Surface-enhanced Raman scattering (SERS) as a powerful and sensitive technique for the detection of chemical and biological agents received more attention since single-molecule detection with SERS was confirmed [1, 2]. The enhancement of Raman signal was mainly attributed to the electromagnetic enhancement on the metal surface which was induced by the surface plasmon resonance (SPR). To obtain the huge Raman enhancement, noble metal nanogap structures, especially of sub-10-nm gap structures, have attracted considerable scholarly attention, which can support strong SERS due to the existence of enormous electromagnetic enhancement in the gap of metal nanostructure [3–16]. The enormous electromagnetic enhancement in the gap of metal nanostructure is caused by the strong coupling of the SPR, which is called ‘hot spot’. Apart from having a huge Raman enhancement, the high-performance SERS substrates should also be uniform and reproducible. Taking into account the commercial application, the high-performance SERS substrates should also be low cost and should achieve high output. Fabrication of high-performance SERS substrates has been the focus of attention [3–16]. Many low-cost methods and techniques have been proposed, like self-assembly [17, 18], indentation lithography [6, 19–24], corroding ultrathin layer , and femtosecond laser fabrication [26–29]. However, to date, for the existence of many limits for these low-cost techniques, the fabrication of large-area high-performance SERS substrate with sub-10-nm gap size is still critical for the practical applications of SERS.
Porous anodized aluminum oxide (AAO) was widely used in the SERS substrate fabrication for the existence of large-area high-ordered array of nanopores and the simple production process. Porous AAO can be used directly as SERS substrate after depositing Au or Ag on the surface  and can also be used as template to fabricate ordered array nanostructure SERS substrate [31–36]. Previous studies have shown that nanorod array and nanowire network, with dense nanojunctions and nanogaps, can support stronger SERS than porous structures [37–41]. The question, whether the nanorod array and nanowire network structure can be fabricated just by making a simple change to the production process of porous AAO, has not attracted the researcher's attention.
In this work, a simple film-eroding process was added after the production process of porous AAO to fabricate large-area low-cost nanowire network AAO which can be used as high-performance SERS substrate after depositing 50 nm of Au onto its surface. The Raman spectra of benzene thiol on the nanowire network AAO SERS substrates are measured and the average Raman enhancement factors (EFs) are calculated. Comparing with the porous AAO SERS substrates, the Raman peak intensities and the average EFs of nanowire network AAO SERS substrates have a significant enhancement. The average EF of our sensitive SERS substrate can reach 5.93 × 106, about 35 times larger than that of porous AAO SERS substrate and about 14% larger than that of Klarite® substrates (Renishaw Diagnostics, Glasgow, UK), which indicates an enormous electromagnetic enhancement that exists in the nanowire network AAO SERS substrate. Repeated measurements and spatial mapping show an excellent reproducibility of the nanowire network AAO SERS substrate. The relative standard deviations in the SERS intensities are limited to only approximately 7%. Comparing with other fabrication methods of the high-performance SERS substrates, our method based on the mature production process of porous AAO is simpler, has lower cost, and is easier for commercial production. Therefore, we believe that our nanowire network AAO SERS substrates have great potential for applications.