Label-free fluorescent catalytic biosensor for highly sensitive and selective detection of the ferrous ion in water samples using a layered molybdenum disulfide nanozyme coupled with an advanced chemometric model

Abstract

In this work, we developed a novel layered molybdenum disulfide (MoS₂) nanosheet peroxidase mimetic-based fluorescent catalytic biosensor for the sensitive and selective detection of Fe²⁺. It was found that Fe²⁺ remarkably enhanced the catalytic activity of the MoS₂ nanosheet for oxidation of OPD to form a highly fluorescent substance, 2,3-diaminophenazine (DAPN), and the MoS₂/OPD/H₂O₂ biosensor displayed substantial fluorescence enhancement after addition of Fe²⁺ in a concentration-dependent manner. The fluorescence intensity was proportional to the concentration of Fe²⁺ over a range of 0.005–0.20 μM with a limit of detection of 3.5 nM (signal/noise = 3). When compared with the OPD/H₂O₂ biosensor, the MoS₂/OPD/H₂O₂ biosensor provided a higher sensitivity and selectivity for Fe²⁺, suggesting the validity of the use of the MoS₂ nanosheets. To further demonstrate the feasibility of the MoS₂/OPD/H₂O₂ biosensor for Fe²⁺ detection in real water samples, we measured the three-dimensional excitation–emission spectra of the real system, and submitted the excitation–emission matrix (EEM) data to an advanced chemometrics model based on parallel factor analysis (PARAFAC). The results showed that the use of the PARAFAC model could further enhance the selectivity of the biosensor and determine Fe²⁺ concentration in the presence of unexpected interferents from real water samples. This work opens up new opportunities for the use of the catalytic properties of the MoS₂ nanosheets and advanced chemometrics models in the field of biosensors.