Direct Observations of the Rotation and Translation of Anisotropic

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Direct Observations of the Rotation and Translation of Anisotropic Nanoparticles Adsorbed at a Liquid-Solid Interface See Wee Chee, Utkarsh Anand, Geeta Bisht, Shu Fen Tan, and Utkur Mirsaidov Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.8b04962 • Publication Date (Web): 01 Apr 2019 Downloaded from http://pubs.acs.org on April 2, 2019

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Nano Letters

Direct Observations of the Rotation and Translation of Anisotropic Nanoparticles Adsorbed at a LiquidSolid Interface See Wee Chee1, 2, 3 ‡, Utkarsh Anand1, 2, 3 ‡, Geeta Bisht1, 2, Shu Fen Tan1, 2, and

Utkur Mirsaidov1, 2, 3, 4, 5*

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Department of Physics, National University of Singapore, Singapore 117551

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Center for Bio-Imaging Sciences, Department of Biological Sciences, National University of Singapore, Singapore 117557

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Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117546

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NanoCore, Faculty of Engineering, National University of Singapore, Singapore 117581

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Department of Materials Science and Engineering, National University of Singapore, Singapore 117575

AUTHOR INFORMATION

ACS Paragon Plus Environment

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Corresponding Author

[email protected]

*


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ABSTRACT: We can learn about the interactions between nanoparticles (NPs) in solution and solid surfaces by tracking how they move. Here, we use liquid cell transmission electron microscopy (TEM) to follow directly the translation and rotation of Au nanobipyramids (NBPs) and nanorods (NRs) adsorbed onto a SiNx surface at a rate of 300 frames per second. This study is motivated by the enduring need for a detailed description of NP motion on this common surface in liquid cell TEM. We will show that NPs move intermittently on the timescales of milliseconds. First, they rotate in two ways: 1) rotation around the center of the mass and 2) pivoted rotation at the tips. These rotations also lead to different modes of translation. A NP can move through small displacements in the direction roughly parallel to its body axis (shuffling) or with larger steps via multiple tip-pivoted rotations. Analysis of the trajectories indicates that both displacements and rotation angles follow heavy-tailed power law distributions, implying anomalous diffusion. The spatial and temporal resolution afforded by our approach also revealed differences between the different NPs. 50-nm NRs and 100-nm NBPs moved with a combination of shuffles and rotation-mediated displacements after illumination by the electron beam. With increasing electron fluence, 50-nm NRs also started to move via desorption-mediated jumps. 70-nm NRs did not exhibit translational motion and only made small rotations. These results describe how NP dynamics evolve under the electron beam and how intermittent pinning and release at specific adsorption sites on the solid surface control NP motion at the liquid-solid interface. We also discuss the effect of SiNx


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surface treatment on NP motion, demonstrating how our approach can provide broader insights into interfacial transport.

TOC GRAPHICS

KEYWORDS. Anisotropic Nanoparticles, Nanoparticles, Anomalous Diffusion, Liquid Cell Transmission Electron Microscopy, Rotational Diffusion, Single Particle Tracking.

INTRODUCTION

Recently, liquid cell transmission electron microscopy (TEM) has emerged as a new tool for tracking the motion of nanoscale particles in liquids at high spatial resolution. So far, it has been used to follow the dynamics of nanoparticles (NPs),1–5 NP aggregates3,5–8 and DNA-NP conjugates.9–11 Similar to particle tracking techniques that employ light as an illumination source,12,13 liquid cell TEM studies can help us understand the mechanisms behind various biological and chemical processes that take place in solution.14–16 Furthermore, we can obtain direct information about the rotational dynamics of NPs from


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liquid cell TEM, something which is more challenging for light-based techniques because there are fewer direct probes available for tracking rotations.17,18 Insights into the rotations are needed to understand how NPs and molecules interact with surfaces and orient themselves during processes such as self-assembly19,20 and bio-molecular reactions.17,21 It has also been suggested that there are intermediate states during the adsorption and desorption of NPs at solid surfaces where the NPs are stuck on the surface but retain rotational freedom.22,23 Visualizing these intermediate states will allow us to obtain valuable information about the parameters that control NP transport at the liquid-solid interface.

A high temporal resolution is required to track the rotations of NPs with TEM. For example, the characteristic time for a Au nanorod (NR) to rotate one radian is in the millisecond range for surface-adsorbed NRs and in the microsecond range for free-moving NRs.23 Liquid cell TEM experiments typically record movies at rates of 10-30 frames per second (fps) and so, we need to follow the dynamics either with a higher frame rate camera (milliseconds) or with a dynamic TEM24 (nanoseconds). In particular, a fast camera will allow us to track both rotational and translational dynamics of diffusing NPs over observation windows of several seconds to a few minutes. We emphasized here that earlier studies largely focused on NP translation and so, a complete description of NP motion in these liquid cells is still needed.25 By coupling high frame rates with extended


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imaging times, we can generate enough statistics to elucidate how NP motion evolves with time and make general conclusions from the behavior of individual NPs.

In this paper, we demonstrate that we can capture the rotations of Au nanobipyramids (NBPs) and NRs adsorbed at the liquid-solid interface and reveal their detailed dynamics in water (~300 nm thick), a ubiquitous solvent in NP studies, with this approach. More importantly, we use both rotational and translational information to understand how these NPs interact with the silicon nitride (SiNx) surface, a common window material in liquid cell TEM experiments. The movies were recorded at 300 fps using a direct electron detection camera and with low electron fluxes of 20 e-/(Å2·s) to 80 e-/(Å2·s). Incidentally, Au NRs are also common probes for rotational tracking.26 Previously, we looked at the diffusion of Au nanocubes (NCs) in these liquid cells and showed that they did not translate continuously.4 Instead, they adsorbed onto the SiNx surface for extended durations before making short-lived desorption-mediated jumps. In addition, these NCs rotated intermittently when adsorbed, but we did not have enough temporal resolution with our earlier camera (100 fps) to characterize these rotations fully. Our current results show that anisotropic NPs also exhibit intermittent rotation and translation on the order of milliseconds when adsorbed. Their behaviors are again in agreement with the anomalous dynamics of a continuous-time random walk (CTRW).4,27 More importantly, our observations reveal how the motion of NPs at the liquid-solid interface is controlled by local pinning sites on the SiNx surface.


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RESULTS

Figure 1A shows the sample trajectories of a NBP (~100 nm × 40 nm, Supporting Movie S1) and a NR (~50 nm × 15 nm, Supporting Movie S2). Due to the large dataset size (50300 GB per movie), we only present results from representative NPs even though we had recorded several movies during our experiments. The image sequences indicate that there are two types of rotations: one where the anisotropic NP rotates about its center of mass without significant translations, and the other where it pivots about one tip, producing a displacement of its center of mass. The first two panels of Figure 1B depict these two types of rotations with image sequences of the NBP. It is also clear that the rotational motion is discontinuous where the NBP only moves during t = 1.890 to 1.900 s in (I) and t = 2.020 to 2.030 s in (II).


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Figure 1. (A) Trajectories of a NBP and a NR captured within the same movie (the NR moves out of the field of view at ~12 s). The sequences are acquired at an electron flux of ~50 e-/(Å2·s). (B) Image sequences showing the different types of motion observed from the NBP (Supporting Movie S1). (C) Extended image sequence showing the motion of the NR (Supporting Movie S2). The images in this sequence have been summed by 3 to improve contrast, see Supporting Figure S6 for the image sequence before averaging. The dashed outlines indicate the initial positions of the NPs in the first frame of the sequences.

The next two panels of Figure 1B provide examples of image sequences where the NBP exhibits both rotational and translational motion. In the sequence labeled (III), the NBP makes small displacements from the right to left (shuffles), while making small rotations,


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whereas in (IV), the NBP makes more substantial displacements via tip-pivoted rotations (rotation-mediated motion) in a manner similar to hand-over-hand motion found in molecular motors.28 Unlike our previous results with Au NCs, there are no instances of desorption-mediated jumps with the NBP trajectory at this electron flux, despite the extended imaging time. All the displacements were within 30 nm, which is less than half the body length of the NBP (only one pyramidal face will be in contact with the surface, also see Figure 2), suggesting that all the displacements can be attributed to shifts of the NP body-center due to either shuffling or rotation-mediated motion. Figure 1C shows a NR exhibiting similar rotational and translational behaviors.

In Figure 2, we plot the time-averaged mean square displacement (MSD) curves (Figure 2A) and probability density functions (PDFs) (Figure 2B) for the displacements (Δr) and rotation angles (Δθ) obtained from the NBP and NR (denoted as NR1) in Figure 1, and another NR (denoted as NR2, Supporting Movie S3). NR2 was tracked at the same electron flux in a different liquid cell for a longer duration of 33 s. The time-averaged MSD is given by:

〈𝒓𝟐(𝚫𝒕)〉 = 〈|𝒓(𝒕 + 𝚫𝒕) ― 𝒓(𝒕)|𝟐〉𝒕

(Eq. 1)

〈𝜽𝟐(𝚫𝒕)〉 = 〈|𝜽(𝒕 + 𝚫 𝒕) ― 𝜽(𝒕)|𝟐〉𝒕

(Eq. 2)


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where, 〈𝒓2〉 and 〈𝜃2〉 are the translational and rotational MSD, respectively, and 𝒓(𝑡) and 𝜃 (𝑡) correspond to the position and orientation of the NP at time 𝑡. 〈𝒓2〉 and 〈𝜃2〉 are calculated for all time points which are Δ𝑡 seconds apart and averaged. The MSDs for translation (Equation (1)) in all 3 cases suggest a linear dependence (power exponent for NBP = 0.87 ± 0.01, NR1 = 0.88 ± 0.01, NR2 = 1.05 ± 0.01) on lag time (Δt). However, a linear MSD does not necessarily mean that the motion follows conventional Brownian diffusion. The CTRW process, which described the NC motion in ref. 4, can have a linearlike time-averaged MSD.29,30 Here, the PDFs indicate that the displacements have a heavy-tailed power law distribution with an exponent of -3.1 ± 0.1 for the NBP, -3.4 ± 0.1 for NR1 and -2.8 ± 0.1 for NR2, confirming anomalous diffusion dynamics with the nonGaussian displacement distribution.31 For rotations, the NPs clearly show subdiffusion with the time-averaged MSD curves (Equation (2)) having power law exponents of 0.31 ± 0.01 for the NBP, 0.45 ± 0.01 for NR1 and 0.25 ± 0.01 for NR2. Their PDFs have power law exponents of -2.4 ± 0.1 for the NBP, -2.5 ± 0.1 for NR1 and -2.4 ± 0.1 for NR2. Hence, NP diffusion in both rotation and translation are slower than that expected from conventional Brownian motion. While different hypotheses have been proposed to explain this suppressed diffusion in liquid cell TEM experiments,1,3,4,25,32,33 these observations add to the growing evidence that the reduced motion is due to adsorption of NPs on the membrane surface and their associated anomalous dynamics.4,27


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Figure 2. (A) Time-averaged mean square displacement (MSD) curves and (B) probability density functions obtained from tracking the translations and rotations of a NBP and two NRs recorded with electron flux of 50 e-/(Å2·s). The dashed lines illustrate the corresponding MSD curves for a NR that is exhibiting bulk translational and rotational diffusion. The dashed lines in (B) indicate the probability density profiles of a NP that follow Gaussian dynamics. (C) A comparison of the two NR trajectories. The dots with red outlines denote the initial positions of the NRs. (D) The displacements of the two NRs in x- (dark green, dark blue) and y- (light green, light blue) directions showing the onset of desorption-mediated jumps at extended imaging times. The displacement profiles are displaced from each other for clarity.

Interestingly, the two NRs did not exhibit identical features. NR2 made several displacements (up to ~100 nm) similar to the desorption-mediated jumps we reported for the Au NCs.4 We illustrate the difference by overlaying the two trajectories in a single plot


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in Figure 2C and comparing the displacements in x- and y- directions for each NR in Figure 2D. This difference is not the result of variability between liquid cells. It is clear from Figure 2D that the larger displacements only appear more frequently after ~20 s of imaging, suggesting a delay between the initial illumination of NR2 by the electron beam and the initiation of larger displacements (Supporting Information Section 3).

To further study the effect of electron beam illumination, we tracked the 50-nm NRs using different electron fluxes. In general, the time needed to induce repeated desorptionmediated jumps decreases with increasing electron flux. Supporting Figure S7 shows scatter plots of the rotation angles and displacements measured for these NRs. We normalized the plots to the same range of electron fluence to make it easier to visualize the overall effect of the beam. At electron fluxes between 30 e-/(Å2·s) and 80 e-/(Å2·s), the instances of large rotation angles and large displacements increases as the electron fluence increases, and the rotations precede the displacements. By comparing the rotation angle distribution, we can classify the progression of NR displacements as: (1) short shuffles (less than 10 nm), (2) rotation-mediated displacements (10 nm to 35 nm, where 35 nm is the body center displacement of a 50-nm NR when it performs a 90° endpivoted rotation) and (3) desorption-mediated jumps (larger than 35 nm). Supporting Movie S4 shows a sequence where four moving NPs were captured together and they presented similar developments in their dynamics.


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Within this framework, the higher initial mobility of NR1 compared to NR2 can be rationalized as NR1 already moving by rotation-mediated motion at the start of the movie but it was not tracked long enough for desorption-mediated jumps to be observed (Supporting Figure S8). We also mention here that the longest jumps (~100 nm) found in NR2 are still shorter than the displacements expected from conventional Brownian diffusion (~460 nm, Supporting Information Section 4), suggesting that NP motion continues to be influenced by interactions with the surface during desorption-mediated motion.4,27,34 For the lowest electron flux of 20 e-/(Å2·s), the scatter profiles remain approximately constant and desorption-mediated jumps were not seen under sustained electron irradiation (Figure S7). This behavior suggests that a minimal electron flux is required to initiate NP motion with the electron beam. We also highlight that the electron flux was turned up to 50 e-/(Å2·s) after imaging the NR at 20 e-/(Å2·s) for ~120 s (Supporting Movie S5). The NR started moving via desorption-mediated jumps within a few seconds, similar to the NR imaged at 50 e-/(Å2·s). We include the image sequence around this transition as Supporting Movie S5 (the electron flux was increased at t = 10 s in the movie).


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Figure 3. Residence-time plots depicting the positions of NRs recorded over 30 s at three electron fluxes of (A) 20 e-/(Å2·s) (full movie is ~120 s long), (B) 50 e-/(Å2·s) (Supporting Movie S3, full movie is ~33 s long), and (C) 80 e-/(Å2·s) (Supporting Movie S6, full movie is ~31 s long). The initial positions of the NRs are indicated with a black dot. The residence-time (color scale) is represented in natural logarithmic scale for clarity. (D-F) Corresponding displacement and rotation angle over time plots for the three NRs. Note that a 35-nm step is our threshold for defining large desorption-mediated jumps.

Next, we use the image sequences recorded at different electron fluxes to generate a series of “residence-time” maps, which gives us information on the time a NP spends at each pixel in the field-of-view. Each frame in the movie is segmented to generate a binary image where a pixel is marked as 1 if the NP is present there and 0 otherwise. Then, we


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add together all the segmented images for a fixed duration of the movie to form a map where pixels over which the NP stays for longer times have a larger value and vice versa. A pixel not visited by the NP will have a value 0. In Figure 3A-C, we show residence-time maps for the movies recorded with electron flux of 20 e-/(Å2·s), 50 e-/(Å2·s) and 80 e/(Å2·s). We plot the maps on a natural logarithmic scale to express the dynamic range more clearly. The maps have been truncated to display the same number of frames, which we extract from last 30 s of the 20 e-/(Å2·s) movie and the first 30 s of the 50 e-/(Å2·s) and 80 e-/(Å2·s) movies respectively. The corresponding displacements and rotation-angles versus time plots are provided in Figure 3D-F. Residence-time maps of additional NRs are provided as Supporting Figure S9.

The maps in Figure 3B-C (50 e-/(Å2·s) and 80 e-/(Å2·s)) indicate that the NRs reside longer at certain sites after the initiation of desorption-mediated motion. The shape of these long residence time clusters further show that the NRs performed tip-pivoted rotations when adsorbed, and during these tip-pivoted rotations, they were stuck more often in certain orientations. To illustrate this point more clearly, we separated the 80 e-/(Å2·s) potential map into 10.5 s segments in Figure 4A-C. In particular, there is a cluster in the last 10.5 s segment (denoted with a black dashed circle in Figure 4C) with very high intensity (Supporting Movie S7). The extracted residence time map and trajectory of this segment are provided as Figure 4D-E. Note that the localization was not due to a single adsorption event. The NR readsorbed at this site three times over the entire sequence (three different


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overlapping colored lines in the trajectory shown in Figure 4E-Left), despite significant displacements away from the site via desorption-mediated jumps. The high concentration of NR adsorption events described here (Figure 4E-Right) suggests that the NR only pins to specific locations on the membrane surface.4,7 Using both rotational and translational information, we can derive the nature of this surface pinning.

Figure 4. (A-C) The residence-time map from Figure 3C of a NR recorded at 80 e-/(Å2·s) extracted into 10.5 s segments. Note the development of the NR dynamics with time and the localization in certain positions and orientation. (D) Expanded residence time map for t = 25.0 s – 31.0 s shows the highest degree of localization around the area denoted with black dashed circle. (E) Corresponding trajectory (left) and scatter plot (right) of the NR’s centroid positions highlights its jumps and pinning states.

DISCUSSION


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So far, we have shown that anisotropic NPs adsorbed at the liquid-solid interface exhibit intermittent dynamics indicative of anomalous diffusion and that these NPs still rotate and move when adsorbed. Short NRs can also diffuse with desorption mediated jumps, but not NBPs. Furthermore, longer NRs (~70 nm × 20 nm) do not move significantly and only make small rotations (Supporting Movie S8). The most common explanation for the motion of NPs in these liquid cells is that the electron beam induces repulsive electrostatic interactions between the NPs and SiNx surface, which in turn causes the NPs to be repelled from the surface.2,3,25 One hypothesis suggests that positive charges accumulate on the membrane surface due to the emission of secondary electrons from SiNx membrane,2,3,25,35 but it cannot adequately explain our observations. Our NPs are capped with cetyltrimethylammonium bromide (CTAB) and have a positive surface charge. Under the broad electron beam used in TEM, charging should occur over the entire irradiated area35 and lead to complete repulsion of NPs from the membrane surface. Instead, the NPs readsorb intermittently and pin to certain sites during their motion. Direct charging also does not explain the low mobility of the longer NRs. If the motions were due to beaminduced charging, we would observe desorption mediated motion for both 50-nm and 70nm NRs as the balance between van der Waals (vdW) attraction to the surface, and the electrostatic repulsion does not depend on NR length.36 Conversely, this limited motion is reasonable if the longer NR is constrained by multiple pinning sites on the SiNx surface.


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We use the rotational dynamics observed for these anisotropic NPs to obtain a rough estimate of the spatial dimensions and distribution of these pinning sites. While the tippivoted rotations in the 50-nm NRs during the wait times between jumps can be explained by weaker electrostatic repulsion at the NR tips due to a lower concentration of CTAB,37,38 the localized pinning can only be due to the surface. A tip-pivoted rotation means that the NR must be free at one of the tips and so, the body length of a NR is not fully adsorbed. Therefore, these pinning sites cannot be larger than 50 nm. The residence-time map of the NBP (Supporting Figure S10) also indicates that a NBP is pinned differently. The face of a NBP is triangular with two long sides ~55 nm long and the short side is ~25 nm. It is possible that the NBP is pinned by two or more sites due to its larger contact surface with the membrane. If the NR is pinned by single sites and the NBP is pinned by more than one site, the pinning sites will have to be distributed roughly 50 nm from each other, the length of a 50-nm NR and the half body length of a 100-nm NBP. In this case, the longer 70-nm NRs will also be held by two or more pinning sites. This distribution of pinning sites matches well with undulations in the surface topology of silicon nitride measured under aqueous conditions using atomic force microscopy (AFM) and with different applied loads.39 These undulations can be understood as a convolution of the inherent roughness of the SiNx surface and the electrostatic double layer repulsion from a heterogeneous surface charge distribution,39 which will be similar to the interactions experienced by the NPs as illustrated in Figure 5.


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Figure 5. Schematic illustration showing the pinning of a NR due to local depressions in the electrostatic double layer repulsion of the SiNx surface. The darker areas reflect pinning sites where the NR experiences a stronger attraction to the surface.

The shift in NP dynamics as a function of electron flux also indicates that electron irradiation modifies the interactions between the NPs and the SiNx surface. If we assume the vdW attraction dominates the NP-surface interaction and the electron beam only changes the electrostatic component, we can use the residence-time maps described in Figure 3 to estimate the beam-induced change in surface charge and electrostatic potential of the SiNx membrane. The assumption of a generally attractive interaction potential is supported by the low NP mobility observed at electron flux of ≤ 20 e-/(Å2·s) (Figure 3A, 3D). Using an appropriate normalization factor, we can convert the residencetime map to a 2-dimensional probability density map 𝑝(𝑥,𝑦), which describes the likelihood of finding a NP at a certain pixel. Next, using the Boltzmann distribution:

(

𝑝(𝑥,𝑦)~exp ―

)

𝑈(𝑥,𝑦) 𝑘B𝑇

(Eq. 3)


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we can map the relative interaction potential 𝑈(𝑥,𝑦) at all pixels (𝑥,𝑦). With Equation (3), we calculate 𝑈(𝑥,𝑦) at different electron fluxes and find that the interaction potential decreases by ~1 kBT as the electron flux increases from 20 e-/(Å2·s) to 50 e-/(Å2·s) and 80 e-/(Å2·s), which corresponds to increased electrostatic repulsion for positively charged NPs (Supporting Information Section 5).

Next, we estimate the shift in the surface potential of the SiNx surface using standard DLVO theory36 (Supporting Information Section 5). For these redispersed NPs, ζ-potential measurements from our earlier study38 indicate a potential of 6.8 mV for the NRs and 8.2 mV for the NBPs, whereas the vdW attraction to a flat surface is similar for both types of NPs. From these values, we calculate the total positive charge on the NPs to be 0.6e for the NR and 1.2e for the NBP by modeling them as solid metallic spheres with equivalent volume. Assuming that these charges do not change at the different electron fluxes, the 1 kBT increase in electrostatic repulsion potential translates to a gain of positive 1e per ~65 nm2 for the SiNx surface. This surface charge increase corresponds to a surface potential increase of 40 mV using the NR data and 61 mV using the NBP data, which are smaller than the surface potential shift induced by electron beam charging of a dry SiNx surface.40

Hence, the observed behavior is better explained by a change in surface potential due to radiolytic effects of the electron beam41 rather than direct electron beam charging. The


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most likely effect is a shift in pH42 (we consider the other possible beam-induced effects in Supporting Information Section 3). The SiNx surface has a mixture of silanol (SiOH) and silylamine end groups (Si2NH, SiNH2), and these surface groups can protonate and deprotonate with changing pH.43,44 The electron fluxes used in our experiments translate to a dose rate of ~107-108 Gy/s, which is expected to shift the pH towards 5 at the low end of the range and 4 at the high end.42 In this pH range, the relevant acid-base equilibrium reactions are:43,44

Si ― OH⇌Si ― O ― + H +

pK ~ 6

(Eq. 4)

Si2 ― NH2+ ⇌Si2 ―NH + H +

pK ~ 10-11

(Eq. 5)

Si ― NH3+ ⇌Si ― NH2 + H +

pK ~ 10-11

(Eq. 6)

These pK values tell us that the silylamine groups are already protonated under typical solution conditions of deionized water. Hence, the apparent development of a positively charged surface caused by the electron beam is due to the loss of negative surface charges as the silanol-groups become pronated when the pH decreases, rather than the surface gaining additional positive charges. This hypothesis explains why NPs continue to readsorb on the surface. The silanol-terminated areas only become neutral, whereas the positively charged silylamine-terminated areas are unchanged. Hence, the strength of NP attraction to the surface decreases but the NPs are not repelled because vdW attraction remains dominant. We showed previously that a change in pH of the liquid environment can indeed affect the dynamics of NCs under the same electron flux, where


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the NCs displayed higher mobility in acidic medium.4 Our hypothesis is also consistent with the incremental development of NP dynamics described earlier where the lag can be attributed to the time required for the radiolysis products of water to reach their steadystate concentrations.42

Thus, our results can be understood by considering that the positively charged NPs goes from being strongly adsorbed to weakly adsorbed on the surface as the negatively charged silanol end-group terminated areas of the SiNx surface protonate under the influence of the electron beam. The pinning sites are, therefore, areas with a higher concentration of silanol groups. Note that it is a common strategy to shift the balance between the adsorption and desorption of NPs23,45 and molecules46 on silica surfaces (SiO2) by increasing the pH of a solution. In the references 23 and 45, the negatively charged surface created by deprotonation of silanol groups is used to control desorption of negatively charged NPs. A recent paper also showed that the desorption-mediated jumping of tracer molecules on silica can be controlled by surface modification with positively charged amino (NH2) silanes.34 To test our hypothesis, we prepared liquid cell chips with two surface treatments, pure oxygen plasma and silanization with 3aminopropyltriethoxysilane (APTES). It was previously shown that APTES can be applied to these chips and it selectively binds to the silanol surface groups, leading to a surface decorated by more positively charged amine groups.47 Our observations of NRs imaged at 20 e-/(Å2·s) are compared in Figure 6. As expected, oxygen plasma treatment appeared


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Nano Letters

to result in reduced NR motion due to the creation of more pinning sites, whereas there is a noticeable increase in NR mobility in the liquid cells treated with APTES. We emphasize here that the treatments did not change how the NR moved; instead, they changed the frequency of motion. The details about these experiments are discussed further in Supporting Information Section 7.

Figure 6. A comparison of the residence time maps extracted from (A) the first 40 s of the 20 e-/(Å2·s) movie depicted in Figure 3A, (B) a 40 s movie of a NR within an oxygen plasma treated liquid cell and (C) a 40s movie of a NR in an APTES treated liquid cell. (B) and (C) are also imaged at 20 e-/(Å2·s). A small mechanical drift is present in the NR positions because we started recording immediately after locating a NR in the field of view. The black dot denotes the initial position of the NRs.

Lastly, these results represent what can be achieved with NP tracking using liquid cell TEM with current state-of-the-art camera technology. Although we can increase the imaging rate to about 1000 fps by reducing the camera acquisition area, the electron flux needs to increase concomitantly because the signal-to-noise ratio in each image also degrades with decreasing electron fluence per frame. The lower signal-to-noise ratio leads to poorer image resolution48 (also see Supporting Information Section 8 where we measure the change in localization error as a function of the number of counts in each


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frame). However, increasing electron flux can lead to undesirable beam induced artifacts, such as NP dissolution (for example, the NBPs start to dissolve at > 80 e-/(Å2·s)). On the other hand, lowering the magnification to reduce the electron flux needed for imaging with reasonable signal-to-noise ratios compromises our ability to resolve the rotations. Although the resolution for NP tracking with liquid cell TEM is ultimately limited by the sample’s tolerance to electron beam induced damage, we can still improve our ability to extract useful information from noisy datasets. Our view is that improved automated image processing and object detection schemes will eventually allow us to make full use of the capabilities of these cameras for low electron flux in situ studies.

CONCLUSIONS

In summary, we have shown that we can concurrently track the rotation and translation of surface-adsorbed anisotropic NPs with liquid cell TEM. Our results indicate that even when adsorbed, these NPs display significant rotational motion. Moreover, we use the motion to understand the shift in NP dynamics as a function of electron flux. Our analysis indicates that at the electron fluxes used, the surface potential of the SiNx surface shifts by about 1 kBT. We attribute this shift to the protonation of silanol surface groups on SiNx in response to a change in solution pH induced by the electron beam. This hypothesis also accounts for the local pinning sites observed in liquid cell TEM experiments, which can be explained by an inhomogeneous distribution of SiNx surface groups. Furthermore,


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Nano Letters

our experiments suggest that the solution chemistry changes due to radiolysis and surface treatments are more important in controlling the beam-induced motion of these NPs, compared to direct charging by the electron beam. Lastly, these results provide insights into the movement of NPs on a flat surface under different adsorption conditions where the NP-surface interactions go from strongly to weakly attractive and improve our understanding of interfacial transport.

Experimental Methods

The cetyltrimethylammonium (CTA+)-stabilized 50-nm Au NRs (Cat. No. NR-10-750-50) and CTA+-stabilized Au NBPs (Cat. No. NBP-20-700-20) were purchased from Nanoseedz Ltd. (Shatin, N.T., Hong Kong). To obtain longer NRs with diameters similar to the purchased ones, we used a synthesis protocol similar to that described in reference 49. Gold (III) chloride trihydrate (HAuCl4·3H2O, Cat. No. 520918, Sigma-Aldrich Co., St Louis, MO, USA), sodium borohydride (NaBH4, Cat. No. 213462, Sigma-Aldrich Co., St Louis, MO, USA), silver nitrate (AgNo3, Cat. No. 209139-25G, Sigma-Aldrich Co., St Louis, MO, USA), hydroquinone (C6H4-1,4-(OH)2, Cat. No. H9003, Sigma-Aldrich Co., St Louis, MO, USA) and cetyltrimethylammonium bromide (CTAB, Cat. No. 52370-500G, Sigma-Aldrich Co., St Louis, MO, USA) were used as received without further purification.

Prior to the start of experiments, 300 µL of the Au NP solution was first loaded into a 1.5 mL centrifuge tube. Then, it was centrifuged at 10,000 rpm for 5 min and redispersed in


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deionized water twice to minimize background cetyltrimethylammonium bromide (CTAB) concentration to < 1×10−3 M. The final working concentrations of NR and NBP solution were ~4 × 1012 NRs mL−1 and ~1 × 1013 NBPs mL−1, respectively. The solutions were left to age for a few hours to allow the CTAB concentration on the NPs to stabilize before they were transferred onto the liquid cell chips.

For liquid cell experiments, ~500 nL of the redispersed NP solution was loaded into a custom microfabricated liquid cell,50 with ~20-nm thick electron translucent SiNx membranes. These liquid cells were treated with a glow discharge prior to solution loading to render their SiNx membrane surfaces hydrophilic using an Emitech K100X system (Quorum Technologies, Ashford, Kent, UK). The treatment conditions were a negative discharge with air at 15 mA and a duration of 45 seconds. A Liquid Flow holder (Hummingbird Scientific, Lacy, WA, USA) and a JEOL 2200FS TEM (JEOL Ltd, Akishima, Tokyo, Japan) operated at 200 kV were used for in situ TEM imaging. TEM image sequences were recorded at a rate of 300 fps with a DE-16 direct electron camera (Direct Electron, San Diego, CA, USA) and with electron flux ranging from 20 e-/(Å2·s) to 80 e/(Å2·s) (Supporting Information Section 1). The liquid layer thicknesses were estimated using electron energy loss spectroscopy.4 In general, the liquid thickness can vary between 100 nm to 500 nm. The datasets presented here come from liquid cells where the thicknesses are ~300 nm. The image sequences displaying the dynamics of NRs and


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Nano Letters

NBPs were analyzed using our custom automated NP segmentation and tracking algorithm (Supporting Information Section 2).

ASSOCIATED CONTENT

Supporting Information The following files are available free of charge. Supplementary text discussing additional details of the experiments, image processing methods, electron beam related effects, displacement in bulk water calculations, surface charge calculations, effect of surface treatments, localization accuracy and additional figures (PDF).

Motion of a NBP imaged at 50 e-/(Å2∙s). Movie playback is in real time (AVI).

Motion of a NR imaged at 50 e-/(Å2∙s). Movie playback is in real time (AVI).

Motion of a second NR imaged at 50 e-/(Å2∙s). Movie playback is in real time (AVI).

Motion of three NRs imaged at 30 e-/(Å2∙s). Movie playback is in real time (AVI).

20 s segment of the NR imaged at 20 e-/(Å2∙s) where the electron flux was increased to 50 e-/(Å2∙s) at t = 10 s. The NR was imaged at 20 e-/(Å2∙s) for 120 s prior to increasing the flux. Movie playback is in real time (AVI).


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Page 28 of 41

Motion of a NR imaged at 80 e-/(Å2∙s). Movie playback is in real time (AVI).Extracted sequence from Supporting Movie S6 where the NR repeated readsorbed at the same location over a time period of 5.00 s (t = 25.00 s to 31.00 s). Movie playback is slowed by 5. (AVI).

Motion of a longer 70-nm NR imaged at 50 e-/(Å2∙s). Movie playback is in real time (AVI).

Motion of a 50-nm NR imaged at 20 e-/(Å2∙s) in an oxygen plasma treated liquid cell. Movie playback is in real time (AVI).

Motion of a 50-nm NR imaged at 20 e-/(Å2∙s) in a liquid cell silanized with APTES. Movie playback is in real time (AVI).

AUTHOR INFORMATION

Notes

*

Corresponding author.

‡

S.W.C. and U.A. contributed equally to this work.

The authors declare no competing financial interests.

ACKNOWLEDGMENT


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Nano Letters

This work was supported by the Singapore Ministry of Education Academic Research Fund Tier 2 (MOE2016-T2-2-009) and the Singapore National Research Foundation’s Competitive Research Program funding (NRF-CRP16-2015-05). We also acknowledge Prof. Kristian Mølhave for many helpful comments on the manuscript.

ABBREVIATIONS

TEM, transmission electron microscopy; NP; nanoparticle, NBP, nanobipyramid; NR, nanorod; NC, nanocube; SiNx, silicon nitride. CTRW; continuous-time random walk, MSD; mean squared displacement

REFERENCES

(1)

Zheng, H.; Claridge, S. A.; Minor, A. M.; Alivisatos, A. P.; Dahmen, U. Nano Lett. 2009, 9 (6), 2460–2465.

(2)

Liu, Y.; Lin, X.-M.; Sun, Y.; Rajh, T. J. Am. Chem. Soc. 2013, 135 (10), 3764–3767.

(3)

Woehl, T. J.; Prozorov, T. J. Phys. Chem. C 2015, 119, 21261–21269.

(4)

Chee, S. W.; Baraissov, Z.; Loh, N. D.; Matsudaira, P. T.; Mirsaidov, U. J. Phys.

Chem. C 2016, 120 (36), 20462–20470.

(5)

Li, C.; Chen, X.; Liu, H.; Fang, J.; Zhou, X. Nano Res. 2018, 11 (9), 4697–4707.


29

Nano Letters 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

(6)

Page 30 of 41

Lin, G.; Chee, S. W.; Raj, S.; Král, P.; Mirsaidov, U. ACS Nano 2016, 10 (8), 7443– 7450.

(7)

Tian, X.; Zheng, H.; Mirsaidov, U. Nanoscale 2017, 9 (28), 10044–10050.

(8)

Powers, A. S.; Liao, H. G.; Raja, S. N.; Bronstein, N. D.; Paul Alivisatos, A.; Zheng, H. Nano Lett. 2017, 17 (1), 15–20.

(9)

Chen, Q.; Smith, J. M.; Park, J.; Kim, K.; Ho, D.; Rasool, H. I.; Zettl, A.; Alivisatos, A. P. Nano Lett. 2013, 13 (9), 4556–4561.

(10) Chen, Q.; Smith, J. M.; Rasool, H. I.; Zettl, A.; Alivisatos, A. P. Faraday Discuss. 2014, 175, 203–214.

(11) Keskin, S.; Besztejan, S.; Kassier, G.; Manz, S.; Bücker, R.; Riekeberg, S.; Trieu, H. K.; Rentmeister, A.; Miller, R. J. D. J. Phys. Chem. Lett. 2015, 6 (22), 4487– 4492.

(12) Manzo, C.; Garcia-Parajo, M. F. Reports on Progress in Physics. IOP Publishing 2015, p 124601.

(13) Shen, H.; Tauzin, L. J.; Baiyasi, R.; Wang, W.; Moringo, N.; Shuang, B.; Landes, C. F. Chemical Reviews. 2017, pp 7331–7376.


30

Page 31 of 41 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

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(14) de Jonge, N.; Ross, F. M. Nat. Nanotechnol. 2011, 6 (11), 695–704.

(15) Ross, F. M. Science. 2015, 350 (6267), aaa9886.

(16) Liao, H.-G.; Zheng, H. Annu. Rev. Phys. Chem. 2016, 67 (1), 719–747.

(17) Anthony, S. M.; Yu, Y. Anal. Methods 2015, 7 (17), 7020–7028.

(18) Gao, Y.; Yu, Y.; Sanchez, L.; Yu, Y. Micron 2017, 101, 123–131.

(19) Luo, B.; Smith, J. W.; Ou, Z.; Chen, Q. Acc. Chem. Res. 2017, 50 (5), 1125–1133.

(20) Tan, S. F.; Chee, S. W.; Lin, G.; Mirsaidov, U. Acc. Chem. Res. 2017, 50 (6), 1303– 1312.

(21) Newton, A. C.; Groenewold, J.; Kegel, W. K.; Bolhuis, P. G. Proc Natl Acad Sci 2015, 112 (50), 15308–15313.

(22) Xu, D.; He, Y.; Yeung, E. S. Angew. Chemie - Int. Ed. 2014, 53 (27), 6951–6955.

(23) Neupane, B.; Chen, F.; Wei, Y.; Fang, N.; Ligler, F.; Wang, G. ChemPhysChem 2016, 17 (14), 2218–2224.

(24) Fu, X.; Chen, B.; Tang, J.; Hassan, M. T.; Zewail, A. H. Science. 2017, 355 (6324),


31

Nano Letters 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

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494–498.

(25) Abellan, P.; Woehl, T. J. In In-situ Characterization Techniques for Nanomaterials; Kumar, C. S. S. R., Ed.; Springer: Berlin, Heidelberg, 2018; pp 1–31.

(26) Chen, H.; Shao, L.; Li, Q.; Wang, J. Chem. Soc. Rev. 2013, 42 (7), 2679–2724.

(27) Parent, L. R.; Bakalis, E.; Proetto, M.; Li, Y.; Park, C.; Zerbetto, F.; Gianneschi, N. C. Acc. Chem. Res. 2018, 51 (1), 3–11.

(28) Yildiz, A.; Tomishige, M.; Vale, R. D.; Selvin, P. R. Science. 2004, 303 (5658), 676– 678.

(29) Metzler, R.; Jeon, J.-H.; Cherstvy, A. G.; Barkai, E. Phys. Chem. Chem. Phys. 2014,

16 (44), 24128–24164.

(30) Meroz, Y.; Sokolov, I. M. Phys. Rep. 2015, 573, 1–29.

(31) Wang, B.; Kuo, J.; Bae, S. C.; Granick, S. Nat. Mater. 2012, 11 (6), 481–485.

(32) Lu, J.; Aabdin, Z.; Loh, N. D.; Bhattacharya, D.; Mirsaidov, U. Nano Lett. 2014, 14, 2111–2115.

(33) Verch, A.; Pfaff, M.; de Jonge, N. Langmuir 2015, 31, 6956–6964.


32

Page 33 of 41 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

Nano Letters

(34) Wang, D.; Wu, H.; Schwartz, D. K. Phys. Rev. Lett. 2017, 119, 268001.

(35) Jiang, N. Ultramicroscopy 2017, 179, 81–83.

(36) Israelachvili, J. N. Intermolecular and surface forces: revised third edition.; Academic Press, 2011.

(37) Chen, Q.; Cho, H.; Manthiram, K.; Yoshida, M.; Ye, X.; Alivisatos, A. P. ACS Cent.

Sci. 2015, 1 (1), 33–39.

(38) Tan, S. F.; Raj, S.; Bisht, G.; Annadata, H. V.; Nijhuis, C. A.; Král, P.; Mirsaidov, U.

Adv. Mater. 2018, 30 (16), 1707077.

(39) Senden, T. J.; Drummond, C. J.; Kekicheff, P. Langmuir 1994, 10 (2), 358–362.

(40) Mirsaidov, U. M.; Zheng, H.; Bhattacharya, D.; Casana, Y.; Matsudaira, P. Proc.

Natl. Acad. Sci. 2012, 109 (19), 7187–7190.

(41) Abellan, P.; Woehl, T. J.; Parent, L. R.; Browning, N. D.; Evans, J. E.; Arslan, I.

Chem. Commun. 2014, 50 (38), 4873–4880.

(42) Schneider, N. M.; Norton, M. M.; Mendel, B. J.; Grogan, J. M.; Ross, F. M.; Bau, H. H. J. Phys. Chem. C 2014, 118 (38), 22373–22382.


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(43) Senden, T. J.; Drummond, C. J. Colloids Surfaces A Physicochem. Eng. Asp. 1995,

94 (1), 29–51.

(44) Tsukruk, V. V; Bliznyuk, V. N. Langmuir 1998, 14 (2), 446–455.

(45) So, C.; Alivisatos, A. P. Nano Lett 2005, 5 (2), 301–304.

(46) Yu, C.; Guan, J.; Chen, K.; Bae, S. C.; Granick, S. ACS Nano 2013, 7 (11), 9735– 9742.

(47) Robertson, A. W.; Zhu, G.; Mehdi, B. L.; Jacobs, R. M. J.; De Yoreo, J.; Browning, N. D. ACS Appl. Mater. Interfaces 2018, 10 (26), 22801–22808.

(48) Taheri, M. L.; Stach, E. A.; Arslan, I.; Crozier, P. A.; Kabius, B. C.; LaGrange, T.; Minor, A. M.; Takeda, S.; Tanase, M.; Wagner, J. B.; Sharma, R. Ultramicroscopy 2016, 170, 86–95.

(49) Vigderman, L.; Zubarev, E. R. Chem. Mater. 2013, 25 (8), 1450–1457.

(50) Liu, Q.; Leong, F. Y.; Aabdin, Z.; Anand, U.; Si Bui Quang, T.; Mirsaidov, U. ACS

Nano 2015, 9 (9), 9020–9026.


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In-plane rotation

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Au NR

1.886 s 1.890 s 1.893 s 1.896 s II. Rotation Pivoted at Bi-Pyramid End

1.900 s

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2.023 s

2.026 s

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5.533 s

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5.553 s

5.556 s

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5.92 s

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