A Low-Cost, Open-Source, In Situ, Near-Real-Time Sensor for the Detection of Nitrate and Ammonia in Environmental Waters

Elevated levels of ammonia and nitrate in water bodies contribute to environmental issues such as eutrophication and pose serious risks to human health and aquatic life. Traditional monitoring methods rely on grab sampling, and existing in situ sensor technologies are often prohibitively expensive, which limits their widespread deployment. This study presents a low-cost, in situ, near-real-time sensor and a hand-held device for the detection and monitoring of ammonia and nitrate in water. The hand-held device demonstrated excellent performance during laboratory testing, achieving an R 2 of 0.96 when estimating both ammonia and nitrate concentrations in real environmental samples. It reliably quantified both nutrients across a broad range, with accurate measurements observed up to 10 mg/L. The in situ system showed reliable performance for ammonia in environmental samples ( R 2 = 0.76) and detected ammonia down to 0.1 mg/L. However, below this threshold, signal variability increased, and measurements became less consistent. During four field sampling periods, it demonstrated reliable performance in measuring ammonia concentrations, achieving an R 2 of 0.86 and a Nash–Sutcliffe efficiency (NSE) of 0.83. The results showed that the low-cost sensor can operate for 2 weeks by sampling every 40 min using just one kit of low-cost reagents (16 USD per kit, and 0.09 USD per sample).