The optoelectronic nose from nano-assembly and nano-optics

Lead Research Organisation: University of Cambridge
Department Name: Physics

Abstract

The growing demand for accessible information about our health, food, and environment has prompted the need for sensing tools that are simple, fast, reliable, low-cost, and can be deployed for a wide range of applications. A promising technique that can fulfil this need is Surface-Enhanced Raman Spectroscopy (SERS). SERS is based on the enhancement of Raman or inelastic light scattering that arises from the strong electromagnetic fields generated by the optical excitation of localized surface plasmons on nano-patterned metal surfaces, such as gold nanoparticle (AuNP) assemblies. The Raman scattering of molecules adsorbed on the metal surface, known as the SERS substrate, can be enhanced by factors of up to 8 orders of magnitude, making SERS a highly sensitive and selective molecular fingerprinting method capable of even single-molecule detection.

Since the discovery of SERS by Jeanmaire and van Duyne in 1977, the technique has developed into a flourishing field of research, particularly in exploring its potential for a broad range of sensing applications. A key advantage of SERS is its ability to generate information-rich vibrational spectra, which can be used for label-free, multiplexed qualitative and quantitative analysis. However, the technique still remains constrained by the limited availability of a reproducible substrate. Variations in the fabrication of the SERS substrate can result in inconsistent optical properties and enhancement factors, therefore limiting the widespread deployment of SERS for reliable quantitative analysis.

A promising approach to fabricate reproducible SERS substrates is through the controlled assembly of AuNPs using the rigid molecular linker, cucurbit[n]uril (CB[n], n=5, 6, 7, 8). Use of the linker results in the formation of precisely-spaced plasmonic nanogaps between adjacent nanoparticles. Analytes that bind at the plasmonic nanogaps, or "hotspots," can be sensed reproducibly via SERS, which makes CB[n]:AuNP assemblies a promising substrate for multiplexed quantitative analysis. Since the discovery of this strategy to precisely control the preparation of AuNP aggregates as SERS substrates, further research on the CB[n]:AuNP assembly has since unveiled factors that affect its sensing performance and further questions on how it can be applied for multi-analyte sensing.

The aim of this PhD project is to develop a robust, low-cost CB[n]:AuNP-based SERS sensor system that is capable of widespread quantitative analysis of complex samples. Specifically, the project's objectives are divided into two major parts related to expanding the scientific understanding of nanogap sensing in CB[n]:AuNP substrates, and engineering a practical implementation of the sensor system. This closely aligns with the ESPCR's research areas in analytical science, clinical technologies, and light-matter interaction and optical phenomena. Key outcomes of this project will be an improved fundamental understanding and control of multianalyte binding at the nanogap and a practical lab-on-a-chip sensor system for the multiplexed quantitative analysis of real samples such as urine for health monitoring and other complex samples relevant for food, environmental, and agritech applications.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/S023046/1 30/09/2019 30/03/2028
2394971 Studentship EP/S023046/1 30/09/2020 29/09/2024 Sarah May Sibug-Torres