Detection of L-cysteine in urine samples based on CdS/TiO-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 was initially modified on the ITO electrode by the sol-gel dip-coating method and calcined to produce TiO/ITO. Then, CdS was synthesized on the TiO surface by hydrothermal method to obtain the CdS-TiO heterojunction material. CdS/TiO/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 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) of the sensor exhibited a good linear relationship with the logarithm of L-Cys in the range of 5.0 × 10-1.0 × 10 mol/L, and the detection limit was 1.3 × 10 mol/L (S/N = 3), which is lower than the values reported by other detection methods. Results showed that the CdS/TiO/ITO EGFET PEC sensor revealed high sensitivity and good selectivity. The sensor has been used to determine L-Cys in urine samples.