Spatiotemporal Heterogeneity of Reactions in Solution Observed with High‐Speed Single‐Nanorod Rotational Sensing

Abstract

Ah igh-speed darkfield microscope has been developed to monitor the rapid rotation of single gold nanorods (AuNRs) and used to study the spatiotemporal heterogeneity of chemical reactions in free solution. Awide range of viscosities from 237 cP to 0.8 cP could be detected conveniently.W e studied H 2 O 2 decomposition reactions that were catalyzedb y AuNRs coated with Pt nanodots (AuNR@PtNDs) and observed two different rotational states.T he two states and their transitions are related to the production and the amalgamation of O 2 nanobubbles on the nanorod surface depending on H 2 O 2 concentration. In addition, the local fluidic environment of pure water was found to be non-uniform in time and space.This technique could be applied to study other chemical and biochemical reactions in solution.The reaction mechanisms in nanoscopic systems often differ considerably in time and space due to their structural and dynamic heterogeneity, [1] so it is imperative to develop effective methods capable of following spatiotemporal changes directly at the single-particle level, [2] especially for nanoscale catalysts and self-propelled micro/nanomotors in complex fluidic surroundings.T oa void important intermediates and rare events being masked by ensemble-averaged measurements,p eople have established an umber of techniques that can monitor the activity and chemical states of single nanoparticles (NPs) under reaction conditions, [3] including single-molecule fluorescence imaging, [4] tipenhanced Raman spectroscopy, [5] surface plasmon resonance imaging, [6] and electrochemical methods. [7] Nevertheless,s o far these techniques have only been applied to nanoparticles immobilized on as olid substrate,w here the interfacial microenvironment and the information obtained on the reaction may not be the same as those in the homogeneous solution.Due to their high brightness and great photostability, plasmonic nanoparticles have been used recently as nonfluorescent single-particle optical probes. [8] With darkfield microscopy (DFM) or differential interference contrast microscopy,weand others have reported that the orientation and rotation of single AuNRs can be used to elucidate the dynamic processes of chromatographic desorption, endocy-tosis,a nd intracellular traffic of NPs. [9] However,d ue to the sampling rate of the cameras in these studies,only the nearly stationary AuNRs or slowly rotating AuNRs in high-viscosity environments have been monitored. Here,w er eport highspeed laser darkfield microscopy (HSLDFM) that is capable of sensing the transient rotational dynamics of single AuNRs in free solution at > 10 000 frames per second. With HSLDFM, we directly monitored the spatiotemporal variation of rotational diffusion of individual AuNR@PtNDs during the H 2 O 2 decomposition process,a nd observed behaviors related to the reaction dynamics of heterogeneous catalysis as well as the structure of water that were unexpected from ensemble measurements.Theo ptical measurement principle of HSLDFM (Figure 1a)issimilar to that previous...

Unveiling Cellular Internalization Dynamics of Single Gold Nanorods by Tracking Their Orientational and Translational Motions

“…From these time-dependent intensity profiles, the azimuth and polar angles of AuNRs in every frame could be calculated. The orientation distribution pattern obtained through this information, together with the rotational diffusion coefficients, D r , obtained from the autocorrelation analysis of the AuNR intensities, 34,35,42 the centroid trajectories, and the translational diffusion coefficients, D 2 , allowed us to reveal unprecedented details of the orientation states and state transitions of AuNRs during their entire cellular internalization process.…”

“…Here, we investigated the cellular internalization dynamics and kinetics of single AuNRs by following their translational and rotational motions at cell sidewall by dual-channel polarization microscopy, according to our previously reported technique. [33][34][35] Although the number of AuNRs experiencing cellular internalization, observable at cell sidewall, is relatively smaller than on cell top, the whole process could be captured readily, with an improvement of the angular precision. Particularly, we integrated the azimuth and polar angles into a polar coordinate system and found three general orientation distribution patterns closely associated with cellular internalization dynamics, which provided tips to aid in confirming one-dimensional contact of the nanomaterials with the membrane by tips after landing on the cell surface.…”

Real-Time Visualization of the Single-Nanoparticle Electrocatalytic Hydrogen Generation Process and Activity under Dark Field Microscopy

“…Many physical and chemical processes can form nanobubbles, e.g., H 2 O 2 decomposition, , formic acid dehydrogenation, and water electrolysis. , Until now, nanobubbles have played an important role in many investigations. ,, Different from gas molecules dissolved in solution, nanobubbles generated at the interface between a solution and a substrate are easier to detect . Many works have reported the existence of nanobubbles based on a number of methods, such as electrochemical techniques, , atomic force microscopy, − total internal reflection fluorescence microscopy, − and dark field microscopy (DFM). , Among these methods, DFM has attracted much attention, because it can conveniently detect the scattering signals of nanoparticles (e.g., gold nanospheres and silver nanospheres) and nanobubbles.…”

“…Many physical and chemical processes can form nanobubbles, e.g., H 2 O 2 decomposition, 22,23 formic acid dehydrogenation, 21 and water electrolysis. 2,24 Until now, nanobubbles have played an important role in many investigations.…”

“…2,24 Until now, nanobubbles have played an important role in many investigations. 22,23,25 Different from gas molecules dissolved in solution, nanobubbles generated at the interface between a solution and a substrate are easier to detect. 21 Many works have reported the existence of nanobubbles based on a number of methods, such as electrochemical techniques, 26,27 atomic force microscopy, 28−30 total internal reflection fluorescence microscopy, 31−33 and dark field microscopy (DFM).…”