Researchers report a new sensor surface that can be cleaned electrochemically and used repeatedly to record two complementary kinds of vibrational spectra at once. The device combines surface-enhanced infrared absorption (SEIRA) and surface-enhanced Raman spectroscopy (SERS). Together these techniques give more complete “molecular fingerprints” than either method alone, and the new substrate works in flowing liquid and under an applied voltage.

The core of the device is a metamaterial film made from stacked layers of gold nanoparticles (100 nm or 250 nm across) packed so that each particle is separated by about 0.9 nanometres. Those tiny gaps are set by a spacer molecule called cucurbit[5]uril (CB[5]). The film sits on a thin, conducting sheet of graphene that is on an infrared‑transparent zinc selenide (ZnSe) window. The stack is mounted in a small flow cell that holds a working, reference and counter electrode and fits under an infrared/Raman microscope.

Because the gaps are only a nanometre wide, incoming light is squeezed into intense “hotspots” that boost both IR and Raman signals. By changing the number of nanoparticle layers and the particle size, the authors tune the mid‑infrared resonance into the molecular fingerprint region. The device shows strong SEIRA signals in water because water absorption bands do not fully mask the target vibrations (for example the CB[5] carbonyl band around 1750 cm−1 sits above the water O–H bend near 1600 cm−1). In the near‑infrared (785 nm), the enhanced field is concentrated near the top layer, which gives strong SERS from species at the surface.

A key advance is that the film can be electrochemically regenerated. By sweeping the electrode potential through gold oxidation and then reducing gold in the presence of CB[5], the authors remove bound analytes and restore the nanogaps. They show cyclic voltammetry (CV) peaks consistent with gold oxidation and reduction in 1 M, pH 7 potassium phosphate buffer (KPB) with 1 mM CB[5] (5 mV s−1). The combined SEIRA and SERS measurements were used to follow a standard redox pair, ferrocyanide/ferricyanide, and to highlight how molecules change when they adsorb to the metal surface. The metamaterial also responds to changes in gap refractive index with a large spectral shift reported as 1400 nm per refractive index unit (RIU), and it can detect small molecules such as a pharmaceutical (amantadine) and DNA bases at low concentrations.