Abstract
New aromatic molecule–seed particle interactions are examined and exploited to control and guide seed‐mediated gold nanorod (Au NR) growth. This new approach enables better understanding of how small molecules impact the synthesis of metallic nanostructures, catalyzing their use in various biomedical applications, such as plasmonic biosensing. Experimental studies and theoretical molecular simulations using a library of aromatic molecules, making use of the chemical versatility of the molecules with varied spatial arrangements of electron‐donating/withdrawing groups, charge, and Au‐binding propensity, are performed. Au NR growth is regulated by two principal mechanisms, producing either a red or blue shift in the longitudinal localized surface plasmon resonance (LLSPR) peaks. Aromatic molecules with high redox potentials produce an increase in NR aspect ratio and red shift of LLSPR peaks. In contrast, molecules that strongly bind gold surfaces result in blue shifts, demonstrating a strong correlation between their binding energy and blue shifts produced. Through enzymatic conversion of selected molecules, 4‐aminophenylphosphate to 4‐aminophenol, opposing growth mechanisms at opposite extremes of target concentration are obtained, and a chemical pathway for performing plasmonic enzyme‐linked immunosorbent assays is established. This unlocks new strategies for tailoring substrate design and enzymatic mechanisms for controlling plasmonic response to target molecules in biosensing applications.
Highlights
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Despite having similar molecular structures, AP and aminophenyl phosphate (APP) exhibited completely opposing effects on Au NR growth; AP resulted in a red shift of the localized surface plasmon resonance (LLSPR) peaks, while APP caused a blue shift (Figure 1a)
The red shift was consistent with an increase in the aspect ratio of grown Au NRs, as seen from transmission electron microscopy (TEM) images (Figure 1b)
Summary
Significant differences in the growth of Au NRs could be achieved from seeds that were incubated with subtly different aromatic compounds, differing only by a single functional group. We have discovered this to be pronounced in the case of AP and APP. In a typical Au NR growth reaction in our study, the seed particles were first incubated with aromatic molecules for 10 min, followed by the addition of the growth solution. The aspect ratio distribution was not affected by AP/APP treatment. We hypothesized that there were two likely effects governing the anisotropic growth of Au NRs: (i) a capping effect, where molecules bound to the seed particles and interfered with the CTAB/AgBr templated anisotropic growth,[15] and (ii) a reducing effect, where molecules acted predominantly as reducing agents.[16]
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