Dual Molecularly Imprinted Polymer-Based Plasmonic Immunosandwich Assay for the Specific and Sensitive Detection of Protein Biomarkers

Molecularly imprinted polymers (MIPs), which are synthesized in the presence of a template, have been widely used as antibody mimics for important applications. Through the combination with a highly sensitive detection scheme such as chemiluminescence and surface-enhanced Raman scattering (SERS), MIP-based sandwich assays have emerged as promising analytical tools for the detection of disease biomarkers. However, so far, MIPs have been used only as target-capturing probes, whereas labeling by other means was needed, which limits the application range. Herein, we present a new approach, called a dual MIP-based plasmonic immunosandwich assay (duMIP-PISA), for the specific and sensitive detection of protein biomarkers in complex biological samples. A C-terminal epitope-imprinted self-assembled gold nanoparticle monolayer-coated glass slide was prepared as a plasmonic substrate for the specific extraction of target protein, while N-terminal epitope-imprinted Raman-responsive Ag@SiO₂ nanoparticles were prepared as nanotags for the specific labeling of captured protein. The formed MIP–protein–MIP sandwich-like complexes could produce a significantly enhanced SERS signal. The dual MIP-based recognitions ensured high specificity of the assay, while SERS detection provided ultrahigh sensitivity. The duMIP-PISA of neuron-specific enolase (NSE) in human serums was demonstrated, which permitted the differentiation of small cell lung cancer patients from healthy individuals. As compared to regular ELISA, the duMIP-PISA exhibited multiple merits including a simpler procedure, faster speed, lower sample volume requirement, and wider linear range. The approach well demonstrated the great potentials of MIPs and can be easily modified and extended to other protein biomarkers. Therefore, the duMIP-PISA approach holds great promise in many important applications such as disease diagnosis.