DFT insights into dopamine adsorption on pristine and Ag-doped carbon nanotubes: implications for SERS sensing applications

: In this work, DFT was used to investigate the adsorption behaviour of dopamine on pristine and Ag-doped carbon nanotubes. Two adsorption orientations, involving hydroxyl and amine groups of dopamine, were examined to clarify role of functional-group direction in molecule-surface interactions. The results show that Ag doping strongly enhances dopamine adsorption by increasing charge transfer, surface polarization, and orbital coupling. Among the studied systems, CNTAgNH2 exhibited strongest adsorption energy, highest dipole moment, and most favourable thermodynamic stability, indicating strong Ag-mediated interaction through amine group. FMOs, MEP, DOS, NCI, and RDG analyses further confirmed that Ag incorporation narrows the electronic gap and introduces active interaction sites. Vibrational analysis revealed significant shifts in OH, NH2, phenyl, and CH2 modes after adsorption, supporting enhanced chemical interaction and possible SERS signal amplification. Overall, Ag-doped CNTs, particularly the CNTAgNH2 configuration, appear to be promising nanosubstrates for dopamine detection, although very strong adsorption may reduce sensor recyclability.