Post-synthesis surface modification of Cu/Zr metal azolate framework: A pathway to highly sensitive electrochemical...

Atrazine (ATZ), a pesticide that poses serious health problems, is observed in the environment, thereby prompting its periodic monitoring and control using functional biosensors. However, established methods for ATZ detection have limited applicability. Two-dimensional (2D) metal azolate frameworks (MAF) have a higher surface area per unit volume and provide easier access to active sites. The shorter diffusion path for guest molecules increases the diffusion rates, which is suitable for electrochemical detection. The sensing performance of electrochemical biosensors can be improved by modifying MAFs, resulting in their high affinity for highly sensitive and selective detection of ATZ in the environment.

Cu/Zr-based MAF synthesized via a simple sonochemical method and surface-engineered ozonation are demonstrated for the electrochemical sensing of ATZ. The combination of ultrasonication and ultraviolet/ozone surface functionalization significantly enhance the properties of a two-dimensional MAF, including a reduction in resistance, an increase in specific surface area, and the creation of numerous active sites. The developed electrochemical biosensors exhibit a high sensitivity (8.8 μA μM^-1 cm^-2), low detection limit of 0.236 zM, and wide linear range of 1 zM to 1 M towards ATZ. Furthermore, excellent selectivity in the presence of diverse interferents and a long shelf life in ambient air for 60 d are achieved. The practical feasibility of the biosensor consisting of surface-engineered Cu/Zr-MAF is demonstrated by detecting the ATZ in agricultural wastewater and river water.

Cu and Zr transition metals with multiple valence states in MAF facilitate the reduction of ATZ through coordination bonding, while the increased oxygenating active sites in 2D structure collectively accelerates the charge transfer. This synergy between the structural design and surface engineering ultimately improves the biosensor's sensitivity and efficiency for the detection of ATZ. This work can provide a new perspective on practical biosensor applications for the electrochemical detection of pesticides at extremely low concentrations.