Nanostructured plasmonic substrates for use as SERS sensors

Abstract

Plasmonic nanostructures strongly localize electric fields on their surfaces via the collective oscillations of conducting electrons under stimulation by incident light at a certain wavelength. Molecules adsorbed onto the surfaces of plasmonic structures experience a strongly enhanced electric field due to the localized surface plasmon resonance (LSPR), which amplifies the Raman scattering signal obtained from these adsorbed molecules. This phenomenon is referred to as surface-enhanced Raman scattering (SERS). Because Raman spectra serve as molecular fingerprints, SERS has been intensively studied for its ability to facilely detect molecules and provide a chemical analysis of a solution. Further enhancements in the Raman intensity and therefore higher sensitivity in SERS-based molecular analysis have been achieved by designing plasmonic nanostructures with a controlled size, shape, composition, and arrangement. This review paper focuses on the current state of the art in the fabrication of SERS-active substrates and their use as chemical and biosensors. Starting with a brief description of the basic principles underlying LSPR and SERS, we discuss three distinct nanofabrication methods, including the bottom-up assembly of nanoparticles, top-down nanolithography, and lithography-free random nanoarray formation. Finally, typical applications of SERS-based sensors are discussed, along with their perspectives and challenges.

Surface Energy‐Controlled SERS Substrates for Molecular Concentration at Plasmonic Nanogaps

“…Plasmonic nanostructures enable light concentration, orders‐of‐magnitude higher than the incident light intensity, within the vicinity of tiny nanoscale gaps (so‐called “hot spots”). Plasmonic enhancement via coupled localized surface plasmon resonance results in a high molecular detection sensitivity; however, positioning probe molecules within the nanometer‐scale volume of a hot spot tends to be difficult, resulting in poor reproducibility and controllability among surface‐enhanced Raman spectroscopy (SERS) measurements. Therefore, controlling hot spot design and concentrating probe molecules at plasmonic nanogaps remains a goal for ultrasensitive and reproducible SERS detection.…”

Light enhancement by quasi-bound states in the continuum in dielectric arrays

“…Due to numerous applications [12] trapping, focusing, and concentration of light at the nanoscale have recently emerged as topics of great interest primarily in regard to various plasmonic devices [13][14][15][16][17][18][19] and photonic band-gap structures [20][21][22][23]. Another promising directions of research is all-dielectric nanophotonics [24,25] which employs subwavelength dielectric objects, such as e.g.…”

Self‐Assembly of Nanoparticle‐Spiked Pillar Arrays for Plasmonic Biosensing

“…We investigated the near‐field coupling of these structures using computational finite‐element simulations (Figure g; Figure S2, Supporting Information). The simulations clearly show that the 3D NPOP structures generate multiple hotspots localized at junctions between AuNPs and nanopillars as well as at the nanogap between AuNPs, due to localized surface plasmon resonance (LSPR) coupling effects . High‐field enhancements were achieved at both 633 and 785 nm by normally incident plane‐wave illumination.…”

“…Strongly enhanced electromagnetic fields localized at interstitial nanogap junctions between metallic nanostructures, so‐called “plasmonic hotspots” are the fundamental basis of numerous promising technologies in the fields of plasmon‐enhanced spectroscopy, plasmonic biosensing, photocatalysis, and nanophotonics . One major challenge in expanding the use of plasmon‐enhanced applications lies in reproducible fabrication of high‐density plasmonic hotspots over large areas in a low‐cost, high‐throughput manner.…”