A novel ratiometric electrochemical aptasensor based on graphene quantum dots/Cu-MOF nanocomposite for the on-site...

The sensitive detection of Staphylococcus aureus (S. aureus) holds great practical importance for ensuring public health and food safety. In this study, a sensitivity and stability ratiometric electrochemical aptasensor using graphene quantum dots/[Cu_2.5 (benzotriazole-5-COO)_1.5 (benzotriazole-5-COOH)_0.5 (μ-Cl)_0.5 (μ₃-OH)-(H₂O)]·3 H₂O nanocomposite (GQDs/Cu-MOF) was constructed for S. aureus detection. The GQDs enhanced the sensitivity of the electrochemical aptasensor due to their excellent conductivity and provided stability through their abundant carboxyl groups. The Cu-MOF, possessing electrical activity, not only enhanced the performance of the electrochemical aptasensor but also served as a signal label. The single-stranded DNA1 (S1) was immobilized on the surface of a GQDs/Cu-MOF/screen-printed carbon electrode (S1/GQDs/Cu-MOF/SPCE) as the sensing interface. Subsequently, the S1/GQDs/Cu-MOF/SPCE was hybridized with the probe DNA-ferrocene (S2-Fc), resulting in the generation of electrochemical signals from Cu-MOF (I_Cu-MOF) and S2-ferrocene (I_S2-FC) within the system. However, the electron transfer performance of DNA at the sensing interface was compromised, leading to a reduction in the I_Cu-MOF. When S. aureus was present in the system, S2-Fc reacted with it and detached from the sensing surface, resulting in a gradual decrease in I_S2-FC and an increase in I_Cu-MOF. Then a ratiometric electrochemical aptasensor was established for S. aureus detection with remarkable sensitivity (0.97 CFU·mL^-1), excellent stability, and a broad linear range. Furthermore, the aptasensor was successfully applied to detect S. aureus in tap water, milk, Lonicera japonica, urine, and Zhangjiang River. Additionally, this aptasensor design can be adapted for the detection of other foodborne pathogens, which indicates that the design scheme of the aptasensor has good universality.