Anti-fouling SERS-based immunosensor for point-of-care detection of the B7–H6 tumor biomarker in cervical cancer patient serum

Herein, we report the development of sandwich type Surface Enhanced Raman Spectroscopy (SERS) immunosensor modified to be zwitterionic for the detection of soluble B7–H6 biomarker in blood serum from cervical cancer patients. Anti-fouling capture SERS substrate of biosensor based on gold (Au) thin film was modified with a self-assembled monolayer of zwitterionic L-cysteine to combat serum fouling and was then conjugated with NKp30 receptor protein to capture the B7–H6 biomarker in blood serum. The SERS nanoprobe based on spiky gold nanoparticles (AuNPs) was functionalized with ATP reporter molecule, that is stable at a wide range of pH, making the SERS signal reliable in complex media. Then, it was conjugated with anti-B7-H6 antibody forming the complex anti-B7-H6@ATP@AuNPs (i.e., SERS nanoprobe). The proposed immunosensor demonstrated high reproducibility for the quantitative detection of soluble tumor biomarker B7–H6 within the range of 10⁻¹⁰ M to 10⁻¹⁴ M with limit of detection (LOD) of 10⁻¹⁴ M or 10.8 fg mL⁻¹, in the cancer patient serum, greatly exceeding (100 fold) the LOD of commercially available ELISA kits. Such low LOD is partially the result of zwitterionic modification which reduces the serum fouling by 55% compared to traditionally used BSA blocked capture substrates (i.e., control). Notably, this immunosensors demonstrated higher accuracy for detecting the B7–H6 biomarker in undiluted blood serum samples from cervical cancer patients and outperforms the currently available analytical techniques, making it reliable for point of care (POC) testing.