เอกสารประชุมวิชาการระดับขาติมหาวิทยาลัยทักษิณ ครั้งที่ 28 2561

926 การประชุมวิชาการระดับชาติมหาวิทยาลัยทักษิณ ครั้งที่ 28 ประจ�าปี 2561 The morphology of CdTe QDs was also characterized by TEM. The TEM image in Figure 1B shows monodisperse and uniform CdTe QDs and their appearance agreed with the estimation of their particle size. Figure 1 UV-vis absorption (dotted line) and fluorescence emission spectra (solid line) of CdTe QDs (A) and TEM image of CdTe QDs (B) Optimization condition Effect of pH The effect of solution pH on the fluorescence response of CdTe QDs for Pb 2+ detection was investigated in the range of pH 6.0 to 10.0 (Figure 2). The most suitable pH of the TGA–capped CdTe QDs to react with Pb 2+ was 9.0. When the pH was lower than 9.0, the change in fluorescence intensity decreased due to protonation of the surface-binding thiolates [9]. However, the fluorescence intensity also decreased when the pH was higher than 9.0, because Cd 2+ on the surface of the QDs reacted with OH  in the solution to form Cd(OH) 2 coated on the surface of the QDs [10]. Figure 2 Effect of pH on the fluorescence quenching of TGA-capped CdTe QDs for Pb 2+ detection Effect of stabilizer The effect of the cap on the CdTe QDs is an important factor for analytical applications, so the CdTe QDs were capped with different thiol molecules and their performances were investigated. The capping molecules were TGA, MPA, GSH and MSA. The TGA-capped CdTe QDs provided the highest sensitivity followed by the MPA, GSH and MSA-capped CdTe QDs, respectively (Figure 3). The TGA molecule is the smallest so the Pb 2+ could easily pass through and accumulate within the CdTe QDs core.