Real-Time, Highly Sensitive Detection of Alpha-Fetoprotein in Biological Fluids Using a QCM Sensor Based on a Cu₂O@MoS₂–Au nanocomposite and Gold Staining

Herein, a highly sensitive, sandwich-type quartz crystal microbalance (QCM) immunosensor is proposed for the quantitative monitoring of alpha-fetoprotein (AFP), a representative tumor marker for hepatocellular carcinoma. A cuprous oxide @ molybdenum disulfide (Cu₂O@MoS₂) nanohybrid was synthesized and combined with gold nanoparticles. The yield, a Cu₂O@MoS₂–Au nanocomposite, exhibited coral morphology with an increased surface area for loading more secondary antibodies (Ab₂), which amplified the mass loading on the QCM electrode’s surface. The immunosensor’s sensitivity was further enhanced by injecting the gold-staining solution for signal amplification. A self-assembled monolayer of primary antibody (Ab₁) was also fabricated on the QCM electrode’s surface via mercaptoacetic acid immobilization in EDC and NHS. The immunosensor’s limit of detection dropped to 35 pg/mL and 90 pg/mL with and without the gold enhancement, respectively. When used to detect AFP in human saliva and serum samples, the immunosensor displayed high selectivity and long-term stability, which indicates its potential for clinically monitoring of biomarkers.