A New Approach to Solution‐Phase Gold Seeding for SERS Substrates

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Abstract
Surface‐enhanced Raman scattering (SERS) vastly improves signal‐to‐noise ratios as compared to traditional Raman scattering, making sensitive assays based upon Raman scattering a reality. However, preparation of highly stable SERS‐active gold substrates requires complicated and expensive methodologies and instrumentation. Here, a general and completely solution‐phase, seed‐based approach is introduced, which is capable of producing gold films for SERS applications on a variety of substrates, not requiring surface modification or functionalization. SERS enhancement factors of ≈107 were observed. Moreover, solution‐phase gold film deposition on highly complex surfaces, such as protein‐coated bioassays, is demonstrated for the first time. Protein bioassays coated with such SERS‐active gold films are combined with bioconjugated single‐walled carbon nanotube Raman labels, affording highly sensitive detection of the cancer biomarker, carcinoembryonic antigen in serum, with a limit of detection of ≈5 fM (1 pg mL−1).