title: Direct synthesis of aqueous quantum dots through 4,4'-bipyridine-based twin ligand strategy.
abstract: We report a new class of derivatized 4,4'-bipyridinium ligands for use in synthesizing highly fluorescent, extremely stable, water-soluble CdSe and CdTe quantum dots (QDs) for bioconjugation. We employed an evaporation-condensation technique, also known as solvated metal atom dispersion (SMAD), followed by a digestive ripening procedure. This method has been used to synthesize both metal nanoparticles and semiconductors in the gram scale with several stabilizing ligands in various solvents. The SMAD technique comprised evaporation condensation and stabilization of CdSe or CdTe in tetrahydrofuran. The as-prepared product was then digestively ripened in both water and dimethyl formamide, leading to narrowing of the particle size distributions. The ligands were synthesized by nucleophilic substitution (S(N)2) reactions using 4,4'-bipyridine as a nucleophile. Confocal microscopy images revealed the orange color of the nanocrystalline QDs with diameters of ~5 nm. The size has been confirmed by using transmission electron microscopy. As a part of our strategy, 85% of the 4,4'-bipyridinium salt was synthesized as propionic acid derivative and used to both stabilize the QDs in water and label basic amino acids and different biomarkers utilizing the carboxylic acid functional group. Fifteen percent of the 4,4'-bipyridinium salt was synthesized as N-propyl maleimide and used as a second ligand to label any protein containing the amino acid cysteine by means of a 1,4-Michael addition.
authors.affiliation: Department of Chemistry, Kansas State University, 213 CBC Building, Manhattan, Kansas 66506-0401, USA.
authors.forename: Mausam
authors.initials: M
authors.lastname: Kalita
authors.forename: Sreeram
authors.initials: S
authors.lastname: Cingarapu
authors.forename: Santanu
authors.initials: S
authors.lastname: Roy
authors.forename: Seok Chan
authors.initials: SC
authors.lastname: Park
authors.forename: Daniel
authors.initials: D
authors.lastname: Higgins
authors.forename: Ryszard
authors.initials: R
authors.lastname: Jankowiak
authors.forename: Viktor
authors.initials: V
authors.lastname: Chikan
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Klabunde
authors.forename: Stefan H
authors.initials: SH
authors.lastname: Bossmann
mesh_terms: D019187:Cadmium Compounds / Q000138:chemical synthesis / Q000737:chemistry; D060326:Chemistry Techniques, Synthetic / Q000379:methods*; D008024:Ligands; D011725:Pyridines / Q000737:chemistry*; D045663:Quantum Dots; D018036:Selenium Compounds / Q000138:chemical synthesis / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D013691:Tellurium / Q000737:chemistry; D013997:Time Factors; D014867:Water / Q000737:chemistry*
chemical_list: D019187:Cadmium Compounds; D008024:Ligands; D011725:Pyridines; D018036:Selenium Compounds; D012997:Solvents; D014867:Water; C058667:cadmium selenide; D013691:Tellurium; C028337:cadmium telluride; C034306:4,4'-bipyridyl