Nanozyme-mediated cascade reaction system for ratiometric fluorescence detection of sarcosine

This work proposed a nanozyme-mediated cascade reaction system for ratiometric fluorescence detection of sarcosine. H2O2-sensitive MnO2 nanosheets (MnO2 NSs) were synthesized and employed as quenchers of blue fluorescent carbon dots (BCDs), the reference fluorophores in the system. With oxidase-like activity, MnO2 NSs enable the oxidation of non-fluorescence o-phenylenediamine (OPD) to 2, 3-diaminophenazine (DAP), producing another fluorescence signal at 562 nm. As mediators, MnO2 NSs will be decomposed in the presence of H2O2, leading to the fluorescence recovery of BCDs and a decrease of DAP. Thus, a H2O2 responsive dual-emission fluorescence sensing strategy is established. Sarcosine, a prostate cancer biomarker, could be catalyzed by sarcosine oxidase and H2O2 would be generated in the process. Under optimal conditions, it offered the capability to detect sarcosine as low as 0.36 mu M. The practicability was demonstrated by the detection of sarcosine in human urine samples with satisfactory recoveries of 94.9-98.6%. The proposed MnO2 NSs-mediated cascade reaction system has exhibited great potential in versatile sensing of H2O2-related biomarkers, suggesting immense significance for bioanalysis and clinical diagnosis.