Real-time, in situ accurate monitoring of nitrogen contaminants in wastewater over a long-term period is critical for swift feedback control, enhanced nitrogen removal efficiency, and reduced energy consumption of wastewater treatment processes. Existing nitrogen sensors suffer from high cost, low stability, and short life times, posing hurdles for their mass deployment to capture a complete picture within heterogeneous systems. Tackling this challenge, this study presents solidstate ion-selective membrane (S-ISM) nitrogen sensors for ammonium (NH 4 + ) and nitrate (NO 3 − ) in wastewater that were coupled to a wireless data transmission gateway for real-time remote data access. Lab-scale test and continuous-flow field tests using real municipal wastewater indicated that the S-ISM nitrogen sensors possessed excellent accuracy and precision, high selectivity, and multiday stability. Importantly, autocorrections of the sensor readings on the cloud minimized temperature influences and assured accurate nitrogen concentration readings in remote-sensing applications. It was estimated that real-time, in situ monitoring using wireless S-ISM nitrogen sensors could save 25% of electric energy under normal operational conditions and reduce 22% of nitrogen discharge under shock conditions.

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The creation and engineering of artificial enzymes remain a challenge, especially the arrangement of enzymes into geometric patterns with nanometer precision. In this work, we fabricated a series of novel DNA-tetrahedron-scaffolded-DNAzymes (Tetrazymes) and evaluated the catalytic activity of these Tetrazymes by electrochemistry. Tetrazymes were constructed by precisely positioning G-quadruplex on different sites of a DNA tetrahedral framework, with hemin employed as the co-catalyst. Immobilization of Tetrazymes on a gold electrode surface revealed horseradish peroxidase (HPR)-mimicking bioelectrocatalytic property. Cyclic voltammogram and amperometry were employed to evaluate the capability of Tetrazymes of different configurations to electrocatalyze the reduction of hydrogen peroxide (H2O2). These artificial Tetrazymes displayed 6- to 14-fold higher enzymatic activity than G-quadruplex/hemin (G4-hemin) without the DNA tetrahedron scaffold, demonstrating application potential in developing novel G-quadruplex-based electrochemical sensors.

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