Zirconium-Based Metal-Organic Framework and Ti₃C₂T_xNanosheet-Based Faraday Cage-Type Electrochemical Aptasensor for Escherichia coli Detection

A Faraday-cage-type electrochemical aptasensor based on two-dimensional (2D) nanomaterials was developed for the sensitive detection of Escherichia coli O157:H7. In this electrochemical aptasensor, 2D titanium carbide (Ti₃C₂T_x) MXene was used for electrode modification. 2D Ti₃C₂T_xcould immobilize aptamers via chelation between titanium and phosphate groups and provide a large electroactive surface for signal transduction. Another 2D zirconium ferrocene-based metal-organic framework (Zr-Fc MOF) combined with gold nanoparticles (AuNPs) and 4-mercaptophenylboronic acid (4-MPBA) (Zr-Fc MOF/AuNPs/4-MPBA) was used as an electrochemical signal label, in which Fc was a signal molecule and AuNPs could improve the electroactivity and combine with 4-MPBA via Au-S bonds. 4-MPBA could bind with E. coli O157:H7 via covalent bonding between boronic acid and the cis-diol of lipopolysaccharides on bacteria cell walls. So, the signal labels could immobilize on the electrode to form a Faraday-cage-type structure owing to the large surface area of Zr-Fc MOF. In this structure, electrons flowed directly between the electrode and ferrocene, and the electrochemical signal could be amplified. When the application of 2D nanomaterials and the Faraday-cage strategy were combined, E. coli O157:H7 was sensitively detected with a detection limit of 3 CFU·mL^-1. The aptasensor was applied for milk sample detection. This aptasensor has practical application potential because of its properties of satisfactory sensitivity, specificity, and stability.