The optoelectronic nose from nano-assembly and nano-optics

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.

The primary outputs from the CDT will be cohorts of highly qualified, interdisciplinary postgraduates who are experts in a wide range of sensing activities. They will benefit from a world leading training experience that recognises sensor research as an academic discipline in its own right. The students will be taught in all aspects of Sensor Technologies, ranging from the physical and chemical principles of sensing, to sensor design, data capture and processing, all the way to applications and opportunities for commercialisation, with a strong focus in entrepreneurship, technology translation and responsible leadership. Students will learn in extensive team and cohort engaging activities, and have access to cutting-edge expertise and infrastructure. 90 academics from 15 different departments participate in the programme and more than 40 industrial partners are actively involved in delivering research and business leadership training, offering perspectives for impact and translation and opportunities for internships and secondments. End users associated with the CDT will benefit from the availability of outstanding, highly qualified and motivated PhD students, access to shared infrastructure, and a huge range of academic and industrial contacts.

Immediate beneficiaries of our CDT will be our core industrial consortium partners (MedImmune, Alphasense, Fluidic Analytics, ioLight, NokiaBell, Cambridge Display Technologies, Teraview, Zimmer and Peacock, Panaxium, Silicon Microgravity, etc., see various LoS) who incorporate our cross-leverage funding model into their corporate research strategies. Small companies and start-ups particularly benefit from the flexibility of the partnerships we can offer. We will engage through weekly industry seminars and monthly Sensor Cafés, where SME employees can interact directly with the CDT students and PIs, provide training in topical areas, and, in turn, gain themselves access to CDT infrastructure and training. Ideas can be rapidly tested through industrially focused miniprojects and promising leads developed into funded PhD programmes, for which leveraged funding is available through the CDT.

Government departments and large research initiatives are formally connected to the CDT, including the Department for the Environment, Food and Rural Affairs (DEFRA); the Cambridge Centre for Smart Infrastructure and Construction (CSIC); the Centre for Global Equality (CGE); the National Physics Laboratory (NPL); the British Antarctic Survey (BAS), who all push our CDT to generate impacts that are in the public interest and relevant for a healthy and sustainable future society. With their input, we will tackle projects on assisted living technologies for the ageing population, diagnostics of environmental toxins in the developing world, and sensor technologies that help replace the use of animals in research. Developing countries will benefit through our emphasis on open technologies / open innovation and our exploration of responsible, ethical, and transparent business models. In the UK, our CDT will engage directly with the public sector and national policy makers and regulators (DEFRA, and the National Health Service - NHS) and, with their input, students are trained on impact and technology translation, ethics, and regulatory frameworks.