Molecular Sensing using Surface-Sensitised Plasmonic Nanogaps

Surface-enhanced Raman spectroscopy (SERS) is a highly sensitive optical technique that offers both high specificity and the potential for real-time sensing solutions, addressing many unmet needs in current applications. Plasmonic effects can significantly enhance the Raman scattering of molecules located in metal nanostructures, enabling improved detection sensitivity. However, further development is essential to maximise signal enhancement and broaden the applicability of this technology. This thesis explores SERS sensing using self-assembled substrates, composed of near-monolayer films of close-packed gold nanoparticles (MLagg). Rigid cucurbit[n]uril spacers precisely define the sub-nm interparticle gaps, enabling reproducible SERS enhancements. Pristine nanogaps are achieved through oxygen plasma cleaning, which removes all ligands, analytes and contaminants and oxidises the top gold atomic layers, followed by regeneration via reintroduction of a scaffold molecule and chemical reduction of the gold surface. The high signal enhancement enables the study of water monolayers trapped in nominally dry, sub-nm MLagg nanogaps, even in ambient conditions. These water monolayers can only be removed from the nanoparticle surfaces by heating or by solvents with a stronger affinity for gold. The interactions between water and a metal surface or nanogap scaffold molecule were studied under a range of conditions including varying temperatures, salt concentrations and applied electric potentials. These water monolayers provide surface sensitisation for gas sensing, as the analyte can interact with both the water monolayer and the nanogap scaffold. By selecting the nanogap scaffold and the solvent on the nanoparticle surfaces, the MLagg response to gases can be tuned. Using a water sensitisation layer, ammonia was detected down to parts per billion. MLaggs are also sensitive to small molecules in solution, enabling the detection of E. coli signalling molecules through SERS measurement of the liquid culture supernatant. By using a gene-knockout E. coli strain, the influence of the targeted gene on cell signalling molecules was investigated for cultures grown in media supplemented with different amino acids and can reveal previously unstudied effects.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2025

Author dc:creator

• Wyatt, Eleanor

Advisor dc:contributor.advisor

• Baumberg, Jeremy

• SERS
• Raman
• Sensing
• VOC
• E.coli signalling

Licence

• https://www.repository.cam.ac.uk/bitstreams/8f921243-4046-4c5e-b8f5-8086488013e2/download
• http://purl.org/NET/rdflicense/allrightsreserved

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.121766

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/390092