เอกสารประชุมวิชาการระดับขาติมหาวิทยาลัยทักษิณ ครั้งที่ 28 2561

924 การประชุมวิชาการระดับชาติมหาวิทยาลัยทักษิณ ครั้งที่ 28 ประจ�าปี 2561 Introduction Lead (Pb 2+ ) is widely used in many applications such as photovoltaic cells, paints, pigments, industrial chemical processes and lead-acid batteries. It is one of the most widespread toxic substances in the environment and large amount have entered the food chain. Exposure to Pb 2+ can cause serious health problems including anemia, mental retardation and damaged kidneys, nervous system, liver and brain [1, 2]. To protect human health and the environment, the US Environmental Protection Agency (EPA) set the safety limit for Pb 2+ in drinking water at 15 µg L -1 . Clearly, the monitoring of Pb 2+ levels in is an important safeguard. Several methods have been reported for determining the presence of Pb 2+ . Techniques include atomic absorption spectroscopy [3], inductively coupled plasma mass spectrometry [4] and electrochemistry [5]. However, these techniques are complicated, costly and time consuming. On the other hand, fluorescence spectroscopy has attracted attention for its rapidity, simplicity and low cost. In recent years, quantum dots (QDs) nanoparticles have been used as fluorescence probes for the determination of various target analytes. They possess good optical properties, good photochemical stability, long fluorescence lifetime and good water solubility [6, 7]. However, to improve the selectivity and sensitivity of the method, the surfaces of QDs need to be modified, or capped, with suitable stabilizing agents. QDs have been capped with stabilizers such as thioglycolic acid (TGA), mercaptopropionic acid (MPA), glutathione (GSH) and mercaptosuccinic acid (MSA). In this work, thiol-capped cadmium telluride (CdTe) quantum dots (QDs) were synthesized and used as highly sensitive fluorescence probes for the detection of Pb 2+ based on fluorescence quenching. Experimental Materials and Methods All chemicals used were of analytical grade. Tellurium powder (-200 mesh, 99.8%), sodium borohydride (NaBH 4 ), thioglycolic acid (TGA), mercaptosuccinic acid (MSA) and lead nitrate (PbNO 3 ) were obtained from Sigma-Aldrich (St. Louis, MO, USA). Mercaptopropionic acid (MPA) and glutathione reduced (GSH) were from Merck (Darmstadt, Germany). Cadmium chloride (CdCl 2 ·H 2 O) was purchased from Asia Pacific Specialty Chemicals Co. Ltd (NSW, Australia). All aqueous solutions were prepared with ultrapure water obtained from a water purification system (ELGA, High Wycombe, UK). UV/vis absorption spectra were recorded using an Avaspec 2048 spectrometer (Avantes, Apeldoorn, The Netherlands). Fluorescence Spectroscopy was performed with an RF-5301 spectrofluorometer (Shimadzu, Tokyo, Japan). Transmission electron microscopy (TEM) was performed using a JEM-2010 transmission electron microscope (JEOL, Tokyo, Japan). Fourier transform infared spectra (FTIR) were recorded with a Spectrum BX FTIR spectroscope (PerkinElmer, Waltham, MA, USA).