Nanosecond Time‐Resolution Study of Gold Nanorod Rotation at the Liquid–Solid Interface

Abstract

Early studies showed that the adsorption of nanorods may start from a special "anchored" state, in which the nanorods lose translational motion but retain rotational freedom. Insight into how the anchored nanorods rotate should provide additional dimensions for understanding particle-surface interactions. Based on conventional time-resolution studies, gold nanorods are thought to continuously rotate following initial interactions with negatively charged glass surfaces. However, this nanosecond time-resolution study reveals that the apparent continuous rotation actually consists of numerous fast, intermittent rotations or transitions between a small number of weakly immobilized states, with the particle resting in the immobilized states most of the time. The actual rotation from one immobilized state to the other happens on a 1 ms timescale, that is, approximately 50 times slower than in the bulk solution.

Direct Observations of the Rotation and Translation of Anisotropic Nanoparticles Adsorbed at a Liquid–Solid Interface

“…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), − NP aggregates, ,− and DNA–NP conjugates. − Similar to particle tracking techniques that employ light as an illumination source, , liquid cell TEM studies can help us understand the mechanisms behind various biological and chemical processes that take place in solution. − Furthermore, we can obtain direct information about the rotational dynamics of NPs from liquid cell TEM, something that is more challenging for light-based techniques because there are fewer direct probes available for tracking rotations. , Insights into the rotations are needed to understand how NPs and molecules interact with surfaces and orient themselves during processes such as self-assembly , and biomolecular reactions. , 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. , Visualizing these intermediate states will allow us to obtain valuable information about the parameters that control NP transport at the liquid–solid interface.…”

“…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.…”

“…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 TEM 24 (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.…”

Exploring dynamic interactions of single nanoparticles at interfaces for surface-confined electrochemical behavior and size measurement

“…One of the fundamental challenges underlying particle motion is to understand the dynamic forces that shape these interactions. Available experimental evidence has demonstrated a dominant mechanism of desorption-mediated NP motion at the liquid−solid interface with a transient weakly adsorbed state between desorption and adsorption [32][33][34][35] . Thus, adsorptive interactions play a key role in the physical motion of NPs at the electrode interface.…”

Seeing the unseen: Imaging rotation in cells with designer anisotropic particles

“…Among them, the most widely used are rod-shaped particles, including gold nanorods (Gu et al, 2012, 2011; Neupane et al, 2016; Chaudhari and Pradeep, 2014; Xiao et al, 2011a), colloidal ellipsoids (Han et al, 2006; Mukhija and Solomon, 2007), quantum rods (Tsay et al, 2006; Ohmachi et al, 2012), filamentous viruses (Lettinga et al, 2005), and dumbbell particles (Uspal et al, 2013; Uspal and Doyle, 2014), Typically, the rotation of rod-shaped imaging probes can be measured along two of the three possible rotational axes: in-plane rotational angle φ and out-of-plane rotational angle θ (Fig. 1a) (Anthony and Yu, 2015).…”