Gold nanoparticles-decorated M13 phage SPR probe for dual detection of antigen biomarkers in serum

Label-free SPR is rarely used for biomarker detection in real samples due to its low sensitivity. Herein, we report a phage-based SPR (P-SPR) strategy for the detection of carcinoembryonic antigen (CEA) in undiluted serums. M13 phage is genetically engineered to display an anti-CEA single-chain variable region fragment on pIII protein for antigen targeting and to display the gold binding peptide (GBP) at the pVIII protein for gold nanoparticles (GNPs) binding to form the GNPs decorated M13 phage probe that can amplify the plasmon resonance signal. The proposed P-SPR method demonstrated ultrasensitive detection of CEA within 10 min. Under ideal conditions, P-SPR showed exceptional sensitivity with a limit of detection (LOD) of 0.83 fM, which is approximately 2000 times that of the conventional SPR and four orders of magnitude more sensitive than enzyme-linked immunosorbent assay. In particular, the proposed strategy can cross-validate the SPR results through naked-eye counting of the plaques generated by the P-SPR probes, enabling a reliable dual detection system. In addition, P-SPR scheme has excellent sensing performance for the detection of real samples at concentrations lower than LOD of ELISA. Therefore, the proposed P-SPR strategy holds potential for early detection of tumour biomarkers in liquid biopsy.