Tailoring Graphene for Enhanced Biosensing: Structural Modifications and Modeling of Electronic and Optical Properties

The main objective of this study was to investigate the impacts of structural modifications on the electronic and optical properties of graphene to improve its biosensing capabilities. The remarkable optical and electrical properties of two-dimensional graphene were found to make it highly promising for use in a wide range of technological applications. However, the absence of a band gap in pure graphene has been identified as a limitation for its use in critical applications such as biosensing. To address this, modeling and simulation approaches were employed for structural alterations using the Material Studio 7.0 CASTEP module. The electronic and optical properties of monolayer and bilayer graphene crystals, including doped and defective forms, were examined. Doping with phosphorus and aluminum was found to induce band gaps of 0.0147 eV and 0.0103 eV, respectively, while vacancies significantly altered the density of states. A band gap energy of 0.110 eV was observed in bilayer graphene, signifying a transition from a metallic or semi-metallic state to a semiconductor state. This energy range corresponds to the infrared region of the electromagnetic spectrum, suggesting that bilayer graphene with such a band gap could be useful for devices like infrared detectors and sensors. The greatest peak energy of 11.4 eV was observed in monolayer graphene with vacancy, which is higher than that of its pure and doped counterparts, indicating the presence of electronic states in the conduction band region. The defect-induced generation of electronic states within the band structure was responsible for the significant increase in the density of states, with a DOS value of 47.3 electrons per eV. Refractive indices ranging from 1.45 to 3.47 were recorded, with bilayer graphene showing a higher refractive index of 3.06, indicating greater light absorption and reduced transparency. The absorption coefficient characteristics of vacancy-containing bilayer structures were found to differ from those of monolayer structures. Moreover, dielectric function analysis revealed a stronger imaginary peak of approximately 40 for bilayer graphene with vacancy, followed by the bilayer structure with a peak of 15, indicating increased light absorption due to the introduction of vacancies and additional layers. In the conductivity analysis of bilayer graphene, the highest imaginary peak at 17 eV was identified as the wavelength where graphene absorbed light most effectively. For biosensing systems relying on light-matter interactions, this peak represents the energy required for electronic transitions within the material. In conclusion, the findings demonstrate the potential of specially tailored graphene-based biosensors with enhanced sensitivity and specificity, which could be applied in biological and environmental monitoring, paving the way for highly efficient sensing platforms.