Nano-optical transduction sensor for ultra-sensitive detection of lead and arsenic using quantum dot nanoprobes

In North India, groundwater contamination with heavy metals, including Pb²⁺ and As³ + , poses major public health concerns. Here, we report AquaFluoSense, a portable fluorescence based biosensor for the rapid and ultra-sensitive detection of Pb²⁺ and As³⁺ ions in environmental water samples. The sensing platform employs cadmium telluride-mercaptopropionic acid quantum dots (CdTe-MPA QDs) functionalized with metal specific aptamers, enabling highly selective target recognition and fluorescence based signal transduction. A compact optoelectronic system integrating UV excitation, fluorescence detection, and microcontroller assisted signal processing enables real-time quantitative analysis under field conditions. Target induced modulation of the quantum dot (QD) fluorescence generated concentration dependent responses toward both analytes, enabling sensitive and quantitative detection of Pb²⁺ and As³⁺ in aqueous samples. The platform achieved detection limits of 1.2 nM for Pb²⁺ and approximately 0.45 nM for As³⁺, demonstrating high sensitivity for trace level contaminants. The analytical performance of the platform was evaluated using laboratory prepared standards and environmental water samples collected from different regions of North India. The results showed strong agreement with inductively coupled plasma mass spectrometry (ICP-MS), confirming the accuracy and reliability of the sensing platform. By integrating aptamer based molecular recognition, QD fluorescence transduction, and portable signal processing, AquaFluoSense provides a low cost, field deployable approach for real time monitoring of heavy metal contamination in water resources.