Detection of L-cysteine in urine samples based on CdS/TiO2-modified extended-gate field-effect transistor photoelectrochemical sensor

A novel extended-gate field-effect transistor (FET) photoelectrochemical (EGFET PEC) sensor was designed for highly sensitive detection of L-cysteine (L-Cys). TiO 2 was initially modified on the ITO electrode by the sol–gel dip-coating method and calcined to produce TiO 2 /ITO. Then, CdS was synthesized on the TiO 2 surface by hydrothermal method to obtain the CdS–TiO 2 heterojunction material. CdS/TiO 2 /ITO was connected to the gate of the FET to obtain an EGFET PEC sensor. Under the irradiation of a xenon lamp simulating visible light, the CdS/TiO 2 heterojunction composite absorbs light energy to produce photogenerated electron–hole pairs, which have strong photocatalytic oxidation activity and oxidize L-Cys covalently identified by Cd(II) through CdS covalent. These pairs generate a photovoltage that controls the current between the source and the drain to detect L-Cys. Under the optimized experimental conditions, the optical drain current ( I D ) of the sensor exhibited a good linear relationship with the logarithm of L-Cys in the range of 5.0 × 10 −9 –1.0 × 10 −6 mol/L, and the detection limit was 1.3 × 10 −9 mol/L (S/N = 3), which is lower than the values reported by other detection methods. Results showed that the CdS/TiO 2 /ITO EGFET PEC sensor revealed high sensitivity and good selectivity. The sensor has been used to determine L-Cys in urine samples. Graphical abstract