Plasmonic sensing has been an important multidisciplinary research field and has been extensively used in detection of trace molecules in chemistry and biology. The sensing techniques are typically based on surface-enhanced spectroscopies and surface plasmon resonances (SPRs). This review article deals with some recent advances in surface-enhanced Raman scattering (SERS) sensors and SPR sensors using either localized surface plasmon resonances (LSPRs) or propagating surface plasmon polaritons (SPPs). The advances discussed herein present some improvements in SERS and SPR sensing, as well as a new type of nanowire-based SPP sensor.

The fast development of plasmonics have greatly advanced our understanding to the abundant phenomena related to surface plamon polaritons (SPPs) and improved our ability to manipulate light at the nanometer scale. With tightly confined local field, SPPs can be transmitted in waveguides of subwavelength dimensions. Nanophotonic circuits built with plasmonic elements can be scaled down to dimensions compatible with semiconductor‐based nanoelectronic circuits, which provides a potential solution for the next‐generation information technology. Different structures have been explored as plasmonic waveguides for potential integration applications. This review is focused on metallic nanowire waveguides and functional components in nanowire networks. We reviewed recent progress in research about plasmon generation, emission direction and polarization, group velocity, loss and propagation length, and the near‐field distribution revealed by quantum dot fluorescence imaging. Electrical generation and detection of SPPs moves towards the building of plasmonic circuits, where bulky external light sources and detectors may be omitted. The coupling between metal nanowires and emitters is important for tailoring light‐matter interactions, and for various potential applications. In multi‐nanowire structures, plasmon signal control and processing are introduced. The working principles of these nanowire‐based devices, which are based on the control to the near field distributions, will become the design rule for nanophotonic circuits with higher complexity for optical signal processing. The recent developments in hybrid photonic‐plasmonic waveguides and devices are promising for making devices with unprecedented performance.

The strong coupling between excitons and single plasmonic nanocavities enables plexcitonic states in nanoscale systems at room temperature. Here we demonstrate the strong coupling of surface plasmon modes of metal nanowires and excitons in monolayer semiconductors, with Rabi splitting manifested in both scattering and photoluminescence (PL) spectra. By utilizing the propagation properties of surface plasmons on the nanowires, the PL emitted through the scattering of plasmon-exciton hybrid modes is extracted. The analytically calculated scattering and PL spectra well reproduce the experimental results. These findings unify the scattering and PL spectra in the plexcitonic system and eliminate the ambiguities of PL emission, shedding new light on understanding the rich spectral phenomena in the plasmon-exciton strong coupling regime.

Plasmonics is a rapidly developing research field with many potential applications in fields ranging from bioscience, information processing and communication to quantum optics. It is based on the generation, manipulation and transfer of surface plasmons (SPs) that have the ability to manipulate light at the nanoscale. Realizing plasmonic applications requires understanding how the SP-based properties depend on the nanostructures and how these properties can be controlled. For that purpose composite nanostructures are particularly interesting because many novel and extraordinary properties unattainable in single nanostructures can be obtained by designing composite nanostructures with various materials. Here, we review recent advances in the studies of three classes of composite nanostructure that are important for plasmonics: metal–metal, metal–dielectric, and metal–semiconductor composite nanostructures.