Self‐Regulated Assembly and Disassembly of Gold Nanoparticles for Low‐Temperature Time Indication

• Published in: Small (Weinheim an der Bergstrasse, Germany) Germany), 2024-11, Vol.20 (45), p.e2403216-n/a
• Main Authors: He, Yi, Liu, Mingqin, Wang, Yuan, Liu, Yiding
• Format: Article
• Language: English
• Subjects: Charge reversal; Color; Dismantling; Gold; gold nanoparticles; Hydration; Ligands; nanoparticle self‐assembly; Nanoparticles; Phosphines; Polyethylene glycol; Self-assembly; self‐regulation; stimuli‐responsive nanomaterials; Surface charge; time‐temperature indicators
• ISSN: 1613-6810; 1613-6829; 1613-6829
• DOI: 10.1002/smll.202403216

The color‐changing self‐assembly and autonomous disassembly of colloidal gold nanoparticles (AuNPs) is reported by simply mixing negatively charged phosphine ligand‐capped AuNPs with partially oxidized polyethylene glycol (PEG). The assembly of AuNPs is initiated by PEG adsorption, which disrupts the hydration layer of AuNPs, leading to depletion attraction and reduction of hydration repulsion among the AuNPs. The oxidative species in PEG subsequently oxidize and remove the charged ligands from the AuNP surface, resulting in a decrease and reversal of the negative surface charge. This causes the PEG to adsorb on AuNPs in a tighter and more direct manner, providing strong steric shielding to the AuNPs, thereby triggering the disassembly of the AuNP assemblies. The self‐regulated assembly–disassembly process can be tuned widely by controlling chemical conditions of PEG, nanoparticle concentration, and the environmental conditions, suggesting potential applications as colorimetric time‐temperature indicators for food and medicine storage conditions. As a proof of concept, it is demonstrated that the lifetime of the color‐changing assembly–disassembly process can be extended from tens of minutes to weeks when subjected to a refrigerated environment, with tunability achievable through varying polymer conditions and storage atmospheres. This study introduces a dynamic assembly of gold nanoparticles through a self‐regulated temporally programmed self‐assembly and disassembly process. The process involves the responsive interactions between gold nanoparticles and polymers which can dynamically influencing colloidal interactions in response to the nanoparticle assembly state. The lifetime of the process is highly tunable and sensitive to environmental conditions, allowing it to play the role of low‐temperature time indicator.