportional to the viscous force, increases, in turns causing the increment of the phase-locked angle, of which maximum value is 50° (curve-Ⅲ). When the field rotational frequency increases over a critical value (ƒc), the drag force is larger than the maximum tangential force, and then the particle is unable to keep pace with the field entering the phase-slipping mode (curve-Ⅳ).

Figure 2b,c present the experimental and simulated trajectories of a particle just starting to jump under the 2 mT field with 1.4 Hz frequency in the clockwise direction. Here, the time variation of particle trajectory in circumferential and radial components was numerically obtained by net forces on the particle (see Supporting Information for trajectory simulation of particle motion). Under the higher frequency over the critical frequency, the multiple jumping is revealed (Figure 2d,e). The particle jumping is occurred due to a repulsive radial force

as shown in Figure 3. Eventually the particle doesn’t rotate circularly along the micromagnet periphery, but it is erratically mobile at a fixed position, so-called phasedecoupling mode. Figure 4a illustrates the different phase regimes at the strept/DNA and strept/SiO2 interfaces under low magnetic fields (~ 1.4 mT) with 0.1 Hz frequency. With increasing the applied field, the phase-decoupling (black area), phase-slipping (red area) and phase-locked (blue area) regimes are observed, respectively. In the phase-decoupling mode, the streptavidin-coupled particles just can jump near the fixed periphery of micromagnets, but not rotate circularly along the micromagnets, quasi-stationary mode. The transition fields to 6


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the quasi-stationary motion at the strept/DNA and strept/SiO2 interfaces are 0.5 and 0.7 mT respectively, which indicates a lower friction at the strept/DNA interface compared with the strept/SiO2 interface. Moreover, the lubrication is enhanced by DNA coating on the micromagnets. As more specifically shown in Figure 4b, there are more particles rotating on the strept/DNA substrate than that of the strept/SiO2 substrate at high frequency region of the field (5 mT) from 14 to 20 Hz. The maximum particle velocity was measured by using the critical frequencies of the particles at the strept/DNA and strept/SiO2 interfaces depending on the applied field strength (Figure 5a). The streptavidin particles on the DNA substrate reveals a higher velocity due to a smaller friction. For an example, under 5 mT field the velocities at the strept/DNA and strept/SiO2 interfaces are 290 and 219 µm/s at maximum phase angles, respectively. The viscous force is given by = 32.η/#/3 considering the wall effect,19 where η, #, and / are the viscosity of the aqueous medium, the particle radius, and the particle velocity, respectively. As for the frictional force evaluation, the critical modulation frequency from the phaselocked to slipping modes is measured, that is the frequency for 1st jumping of particles. As described proceeding section, the maximum phase-locked angle is 50°. Figure 5b shows the

calculated magnetic forces (50°) and (50°) from equations (2) and (4), and viscous

force from Figure 5a. Therefore, the frictional forces at the strept/DNA and strept/SiO2 interfaces can be evaluated. Here, both the buoyant and gravitational forces are neglected for considering the effective vertical force on the particles. The root mean squared surface roughnesses of the SiO2 and DNA coated substrates are approximately 0.76 and 0.71 nm respectively. The topography images in 3 × 3 µm area are shown in Figure 6a,b measured by AFM. The frictional force , being equal to )1 (50°),

is evaluated by subtracting from the tangential magnetic force (50°). Figure 6c depicts the frictional forces with the sub-pN scale at two kinds of nano-bio interfaces as a

7



function of the vertical forces. A good linear relationship between the frictional and vertical forces is observed. Therefore, the friction coefficients for the strept/DNA and strept/SiO2 interfaces are evaluated as 0.07 ± 0.01 and 0.11 ± 0.02 respectively (inset of Figure 6c), regardless of both the vertical force and the velocity. Although a surfactant (0.1% Sodium dodecyl sulfate solution) was used to exclude nonspecific adhesion, the streptavidin-coupled particles don’t have any mobility on the Au-coated substrate. As a result, the DNA immobilization on the Au-coated substrate presents a prominent function of molecule lubrication, such as the functions of hyaluronic acid, lubricin, or phospholipids on the articular cartilage surface.20,21 The above demonstration thus reveals the capability of the micromagnet arrays to serve as the practical application devices for the rapid determination of very low friction at nano-bio interfaces in a liquid environment. 4. CONCLUSION We developed an efficient technique for the quantification of frictional forces (sub-pN scale) at nano-bio interfaces between the bio-functionalized particles and DNA, SiO2 functionalized micromagnets using an applied magnetic field. The novel technique can simultaneously evaluate the ensemble average of frictional forces on massive particles by measuring the maximum velocities occurred at the maximum phase angle (50°) around the micromagnet periphery. This proposed method is much easier and faster to determine the frictional force than the previous method of measuring the varied phase-locked angles.14 DNA coating on Au surface increases maximum velocity about 30 %, compared with SiO2 interface, and in turn a higher operation velocity is afforded by optimization of the micromagnet size.22 The friction coefficients at the strept/DNA and strept/SiO2 interfaces were evaluated as 0.07 and 0.11 respectively, regardless of both the vertical force and the velocity. Consequently, our proposed approach has paved a new methodology for the evaluation of friction in protein-loaded cargos,23 metastasis of cancer cells,24 and molecular motor proteins,25 as well as evaluation of frictional forces at nano-bio interfaces in bioMEMS/NEMS.26,27 8


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■ ASSOCIATED CONTENT Supporting Information Trajectory simulation of particle motion, magnetic tangential and vertical forces (PDF)

■ AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. Notes The authors declare no competing financial interest.

■ ACKNOWLEDGEMENTS This research was supported by DGIST R&D program of the ministry of science, ICT and Future Planning (18-BT-02). Authors acknowledge Jeesoo Kim (UIUC) for data acquisition of particle mobility.

■ (1)

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Recognition Events Using Atomic Force Microscopy. Nat. Methods 2006, 3 (5), 347. (10) Guo, S.; Zhu, X.; Jańczewski, D.; Lee, S. S. C.; He, T.; Teo, S. L. M.; Vancso, G. J. Measuring Protein Isoelectric Points by AFM-Based Force Spectroscopy Using Trace Amounts of Sample. Nat. Nanotechnol. 2016, 11 (9), 817–823. (11) Gunnewiek, M. K.; Ramakrishna, S. N.; di Luca, A.; Vancso, G. J.; Moroni, L.; Benetti, E. M. Stem-Cell Clinging by a Thread: AFM Measure of Polymer-Brush Lateral Deformation. Adv. Mater. Interfaces 2016, 3 (3), 1500456. (12) Neuman, K. C.; Nagy, A. Single-Molecule Force Spectroscopy: Optical Tweezers, Magnetic Tweezers and Atomic Force Microscopy. Nat. Methods 2008, 5 (6), 491. (13) Swain, P. S.; Lipowsky, R. Contact Angles on Heterogeneous Surfaces: A New Look at Cassie’s and Wenzel’s Laws. Langmuir 1998, 14 (23), 6772–6780. (14) He, G.; Müser, M. H.; Robbins, M. O. Adsorbed Layers and the Origin of Static Friction. Science 1999, 284 (5420), 1650–1652. (15) Dai, L.; Sorkin, V.; Zhang, Y.-W. Effect of Surface Chemistry on the Mechanisms and Governing Laws of Friction and Wear. ACS Appl. Mater. Interfaces 2016, 8 (13), 8765– 8772. (16) Hu, X.; Rani Goudu, S.; Ramulu Torati, S.; Lim, B.; Kim, K.; Kim, C. An On-Chip Micromagnet Frictionometer Based on Magnetically Driven Colloids for Nano-Bio Interfaces. Lab. Chip 2016, 16 (18), 3485–3492. (17) Robinson, J. W.; Zhou, Y.; Bhattacharya, P.; Erck, R.; Qu, J.; Bays, J. T.; Cosimbescu, L. Probing the Molecular Design of Hyper-Branched Aryl Polyesters towards Lubricant Applications. Sci. Rep. 2016, 6, 18624. (18) Hu, X.; Abedini-Nassab, R.; Lim, B.; Yang, Y.; Howdyshell, M.; Sooryakumar, R.; Yellen, B. B.; Kim, C. Dynamic Trajectory Analysis of Superparamagnetic Beads Driven by OnChip Micromagnets. J. Appl. Phys. 2015, 118 (20), 203904. (19) Leach, J.; Mushfique, H.; Keen, S.; Di Leonardo, R.; Ruocco, G.; Cooper, J. M.; Padgett, M. J. Comparison of Faxén’s Correction for a Microsphere Translating or Rotating near a Surface. Phys. Rev. E 2009, 79 (2), 026301. (20) Singh, A.; Corvelli, M.; Unterman, S. A.; Wepasnick, K. A.; McDonnell, P.; Elisseeff, J. H. Enhanced Lubrication on Tissue and Biomaterial Surfaces through Peptide-Mediated Binding of Hyaluronic Acid. Nat. Mater. 2014, 13 (10), 988. (21) Liu, G.; Liu, Z.; Li, N.; Wang, X.; Zhou, F.; Liu, W. Hairy Polyelectrolyte Brushes-Grafted Thermosensitive Microgels as Artificial Synovial Fluid for Simultaneous Biomimetic Lubrication and Arthritis Treatment. ACS Appl. Mater. Interfaces 2014, 6 (22), 20452– 20463. (22) Hu, X.; Lim, B.; Jeong, I.; Sandhu, A.; Kim, C. Optimization of Pathway Pattern Size for Programmable Biomolecule Actuation. IEEE Trans. Magn. 2013, 49 (1), 408–413. 10


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(23) Lim, B.; Torati, S. R.; Kim, K. W.; Hu, X.; Reddy, V.; Kim, C. Concentric Manipulation and Monitoring of Protein-Loaded Superparamagnetic Cargo Using Magnetophoretic Spider Web. NPG Asia Mater. 2017, 9 (3), e369. (24) Madsen, C. D.; Hooper, S.; Tozluoglu, M.; Bruckbauer, A.; Fletcher, G.; Erler, J. T.; Bates, P. A.; Thompson, B.; Sahai, E. STRIPAK Components Determine Mode of Cancer Cell Migration and Metastasis. Nat. Cell Biol. 2015, 17 (1), 68. (25) Heuvel, M. G. L. van den; Dekker, C. Motor Proteins at Work for Nanotechnology. Science 2007, 317 (5836), 333–336. (26) Byun, S.; Son, S.; Amodei, D.; Cermak, N.; Shaw, J.; Kang, J. H.; Hecht, V. C.; Winslow, M. M.; Jacks, T.; Mallick, P.; Manalis, S. R. Characterizing Deformability and Surface Friction of Cancer Cells. Proc. Natl. Acad. Sci. 2013, 110 (19), 7580–7585. (27) Otto, O.; Sturm, S.; Laohakunakorn, N.; Keyser, U. F.; Kroy, K. Rapid Internal Contraction Boosts DNA Friction. Nat. Commun. 2013, 4, 1780.

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Figure captions Figure 1. (a) Inhomogeneous field distribution above the micromagnet array. Each micromagnet produces regions of high induced-field (red) and low induced-field (blue) under an in-plane magnetic field in the x-direction. Inset shows scanning electron microscopy (SEM) image of the micromagnet array. (b) Illustration of the governing force components on a moving particle around the micromagnet periphery, with a phase-locked angle φ from the

field direction, where , , and denote the tangential, radial, vertical and

drag forces, respectively. The simulated magnetic domain in the micromagnet (10 µm diameter, 100 nm thick) is obtained under an in-plane field (10 mT) using OOMMF software. (c) SEM image of Dynabeads M-280 beads (2.8 µm diameter). (d) Schematic of molecule friction between a streptavidin-coupled particle and a DNA functionalized substrate. Figure 2. (a) Normalized drag force FD/Fφ as a function of the particle angle from the field direction. The phase-slipping is initiated at FD3, which indicates the maximum phase-locked angle as 50°. (b and c) The experimental and simulated trajectories of a particle just entering the phase-slipping regime under the rotating Happ of 2 mT with the 1.4 Hz frequency in clockwise direction. φc represents the maximum phase-locked angle. (d and e) The experimental and simulated trajectories of the particle under the rotating Happ of 2 mT with the 1.45 Hz frequency.

Figure 3. Normalized radial magnetic force ( ) around a full-disk micromagnet with 10 µm diameter. Figure 4. (a) Divergence of particles at three phase regimes (phase-locked, slipping and decoupling) on the substrates coated with DNA and SiO2 in low field regions with 0.1 Hz frequency. (b) Particle mobility on the substrates coated with DNA and SiO2 based on the rotating frequency under 5 mT field. Figure 5. (a) The measured velocity of particles for the strept/DNA and strept/SiO2 interfaces

as a function of the field strength. (b) The simulated and corresponding to the

phase angle φ = 50°, and the viscous forces as a function of the applied field strength. Figure 6. (a and b) AFM topography images of the micromagnet substrates coated with SiO2 and DNA (image size: 3 × 3 µm). The root mean squared surface roughnesses of the SiO2 and DNA coated substrates are approximately 0.76 and 0.71 nm, respectively. (c) Friction forces at strept/SiO2 and strept/DNA interfaces as a function of the vertical force. Inset shows the averaged friction coefficients.

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Magnetically Characterized Molecular Lubrication between

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