Real-time detection of mercury ions in water using a reduced graphene oxide/DNA field-effect transistor with assistance of a passivation layer

• Ultra-sensitive and label-free reduced graphene oxide (rGO)-based field-effect transistor (FET) sensors have been developed.
• Al2O3 on the rGO as a passivating layer can avoid free ions’ contribution to the sensing signals and can prevent the degradation of the intrinsic electrical properties of rGO during the immobilization of probes on rGO.
• The rGO FET sensor, using a single-stranded Hg2+-dependent DNA probe, shows high sensitivity and selectivity for real-time detection of Hg2+ in an underwater environment.
• Our work shows that optimization of an rGO FET structure can provide significant performance enhancement and profound fundamental understanding for the sensor mechanism.

Field-effect transistor (FET) sensors based on reduced graphene oxide (rGO) for detecting chemical species provide a number of distinct advantages, such as ultra-sensitivity, label-free, and real-time response. However, without a passivation layer, channel materials directly exposed to an ionic solution could generate multiple signals from ionic conduction through the solution droplet, doping effect, and gating effect. Therefore, a method that provides a passivation layer on the surface of rGO without degrading device performance will significantly improve device sensitivity, in which the conductivity changes solely with the gating effect. In this work, we report rGO FET sensor devices with Hg2+-dependent DNA as a probe and the use of an Al2O3 layer to separate analytes from conducting channel materials. The device shows good electronic stability, excellent lower detection limit (1 nM), and high sensitivity for real-time detection of Hg2+ in an underwater environment. Our work shows that optimization of an rGO FET structure can provide significant performance enhancement and profound fundamental understanding for the sensor mechanism.

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