The interaction of small gas molecules (CCl$_4$, CH$_4$, NH$_3$, CO$_2$, N$_2$, CO, NO$_2$ CCl$_2$F$_2$, SO$_2$, CF$_4$, H$_2$) on pure and aluminium-doped graphene were investigated by using the density functional theory to explore their potential applications as sensors. It has been found that all gas molecules show much stronger adsorption on the Al-doped graphene than that of pure graphene (PG). The Al-doped graphene shows the highest adsorption energy with NO$_2$, NH$_3$ and CO$_2$ molecules, whereas the PG binds strongly with NO$_2$. Therefore, the strong interactions between the adsorbed gas molecules and the Al-doped graphene induce dramatic changes to graphene’s electronic properties. These results reveal that the sensitivity of graphene-based gas sensor could be drastically improved by introducing the appropriate dopant or defect. It also carried out the highest occupied molecular orbital–lowest unoccupied molecular orbital energy gap of the complex molecular structure that has been explored by M06/6-31++G$^{**}$ method. These results indicate that the energy gap fine tuning of the pure and Al-doped graphene can be affected through the binding of small gas molecules.

In order to design biosensors, it is quite necessary to have an insight upon the nature of interaction between the modified nucleic bases (MNBs) and carbonaceous materials. This study is focussed upon the interaction of the various doped graphene models like graphene (GR), aluminium doped graphene (AlG), sulphur doped graphene (SG), nickel doped graphene (NiG), chromium doped graphene (CrG) and germanium doped graphene (GeG) with MNBs (caffeine, hypoxanthine, uric acid and xanthine) by employing the electronic structure calculations and the associated methodology. All the geometries considered in this study (MNBs and graphene models)were initially optimized at M06-2X/6-31$+$G$^{**}$ basis set without any constraints followed by the single point energy calculation at three different and well established methodsusing the Gaussian 09 software package. A detailed comparison of the interaction energy is accomplished in this study. The interaction energy values were further corrected for the basis set superposition error. The theory of atoms in molecules analysis is also performed in detail, which showcases the bond critical points, Laplacian and various other parameters of interest. The variation of frontier molecular orbitals, i.e., highest occupied molecular orbital–lowest unoccupied molecular orbital gap for different models of graphene have been discussed in detail upon the adsorption of MNBs. Among the dopedgraphene models, the graphene model doped with Cr seems to be more suitable for the application of sensors, also it is found that the MNBs interact primarily via $\pi-\pi$ interaction. The results highlight that the CrG can act as a sensor for the detection of MNBs.