Surface-enhanced Raman spectroscopy for chemical and biological sensing using nanoplasmonics: The relevance of interparticle spacing and surface morphology

In this review, the weightiest decadal developments of surface-enhanced Raman scattering (SERS) and nanoplasmonic materials in sensing applications are discussed. Today, there are several well-established research directions where plasmonic detection is employed extensively, namely, food and water quality monitoring, viruses, pathogenic bacteria and hazardous toxin investigations for theranostic applications, and explosive substance detection for military and civil protection purposes. A combination of vibrational spectroscopy and surface nanoengineering has gained a reputation as a powerful weapon for rapid and accurate determination of submolecular quantities of nanoanalytes. Signal enhancement achieved by employing various metallic nanoparticles and nanostructures can be amplified significantly due to the electromagnetic field confinement effect. Localized surface plasmon waves, which are responsible for the phenomenon, promote light absorption at nanovolume, generating 'hot spots' with an incredibly intense and confined electromagnetic field close to the nanosculptured metallic surface. However, the formation of the hot spot network is heavily dependent on morphology, size, and spatial arrangement of plasmonic nanomaterials. Under optimal excitation conditions, the interaction between the optically induced electromagnetic field in the hot spot region and a probing analyte attached to the nanosculptured metallic substrate enlarges photon scattering cross section, increasing signal intensity by 106-1010. As a result, fast single-molecule vibrational fingerprint recording is possible. This focused review collects recent state-of-the-art developments in nanoplasmonic SERS sensing, highlighting the most efficient surface morphology designs that hold the most promise for future developments.