Surface-enhanced Raman spectroscopic sensing of the herbicide alachlor using Au₁₆ nanocluster

This study explored the interaction between the herbicidal pollutant alachlor and the Au₁₆ nanocluster employing density functional theory (DFT) described by the functional M062X and basis set SDD. The adsorption energy of alachlor on the Au₁₆ cluster is negative, signifying a strong interaction between the herbicide and the Au cluster. The molecular structures, HOMO-LUMO energies, molecular electrostatic potential (MEP), non-covalent interactions (NCI), and reduced density gradient (RDG) scatter plots were analyzed in detail. NCI analysis suggests van der Waals forces, strong attractive, and repulsive steric interactions in the studied complex. Mulliken charge analysis revealed changes in the atomic charges of alachlor upon interaction with the Au₁₆ nanocluster whereas quantum theory of atoms in molecules (QTAIM) analysis unraveled the nature of intermolecular interactions. Electron delocalization in the cluster complex was detected using average local ionization energy (ALIE), electron localization function (ELF), and localized orbital locator (LOL) calculations. The Raman spectrum shows enhanced wavenumbers for various functional groups, indicating the potential for developing Au₁₆ nanosensors for alachlor detection using surface-enhanced Raman scattering (SERS).