Highly selective and quantitative in situ monitoring of cell surface proteins by SERS immunoassay system

Due to their pivotal roles in many biological functions, cell surface proteins (CSPs) are often used for cancer prognosis, as evidenced by a number of studies that have reported significant changes in the expression levels of specific surface proteins depending on the stage of tumorigenesis and selection/variety of reprogrammed cells during cell fate conversion. Current CSP detection strategies suffer from poor selectivity and lack the ability for in situ analysis but maintain the spatial information between cells. Here, we have fabricated nanoprobes for surface-enhanced Raman scattering (SERS) immunoassays by conjugating a specific antibody onto silica-coated gold nanoparticles incorporating an individual Raman reporter (Au-tag@SiO2-Ab NPs) for highly sensitive and se-lective in situ detection in different types of cells. When multiple HEK293 cell lines stably expressing different levels of the CSP, ACE2, were investigated by the SERS immunoassay, we demonstrated that the level of ACE2 expression in each cell line could be statistically distinguished from that in the other cell lines, indicating the quantitative feature of this biosensing system. When detecting living cells without cell lysis or fixation, as well as fixed cells, the levels of the epithelial CSPs, EpCAM (epithelial cell adhesion molecule) and E-cadherin, were successfully determined using our Au-tag@SiO2-Ab NPs and SERS immunoassay system in a highly selective and quantitative manner without significant cytotoxicity. Hence, our work provides technical insight into the development of a biosensing platform for a variety of biomedical applications, such as cancer metastasis prog-nosis and the in situ monitoring of stem cell reprogramming and differentiation.

Automated summary

Cell surface proteins (CSPs) play important roles in biological functions and are used for cancer prognosis. Current detection strategies lack selectivity and in situ analysis capability. In this study, we developed nanoprobes for surface-enhanced Raman scattering (SERS) immunoassays to achieve highly sensitive and selective in situ detection of CSPs in different types of cells. Our biosensing system demonstrated quantitative features and showed high selectivity and low cytotoxicity, making it suitable for various biomedical applications.