Abstract
The challenge to obtain plasmonic nanosystems absorbing light in the near infrared is always open because of the interest that such systems pose in applications such as nanotherapy or nanodiagnostics. Here we describe the synthesis in an aqueous solution devoid of any surfactant of Au-nanowires of controlled length and reasonably narrow dimensional distribution starting from Au-nanoparticles by taking advantage of the properties of glucosamine phosphate under aerobic conditions and substoichiometric nanoparticle passivation. Oxygen is required to enable the process where glucosamine phosphate is oxidized to glucosaminic acid phosphate and H2O2 is produced. The process leading to the nanosystems comprises nanoparticles growth, their aggregation into necklace-like aggregates, and final fusion into nanowires. The fusion requires the consumption of H2O2. The nanowires can be passivated with an organic thiol, lyophilized, and resuspended in water without losing their dimensional and optical properties. The position of the broad surface plasmon band of the nanowires can be tuned from 630 to >1350 nm.
Highlights
The aggregation of gold nanoparticles (AuNPs) into clusters is a well-known phenomenon that can be induced by crosslinking agents, cationic surfactants, or salts
We describe the synthesis in an aqueous solution devoid of any surfactant of Au-nanowires of controlled length and reasonably narrow dimensional distribution starting from Au-nanoparticles by taking advantage of the properties of glucosamine phosphate under aerobic conditions and substoichiometric nanoparticle passivation
Oxygen is required to enable the process where glucosamine phosphate is oxidized to glucosaminic acid phosphate and H2O2 is produced
Summary
The aggregation of gold nanoparticles (AuNPs) into clusters is a well-known phenomenon that can be induced by crosslinking agents, cationic surfactants, or salts. Conditions for forming linear, necklace-like [8,9] or globular [10] aggregates have been reported. A necklace-like aggregate formation is highlighted by the development of an additional, new surface plasmon resonance (SPR) band at 650–750 nm, red-shifted with respect to the 520–525 nm band of the single, isolated AuNP. We were looking for a mild passivating agent to replace citrate [28] in AuNPs. the presence of the glucose moiety on GAP, as we will show below, resulted in a cascade of redox processes [29] starting with AuNPs aggregation in a linear fashion and ending with their fusion into nanowires
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