pH-sensitive response of a highly photoluminescent MoS2 nanohybrid material and its application in the nonenzymatic detection of H2O2

The mechanism behind the variation in the photoluminescence (PL) of a MoS2 nanohybrid material with pH was investigated. Highly fluorescent MoS2 quantum dots dispersed across MoS2 nanosheets (MoS2 QDNS) were synthesized by a hydrothermal route in the presence of NaOH. Upon reducing the pH from 13 to 6.5, the PL intensity was markedly quenched. The removal of dangling sulfur atoms by adding mineral acids could be a plausible mechanism for this PL quenching, together with the inner filter effect and Forster resonance energy transfer due to the resulting species. A label-free turn-on fluorescence sensor for H2O2 was developed using this hybrid material. The PL of the acidified MoS2 QDNS at pH 6.5 increased (i.e., recovered) linearly with the concentration of H2O2. The dynamic range of the sensor was found to be 2-94 mu M with a limit of detection (LOD) of 2 mu M. This sensing strategy was also extended for the detection of glucose by appending glucose oxidase (GOx) as a catalyst. In the presence of GOx, glucose oxidizes to gluconic acid and H2O2, so the original level of glucose can be estimated by determining the H2O2 present. The absence of a complicated enzyme immobilization step is the prime advantage of the present glucose sensor. The current work exemplifies the utility of MoS2-based nanoparticle systems in the biological sensor domain.