TITLE:
Detection of Nitrate Ions in Water Using Carbon Quantum Dots Modified with Silver Nanoparticles Functionalized by Cysteine
AUTHORS:
Irié Bi Irié Williams, Aka Alla Martin, Meledje Jean Claude, Loba Kokora Seraphin, Pomi Bi Boussou Narcisse, Koffi Koffi Kra Sylvestre
KEYWORDS:
Nitrate Detection, Colorimetric Sensor, Carbon Quantum Dots, Silver Nanoparticles, Water Monitoring
JOURNAL NAME:
Open Journal of Applied Sciences,
Vol.16 No.3,
March
16,
2026
ABSTRACT: This work presents a novel sensor for detecting nitrates in water using silver nanoparticles (AgNPs) modified with cysteine-functionalized carbon quantum dots (Cys-CQDs) reduced by sodium borohydride (NaBH4). This colorimetric detection method demonstrated a visible color change from yellow to pink, responding to both high nitrate concentrations (160 - 800 mg/L) with a rapid response time and low concentrations (0 - 40 mg/L) within a 30-minute exposure. UV-Vis spectroscopy analysis revealed a broad detection range of 0.0251 to 800 mg/L using the absorption peak associated with AgNPs at 400 nm. A linear calibration curve with excellent correlation (R2 = 0.9995) was established across this range. The developed sensor exhibited remarkable performance, with a detection limit of 2.5 × 10−2 mg/L, a quantification limit of 8.4 × 10−2 mg/L, a recovery rate exceeding of 97%, and high precision (