Improved lateral flow strip based on hydrophilic - hydrophobic SERS substrate for ultra-sensitive and quantitative immunoassay

As a convenience and robust point-of-care diagnostics technique for biomarkers, surface-enhanced Raman scattering (SERS)-based lateral flow immunoassay (LFIA) has attracted attentive attentions. In traditional paper-based LFIA, its hydrophilic surface with the so-called coffee-ring effect will inhibit the sensitivity and quantitative ability, which made the results less satisfying. Here, an attractive hydrophilic-hydrophobic polymer strip with Raman internal standard (IS) was developed by magnetron sputtering hydrophilic Ag nanoparticles (NPs) onto the specific area of the hydrophobic polydimethylsiloxane (PDMS). The target analytes can be enriched on the test and control lines formed by the hydrophilic Ag regions, which significantly improved the adaptability of SERS-based LFIA strip in the ultra-sensitive and quantitative monitoring of trace Ferritin (FER). Typically, assisted by raspberry-like Au NPs as immunoprobes, such hydrophilic-hydrophobic LFIA strip could achieve a limit of detection for FER as low as 0.41 pg/mL. Moreover, calibrated linear relationship with R-2 values of 0.992 in the analysis was successfully demonstrated by rationally using the Raman signals of PDMS as a reference. Such an improved LFIA platform may give another promising technique for the trustworthy monitoring and treatment of cancer.