Electrochemical and colorimetric sensing of P-xylene using doped C60 fullerenes: a dual approach to medical and environmental applications

P-xylene is a type of aromatic hydrocarbon that has growing biomedical and environmental importance. It has been identified as a putative biomarker for prostate cancer and its fast and selective detection in biological fluids (especially urine and blood) is critical in the diagnosis and monitoring of the disease. Similarly, removal of p-xylene from industrial effluents and wastewater is an important environmental consideration due to its toxicity and persistence. These reasons emphasize the importance of developing and calculating the performance of efficient adsorbent and electrochemical sensors for p-xylene. Here, the adsorption and sensing performance of three fullerene-based nanostructures (C₆₀, BC₅₉, NC₅₉) were computationally studied for p-xylene using electronic structure calculations, charge transport analysis, dipole moment calculations, and non-covalent interaction (NCI/RDG) maps. There were significant changes in electrical conductivity induced by adsorption and transduction was strongly analyte-dependent: C₆₀ from 1.92 × 10^{- 5} to 2.93 × 10^{- 4} S/m (C₆₀ @ p-xylene), BC₅₉ from 1.18 × 10^{- 2} to 1.81 × 10^{- 1} S/m (BC₅₉ @ p-xylene), NC₅₉ from 3.68 × 10^{- 3} to 2.07 × 10^{- 3} S/m (NC₅₉@ p-xylene). Recovery times were ultrafast for all three complexes with the fastest recovery time being for NC₅₉ @ p-xylene (3.5 × 10^{- 7} s), C₆₀ = 9.8 × 10^{- 7}, and BC₅₉@ p-xylene (1.9 × 10^{- 5} s). Dipole-moment analysis showed significant polarization upon adsorption for the doped systems. The dipole moment increased from 1.50 to 3.91 D in BC₅₉ and from 1.39 to 3.05 D in NC₅₉. NCI and RDG analyses found that C₆₀@p-xylene is mainly affected by weak van der Waals forces. BC₅₉@p-xylene shows stronger π-π interactions. NC₅₉@p-xylene has intermediate but improved attractive interactions because of nitrogen doping. These trends are consistent with the adsorption energy ranking BC₅₉ > C₆₀ > NC₅₉ and highlight the changes in sensor response and recovery behavior. This study shows that BC₅₉ has the strongest adsorption and is suitable for environmental adsorption and removal of p-xylene. NC₅₉, on the other hand, has extremely high conductivity modulation and ultrafast recovery, along with reasonable adsorption. This makes NC₅₉ the most promising candidate for detecting p-xylene in early prostate cancer detection.