Ultrasensitive sensors based on aluminum oxide-protected reduced graphene oxide for phosphate ion detection in real water

Abstract

Real-time detection of phosphate ions is critical for monitoring the eutrophication status of surface water. We report an ultrasensitive phosphate sensor based on a reduced graphene oxide field-effect transistor (rGO-FET). In this work, rGO nanosheets were employed as sensing channels and an aluminum oxide (Al₂O₃) film was applied as a passivation layer to separate the sensing channels from the sample solution. The critical thickness of the passivation layer – defining a continuous barrier film on the FET sensor – was identified, which fully covers the sensing platform and also enables sensitive responses. The detection results showed that ferritin probes have good affinity to phosphate ions in water. It was also found that providing both a high ferritin concentration and an acidic environment improves the immobilized probe density, which increases the analyte adsorption sites and improves the sensing performance. The sensing platform was used to detect phosphate ions in industrial discharge with a lower detection limit of 10 μg L⁻¹ (105 nM). Ultimately, this inexpensive and micro-sized sensor can provide new opportunities for real-time monitoring of phosphate ions in agriculture and wastewater discharge.