Chiroptically Active Plasmonic Nanoparticles Having Hidden Helicity and Reversible Aqueous Solvent Effect on...

Area of Science:

• Plasmonics
• Nanotechnology
• Chirality

Background:

• Helical structures typically require helical pitch (P) greater than wire diameter (d).
• Current nanofabrication limits hinder the creation of sub-10 nm helical structures, restricting chiral plasmonics research.
• Achieving nanoscale chirality is crucial for advanced optical and biological applications.

Purpose of the Study:

• To develop a facile method for fabricating silver nanoparticles (AgNPs) with helical pitch (P) smaller than wire diameter (d) (P < d).
• To investigate the chiroptical activity of these AgNPs and their response to environmental changes.
• To enable the study of chiral plasmonics at the physical limit and explore chirality-related bioapplications.

Main Methods:

• Utilized glancing angle deposition at 0 °C and high substrate rotation speed to generate AgNPs.
• Fabricated AgNP arrays with varying helical pitch (P) from 3 to 66 nm.
• Investigated the effect of water immersion on the chiroptical activity of hydrophilic and hydrophobic AgNP arrays.

Main Results:

• Generated AgNPs with intrinsic chiroptical activity (circular dichroism) due to hidden helicity, with P < d.
• Observed a logarithmic increase in circular dichroism amplitude with increasing helical pitch.
• Demonstrated a water effect on chiroptical activity, which was reversible for hydrophilic arrays and irreversible for hydrophobic arrays.

Conclusions:

• Introduced a cost-effective approach to minimize helical pitch to sub-10 nm at regular substrate temperatures.
• Paved the way for studying chiral plasmonics at the physical limit.
• Highlighted potential for exploiting chirality-related bioapplications in aqueous environments for health and environmental solutions.