Sensitive Detection of Specific Volatile Organic Compounds by Functionalized Transition Metal Dichalcogenide Monolayers

Abstract

Timely detection of liver cirrhosis (LC) is critical for effective clinical management and improved patient outcomes. Among emerging diagnostic approaches, detection of volatile organic compounds (VOCs), related to LC, offers a noninvasive, rapid, and cost-effective alternative to conventional methods. In this work, we employed spin-polarized density functional theory (DFT) to systematically investigate the interaction of LC-related VOCs using transition-metal dichalcogenides (TMDs), specifically WX₂ monolayers (X = S, Se₂). Five VOCs, namely, 2-pentanone, dimethyl sulfide (DMS), isoprene, limonene, and methanol, were selected based on their experimental association with LC. To enhance the sensitivity and selectivity of TMDs, Mn and Fe atoms were used to dope the chalcogen sites of WX₂, inducing strong dipole moments and improved van der Waals (vdW) interactions. The doped systems demonstrated significantly higher adsorption energies (E_ads, 1.5-2.1 eV), charge transfer (Δq = 0.4-0.8 e), and magnetization changes (ΔM ≠ 0) for VOCs compared to air molecules (E_ads < 0.5 eV, Δq < 0.1 e, ΔM = 0), confirming strong selectivity. Work function shifts Δϕ > 0.4 eV (for VOCs) and changes in the density of states near the Fermi level further support enhanced electronic response upon VOC adsorption. Our study offers atomic-scale insights into adsorption energetics, charge transfer, and electronic structure modulation that can guide future experimental efforts in nanobiosensor development. We also critically examine the scope and limitations of our theoretical framework, emphasizing the need for experimental validation to translate these findings into practical diagnostic technologies.

1

Relaxed atomic structures of pristine and TM-doped TMDs (WX₂, X = S, Se) with TM = Mn and Fe, (a)­WS₂, (b) WS₂:Mn, (c) WS₂:Fe, (d) WSe₂, (e) WSe₂:Mn, and (f) WSe₂:Fe. Both top and side views are shown. A computational sample of 5 × 5 primitive cells is used.

2

Spin-polarized band structure, PDOS and TDOS for pristine and TM-doped WS₂: (a) Pristine WS₂, (b) WS₂:Mn, and (c) WS₂:Fe. Fermi level is taken as energy reference (E _F = 0) and the energy range of [E _F −4, E _F +4] eV is shown. In the bands, the spin-up and spin-down states are shown in red and green lines, respectively.

3

Relaxed atomic structures after the adsorption of five VOCs related to liver cirrhosis biomarkers on two samples: (A) WS₂:Mn and (B) WS₂:Fe. Atomic species are colored as follows: W (gray), S (yellow), Mn (purple), Fe (big brown), C (small brown), H (green), and O (red).

3

Relaxed atomic structures after the adsorption of five VOCs related to liver cirrhosis biomarkers on two samples: (A) WS₂:Mn and (B) WS₂:Fe. Atomic species are colored as follows: W (gray), S (yellow), Mn (purple), Fe (big brown), C (small brown), H (green), and O (red).

4

Absolute values of adsorption energy, charge transfer, and change in magnetization due to the adsorption of nine molecules (5 VOCs and 4 air molecules) on (a) WS₂:Mn, (b) WS₂:Fe, (c) WSe₂:Mn, and (d) WSe₂:Fe.

5

Ratio of contribution of vdW interaction energy to the total adsorption energy of five VOCs on four samples (WX₂:TM, X = S, Se and TM = Mn, Fe).

6

Band structures, PDOS, and TDOS of five VOCs adsorbed on two samples. (A) WS₂:Mn: (a) 2-Pentanone@WS₂:Mn, (b) DMS@WS₂:Mn, (c) Isoprene@WS₂:Mn, (d) Limonene@WS₂:Mn, and (e) Methanol@WS₂:Mn; (B) WS₂:Fe: (a) 2-Pentanone@WS₂:Fe, (b) DMS@WS₂:Fe, (c) Isoprene@WS₂:Fe, (d) Limonene@WS₂:Fe, and (e) Methanol@WS₂:Fe.

6

Band structures, PDOS, and TDOS of five VOCs adsorbed on two samples. (A) WS₂:Mn: (a) 2-Pentanone@WS₂:Mn, (b) DMS@WS₂:Mn, (c) Isoprene@WS₂:Mn, (d) Limonene@WS₂:Mn, and (e) Methanol@WS₂:Mn; (B) WS₂:Fe: (a) 2-Pentanone@WS₂:Fe, (b) DMS@WS₂:Fe, (c) Isoprene@WS₂:Fe, (d) Limonene@WS₂:Fe, and (e) Methanol@WS₂:Fe.

7

Charge density difference (CDD) due to the adsorptions of five VOC molecules on two samples. (A) WS₂:Mn: (a) 2-Pentanone@WS₂:Mn, (b) DMS@WS₂:Mn, (c) Isoprene@WS₂:Mn, (d) Limonene@WS₂:Mn, and (e) Methanol@WS₂:Mn; (B) WS₂:Fe: (a) 2-Pentanone@WSe₂:Mn, (b) DMS@WSe₂:Mn, (c) Isoprene@WSe₂:Mn, (d) Limonene@WSe₂:Mn, and (e) Methanol@WSe₂:Mn.

7

Charge density difference (CDD) due to the adsorptions of five VOC molecules on two samples. (A) WS₂:Mn: (a) 2-Pentanone@WS₂:Mn, (b) DMS@WS₂:Mn, (c) Isoprene@WS₂:Mn, (d) Limonene@WS₂:Mn, and (e) Methanol@WS₂:Mn; (B) WS₂:Fe: (a) 2-Pentanone@WSe₂:Mn, (b) DMS@WSe₂:Mn, (c) Isoprene@WSe₂:Mn, (d) Limonene@WSe₂:Mn, and (e) Methanol@WSe₂:Mn.

8

Work function before and after the adsorption of nine molecules (5 VOCs and 4 air molecules) on 4 samples: (a) WS₂:Mn, (b) WS₂:Fe, (c) WSe₂:Mn, and (d) WSe₂:Fe.

9

Sensor responses of the adsorption of nine molecules (5 VOCs and 4 air molecules) on four samples: (a) WS₂:Mn, (b) WS₂:Fe, (c) WSe₂:Mn, and (d) WSe₂:Fe.