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Issue 6, 2020
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Dynamic single-molecule counting for the quantification and optimization of nanoparticle functionalization protocols

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Abstract

Applications of colloidal particles in the fields of i.e. biosensors, molecular targeting, or drug-delivery require their functionalization with biologically active and specific molecular ligands. Functionalization protocols often result in a heterogeneous population of particles with a varying density, spatial distribution and orientation of the functional groups on the particle surface. A lack of methods to directly resolve these molecular properties of the particle's surface hampers optimization of functionalization protocols and applications. Here quantitative single-molecule interaction kinetics is used to count the number of ligands on the surface of hundreds of individual nanoparticles simultaneously. By analyzing the waiting-time between single-molecule binding events we quantify the particle functionalization both accurately and precisely for a large range of ligand densities. We observe significant particle-to-particle differences in functionalization which are dominated by the particle-size distribution for high molecular densities, but are substantially broadened for sparsely functionalized particles. From time-dependent studies we find that ligand reorganization on long timescales drastically reduces this heterogeneity, a process that has remained hidden up to now in ensemble-averaged studies. The quantitative single-molecule counting therefore provides a direct route to quantification and optimization of coupling protocols towards molecularly controlled colloidal interfaces.

Graphical abstract: Dynamic single-molecule counting for the quantification and optimization of nanoparticle functionalization protocols

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Supplementary files

Article information


Submitted
02 Dec 2019
Accepted
28 Jan 2020
First published
28 Jan 2020

This article is Open Access

Nanoscale, 2020,12, 4128-4136
Article type
Paper

Dynamic single-molecule counting for the quantification and optimization of nanoparticle functionalization protocols

M. Horáček, D. J. Engels and P. Zijlstra, Nanoscale, 2020, 12, 4128
DOI: 10.1039/C9NR10218C

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    [Original citation] - Published by The Royal Society of Chemistry.

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