Molybdenum disulfide for ultra-low detection of free radicals: electrochemical response and molecular modeling

Two-dimensional (2D) molybdenum disulfide (MoS₂) offers attractive properties due to its band gap modulation and has led to significant research-oriented applications (i.e. DNA and protein detection, cell imaging (fluorescent label) etc.). In biology, detection of free radicals (i.e. reactive oxygen species and reactive nitrogen (NO^*) species are very important for early discovery and treatment of diseases. Herein, for the first time, we demonstrate the ultra-low (pico-molar) detection of pharmaceutically relevant free radicals using MoS₂ for electrochemical sensing. We present pico- to nano- molar level sensitivity in smaller MoS₂ with S-deficiency as revealed by x-ray photoelectron spectroscopy. Furthermore, the detection mechanism and size-dependent sensitivity have been investigated by density functional theory (DFT) showing the change in electronic density of states of Mo atoms at edges which lead to the preferred adsorption of H₂O₂ on Mo edges. The DFT analysis signifies the role of size and S-deficiency in the higher catalytic activity of smaller MoS₂ particles and, thus, ultra-low detection.