Colorimetric Optode Sensor with Tripodal Ionophore for Rapid Urinary Ammonium Determination

The amount of ammonium excreted in urine is a crucial indicator for assessing renal metabolic acidosis. Therefore, there is a significant demand for chemical sensors capable of accurately determining urinary ammonium concentrations with high throughput. In this study, we developed an ammonia chemical sensor based on the ion-selective optode principle. This sensor employs strategically designed ionophores and a PTFE gas-permeable film to enhance selectivity for free NH₃. The low basicity of the chromoionophore indicator and the weak affinity of the tripodal ammonium receptor (L, log β = 4.62 ± 0.18) contributed to a markedly reduced response time, achieving detection within seconds, a significant improvement over previous sensors. A limit of detection (LOD) of approximately 15 nM was obtained in colorimetric mode. Total inorganic ammonia content in undiluted human urine was successfully determined using the sensor. Additionally, the optode was adapted into a multiwell format, offering potential for high-throughput point-of-care testing of urinary ammonium concentrations and other samples.