Surface-enhanced Raman spectroscopy is one of the most sensitive spectroscopic techniques available, with single-molecule detection possible on a range of noble-metal substrates. It is widely used to detect molecules that have a strong Raman response at very low concentrations. Here we present photo-induced-enhanced Raman spectroscopy, where the combination of plasmonic nanoparticles with a photo-activated substrate gives rise to large signal enhancement (an order of magnitude) for a wide range of small molecules, even those with a typically low Raman cross-section. We show that the induced chemical enhancement is due to increased electron density at the noble-metal nanoparticles, and demonstrate the universality of this system with explosives, biomolecules and organic dyes, at trace levels. Our substrates are also easy to fabricate, self-cleaning and reusable.

Surface‐enhanced Raman spectroscopy (SERS) is a powerful analytical technique commonly used in the detection of traces of organic molecules. The mechanism of SERS is of a dual nature, with Raman scattering enhancements due to a combination of electromagnetic (EM) and chemical contributions. In conventional SERS, the EM component is largely responsible for the enhancement, with the chemical contribution playing a less significant role. An alternative technique, called photo‐induced enhanced Raman spectroscopy (PIERS) has been recently developed, using a photo‐activated semiconductor substrate to give additional chemical enhancement of Raman bands over traditional SERS. This enhancement is assigned to surface oxygen vacancies (V o) formed upon pre‐irradiation of the substrate. In this work, the exceptional chemical contribution in PIERS allows for the evaluation of atomic V o dynamics in metal oxide surfaces. This technique is applied to study the formation and healing rates of surface‐active V o in archetypical metal‐oxide semiconductors, namely, TiO2, WO3, and ZnO. Contrary to conventional analytical tools, PIERS provides intuitive and valuable information about surface stability of atomic defects at ambient pressure and under operando conditions, which has important implications in a wide range of applications including catalysis and energy storage materials.

Explosive trace detection (ETD) technologies play a vital role in maintaining national security. ETD remains an active research area with many analytical techniques in operational use. This review details the latest advances in animal olfactory, ion mobility spectrometry (IMS), Raman and colorimetric detection methods. Developments in optical, biological, electrochemical, mass and thermal sensors are also covered in addition to the use of nanomaterials technology. Commercially available systems are presented as examples of current detection capabilities and as benchmarks for improvement. Attention is also drawn to recent collaborative projects involving government, academia and industry, to highlight the emergence of multimodal screening approaches and applications. The objective of the review is to provide a comprehensive overview of ETD by; highlighting challenges in ETD and providing an understanding of the principles, advantages and limitations of each technology and relating this to current systems.

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Surface-enhanced Raman spectroscopy (SERS) has been widely utilised as a sensitive analytical technique for the detection of trace levels of organic molecules. The detection of organic compounds in the gas phase is particularly challenging due to the low concentration of adsorbed molecules on the surface of the SERS substrate. This is particularly the case for explosive materials, which typically have very low vapour pressures, limiting the use of SERS for their identification. In this work, silver nanocubes (AgNCs) were developed as a highly sensitive SERS substrate with very low limit-of-detection (LOD) for explosive materials down to the femtomolar (10 M) range. Unlike typical gold-based nanostructures, the AgNCs were found suitable for the detection of both aromatic and aliphatic explosives, enabling detection with high specificity at low concentration. SERS studies were first carried out using a model analyte, Rhodamine-6G (Rh-6G), as a probe molecule. The SERS enhancement factor was estimated as 8.71 × 10 in this case. Further studies involved femtomolar concentrations of 2,4-dinitrotoluene (DNT) and nanomolar concentrations of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), as well as vapour phase detection of DNT.

A microfluidic reactor offers a controllable and convenient platform for fast synthesis of gold nanoparticles with carbon monoxide.

Indium gallium nitride (InGaN) is an attractive semiconductor, with a tunable direct bandgap for photoelectrochemical water splitting, but it corrodes in aqueous electrolytes. Cobalt oxide (CoOx) is a promising co-catalyst to protect photoelectrodes and to accelerate the charge transfer. CoOx is earth-abundant and stable in extremely alkaline conditions and shows high activity for the oxygen evolution reaction (OER). In this work, we demonstrate that CoOx directly deposited onto InGaN/GaN multiple quantum wells photoanodes exhibits excellent activity and stability in a strong alkaline electrolyte, 1M NaOH (pH=13.7), for water oxidation up to 28 hours, while a reference sample without the catalyst degraded rapidly in the alkaline electrolyte. Under simulated solar illumination, the CoOx-modified InGaN/GaN quantum well photoanode showed a high photocurrent density of 1.26 mA cm-2 at 1.23 V and an onset potential of-0.03 V versus a reversible hydrogen electrode.

Enhanced Raman relies heavily on finding ideal hot-spot regions which enable significant enhancement factors. In addition, the termed "chemical enhancement" aspect of SERS is often neglected due to its relatively low enhancement factors, in comparison to those of electromagnetic (EM) nature. Using a metal-semiconductor hybrid system, with the addition of induced surface oxygen vacancy defects, both EM and chemical enhancement pathways can be utilized on cheap reusable surfaces. Two metal-oxide semiconductor thin films, WO3 and TiO2, were used as a platform for investigating size dependent effects of Au nanoparticles (NPs) for SERS (surface enhanced Raman spectroscopy) and PIERS (photo-induced enhanced Raman spectroscopy-UV pre-irradiation for additional chemical enhancement) detection applications. A set concentration of spherical Au NPs (5, 50, 100 and 150 nm in diameter) was drop-cast on preirradiated metal-oxide substrates. Using 4-mercaptobenzoic acid (MBA) as a Raman reporter molecule, a significant dependence on the size of nanoparticle was found. The greatest surface coverage and ideal distribution of AuNPs was found for the 50 nm particles during SERS tests, resulting in a high probability of finding an ideal hot-spot region. However, more significantly a strong dependence on nanoparticle size was also found for PIERS measurementscompletely independent of AuNP distribution and orientation affectswhere 50 nm particles were also found to generate the largest PIERS enhancement. The position of the analyte molecule with respect to the metal-semiconductor interface and position of generated oxygen vacancies within the hot-spot regions was presented as an explanation for this result.