Recent Progress in the Synthesis of 3D Complex Plasmonic Intragap Nanostructures and Their Applications in Surface-Enhanced Raman Scattering

Abstract

Plasmonic intragap nanostructures (PINs) have garnered intensive attention in Raman-related analysis due to their exceptional ability to enhance light-matter interactions. Although diverse synthetic strategies have been employed to create these nanostructures, the emphasis has largely been on PINs with simple configurations, which often fall short in achieving effective near-field focusing. Three-dimensional (3D) complex PINs, distinguished by their intricate networks of internal gaps and voids, are emerging as superior structures for effective light trapping. These structures facilitate the generation of hot spots and hot zones that are essential for enhanced near-field focusing. Nevertheless, the synthesis techniques for these complex structures and their specific impacts on near-field focusing are not well-documented. This review discusses the recent advancements in the synthesis of 3D complex PINs and their applications in surface-enhanced Raman scattering (SERS). We begin by describing the foundational methods for fabricating simple PINs, followed by a discussion on the rational design strategies aimed at developing 3D complex PINs with superior near-field focusing capabilities. We also evaluate the SERS performance of various 3D complex PINs, emphasizing their advanced sensing capabilities. Lastly, we explore the future perspective of 3D complex PINs in SERS applications.

Keywords: biosensing; intragap; localized surface plasmon resonance; nanostructure synthesis; near field; surface-enhanced Raman scattering.

Figure 1

Schematic illustration of synthetic strategies for 3D complex PINs from polyhedral nanocrystals.

Figure 2

Structural transformation from 3D polyhedral nanocrystals to 3D nanoframes. (A) Synthesis of 3D Au nanosphere hexamer by a three-step method, with the corresponding products in each step. Copyright 2020 American Chemical Society [43]. (B) Structural evolution from Ag nanocubes to AuAg cubic nanoframes. Copyright 2022 American Chemical Society [54].

Figure 3

Rational design of synthesis for 3D complex PINs by outer frame engineering of 3D nanoframes. (A) Au octahedral nanosponges. Copyright 2023 American Chemical Society [59]. (B) Au dual frame-engraved nanoframes. Copyright 2022 Springer Nature [60]. (C) AuAg all-frame-faceted tripod nanoframes. Copyright 2022 American Chemical Society [61]. (D) AuAg nanosphere octamer. Copyright 2024 American Chemical Society [62]. (E) Au cross-gap nanocubes. Copyright 2024 American Chemical Society [63].

Figure 4

Rational design of synthesis for 3D complex PINs by inner structure engineering of 3D nanoframes. (A) Au nanosphere heptamer. Copyright 2024 American Chemical Society [64]. (B) Truncated-octahedral@octahedral PtAu dual nanoframes. Copyright 2023 Wiley-VCH GmbH [65]. (C) Multi-layered Au nanoframes. Copyright 2022 Springer Nature [66]. (D) Au octahedra@Au cubic nanoframes. Copyright 2024 American Chemical Society [67]. (E) Multi-layered AuAg nanoframes. Copyright 2023 Wiley-VCH GmbH [68].

Figure 5

Single-particle SERS activity of 3D complex PINs. (A) Au nanosphere hexamer. (a) FEM calculations of near-field distribution. (b) Single-particle SERS measurements of Au nanosphere hexamer with different structures. (c) Reproducibility of single-particle SERS measurements. Copyright 2020 American Chemical Society [43]. (B) Au nanosphere octamer. (a) Calculated near-field distributions. (b) Single-particle SERS measurements of Au nanosphere octamer with different structures. (c) Calculated enhancement factors. Copyright 2024 American Chemical Society [62]. (C) Au octahedral nanosponges. (a) Calculated near-field distributions. (b) Single-particle SERS measurements of Au octahedral nanosponges with different structures. Copyright 2023 American Chemical Society [59]. (D) Calculated near-field distributions of multi-layered nanoframes with different structures. Copyright 2022 Springer Nature [66].

Figure 6

Potential SERS applications using 3D complex PINs. (A) SERS detection using self-assembled 3D complex PINs. (a) SEM images of self-assembled monolayer of Au octahedral, Au cubic nanoframes, and Au octahedral@Au cubic nanoframes. (b) Calculated near-field distributions of Au octahedral, Au cubic nanoframes, and Au octahedral@Au cubic nanoframes. (c–e) Bulk SERS spectra from Au octahedral (c), Au cubic nanoframes (d), and Au octahedral@Au cubic nanoframes (e). Copyright 2024 American Chemical Society [67]. (B) SERS detections of gas analytes using 3D complex PINs. (a) Schematic illustration for synthesis of an Au octahedral nanosponges@ZIF-8 film substrate. (b) Cross-section SEM images of SERS substrates with different thicknesses. (c) SERS spectra using different substrates. (d) SERS spectra using Au octahedral nanosponges@ZIF-8 substrate with different thicknesses. The characteristic peak of DMMP at 719 cm⁻¹ is marked as asterisk. Copyright 2023 American Chemical Society [59]. (C) SERS immunoassay of HCG using 3D complex PINs. (a) Schematic illustration of SERS immunoassay of Au dual-rim nanoframes. (b,c) SERS spectra using 3D Au dual-rim nanoframes (b) and 2D Au triangular nanoframes (c) as probes. Copyright 2022 Springer Nature [60].