Effects of Substrate Temperature on the SERS- based Sensing Performance of Silver Nanorod Thin Films Fabricated Through Oblique Angle Deposition

Abstract

Surface-enhanced Raman spectroscopy (SERS) possesses the same molecular fingerprint capabilities of Raman spectroscopy but offers much higher sensitivity. However, the size, shape and spatial arrangement of SERS substrates greatly influence the SERS enhancement. As a result, reproducible, uniform SERS substrates are highly desired. In this study, many limitations on the fabrication of traditional SERS substrates were overcome by employing an inexpensive, fast, and fine-tunable oblique angle deposition (OAD) technique at two temperatures, 100 K and 300 K. SEM images showed that AgNRs fabricated at 100 K had a greater surface area (2.6??10-12 m2/??m2) than AgNRs produced at 300 K (1.7??10-12 m2/??m2). Therefore, it was hypothesized that the SERS-based sensing capabilities of 100 K fabricated AgNRs would be significantly improved over those of AgNRs produced at 300 K. To validate the proposed hypothesis, AgNRs were emerged for 24 hours in aqueous solutions of rhodamine 6G (R6G, 2 mL of 10-6 M, 10-7 M, and 10-8 M) and micro-Raman maps were collected following ambient drying. All 100 K AgNR substrates exhibited larger, SERS-active areas with significant SERS signal enhancement than the 300 K AgNR substrates (1.5-fold and 3.7-fold signal enhancement at 10-6 M and10-7 M of R6G, respectively). R6G at 10-8 M was detected for both AgNR substrates, but poor signal to noise ratios made the quantification of the SERS enhancement difficult. The R6G (10-6 M) signal obtained on 100 K AgNRs was approximately 10- fold greater than the signal collected from a Creighton colloid (15.3 ppm Ag) at the same R6G concentration. SEM images of 100 K AgNRs obtained post R6G incubation showed greater polydispersity in size and shape than AgNRs fabricated at 300 K. This observation in combination with the larger areas available for analyte binding demonstrated the improved SERS-sensing capabilities of the 100 K AgNRs and confirmed the proposed hypothesis.