Plasma Deposition and Nanotechnology

Gold nanoparticles (AuNPs) continue to play a central role in a wide range of emerging technologies, even though there are narrowly defined size and morphological specifications in each area. In heterogeneous catalysis and photothermal therapy platforms, particles below 10 nm with dominant plasmonic absorption are preferred, while in vivo imaging and plasmon enhanced spectroscopy benefit from higher order morphologies with twinning that enable intense light scattering and finely tuned optical resonances [1]. Due to these different requirements, two main paradigms for synthesis have emerged: surfactant-assisted and surfactant-free synthesis, each with their own advantages and limitations. Surfactant-assisted protocols offer moderate control over shape, colloidal stability and optical bandwidth; however, the adsorbed ligands hinder surface accessibility and reduce catalytic and sensing performance. In fact, the surface-enhanced Raman scattering (SERS) activity of ligand-coated AuNPs may be reduced by an order of magnitude compared to their surfactant-free analogues. Concerns regarding the toxicity and biocompatibility of surfactants emphasise the need for alternative manufacturing methods. Plasma–liquid chemistry has recently emerged as a rapid, reagent-free and environmentally friendly approach that delivers AuNPs without chemical reducing agents or stabilisers. Beyond pure synthesis, the high-energy species in a non-thermal atmospheric plasma promote a high density of twin boundaries within the AuNP lattice, enhancing local electromagnetic “hot spots”. This twinned architecture achieves maximum SERS efficiency per unit particle volume, outperforming conventional quasi-spherical counterparts. Here we describe our strategies for modulating size, shape, twin density and ultimate SERS performance in surfactant-free AuNPs prepared with such plasmas and present SERS cases for trace aliphatic and aromatic explosives detection and GC ratio monitoring in bacterial DNA [2,3].

References:

1. Hang, Y., et.al. Chemical Society Reviews, 53(6) (2024) 2932-2971.

2. Shvalya, V., et. al . Nano letters, 22(23) (2022) 9757-9765.

3. Olenik, J., et. al. ACS sensors, 10(1) (2024).  387-397.

Funding acknowledgement

ARIS projects J2–4490, J2–50066, NATO “NOOSE” grant no. G5814.