Continuous fabrication of nanostructure arrays for flexible surface enhanced Raman scattering substrate

Abstract

Surface-enhanced Raman spectroscopy (SERS) has been a powerful tool for applications including single molecule detection, analytical chemistry, electrochemistry, medical diagnostics and bio-sensing. Especially, flexible SERS substrates are highly desirable for daily-life applications, such as real-time and in situ Raman detection of chemical and biological targets, which can be used onto irregular surfaces. However, it is still a major challenge to fabricate the flexible SERS substrate on large-area substrates using a facile and cost-effective technique. The roll-to-roll ultraviolet nanoimprint lithography (R2R UV-NIL) technique provides a solution for the continuous fabrication of flexible SERS substrate due to its high-speed, large-area, high-resolution and high-throughput. In this paper, we presented a facile and cost-effective method to fabricate flexible SERS substrate including the fabrication of polymer nanostructure arrays and the metallization of the polymer nanostructure arrays. The polymer nanostructure arrays were obtained by using R2R UV-NIL technique and anodic aluminum oxide (AAO) mold. The functional SERS substrates were then obtained with Au sputtering on the surface of the polymer nanostructure arrays. The obtained SERS substrates exhibit excellent SERS and flexibility performance. This research can provide a beneficial direction for the continuous production of the flexible SERS substrates.

Figure 1. The schematic diagram of fabrication process for the SERS substrates.

(a) The fabrication of master mold by AAO process, (b) the formation of polymer nanostructure array by the UV-NIL process, (c) the formation of Au covered polymer nanostructure array by the sputtering process.

Figure 2. The repeatability investigation of R2R UV-NIL technique to fabricate nanostructure arrays.

(a) The AFM images of nanostructure arrays at the 1st and 1000th roll revolution, (b) the diamters and heights of nanostructure arrays each 200 roll revolutions.

Figure 3. The absorption spectra of substrates with different Au coating thickness within the 300−800 nm wavelength range.

Figure 4. SERS spectra of R6G (10⁻⁶ M) absorbed on nanostructure arrays with different Au coating thickness.

1-mW 785-nm excitation was used, and the integration time was 10 s for each spectrum.

Figure 5. The top view and 45° tilt view SEM images of nanostructure arrays with different Au coating thickness.

(a) 15 nm, (b) 30 nm, (c) 45 nm, (d) 60 nm.

Figure 6. SERS spectra of R6G (10⁻⁶ M) absorbed on nanostructure arrays collected from 8 randomly selected acquisition points from substrates with 30 nm Au coating.

1-mW 785-nm excitation was used, and the integration time was 10 s for each spectrum.

Figure 7. SERS spectra of R6G (10⁻⁶ M) collected from substrates with 30 nm Au coating.

(a) With different bending angles, (b) with different bending circles and 80° bending angle. 1-mW 785-nm excitation was used, and the integration time was 10 s for each spectrum.