Monitoring Cd in oily wastewater using an aptamer-graphene field-effect transistor with a selective wetting surface.

The discharge of oily industrial wastewater containing heavy metal ions with the development of industry severely threatens the environment and human health. Therefore, it is of great significance to monitor the concentration of heavy metal ions in oily wastewater quickly and effectively. Here, an integrated Cd monitoring system consisting of an aptamer-graphene field-effect transistor (A-GFET), oleophobic/hydrophilic surface and monitoring-alarm circuits was presented for monitoring the Cd concentration in oily wastewater. In the system, oil and other impurities in wastewater are isolated by an oleophobic/hydrophilic membrane before detection. The concentration of Cd is then detected by a graphene field-effect transistor with a Cd aptamer modifying the graphene channel. Finally, the detected signal is collected and processed by signal processing circuits to judge whether the Cd concentration exceeds the standard. Experimental results demonstrated that the separation efficiency of the oleophobic/hydrophilic membrane to an oil/water mixture was up to 99.9%, exhibiting a high oil/water separation ability. The A-GFET detecting platform could respond to changes in the Cd concentration within 10 min with a limit of detection (LOD) of 0.125 pM. The sensitivity of this detection platform to Cd near 1 nM was 7.643 × 10 nM. Compared with control ions (Cr, Pb, Mg, Fe), this detection platform exhibited a high specificity to Cd. Moreover, the system could send out a photoacoustic alarm signal when the Cd concentration in the monitoring solution exceeds the preset value. Therefore, the system is practical for monitoring the concentration of heavy metal ions in oily wastewater.