Two-dimensional PtSe2 coatings with antibacterial activity

Abstract

PtSe2, an emerging two-dimensional (2D) transition metal dichalcogenide (TMD), has been considered as excellent electrochemical material however its photocatalytic properties are still unexplored. In the present work, antibacterial activity of few-layer PtSe2 coatings on glass substrate against Escherichia coli in dark and light irradiation conditions is reported. 2D PtSe2 layers were synthesized by selenization of pre-deposited Pt films using thermally assisted conversion (TAC) method. PtSe2 coatings with three different thicknesses were prepared by varying the Pt deposition time (Pt 3s, Pt 8s and Pt 10s), afterwards estimated by ellipsometric measurements to 7 nm, 9 nm and 12 nm, respectively. The X-Ray diffraction (XRD) patterns showed the diffraction peaks characteristic for PtSe2 with improving crystallinity when increasing the Pt deposition time. Similar tendency of increasing roughness was detected by measuring the surface topology using atomic force microscopy (AFM). The Raman spectra revealed typical PtSe2 modes, while a decrease of Se/Pt ratio and a transition from p-doped to n-doped PtSe2 for longer Pt deposition times was found by X-ray photoelectron spectroscopy (XPS) analysis. Examination of the PtSe2 band gap by spectroscopic ellipsometry showed a decrease from 0.77 to 0.64 eV upon increase of the Pt deposition time, well correlated with the UV-VIS transmitted spectra. Formation of reactive oxygen species (ROS), mainly hydroxyl radicals (OH) on the PtSe2 surface under light irradiation was demonstrated by EPR analysis. The antibacterial activity of PtSe2 coatings was investigated applying ISO standard procedure for semiconducting photocatalytic materials: (i) in dark, the antibacterial activity increased with the increase of Pt deposition time and the viability of the bacteria was reduced to 30% (Pt 3s) and 15% (Pt 10s) after treatment for 6 h. The effect was attributed to the increasing film thickness, roughness and surface coverage which facilitate the mechanical destruction of the bacteria cell; (ii) under light irradiation, the activity of PtSe2 (Pt 3s) was similar to that in dark showing low sensitivity to light. On the contrary, the PtSe2 (Pt 8s) and (Pt 10s) appeared very effective under light, with the bacteria viability after 6 h being only 7.3% and 1.2%, respectively. The observed photo-induced antibacterial activity was related to the synergy of several parameters, i.e. high crystallinity, semiconductor behavior and chemical composition. The present work opens the way for further investigation of PtSe2 as photoactive antibacterial material, the mechanism of its antibacterial activity and the possibility for application as antibacterial coating on transparent low-cost substrates.