Design of photoelectrochemical sensor based on graphitic carbon nitride (g-C3N4) coated titanium dioxide nanotube arrays for sensitive determination of glutathione

The photoelectrochemical (PEC) process is an electrochemical process based on the light signal. During PEC process for molecule, ion or semiconductor materials, the electron is excited when absorbing photons, which results in charge transfer and energy transfer from light to electrical [1]. PEC detection based on photon-to-electricity conversion has attracted considerable interest due to its high sensitivity as well as simple and cheap instrumentation [2]. In this work, we report the fabrication of titanium dioxide nanotube array coated by graphitic carbon nitride (g-C3N4/TiO2-NTs) and poly thiophene (PTh) as a novel PEC sensor. This sensor was prepared by anodizing of the Ti foil in the constant potential of 25 V for 2 h. Then the as-prepared TiO2-NTs/Ti was calcinated at 450 °C for 150 min. Herein, in situ growth of g-C3N4 on the surface of TiO2-NTs was achieved via the vapor–pyrolysis of melamine [3]. The content of g-C3N4 in the composite was adjusted by varying the addition quantities of melamine (0 to 8 g) in the calcination process. The photocurrent density generated by the fabricated PTh/g-C3N4/TiO2-NTs/Ti electrode is higher than the photo-response of the pristine TiO2-NTs/Ti. The photocurrent of PTh/g-C3N4/TiO2-NTs/Ti was drastically improved upon the addition of glutathione (GSH),which was attributed to the life improvement of the electron-hole pairs. Based on the enhanced photocurrent signal, a PEC methodology for ultrasensitive determination of GSH has been developed. Finally, the effects of solution pH and applied potential on photoelectrochemical response were studied and results showed that optimum supporting electrolyte is phosphate-citrate buffer solution (pH=5.0) and optimum potential is 2.0 V vs. Ag/AgCl reference electrode. It was found that the photocurrent of GSH was linearly dependent on the concentration of analyte in the range of 5 to 700 nM and the detection limit of GSH determination was found to be 1.0 nM.