A cellulose paper decorated with gold(-silver) nanoparticles for SERS-based immunoassays

Surface-enhanced Raman scattering (SERS)-based immunoassays offer an unprecedented method for the early diagnosis of biomarkers. However, challenges in reliability often hinder their broader applications. This study introduces a novel approach employing in situ-prepared cellulose paper decorated with gold and gold-silver nanoparticles (Au(-Ag) CP) to construct a highly sensitive and stable paper-based SERS substrate. Building on this, we developed robust SERS immunosubstrates and immunoprobes, enabling a versatile immunoassay platform. This platform demonstrated exceptional performance in detecting disease markers. Using gold nanoparticles probe with Au CP, a limit of detection (LOD) of 29.71 fg/mL was achieved for the COVID-19 antigen, while the Au-Ag CP coupled with the Au-core Ag-shell (Au@Ag) probes achieved an LOD of 10.79 fg/mL for cardiac troponin I (cTnI). Both detection modes featured a broad dynamic range from 10^-13 to 10^-8 g/mL and sustained stability, retaining comparable LOD after 5 weeks of storage. The paper-based SERS immunoassay platform presented here holds promise for rapid, ultra-sensitive biomarker detection, offering a transformative tool for advancing diagnostic technologies.