Rapid Detection of Explicit Volatile Organic Compounds for Early Diagnosis of Lung Cancer Using MoSi₂N₄ Monolayer

In this study, we investigate the adsorption and sensing capabilities of pristine (MoSi₂N₄) and nitrogen-vacancy induced (MoSi₂N₄-V_N) monolayers towards five potential lung cancer volatile organic compounds (VOCs), such as 2,3,4-trimethylhexane (C₉H₂₀), 4-methyloctane (C₉H₂₀), o-toluidine (C₇H₉N), Aniline (C₆H₇N), and Ethylbenzene (C₈H₁₀). Spin-polarized density functional theory (DFT) calculations reveal that MoSi₂N₄ weakly adsorb the mentioned VOCs, whereas the introduction of nitrogen vacancies significantly enhances the adsorption energies ( $E_{ads}$ ), both in gas phase and aqueous medium. The MoSi₂N₄-V_N monolayers exhibit a reduced bandgap and facilitate charge transfer upon VOCs adsorption, resulting in enhanced $E_{ads}$ values of -0.83, -0.76, -0.49, -0.61, and -0.50 eV for 2,3,4-trimethylhexane, 4-methyloctane, o-toluidine, Aniline, and Ethylbenzene, respectively. Bader charge analysis and spin-polarized density of states (SPDOS) elucidate the charge redistribution and hybridization between MoSi₂N₄-V_N and the adsorbed VOCs. The work function of MoSi₂N₄-V_N is significantly reduced upon VOCs adsorption due to induced dipole moments, enabling smooth charge transfer and selective VOCs sensing. Notably, MoSi₂N₄-V_N monolayers exhibit sensor responses ranging from 16.2 % to 26.6 % towards the VOCs, with discernible selectivity. Importantly, the recovery times of the VOCs desorption is minimal, reinforcing the suitability of MoSi₂N₄-V_N as a rapid, and reusable biosensor platform for efficient detection of lung cancer biomarkers. Thermodynamic analysis based on Langmuir adsorption model shows improved adsorption and detection capabilities MoSi₂N₄-V_N under diverse operating conditions of temperatures and pressures.