LipoGold Tags: Hybrid Lipid-AuNP Clusters as Highly Efficient SERS substrates for Biomedical Applications

Although Surface Enhanced Raman Scattering (SERS) is widely applied for ultrasensitive in-vitro and in-vivo diagnostics and imaging, the preparation of SERS tags – i.e. metallic nanoparticles (NPs) or NP clusters functionalized with Raman-active molecules (RRs)- typically involves very complex synthetic approaches, often leading to low colloidal stability and poor reproducibility. To overcome these hurdles and promote the widespread use of SERS, novel approaches for the synthesis of efficient and reproducible SERS probes are still needed. Here, we introduce "LipoGold Tags", an innovative and extremely simple platform where gold nanoparticles (AuNPs) clusters are formed by exploiting the self-assembly of AuNPs on the lipid membrane of synthetic vesicles. We show that citrate-stabilized AuNPs spontaneously associate with the membrane of synthetic vesicles forming controlled clusters. Raman-active molecules embedded in the lipid bilayer experience a high enhancement of the electromagnetic field due to the AuNP plasmon coupling, increasing their Raman signals of several orders of magnitude. We optimize SERS enhancement by systematic exploration of RRs and lipid vesicle concentrations and provide a robust structural characterization through techniques like Cryogenic Electron Microscopy (Cryo-EM) and Dynamic Light Scattering (DLS). We further explore the versatility of this approach by functionalizing LipoGold tags with specific targeting antibodies. Validation through Fluorescence Correlation Spectroscopy (FCS) and a tailored sandwich assay confirm efficacy in cell cultures, demonstrating signal and specificity maintenance. Overall, the presented synthetic approach demonstrated major advantages over more traditional methods and may represent a breakthrough in the production of SERS probes with high efficiency and versatility.