MOF-on-MOF tandem nanozymes with autonomous substrate transformation for photoelectrochemical and paper-based colorimetric dual-mode aptasensing of neomycin

The integration of nanotechnology with biocatalysis has advanced robust biosensors through self-cascade systems. Herein, a MOF-on-MOF tandem nanozyme (MOF-818/Cu-TCPP) engineered for autonomous substrate transformation is constructed for the photoelectrochemical (PEC) and paper-based colorimetric dual-mode aptasensor for neomycin (NEO). A polyvinyl pyrrolidone (PVP)-assisted method was employed to synthesize the core heterostructured MOF-818/Cu-TCPP tandem nanozyme, which exhibits integrated catechol oxidase and peroxidase-like activities. MOF-818 oxidizes 3,5-di- tert -butylcatechol (3,5-DTBC) to in-situ generate H 2 O 2 , which is used by Cu-TCPP to produce •OH radicals, oxidizing 4-choro-1-naphthol (4-CN) or 3,3’,5,5’-tetramethylbenzidine (TMB) to establish a “signal-off” state. For detection, a smart glutathione (GSH)-loaded ZIF-90/signal DNA (SA) probe is employed. Target NEO binding triggers probe attachment, and subsequent acidification releases GSH, which scavenges •OH, inhibiting precipitation/color development and switching the sensor to a “signal-on” state. The unique MOF-on-MOF structure ensures proximity between catalytic centers, enhancing cascade kinetics. The dual-mode sensor achieved detection limits of 0.023 pM (PEC) and 0.36 pM (colorimetric), with high specificity. This work provides a sensitive platform for antibiotic monitoring and a versatile strategy for designing self-sufficient nanozyme cascades based on hierarchical MOF architectures.