Metal organic framework enabled “split-type” SERS immunoassay platform for highly sensitive and reproducible biosensing

Surface-enhanced Raman scattering (SERS) holds immense potential for ultrasensitive immunoassays, yet conventional gold nanoparticles (AuNPs) based probe and substrate “two-in-one” designs face critical limitations including low reporter loading capacity, restricted reporter selection, poor signal reproducibility and inefficient antibody conjugation. To overcome these challenges, we propose a metal organic framework (MOF) enabled “split-type” SERS immunosensor, where a MOF material ZIF-90 acts as probe carrier and a uniform silver coated filter paper (Ag@FP) composite serves as external SERS substrate. This MOF based strategy offers four distinct advantages: (i) The abundant porosity of ZIF-90 dramatically increases Raman reporter loading compared to gold nanoparticles (AuNPs) surfaces, enabling significant signal amplification. (ii) Encapsulation of reporters into ZIF frameworks is independent of specific functional groups, thereby highly active, non-thiolated Raman dyes can be used; (iii) The ethylenediaminetetraacetic acid (EDTA)-triggered release of reporters from ZIF-90, coupled with signal acquisition on a uniform external substrate, yields superior signal reproducibility. (iv) Linking antibody to ZIF-90 is achieved via Schiff-base chemistry between their inherent functional groups, eliminating the need for costly coupling reagents. For model biomarker RIgG, this “split-type” SERS immunosensor achieved a detection limit of 2 × 10 −11 g/mL, which is two orders of magnitude lower than that of conventional AuNP-based methods (3 ×10 −9 g/mL), while the relative standard deviation (RSD) was reduced by more than 50%. Excellent recovery and reproducibility in spiked and real serum samples further validate its feasibility in complex biological matrices. This versatile MOF-enabled “split-type” platform provides a compelling new paradigm for sensitive and reproducible SERS biosensing.