Excessive nitrite in water poses serious health and environmental risks, requiring reliable long-term monitoring. Electrochemical sensors offer advantages due to their sensitivity, low cost, and ease of use; however, they suffer from aging, which affects accuracy over time. This thesis addresses this limitation by developing and optimizing a nitrite sensor based on screen-printed carbon electrodes modified with electrodeposited gold. The sensor achieved promising performance, including a 15-day shelf life. A multidisciplinary study investigated aging mechanisms using electrochemical...