Surface plasmon resonance optical sensors involving nanomaterials as reliable analytical tools: A critical view about...

In the last two decades, there has been an increasing interest in the development of a new category of chemical sensors incorporating "nanosensor" devices, which are based on nanomaterials, thus enabling the establishment of more efficient transduction and recognition processes due to their versatile and innovative properties. Among them, the role of metallic nanoparticles (MNPs) for the construction of sensors should be highlighted due to the Localized Surface Plasmon Resonance (LSPR) phenomenon exhibited on their surface. These open interesting analytical possibilities, incorporating new advantages or new alternatives with respect to the present state-of-the-art and today problem solving.

This review aims to provide an overview of the current state of the art in terms of specific transduction mechanisms and performance improvements on substrates, as well as analytical characterisation strategies and the most relevant applications of optical sensors based on the LSPR effect of metallic nanomaterials. Specifically, it is aimed at two major categories of optical techniques, which are grounded by distinct physicochemical transduction mechanisms. The first category encompasses surface-enhanced spectroscopies (SES), which exploit the interaction between analytes and the intense electromagnetic fields generated and localized near metallic nanoparticles (NPs). The second category comprises those optical sensors based on the LSPR band extinction within the visible range, where the absorption of radiation is modulated by changes in the dielectric environment surrounding the NPs. As a conclusive evaluation, a final critical overview is afforded, with particular concern to current challenges and limitations to achieve reliable analytical determinations.

The review tries to highlight, from a technical and critical point of view, the state of art of those nanotechnological and instrumental strategies recently designed involving plasmon resonance optical sensors based on MNPs, which have conducted to a very different maturity and performance degree regarding sensing scopes for the different LSPR techniques. All the outlined strategies have been exemplified with selecting applications of analytical interest.