Water-Soluble Photoluminescence <i>On–Off–On</i> Probe for Speedy and Selective Detection of Fluoride Ions

A CdTe QDs based new type of water-soluble switch <i>on–off–on</i> photoluminescence (PL) probe has been developed for specific detection of fluoride ions (F^–). Europium ions (Eu³⁺) stabilized by the carboxylic groups of 3-mercaptopropanoic acid (MPA) capped CdTe QDs result in quenching of PL (switch <i>off</i>) of QDs. PL is regained (switch <i>on</i>) with the addition of F^– due to the formation of EuF₃ as Eu³⁺ has higher bonding affinity with F^– compared to carboxylic acid groups. The quenching of the PL property of CdTe-MPA QDs toward Eu³⁺ and its regeneration in the presence of F^– is highly selective, sensitive (detection limit 5 ppm to 75 ppm), and prompt (less than 10 s). The technique has been successfully applied for the detection of HF vapors, which is actually an important issue from the industrial perspective. To the best of our knowledge, this is the first report of the use of one step synthesized water-soluble 3-MPA capped CdTe QDs, as a rapid, efficient, and most importantly selective photoluminescence <i>on–off–on</i> probe for fluoride ion detection

Directing the Deposition of Ferromagnetic Cobalt onto Pt-Tipped CdSe@CdS Nanorods: Synthetic and Mechanistic Insights

A methodology providing access to dumbbell-tipped, metal–semiconductor and metal oxide–semiconductor heterostructured nanorods has been developed. The synthesis and characterization of CdSe@CdS nanorods incorporating ferromagnetic cobalt nanoinclusions at both nanorod termini (<i>i</i>.<i>e</i>., dumbbell morphology) are presented. The key step in the synthesis of these heterostructured nanorods was the decoration of CdSe@CdS nanorods with platinum nanoparticle tips, which promoted the deposition of metallic CoNPs onto Pt-tipped CdSe@CdS nanorods. Cobalt nanoparticle tips were then selectively oxidized to afford CdSe@CdS nanorods with cobalt oxide domains at both termini. In the case of longer cobalt-tipped nanorods, heterostructured nanorods were observed to self-organize into complex dipolar assemblies, which formed as a consequence of magnetic associations of terminal CoNP tips. Colloidal polymerization of these cobalt-tipped nanorods afforded fused nanorod assemblies from the oxidation of cobalt nanoparticle tips at the ends of nanorods <i>via</i> the nanoscale Kirkendall effect. Wurtzite CdS nanorods survived both the deposition of metallic CoNP tips and conversion into cobalt oxide phases, as confirmed by both XRD and HRTEM analysis. A series of CdSe@CdS nanorods of four different lengths ranging from 40 to 174 nm and comparable diameters (6–7 nm) were prepared and modified with both cobalt and cobalt oxide tips. The total synthesis of these heterostructured nanorods required five steps from commercially available reagents. Key synthetic considerations are discussed, with particular emphasis on reporting isolated yields of all intermediates and products from scale up of intermediate precursors