Enhancing long-term accuracy and durability of wastewater monitoring using electrosprayed ultra-thin solid-state ion selective membrane sensors

Current membrane deposition approaches (e.g., drop-casting, spin-coating) for solid-state ion selective membrane (S-ISM) sensors suffer from problems including sensor material waste, uncontrollable membrane thickness (100–200 μm), loose contact between sensing membrane and electrode surface, long response time (e.g., >20 s) and poor reading stability (e.g., >3 mV/h). This study addressed these challenges by depositing ISM through electrospray printing technology and enabling accurate and continuous monitoring in water and wastewater. Specifically, the final droplet size and the splash diameter of the electrosprayed droplets deposited a particularly tunable, high resolution and ultra-thin (thickness: ∼1 μm) membrane on the electrode surface, which immensely shortened the sensor response time (9.2 s), strengthened the adhesion between the ISM and the electrode surface, mitigated the formation of water layer in the S-ISM sensor entity, and ultimately enhanced the sensor reading stability (reading drifting <0.66 mV/h). Additionally, the ion diffusion model developed in this study confirmed that fast ion diffusion in the electrosprayed S-ISM polymer matrix effectively shortened the response time of sensors. Electrosprayed S-ISM sensors without anti-fouling protection exhibited high stability and accuracy with an error of less than 2.9 mg/L after continuously monitoring wastewater for 10 days, revealing a great potential for further enhancement.