Ultrasensitive Pb2+ Detection by Glutathione-Capped Quantum Dots

• Published in: Analytical chemistry (Washington) 2007-12, Vol.79 (24), p.9452-9458
• Main Authors: Mohamed Ali, Emril, Zheng, Yuangang, Yu, Hsiao-hua, Ying, Jackie Y
• Format: Article
• Language: English
• Subjects: Analytical chemistry; Chemistry; Exact sciences and technology; Fluorescence; Glutathione; Ions; Lead - analysis; Metals, Heavy - analysis; Quantum Dots; Spectrometric and optical methods
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/ac071074x

Water-soluble and stable quantum dots (QDs), CdTe and CdZnSe, are applied for ultrasensitive Pb2+ detection. These QDs are capped with glutathione (GSH) shells. GSH and its polymeric form, phytochelatin, are employed by nature to detoxify heavy metal ions. As a result of specific interaction, the fluorescence intensity of GSH-capped QDs is selectively reduced in the presence of heavy metal ions such as Pb2+. The detection limit of Pb2+ is found to be 20 nM due to the superior fluorescence properties of QDs. Detailed studies by spectroscopy, microscopy, and dynamic light scattering show that competitive GSH binding of Pb2+ with the QD core changed both the surface and photophysical properties of the QDs. Fluorescence of QDs is quenched, and QD aggregation occurs. Coupling the GSH-capped QDs with a high-throughput detection system, we have developed a simple scheme for quick and ultrasensitive Pb2+ detection without the need for additional electronic devices. In the presence of ionic mixtures, our system is still capable of Pb2+ detection with a detection limit as low as 40 nM. The system only becomes less sensitive when the ionic mixture is present at a very high concentration (i.e., ≥50 μM).