The role of solvent polarity in the electronic properties, stability and reactivity trend of a tryptophane/Pd doped SWCNT novel nanobiosensor from polar protic to non-polar solvents

Carbon nanotubes and amino acids have a high potential to offer specific advantages as the transducer and the recognition elements of biosensors. Their compatible size with biological structures makes them suitable as implantable sensors. In this work solvent effects on the electronic structure properties of a tryptophan hybrid with Pd doped single walled carbon nanotubes as a new novel biosensor were investigated. As the chemical reaction of a nanobiosensor is affected by the nature of the solvents, 5 different solvents, water, DMSO, ethanol, acetone and carbon tetrachloride are employed to study the role of the solvent polarity on the molecular stability, the optimized geometry and charge distribution of Try/Pd-SWCNT nanobiosensor. To derive the optimized geometries, the density functional theory computations were performed at the B3LYP level with the 6-31G(d) basis set. In addition, the molecular orbital calculations such as natural bond orbitals (NBOs), HOMO-LUMO energy gap, mapped molecular electrostatic potential (MEP) surface and density of state (DOS) were also performed. The results show that the presence of a solvent lowers the HOMO and LUMO energy level and increases or decreases the HOMO-LUMO energy gap depending on the chemical system. Different nucleophile and electrophile sites were detected in the molecular electrostatic maps. The softer investigated biosensors were found in more polar media. The highest reorganization energies for the nanobiosensor resulted in water media. The Trp/Pd/SWCNT presents high stability with considerable values of charge transfer, stabilization energies and the energy bond gap in polar medium which confirm both in vitro and in vivo biosensing applications.