First-Principles Insight into a B4C3 Monolayer as a Promising Biosensor for Exhaled Breath Analysis

Abstract

Nanomaterial-based room temperature gas sensors are used as a screening tool for diagnosing various diseases through breath analysis. The stable planar structure of boron carbide (B₄C₃) is utilized as a base material for adsorption of human breath exhaled VOCs, namely formaldehyde, methanol, acetone, toluene along, with interfering gases of carbon dioxide and water. The adsorption energy, charge density, density of states, energy band gap variation, recovery time, sensitivity, and work function of adsorbed molecules on pristine B₄C₃ are analyzed by density functional theory. The computed adsorption energies of VOC are in the range of - 0.176 to - 0.238 eV, and a larger interaction distance validate the physisorption behavior of these VOCs biomarkers on pristine boron carbide monolayer. Minute changes are determined from the electronic band structure of all adsorbed systems conserving the semiconducting nature of the B₄C₃ monolayer. The band gap variation upon adsorption of VOCs and interfering gases is examined between 0.05 and 0.52%. The 13.63 × 10^-9 s recovery time of methanol is slower among VOCs, and 0.556 × 10^-9 s of carbon dioxide (CO₂) is faster for desorption. The results reveal that boron carbide can be utilized as a biosensor at room temperature for the analysis of exhaled VOCs from human breath.

Keywords: B4C3 monolayer; DFT study; Exhaled breath analysis; biosensor.

Fig. 1

(a) The top and side views of B4C3 monolayer. (b) Band structure along with PDOS of pristine B4C3 monolayer. Grey color represents carbon and pink color represents boron (Color figure online).

Fig. 2

The optimized structures (top and side view) of (a) formaldehyde, (b) methanol, (c) acetone, (d) toluene, (e) carbon dioxide and (f) water molecules on pristine B₄C₃ monolayer. Grey, pink, green, and red colors represent Carbon, Boron, Hydrogen and Oxygen (Color figure online).

Fig. 3

Differential charge density (top and side view) of (a) formaldehyde, (b) methanol, (c) acetone, (d) toluene, (e) carbon dioxide and (f) water molecules on pristine B₄C₃ monolayer. Cyan and yellow colors shows the charge depletion and accumulation. Colors represent Carbon (grey), Boron (pink), Hydrogen (green) and Oxygen (red) (Color figure online).

Fig. 4

Energy band structures and density of states of (a) pristine B₄C₃ monolayer, (b) formaldehyde, (c) methanol, (d) acetone, (e) toluene, (f) Carbon dioxide and (g) water molecules on pristine B₄C₃ monolayer. The dashed line indicates the Fermi level. Grey (carbon), Pink (boron), Green (hydrogen) and Red (oxygen), (h) Comparison of work function of pristine and adsorbed gas molecules on B₄C₃ monolayer, P: Pristine B₄C₃ monolayer, F: formaldehyde, M: methanol, A: acetone, T: toluene, C: carbon dioxide and W: water pristine B₄C₃ monolayer (Color figure online).