Polydopamine stabilizes silver nanoparticles as a SERS substrate for efficient detection of myocardial infarction

Rapid and accurate detection of myocardial infarction (MI) can boost the patient's chance of survival. Surface enhanced Raman scattering (SERS) is an outstanding diagnostic technique because of its strong light stability, high resolution, and qualitative and quantitative analysis based on the characteristic fingerprint. However, its reliability, stability and specificity remain to be improved, especially in the quantitative analysis of serum samples. In this study, we developed in situ silver nanoparticles (Ag NPs) on the surface of polydopamine (PDA) as a SERS substrate and found that PDA could act as a reducing agent to support the nucleation and growth of Ag NPs and control the distance and aggregation of Ag NPs to stabilize the Raman signal. In a standard phosphate buffered saline (PBS) environment, PDA@Ag could reach a low detection limit of 0.01 ng mL^-1 cardiac troponin I (cTn I) with a good linear relationship. At the same time, the PDA@Ag substrate also possessed excellent stability, specificity and biocompatibility for cTn I detection. In addition, we verified the application potentiality of PDA@Ag in real serum samples and found that the performance of SERS was almost the same as that in PBS. This excellent detection performance of PDA@Ag could be attributed to both the enhanced electromagnetic field and the increased Raman cross-section, dominated by the gap distance between Ag NPs, reaction force between the antigen and the antibody and excellent biocompatibility and reducibility of PDA. In conclusion, this work may provide a new perspective for the in situ synthesis and growth of a uniform SERS substrate on the carrier to achieve the stability and specificity of SERS-based biological detection of MI.