Highly sensitive nanobody-immunosensor for macrophage-capping protein

Overexpression of macrophage-capping protein or gelsolin-like actin-capping protein (CapG) is associated with incidents of cancer, predominantly breast cancer and ovarian cancer, and it is also considered a novel biomarker for gastric cancer. Herein, a novel LiSmZrO₃ perovskite-tagged nanobody (Nb)-type sandwich immunosensor was developed for the sensitive and selective detection of CapG. The anti-CapG nanobody used for the immunosensor development was a single antigen-binding domain camelid heavy chain-only antibody (HcAb). A biotinylated capture Nb (Nb₁) was reacted with streptavidin-thiol (strep)-modified gold screen-printed electrodes (AuSPE). The signalling nanobody (Nb₂) was tagged with a cysteine-capped LiSmZrO₃ perovskite nanomaterial as an electrochemical redox tracer. The amperometric responses of the CapG Nb-type immunosensor (AuSPE||strep|Nb₁|BSA|CapG|cysteine-capped LiSmZrO₃-Nb₂+BSA) gave a linear calibration range of 0-1200 pg/mL CapG and a limit of detection (LOD) of 326.4 pg/mL CapG in Dulbecco phosphate-buffered saline. A LOD value of 1400 pg/mL CapG was obtained using human serum as a real sample. The CapG Nb-type amperometric immunosensor exhibited high selectivity and stability. The immunosensor would be suitable for application as a cancer screening tool based on detecting elevated levels of CapG.