A sandwich SERS detection system based on optical convergence and synergistic enhancement effects.

In this research, we propose a novel microlens surface-enhanced Raman spectroscopy (SERS) substrate @ Au film detection system, which is shown to have excellent attributes. This scheme involves the construction of a PDMS plano-convex microlens SERS-active substrate in combination with an Au film. Due to the optical convergence from the microlens, the synergistic enhancement effects due to the Au film, and the "Au film-molecules-AgNPs" sandwich structure, an outstanding SERS performance is achieved. Multiple tests using a portable Raman spectrometer show that the optical convergence due to the microlens and the coupling effects contribute around 1.85× and 26.18× enhancement of the Raman signal, respectively. Even for objective lenses with different numerical apertures, simulations show that the microlens SERS substrate can further enhance the signal collection efficiency; this indicates that the detection scheme is universally applicable. Moreover, the microlens SERS substrate @ Au film system shows excellent time stability, and its Raman enhancement performance remains consistently above 98% of the original signal, even one week later. Our proposed system is simple to prepare, is low cost and has many potential practical applications, which include the detection of biochemical samples.