Intense Raman scattering on hybrid Au/Ag nanoplatforms for the distinction of MMP-9-digested collagen type-I fiber detection

• Well-ordered Au or Ag nanoclusters (NCs) on Au nanorods (NRs) are fabricated by combining focused ion beam (FIB) and electron beam deposition methods.
• The diameter and the formation of NCs on NRs affect SERS effect, which can detect a single molecule of crystal violet.
• The small nanogaps between 4-aminobenzenethiol-coated nanoparticles and intra-NCs allowed increase the local field effect.
• NCsfibAu_NR was competent to detect matrix-metalloproteinase-9-digested collagen-I fibers of various concentrations.

Well-ordered Au-nanorod arrays were fabricated using the focused ion beam method (denoted as fibAu_NR). Au or Ag nanoclusters (NCs) of various sizes and dimensions were then deposited on the fibAu_NR arrays using electron beam deposition to improve the surface-enhanced Raman scattering (SERS) effect, which was verified using a low concentration of crystal violet (10–5 M) as the probe molecule. An enhancement factor of 6.92×108 was obtained for NCsfibAu_NR, which is attributed to the combination of intra-NC and NR localized surface plasmon resonance. When 4-aminobenzenethiol (4-ABT)-coated Au or Ag nanoparticles (NPs) were attached to NCsfibAu_NR, the small gaps between 4-ABT-coated NPs and intra-NCs allowed detection at the single-molecule level. Hotspots formed at the interfaces of NCs/NRs and NPs/NCs at a high density, producing a strong local electromagnetic effect. Raman spectra from as-prepared type I collagen (Col-I) and Ag-NP-coated Col-I fibers on NCsfibAu_NR were compared to determine the quantity of amino acids in their triple helix structure. Various concentrations of matrix-metalloproteinase-9-digested Col-I fibers on NCsfibAu_NR were qualitatively examined at a Raman laser wavelength of 785 nm to determine the changes of amino acids in the Col-I fiber structure. The results can be used to monitor the growth of healing Col-I fibers in a micro-environment.

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