Advancing 2D imaging of ammonium for biological application: Planar and nanoparticle-based ion-selective optodes

This study investigates the development and optimization of ammonium-selective chromoionophore-based optodes for two-dimensional (2D) imaging with conventional cameras. Ammonium, vital in various fields like agriculture, ecology, and health, requires accurate measurement. Traditional methods have limitations, leading to the exploration of optical sensors, or optodes, for direct imaging of ammonium gradients. The research covers planar and nanoparticle designs, exploring absorbance and fluorescence readouts with commercial cameras. The study extends to repeatability, response time, and selectivity of the optodes. Planar optodes, utilizing chromoionophores under different background colors, demonstrate improved characteristics with the addition of TiO 2 . The impact of plasticizer choice on response characteristics, including hysteresis, is explored. Nanoparticle designs using PVC and F127 are compared, with autoclaving identified as the superior sterilization method. The work effectively demonstrates 2D real -time NH 4 + visualization using optode nanoparticles in agar gels. Finally, a proof-of-concept was performed to showcase a biological application for identifying urease-producing pathogens ( Bacillus subtilis ) without relying on pH changes. Overall, this study provides a comprehensive exploration of ammonium-selective optodes with promising applications in environmental monitoring and biological studies.