Electroactive and SERS-Active Ag@Cu₂O NP-Programed Aptasensor for Dual-Mode Detection of Tetrodotoxin

Dual-mode nanotags with noninterference sensing signals improved the detection accuracy and sensitivity for the applications of tetrodotoxin (TTX) monitoring. Electroactive and surface-enhanced Raman scattering (SERS)-active Ag@Cu₂O nanoparticles (NPs) were fabricated and displayed two electrooxidation signals at -0.13 and 0.17 V, attributed to the oxidization process of Cu⁺ and Ag⁰, respectively. Ag@Cu₂O NPs were also found to exhibit stronger SERS performances than individual Ag NPs. The dielectric Cu₂O shell with a large dielectric constant inhibited the attenuation of electromagnetic (EM) waves of Ag NPs, which strengthened the EM fields for SERS enhancement. The electron transfer from Ag to Cu₂O to 4-aminothiophenol (4-ATP) also contributed to the SERS performances. Ag@Cu₂O NPs were modified by TTX aptamers and assembled with MXene nanosheets (NSs) due to the large surface, good conductivity, and inherent Raman properties. The assemblies showed two-peaked electrooxidation signals and prominent SERS activity. An electrochemical detection curve was established by using the total peak intensity at -0.13 and 0.17 V as detection signals, and a ratiometric SERS detection curve was developed by applying the intensity at 1078 cm^-1 (4-ATP) as the detection signal and 730 cm^-1 (MXene NSs) as the reference signal. An electrochemical and SERS signal-programed dual-mode aptasensor was proposed for accurate TTX detection, with the limits of detection of 31.6 pg/mL for the electrochemical signal and 38.3 pg/mL for the SERS signal. The rational design of plasmonic metal-semiconductor heterogeneous nanocomposites had important prospects in establishing a multimodal biosensing platform for the quantitative and accurate detection of analytes in complex systems.