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

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 mu M 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.