Bubble-Free Propulsion of Ultrasmall Tubular Nanojets Powered by

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Bubble Free Propulsion of Ultra-small Tubular Nano-jets Powered by Bio-catalytic Reactions Xing Ma, Ana C. Hortelao, Albert Miguel-López, and Samuel Sanchez J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.6b06857 • Publication Date (Web): 09 Oct 2016 Downloaded from http://pubs.acs.org on October 10, 2016

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Journal of the American Chemical Society

Bubble Free Propulsion of Ultra-small Tubular Nano-jets Powered by Bio-catalytic Reactions Xing Ma‡,#, Ana C. Hortelao‡,∥, Albert Miguel-López∥, and Samuel Sánchez*,‡,∥,§ ‡

Max-Planck Institute for Intelligent Systems Institution, Heisenbergstraße 3, 70569 Stuttgart, Germany School of Materials Science and Engineering, Harbin Institute of Technology Shenzhen Graduate School, 518055 Shenzhen, China ∥ Institut de Bioenginyeria de Catalunya (IBEC), Baldiri i Reixac 10-12, 08028 Barcelona, Spain § Institució Catalana de Recerca i Estudis Avancats (ICREA), Pg. Lluís Companys 23, 08010, Barcelona, Spain Supporting Information #

sub-micron up to 30 µm in diameter and from 25 µm to 1 mm in length.17,20,24 Clean room-free “rolling up” methods have been also reported.25-27 Another method is electrochemical deposition on porous membranes (Al2O3 or polycarbonate).8,15,19 which produces micro-tubes from 2 µm to 5 µm in diameter. Up to now, only a very few works reported nano-tubular motors, all of them using high concentrations of H2O2 as fuel and surfactant to reduce the surface tension.17,25,28 Cheap and facile fabrication method which could be up-scaled, enabling a metal-free nanoarchitecture, is sought after. Bio-friendly processes such as enzyme catalysis can provide mechanical force to drive micro/nanostructures, with great potentials towards biocompatible selfpowered systems.29-35 We previously demonstrated that enzymebased silica micromotors show biocompatibility against HeLa cells.33 Additionally, a bubble free propulsion mechanism would avoid accumulation of gas bubbles in the fluidic environment, which is advantageous for future in vivo biomedical use.

ABSTRACT: The motion of self-propelled tubular micro- and nano-jets have so far been achieved by bubble propulsion, e.g. O2 bubbles by catalytic decomposition of H2O2, which renders the future biomedical applications inviable. Alternative selfpropulsion mechanism for tubular engines in the nano-meter scale is still missing. Here, we report the fabrication and characterization of a bubble-free propelled tubular nano-jets (as small as 220 nm in diameter), powered by enzyme triggered bio-catalytic reaction using urea as fuel. We studied the translational and rotational dynamics of the nano-jets depending on the length and location of the enzymes. Introducing tracer nanoparticles into the system, we demonstrated the presence of an internal flow that extends into the external fluid via the cavity opening, which leads to the self-propulsion. One-dimensional nano-size, longitudinal self-propulsion and biocompatibility, make the tubular nano-jets promising in future biomedical applications.

Researchers have fabricated multiple micro/nano motors that mimicking natural systems,1-4 are capable of converting chemical energy into kinetic energy for self-propulsion.5-7 Tubular catalytic motors have been demonstrated as versatile “on-the-fly” microsystems for various proof-of-concept applications, such as heavy metal capture8 or water remediation,9,10 cargo loading and transportation,11,12 drug delivery,13 sensing,14-16 and as micro-drillers for minimally invasive surgery.17,18 Almost all the current tubular motors are driven by bubble propulsion mechanism in the micrometer scale. Usually, an inorganic catalytic component, such as platinum (Pt),13,19,20 silver (Ag),21 or MnO2,22 is included inside the tubes to trigger decomposition of hydrogen peroxide (H2O2) (H2O2→H2O+1/2O2). Alternatively, catalase enzyme has been used as organic catalyst to efficiently provide self-propulsion decomposing much lower concentrations of H2O2.15,16,23 The underlying mechanism involves the formation and continuous ejection of oxygen (O2) bubbles from the tubular confinement provoking the motion in the opposite direction. Up to now, there are two major strategies for the fabrication of tubular motors. One is the “rolling-up” method based on clean room photolithography and electron-beam (e-beam) evaporation techniques, which can produce tubular structures with sizes from

Figure 1. a) Schematic illustration of the fabrication of urease conjugated silica tubular (SNT-Urease) nano-jets; b) Typical SEM image of the SNTs; c) fuel dependent average velocity of SNTUrease with an average length of 10 µm. (The error bars indicate standard error of the mean, N=10) Herein, we present ultra-small tubular silica nano-jets (220 nm diameter in average) self-propelled by enzymatic reactions. The nano-jets are powered by the turnover of urea substrate (at physiological concentrations) triggered by enzyme urease (Urea→NH3(aq)+CO2(aq)). The reaction products (ammonia (NH3(aq)) and carbon dioxide (CO2(aq))) are generated in the inside

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of the nanotubes generating internal flows that extend into the external space via the tube opening. This generates a thrust longitudinally that maintains the directional movement of the nano-jets by “jetting effect”.36 The existence of a flow was supported by analyzing tracer nanoparticles (NPs) expelled from the back side of the nano-jets. The silica nano-tubes were fabricated using silver nano-wires (AgNW, 115 nm×50 µm) as template on which a thin layer of silica was grown by sol-gel chemistry.37 Then, the silica coated nano-wires (AgNW@SiO2) (Figure S1 (a)) were broken down into shorter segments by sonication for 3 hours (see details in the Supporting Information (SI)). After removal of the template of AgNW by etching in aqua regia overnight, the silica nano-tubes (SNT) were obtained (Figure S1 (b) and (c)). We functionalized the SNT with amine groups (-NH2) by grafting method, yielding SNT-NH2. The amine groups on SNT-NH2 were detected by fluorescamine, which can react with primary amine (-NH2) and exhibit fluorescent emission at 477 nm (Figure S2 (a)). Zetapotential measurement showed that surface charge of the SNT changed from -39±11 mV to 44±11 mV for SNT-NH2 proving the success of surface functionalization with amine groups (Figure S2 (b)). We further conjugated enzyme (urease) onto the surface of the SNT by using glutaraldehyde (GA) as a linker molecule,33,34 yielding SNT-Urease (Figure 1 (a)). We confirmed the enzyme conjugation by using protein staining kit to visualize the presence of urease on the SNT-Urease as indicated by red fluorescence color in Figure S3.33 A typical SEM image of the SNT is presented in Figure 1 (b), and its quasi-transparent tubular structure in the inset image. The average diameter of the SNT, determined by SEM images, is D=220±24 nm (average±standard deviation (SD), N=30). The length of the nano-tubes ranges from 3 to 40 µm and can be controlled by using different templates, centrifugation and also by variable sonication time. When the enzymatic nano-jets were placed in solution containing urea, we observed directional self-propulsion along the longitudinal axis (Supporting Video S1 in the SI). The average velocity of tubular nano-jets with an average length of about 10 µm (9-13 µm) showed fuel dependent increasing trend which fits well with the Michaelis-Menten enzymatic kinetics reaching a plateau at 25 mM (Figure 1 (c)). The close correlation between velocity and enzymatic activity suggests that the bio-catalytic reaction provides mechanical power for the motion of the nano-jets. In the absence of urea, the nano-jets only exhibited Brownian motion (Figure S4 and Video S2 in the SI). The translational diffusion coefficient (Dt) retrieved from mean-square displacement (MSD) plot (MSD=4Dt∆t for two-dimensional case) fits well with the theoretical calculation (inset of Figure 2 (b)).38 Upon addition of urea (100 mM), the nano-jets showed longitudinal self-propulsion. Snapshots of tracking trajectories of the selfpropelled nano-jets of three different lengths (3.17, 5.42, 18.03 µm) are presented in Figure 2 (a) (Video S3 in the SI). We characterized the motion of the nano-jets by quantifying the velocity (V), measuring the longitudinal displacement (∆L) within given time (∆t) as for V=∆L/∆t. We found decreasing trend of the velocity with increasing length of the nano-jets (Figure 2 (b)). We further analyzed the rotational diffusion of the nano-jets by automatic tracking of the orientation angle (θ) of the nano-jets, as shown in Video S1 and Figure S5 (a) in the SI. The plot of mean square angular displacement (MSAD) was calculated in order to retrieve the effective rotational diffusion coefficient Dr(eff.) by the equation MSAD=2 Dr(eff.)∆t in one-dimensional case, as shown in Figure S5 (c) in the SI).

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Figure 2. Dynamics of urease powered tubular nano-jets. a) Schematic illustration and tracking trajectories of the tubular nano-jets with varied lengths, and longitudinal average velocity in b) µm s-1 (inset is Brownian translational diffusion coefficient (Dt) of the nano-jets without fuel; the dash line is theoretical value of Dt) and c) Body-lengths s-1; d) effective rotational diffusion coefficient (Dr(eff.)) with (100 mM) and without (0 mM) fuel (the dash line is theoretical value of Brownian Dr); e) angular autocorrelation of the three nano-jets shown in (a). (The error bars indicate standard error of the mean, N=10) In the absence of fuel, the rotational diffusion of the nano-jets was only due to Brownian motion, which is consistent with the theoretical calculation (dash line) (Figure 2 (d)).38 In the presence of urea, the tubular nano-jets showed enhanced rotational diffusion, in particular when the length is shorter than 10 µm. However, the rotational behavior is stabilized and angular changes decrease when the length of the tubular motors is longer than 10 µm. To gain more details into the change of orientation with time of three distinct nano-jets, we analyzed their angular auto-correlation (cos (∆θ)) for a period of 8 sec., where ∆θ is the angular change compared to their initial orientation39 as plotted in Figure 2 (e). A quickly changing auto-correlation value indicates a fast rotation of the nano-jets whereas a constant value close to 1 associates with a stable orientation. The frequency of angular change of the nanojet of length 3.17 µm is substantially higher than the one of 5.42 µm (green and red lines, respectively). Nano-jet of about 18 µm (blue line) maintains undisturbed angular correlation for the represented time.

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Journal of the American Chemical Society NPs along the tube surface (see details in Figure S11 and discussion in the SI). Such external flow field might also contribute to the velocity enhancement for the SNT-Urease-All. However, further in-depth investigation should be carried out before reaching a conclusive understand to this phenomenon. We further analyzed the rotational behavior of the three kinds of nano-jets with an average length of 5.5 µm, at which length obvious non-balance effect was observed. SNT-Urease-A and SNTUrease-O showed three times higher rotational diffusion coefficient compared to SNT-Urease-I (Figure 3 (c)), suggesting that the enzymatic reaction on the external surface of the tubular nanojets indeed enhanced their rotational diffusion.

Figure 3. Enzyme location dependent motion behavior. a) Schematic illustration of SNT-Urease with enzyme all over (SNTUrease-A), inside (SNT-Urease-I) and outside (SNT-Urease-O) the nano-tube, and corresponding SEM images; b) longitudinal average velocity of the three nano-tubular motors with average length of 20 µm; c) rotational diffusion of the three nano-tubular motors with average length of 5.5 µm. (The error bars indicate standard error of the mean, N=10) To identify the driving force of the nano-jets, we selectively functionalized urease inside (SNT-Urease-I), outside (SNTUrease-O), or all over the nano-tube (SNT-Urease-A), as presented in Figure 3 (a) (See experimental procedures in the SI). The presence of urease on the external surface of the samples of SNTUrease-A and SNT-Urease-O were seen in the SEM images (Figure 3 (a)), while smooth bare silica was observed for the SNTUrease-I. The protein concentration conjugated to the different types of nano-tubes was evaluated using a Coomassie Brilliant Blue (CBB) based protein quantification kit (Fig. S10 (a) in the SI). Furthermore, the enzymatic activity of the three urease conjugated tubular nano-jets was evaluated according to previously reported method,34 which indicates that the immobilized enzymes on all the three nano-jets were active (Figure S10b in the SI). The effect of enzyme location on the dynamics of the three types of nano-jets with average length of 20 µm was analyzed (Figure 3 (b)). Although all the three nano-jets were bio-catalytically active, only SNT-Urease-A and SNT-Urease-I demonstrated longitudinal self-propulsion (Video S4 in the SI). On the contrary, SNTUrease-O only showed Brownian motion. The results evidence that the longitudinal self-propulsion of the tubular nano-jets should be attributed to the enzymatic reaction taking place in the inside of the nano-tubes. SNT-Urease-A has the highest velocity among the three tubular nano-jets, implying that the enzymatic reactions on the external surface might contribute to enhancing the longitudinal velocity. The change of surface interaction from silica/H2O molecules for non-active surface, into a much more complex situation, where interactions between multiple molecules (e.g. bio-catalytic products) and enzymatically active surface of SNT-Urease-A were taking place, might alter the interfacial tension and possibly decrease resistance against the self-propulsion, therefore leading to velocity enhancement. We tracked tracer nanoparticles (NPs) located near the nano-jets and found that those were “attracted” towards the outer surface, implying a flow field on the surface of the nano-jet. Similarly to the enzymatic micro-pumps reported by Sen and co-workers,40 the enzymatically active outer surface would create density-driven convective flows which can be indirectly observed by the “trapping” effect of tracer

Figure 4. Nano-propulsion from internal flows. a) Video snapshot of a self-propelled nano-jet (green track) expelling a tracer NP (blue tracking trajectory); b) Propulsion force (Fpropulsion) of the nano-jets calculated by the Eq. 2 based on the velocity value in Figure 2 (b); and c) tracking trajectory of the tracer NP indicates the directional motion of the tracer NP instantly pushed by the repulsion force (Frepulsion) originated from the internal flow. The bio-catalytic nano-jets act as jet engines as they generate thrust from their cavity releasing a jet of fluid backwards (in this case the products of the enzymatic reaction). Up to now, this jetting force provided by catalytic micro-jets has been seen via bubble generation. In the current work, the products do not generate visible bubbles yet induce enough propelling force to move the nano-jets forward. This jet of liquid has been studied using a suspension of tracer NPs with the nano-jets (Figure 4 and Video S5 in the SI). The racking trajectory is presented in Figure 4 (a). At low Reynolds numbers, the propulsion force (Fpropulsion) equals to the drag force (Fdrag) applied on the tubular nano-jets,41 as indicated in Figure 4 (a). We approximated the dynamics of the tubular nano-jets by using the stokes drag equation for nano-rods, Fdrag=2πµLV/(ln(2L/R)-0.72) (Eq. 1),19,42 where µ is viscosity, R, L and V are radius, length and velocity of the nano-rods, we calculated the drag force applied on the tubular nano-jets based on the velocity results presented in Figure 2 (c). As shown in Figure 4 (b), the drag force ranges from 80 to 150 fN. When the NPs were not affected by the flow field of the active nano-jets, they only demonstrated randomized Brownian motion (blue trajectory) without any given directionality. The tracer NPs, once in the vicinity of the rear opening of nano-jets, were repelled and pushed away, which clearly evidenced the internal flow of the biocatalytic products (Figure 4 (c)). We measured the length (∆L=4.07 µm) and time interval (∆t=0.21 s) of the directional motion range of the specific tracer NP in Figure 4 (a), and calculated the instantaneous velocity of the tracer NP by equation V= ∆L/∆t=19.38 µm s-1. By Stokes’ drag law for an active spherical particle in fluid, F=6πµRV (Eq. 2), where µ is viscosity, R and V

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(9) Soler, L.; Magdanz, V.; Fomin, V. M.; Sánchez, S.; Schmidt, O. G. ACS Nano 2013, 7, 9611. (10) Parmar, J.; Vilela, D.; Pellicer, E.; Esqué-de los Ojos, D.; Sort, J.; Sánchez, S. Adv. Funct. Mater. 2016, 26, 4152. (11) Solovev, A. A.; Sánchez, S.; Pumera, M.; Mei, Y. F.; Schmidt, O. G. Adv. Funct. Mater. 2010, 20, 2430. (12) Restrepo-Perez, L.; Soler, L.; Martinez-Cisneros, C.; Sánchez, S.; Schmidt, O. G. Lab Chip 2014, 14, 2914. (13) Wu, Z.; Wu, Y.; He, W.; Lin, X.; Sun, J.; He, Q. Angew. Chem., Int. Ed. 2013, 52, 7000. (14) Wu, J.; Balasubramanian, S.; Kagan, D.; Manesh, K. M.; Campuzano, S.; Wang, J. Nat. Commun. 2010, 1, 36. (15) Singh, V. V.; Kaufmann, K.; Esteban-Fernandez de Avila, B.; Uygun, M.; Wang, J. Chem. Commun. 2016, 52, 3360. (16) Orozco, J.; García-Gradilla, V.; D’Agostino, M.; Gao, W.; Cortés, A.; Wang, J. ACS Nano 2013, 7, 818. (17) Solovev, A. A.; Xi, W.; Gracias, D. H.; Harazim, S. M.; Deneke, C.; Sánchez, S.; Schmidt, O. G. ACS Nano 2012, 6, 1751. (18) Gao, W.; Dong, R.; Thamphiwatana, S.; Li, J.; Gao, W.; Zhang, L.; Wang, J. ACS Nano 2015, 9, 117. (19) Gao, W.; Sattayasamitsathit, S.; Orozco, J.; Wang, J. J. Am. Chem. Soc.2011, 133, 11862. (20) Solovev, A. A.; Mei, Y. F.; Urena, E. B.; Huang, G. S.; Schmidt, O. G. Small 2009, 5, 1688. (21) Mei, Y. F.; Huang, G. S.; Solovev, A. A.; Urena, E. B.; Moench, I.; Ding, F.; Reindl, T.; Fu, R. K. Y.; Chu, P. K.; Schmidt, O. G. Adv. Mater. (Weinheim, Ger.) 2008, 20, 4085. (22) Safdar, M.; Wani, O. M.; Jänis, J. ACS Appl. Mater. Interfaces 2015, 7, 25580. (23) Sánchez, S.; Solovev, A. A.; Mei, Y.; Schmidt, O. G. J. Am. Chem. Soc. 2010, 132, 13144. (24) Harazim, S. M.; Xi, W.; Schmidt, C. K.; Sánchez, S.; Schmidt, O. G. J. Mater.Chem. 2012, 22, 2878. (25) Yao, K.; Manjare, M.; Barrett, C. A.; Yang, B.; Salguero, T. T.; Zhao, Y. The J. Phys. Chem. Lett. 2012, 3, 2204. (26) Zhao, G. J.; Ambrosi, A.; Pumera, M. J. Mater. Chem. A 2014, 2, 1219. (27) Li, J.; Liu, Z.; Huang, G.; An, Z.; Chen, G.; Zhang, J.; Li, M.; Liu, R.; Mei, Y. NPG Asia Mater. 2014, 6, e94. (28) Sánchez, S.; Solovev, A. A.; Harazim, S. M.; Deneke, C.; Feng Mei, Y.; Schmidt, O. G. Chem. Rec. 2011, 11, 367. (29) Schattling, P.; Thingholm, B.; Städler, B. Chem. Mater. 2015, 27, 7412. (30) Dey, K. K.; Zhao, X.; Tansi, B. M.; Méndez-Ortiz, W. J.; CórdovaFigueroa, U. M.; Golestanian, R.; Sen, A. Nano Lett. 2015, 15, 8311. (31) Bunea, A.-I.; Pavel, I.-A.; David, S.; Gáspár, S. Biosens. Bioelectron. 2015, 67, 42. (32) Abdelmohsen, L. K. E. A.; Nijemeisland, M.; Pawar, G. M.; Janssen, G.-J. A.; Nolte, R. J. M.; van Hest, J. C. M.; Wilson, D. A. ACS Nano 2016, 10, 2652. (33) Ma, X.; Wang, X.; Hahn, K.; Sánchez, S. ACS Nano 2016, 10, 3597. (34) Ma, X.; Jannasch, A.; Albrecht, U.-R.; Hahn, K.; Miguel-López, A.; Schäffer, E.; Sánchez, S. Nano Lett. 2015, 15, 7043. (35) Pantarotto, D.; Browne, W. R.; Feringa, B. L. Chem. Commun. 2008, 10, 1533. (36) Spagnolie, S. E.; Lauga, E. Phys. Fluids 2010, 22, 081902. (37) Yin, Y.; Lu, Y.; Sun, Y.; Xia, Y. Nano Lett. 2002, 2, 427. (38) Tirado, M. M.; Martínez, C. L.; de la Torre, J. G. J. Chem. Phys. 1984, 81, 2047. (39) Wang, X.; In, M.; Blanc, C.; Nobili, M.; Stocco, A. Soft Matter 2015, 11, 7376. (40) Sengupta, S.; Patra, D.; Ortiz-Rivera, I.; Agrawal, A.; Shklyaev, S.; Dey, K. K.; Córdova-Figueroa, U.; Mallouk, T. E.; Sen, A. Nat. Chem. 2014, 6, 415. (41) Happel, J.; Brenner, H. Low Reynolds Number Hydrodynamics; 2nd ed.; Martinus Nijhoff Publishers: The Hague, 1983. (42) Wang, W.; Castro, L. A.; Hoyos, M.; Mallouk, T. E. ACS Nano 2012, 6, 6122.

are radius and velocity of the particle, we calculated the drag force (Fdrag (NP)=124 fN) during the directional motion range, which can be used to approximate the repulsion force Frepulsion(NP) applied on the tracer NP. The length and the longitudinal velocity of the specific tubular nano-jet shown in Figure 4 (a) are L=6.93 µm and V=9.58 µm s-1. Thus the drag force (propulsion force) for the specific tubular nano-jet was found to be Fdrag(jet)=Fpropulsion(jet)=134 fN (by Eq. 1), which agrees with the repulsion force (or drag force) of the tracer NP experimentally. These results prove that the motion of the tubular nano-jets can be attributed to active flow of the enzymatic reaction products, providing a new mechanism for tubular motors besides the current bubble propulsion mechanism. In summary, we fabricated a self-propelled tubular nano-jet driven by a bubble-free propulsion mechanism. Distinguished from most of tubular motors based on bubble propulsion by decomposition of H2O2, the mechanical power is generated by the enzymatic decomposition of bio-friendly urea substrate which does not generate visible bubbles. We observed that not only enzymes inside, but also those located outside the nano-jets contribute to their self-propulsion. Considering the small dimension and biofriendly motors and fuel, these nano-jets hold great potentials in biomedical field. In order to provide control on their motion, the use of external sources is necessary in the near future as well as the study of collective behavior of nano-jets. Further experimental and theoretical studies will be performed to better understand the non-bubble propulsion mechanism.

ASSOCIATED CONTENT Supporting Information Experimental section with protocols, methods, characterization, supporting figures and videos are available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Dr. Samuel Sánchez * Email: [email protected]; [email protected]

Notes The authors declare no competing financial interests.

ACKNOWLEDGMENT The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Program (FP7/20072013)/ERC grant agreement no. 311529 (LT-NRBS) and the Alexander von Humboldt Foundation (to X. M.). S.S. thanks the Spanish MINECO under grants CTQ2015-68879-R (MICRODIA) and CTQ2015-72471EXP (Enzwim).

References (1) Sánchez, S.; Soler, L.; Katuri, J. Angew. Chem., Int. Ed. 2015, 54, 1414. (2) Wang, H.; Pumera, M. Chem. Rev. 2015, 115, 8704. (3) Wang, J. Nanomachines: Fundamentals and Applications; WileyVCH: Weinheim, 2013. (4) Lin, X.; Wu, Z.; Wu, Y.; Xuan, M.; He, Q. Adv. Mater. 2016, 28, 1060. (5) Sengupta, S.; Ibele, M. E.; Sen, A. Angew. Chem., Int. Ed. 2012, 51, 8434. (6) Ozin, G. A.; Manners, I.; Fournier-Bidoz, S.; Arsenault, A. Adv. Mater. (Weinheim, Ger.) 2005, 17, 3011. (7) Paxton, W. F.; Sundararajan, S.; Mallouk, T. E.; Sen, A. Angew. Chem., Int. Ed. 2006, 45, 5420. (8) Vilela, D.; Parmar, J.; Zeng, Y.; Zhao, Y.; Sánchez, S. Nano Lett. 2016, 16, 2860.

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Figure 1. a) Schematic illustration of the fabrication of urease con-jugated silica tubular (SNT-Urease) nanomotor; b) Typical SEM image of the SNTs; c) fuel dependent average velocity of SNT-Urease with an average length of 10 µm. (The error bars indicate standard error of the mean, N=10) Figure 1 76x40mm (300 x 300 DPI)


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Figure 2. Dynamics of urease powered tubular nano-jets. a) Schematic illustration and tracking trajectories of the tubular nano-jets with varied lengths, and longitudinal average velocity in b) µm s-1 (inset is Brownian translational diffusion coefficient (Dt) of the nano-jets without fuel; the dash line is theoretical value of Dt) and c) Body-lengths s-1; d) effective rotational diffusion coefficient (Dr(eff.)) with (100 mM) and without (0 mM) fuel (the dash line is theoretical value of Brownian Dr); e) angular auto-correlation of the three nano-jets shown in (a). (The error bars indicate standard error of the mean, N=10) Figure 2 101x136mm (300 x 300 DPI)



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Figure 3. Enzyme location dependent motion behavior. a) Schemat-ic illustration of SNT-Urease with enzyme all over (SNT-Urease-A), inside (SNT-Urease-I) and outside (SNT-Urease-O) the nano-tube, and corresponding SEM images; b) longitudinal average velocity of the three nano-tubular motor with average length of 20 µm; c) rotational diffusion of the three nano-tubular motor with average length of 5.5 µm. (The error bars indicate standard error of the mean, N=10) Figure 3 76x59mm (300 x 300 DPI)


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Figure 4. Nano-propulsion from jetting effect. a) Video snapshot of a self-propelled tubular nano-jet (green track) propelling a tracer NP (blue tracking trajectory) by jetting effect; b) Propulsion force (Fpropulsion) of the nano-jets calculated by the equation (2) based on the velocity value in Figure 2 (b); c) tracking trajectory of the tracer nanoparticle indicates the directional motion of the tracer NP in-stantly propelled by the repulsion force (Frepulsion) of the jetting flow. Figure 4 101x70mm (300 x 300 DPI)



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Table of Contents Table of Contents 67x34mm (300 x 300 DPI)


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Bubble-Free Propulsion of Ultrasmall Tubular Nanojets Powered by

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