DFT and QTAIM insights into C20 fullerene derivatives as advanced sensors for phencyclidine drug detection in clinical settings

The unauthorized use of phencyclidine (PCP) has serious public health consequences, which prompts the need for new sensing approaches that are fast, sensitive and accessible. This study used Density Functional Theory (DFT) and the Quantum Theory of Atoms in Molecules (QTAIM) to examine pristine fullerene C₂₀ and two doped ones (AlC₁₉ and ZnC₁₉) as new sensors for PCP. Geometry optimization and analyses of the molecular electrostatic potential (MEP), electronic properties (HOMO-LUMO gap; chemical potential, electrophilicity-based charge transfer), and sensing performance (adsorption energy, recovery time and electrical conductivity) were performed. Results illustrate that doping significantly changes the electronic and structural properties of the C₂₀ framework. Although pristine C₂₀ and ZnC₁₉ have limited potential, AlC₁₉ is promising as a multifunctional material. AlC₁₉ has the strongest interaction with PCP, with an adsorption energy (Eads) of -49.44 kcal.mol^-1, demonstrating excellent potential to remove PCP in adsorbed form. As an electrochemical sensor, AlC₁₉ showed a large increase in electrical conductivity (from 2.71 × 10⁹ in the pristine AlC₁₉ to 2.77 × 10⁹ in the AlC₁₉@PCP complex) and a long recovery time after PCP binding, making it ideal for disposable sensor application (strong and irreversible binding). Furthermore, AlC₁₉ showed exceptional performance as a colorimetric sensor, exhibiting a significant shift in the UV-Vis absorption maximum (from 470 nm to 524 nm) after complexation with PCP. Both NBO and QTAIM analysis revealed that AlC₁₉@PCP exhibits a very strong donor-acceptor interaction and a moderate hydrogen-bond-like character, which contributed to its strong performance. All of the above establishes that AlC₁₉ is an effective disposable electrochemical sensor, a colorimetric sensor, and an effective adsorbent of PCP that can be further utilized to develop a multi-functional sensing system that could allow for detection of the drug and remediation of the environment.