Nucleation Points: The Forgotten Parameter in the Synthesis of Hydrogel-Coated Gold Nanoparticles.

Adolfo Sepúlveda,Audrey Picard-Lafond,André Marette,Denis Boudreau

doi:10.3390/polym13030373

Adolfo Sepúlveda, Audrey Picard-Lafond + Show 2 more

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https://doi.org/10.3390/polym13030373

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Abstract

The implementation of gold-hydrogel core-shell nanomaterials in novel light-driven technologies requires the development of well-controlled and scalable synthesis protocols with precisely tunable properties. Herein, new insights are presented concerning the importance of using the concentration of gold cores as a control parameter in the seeded precipitation polymerization process to modulate—regardless of core size—relevant fabrication parameters such as encapsulation yield, particle size and shrinkage capacity. Controlling the number of nucleation points results in the facile tuning of the encapsulation process, with yields reaching 99% of gold cores even when using different core sizes at a given particle concentration. This demonstration is extended to the encapsulation of bimodal gold core mixtures with equally precise control on the encapsulation yield, suggesting that this principle could be extended to encapsulating cores composed of other materials. These findings could have a significant impact on the development of stimuli-responsive smart materials.

Highlights

IntroductionThe design and fabrication of core-shell plasmonic nanomaterials possessing hybrid properties, e.g., the plasmonic properties of noble metal nanoparticles [1]and the volume phase transition behavior of external-stimulated microgels [2], have gained increasing attention towards developing novel light-driven technologies such as sensing [3], photovoltaics [4], and plasmon-mediated photothermal therapies [5], among others [6,7,8].The encapsulation of metallic nanoparticles within hydrogels is an important component for the fabrication of these hybrid nanomaterials [9], with most reported protocols employing a seeded precipitation polymerization process where functionalized spherical gold nanoparticles [10,11,12,13,14,15,16] are coated with cross-linked poly(N-isopropylacrylamide) (pNIPAM)hydrogel, the latter having a well documented lower critical solution temperature (LCST)of 32–33 ◦ C in water [17]
The discrepancy in the percentage determined for sample S3: 15 nm AuNPs@pNIPAM-1 compared to samples S1 and S2 with the same number of nucleation points (2.9 × 1012 ) was attributed to a problem in the centrifugation step
The variation in the number of theresulted functionalized gold of cores emencapsulation yield of gold nanoparticles from. This led a perfectly matched ployed in the seeded precipitation polymerization process resulted in the control of the tunability even when different gold core sizes were used at similar particle concentration, successful encapsulation yield of gold nanoparticles from 15% to 99%

Summary

Introduction

The design and fabrication of core-shell plasmonic nanomaterials possessing hybrid properties, e.g., the plasmonic properties of noble metal nanoparticles [1]and the volume phase transition behavior of external-stimulated microgels [2], have gained increasing attention towards developing novel light-driven technologies such as sensing [3], photovoltaics [4], and plasmon-mediated photothermal therapies [5], among others [6,7,8].The encapsulation of metallic nanoparticles within hydrogels is an important component for the fabrication of these hybrid nanomaterials [9], with most reported protocols employing a seeded precipitation polymerization process where functionalized spherical gold nanoparticles [10,11,12,13,14,15,16] are coated with cross-linked poly(N-isopropylacrylamide) (pNIPAM)hydrogel, the latter having a well documented lower critical solution temperature (LCST)of 32–33 ◦ C in water [17]. Since this study was performed for a single core diameter, not much is known about the effect of metallic core size or even polydispersity on the polymerization process It is not clear whether the encapsulation yield of gold nanoparticles in this type of hybrid architectures is modulated by the overall particle surface or by the number of particles (nucleation points) used in the seeded precipitation polymerization process. Understanding this is critical to develop scalable polymerization protocols for hybrid nanomaterials with tunable properties, including optical properties and shell thickness

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