Introduction

Incorporating SERS tags into clinical diagnostics holds the potential to increase the sensitivity of diagnostic techniques. Gold petal-like gap-enhanced Raman tags (pGERTs) exhibit an exceptionally high Raman signal. However, the complexity of pGERT functionalization with recognition molecules limits their application in immunoassays. In this study, we have developed a novel method for biofunctionalization of pGERTs with monoclonal antibodies specific to the SARS-CoV-2 spike protein, employing controlled assembly of polydopamine (PDA) on the nanoparticle surface.

Methods

CTAC-coated pGERTs, containing 4-nitrobenzenethiol (4-NBT), were synthesized and characterized. Prior to PDA layer deposition, pGERTs were pre-functionalized with various polymers. Conjugation of PDA-coated pGERTs with monoclonal antibodies specific for S-protein was conducted, and the success of conjugation was confirmed via a dot-immunoassay.

Results

It was demonstrated that replacing CTAC with polystyrene sulfonate on the surface of 60 nm pGERTs allows for controlled PDA growth, resulting in a 3-4 nm-thick PDA layer. Spectrophotometry revealed a broadening of the absorption spectrum and a 4 nm red-shift in the absorption peak of PDA-coated pGERTs. The SERS spectrum of these particles exhibited all characteristic bands of 4-NBT. A dot-immunoassay confirmed the selective staining of the S-protein at varying concentrations (1, 10, 50 μg/mL) by the resulting conjugates.

Conclusions

We have developed a method for the biofunctionalization of pGERTs with monoclonal antibodies specific to the S-protein. The obtained results offer potential applications in the development of SERS-based immunoassay systems.

Acknowledgements

This research was supported by the Russian Science Foundation, grant number № 23-24-00246 (https://rscf.ru/project/23-24-00246/).