Rapid electrochemically-driven assembly of two-dimensional metal-organic framework nanozymes on Cu foil for boosting sensitive SERS detection of ochratoxin A

Nanozymes, as catalytic nanomaterials mimicking natural enzymes, have emerged as powerful tools for analytical sensing. However, conventional methods for nanozyme synthesis and immobilization often suffer from time-consuming processes and inefficient substrate integration. Herein, we develop an innovative electrochemical strategy that achieves simultaneous synthesis and immobilization of sponge-like two-dimensional tetrakis(4-carboxyphenyl)porphyrin-Fe (Cu-TCPP(Fe)) nanozymes (termed as STCTFzymes) on Cu foils within only 6 min. Kinetic analysis confirms that the electrochemical growth follows a diffusion-controlled instantaneous nucleation mechanism. The resulting STCTFzymes exhibit enhanced operational stability enabled by firm substrate anchoring and facile recyclability through physical retrieval of the copper support. Leaching tests and post-recycling structural analysis further validate the excellent structural integrity and anti-leaching capability of STCTFzymes. Given the excellent peroxidase-like (POD) activity of STCTFzymes, a surface-enhanced Raman scattering (SERS) method based on aptamer-specific recognition was developed using ochratoxin A (OTA) as a model analyte. The OTA aptamer was adsorbed on the surface of STCTFzymes to block the catalytic site and turn off the POD-like activity. Upon specific binding of OTA to the aptamer, the enzyme activity of STCTFzymes was reactivated, resulting in a favorable change in SERS signal. The established method showed a wide linear range (0.3–500 ng/mL) and low detection limit (0.091 ng/mL) for OTA, with superior selectivity, high sensitivity and satisfactory stability. This electrochemically-assisted self-assembly provides a new approach for developing robust nanozymes architectures on heterogeneous substrates. When synergistically integrated with aptamer-based recognition, the STCTFzymes presents a universal strategy for sensitive detection of biotoxins exhibiting inherently weak Raman response.