SERS Assay for Copper(II) Ions Based on Dual Hot-Spot Model Coupling with MarR Protein: New Cu2+-Specific Biorecognition Element

We have developed a rapid and ultrasensitive surface-enhanced Raman scattering (SERS) assay for Cu2+ detection using the multiple antibiotic resistance regulator (MarR) as specific bridging molecules in a SERS hot-spot model. In the assay, Cu2+ induces formation of MarR tetramers, which provide Au nanoparticle (NP)–AuNP bridges, resulting in the formation of SERS hot spots. 4-Mercaptobenzoic acid (4-MBA) was used as a Raman reporter. The addition of Cu2+ increased the Raman intensity of 4-MBA. Use of a dual hot-spot signal-amplification strategy based on AuNP–AgNP heterodimers combined through antigen–antibody reactions increased the sensitivity of the sensing platform by 50-fold. The proposed method gave a linear response for Cu2+ detection in the range of 0.5–1000 nM, with a detection limit of 0.18 nM, which is 5 orders of magnitude lower than the U.S. Environmental Protection Agency limit for Cu2+ in drinking water (20 μM). In addition, all analyses can be completed in less than 15 min. The high sensit...