Growth Kinetics of Single Polymer Particles in Solution via Active-Feedback 3D Tracking

Abstract

The ability to directly observe chemical reactions at the single-molecule and single-particle level has enabled the discovery of behaviors otherwise obscured by ensemble averaging in bulk measurements. However powerful, a common restriction of these studies to date has been the absolute requirement to surface tether or otherwise immobilize the chemical reagent/reaction of interest. This constraint arose from a fundamental limitation of conventional microscopy techniques, which could not track molecules or particles rapidly diffusing in three dimensions, as occurs in solution. However, many chemical processes occur entirely in the solution phase, leaving single-particle/-molecule analysis of this critical area of science beyond the scope of available technology. Here, we report the first kinetics studies of freely diffusing and actively growing single polymer−particles at the singleparticle level freely diffusing in solution. Active-feedback single-particle tracking was used to capture three-dimensional (3D) trajectories and real-time volumetric images of freely diffusing polymer particles (D ≈ 10 −12 m 2 /s) and extract the growth rates of individual particles in the solution phase. The observed growth rates show that the average growth rate is a poor representation of the true underlying variability in polymer−particle growth behavior. These data revealed statistically significant populations of fasterand slower-growing particles at different depths in the sample, showing emergent heterogeneity while particles are still freely diffusing in solution. These results go against the prevailing premise that chemical processes in freely diffusing solution will exhibit uniform kinetics. We anticipate that these studies will launch new directions of solution-phase, nonensemble-averaged measurements of chemical processes.

Structure–Reactivity–Property Relationships in Covalent Adaptable Networks

“…Significant advances in single-particle tracking and superresolution microscopy provide time-resolved, nano- to microscale insight into polymerization kinetics − and conformations of neat polymer chains. , We believe that the development of fluorescent probes that are responsive to dissociative bond formation/breaking or even associative, (quasi)-degenerate bond exchange would allow these optical techniques to be applied to CANs. The ability to map molecular events in time and space, as a function of applied deformations, will illuminate open questions in this field.…”

Observation of reactions in single molecules/nanoparticles using light microscopy

“…[69][70][71] The advancement in the method has enabled analyzing the diffusion coefficients of products and deriving spatiotemporal data about polymerization. 72,73 Thus far, interpretations at a single level have been studied for various problems; however, questions pertaining to chemical reactions remain unsolved. Therefore, advancements in optical microscopic analysis techniques can be expected.…”

“…For example, by carefully planning the reaction of the probe, fluorescence microscopy has enabled the super‐resolution observation of the reactivity of the surface facet of heterogeneous catalysts 67,68 and the nanoconfinement effects 69–71 . The advancement in the method has enabled analyzing the diffusion coefficients of products and deriving spatiotemporal data about polymerization 72,73 . Thus far, interpretations at a single level have been studied for various problems; however, questions pertaining to chemical reactions remain unsolved.…”

Single-Molecule Tracking of Reagent Diffusion during Chemical Reactions

“…This makes SMT very suitable for acquiring the precise value of D in different timescales . The SMT enabled the scientists to understand details about, for example, the polymerization, the molecular movement in cells, − and dynamics in complex environments, − at the plasma membranes, − and on solid–liquid − and liquid–liquid , interfaces. Because SMT is essentially an imaging method, this technique can circumvent the inconsistent signal fitting and interpretation ,, and rule out concerns in which photophysical artifacts , and bulk fluid convection were erroneously interpreted as the variation of D .…”