Self-Cascade MOF@MOF nanozyme for ultrasensitive and Low-Background detection of Multidrug-Resistant bacteria

The accurate, timely, and convenient detection of multidrug-resistant bacteria (MDRB) is of enormous value in clinical treatment and food safety. Traditional methods include plate culture and polymerase chain reaction, but these strategies are time-consuming, costly, or cumbersome to operate, making it difficult to meet the increasingly severe demands. Here, we describe the synthesis of a metal–organic framework (MOF) heterostructure hybrid (MOF@MOF) self-cascade nanozyme that promotes signal amplification for colorimetric MDRB aptasensing. The MOF@MOF was composed of copper-functionalized MOF-808 with catechol oxidase-mimicking activity and an iron porphyrin MOF with peroxidase-mimicking activity; MOF-808 with open copper sites hydrolyzed the substrate 3,5-ditert-butylcatechol, producing H 2 O 2 in situ , and the iron porphyrin MOF catalyzed H 2 O 2 to further oxidize 3,3′,5,5′-tetramethylbenzidine into a colored product. Benefitting from the nanoproximity effect and confinement effect, the biocatalytic ability of the biomimetic cascade was significantly facilitated, generating a strengthened colorimetric signal. Taking methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa (PA) as examples, the MOF@MOF nanozyme coordinated with aptamers to construct a colorimetric aptasensing platform for ultrasensitive detection of MDRB. Compared to frequently used probes containing H 2 O 2 , the inactive substrate did not oxidize TMB to induce a color change, resulting in low background signal. The limit of detection was 5 CFU/mL for MRSA and 2 CFU/mL for PA, with a wide linear range for both (10–10 8 CFU/mL). The proposed aptasensing platform was used to analyze MDRB in biological samples, indicating excellent practicability. The self-cascade MOF@MOF may offer valuable insights into the rational construction of biomimetic sensors based on nanozymes.