Ag nanoparticle in situ decorated on Ti₃C₂T_x with excellent SERS and EIS immunoassay performance for beta-human...

Two-dimensional transition metal carbides, nitrides, and carbonitrides (MXene), with excellent optical and electrical properties, are promising substrates for surface-enhanced Raman scattering (SERS) and electrochemical sensors. Therefore, a unique 3D-decorated structure containing silver (Ag) nanoparticles and Ti₃C₂T_x was designed as the substrates of SERS and electrochemical impedance spectroscopy (EIS) immunosensors. The Ag/Ti₃C₂T_x composite significantly increases Raman intensity, which is attributed to the synergistic effect of Ti₃C₂T_x and Ag nanoparticles. Based on the SERS performance of the Ag/Ti₃C₂T_x composite, the magnetic properties of Fe₃O₄ and the specificity of antigen-antibody, a sandwich-structured SERS immunosensor is constructed, which can effectively detect trace amounts of beta-human chorionic gonadotropin (β-hCG). The SERS immunosensor exhibits a wide linear range of 5.0 × 10^-6-1.0 mIU mL^-1, and a low detection limit of 9.0 × 10^-7 mIU mL^-1. Meanwhile, the Ag/Ti₃C₂T_x-based EIS immunosensor is constructed for the portable detection of β-hCG, which exhibits a wide linear range of 5.0 × 10^-2-1.0 × 10² mIU mL^-1, a low detection limit of 9.5 × 10^-3 mIU mL^-1. Moreover, two immunosensors can be used to detect actual serum samples with satisfactory recovery (98.5-102.2%). This work could guide the design of low-cost, sensitive, flexible, and portable biosensors. The SERS and EIS substrates composited with Ti₃C₂T_x and Ag nanoparticles enable excellent performance for detecting β-hCG.