Rational fabrication of a ratiometric electrochemical aptasensor based on 3D AuNPs/MXene/rGO composite for ultrasensitive homocysteine biosensing

Homocysteine (Hcy) is a key biomarker for various diseases, and its precise detection is essential for early clinical diagnosis. Herein, an innovative ratiometric electrochemical aptasensor was constructed to overcome the limitations in sensitivity, selectivity, and stability in conventional Hcy detection methods. Firstly, we synthesized a novel 3D MXene/rGO aerogel loaded AuNPs composite (Au/MGA-40) with outstanding specific surface area and remarkable electrical conductivity. Next, the Hcy aptamer was self-assembled to the Au/MGA-40/MB modified electrode surface by gold sulfur bonds (Au-S). Finally, a ratiometric detection mode was established based on the linear relationship between the oxidation peak current ratios (I Hcy /I MB ) and the Hcy concentrations. The aptasensor exhibited excellent analytical behavior for Hcy, with a ultrawide detection range from 2.14   nM to 200   μM and a detection limit as low as 0.835   nM. It also displayed remarkable selectivity due to the specific recognition between Hcy and the aptamer, enabling discrimination of Hcy from structurally similar molecules such as cysteine (Cys), glutathione (GSH) and methionine (Met). The ratio signal mode demonstrated superior long-term stability performance compared to conventional single signal sensors. As evidenced by the successful detection of Hcy in human serum, which underscores its potential for early screening of Hcy-related diseases.