Luminescent CdS Quantum Dots as Selective Ion Probes

Abstract

Water-soluble luminescent CdS quantum dots (QDs) capped by polyphosphate, L-cysteine, and thioglycerol were synthesized in aqueous solution. The ligands were found to have a profound effect on the luminesence response of CdS QDs to physiologically important metal cations. Polyphosphate-capped CdS QDs were sensitive to nearly all mono- and divalent cations, showing no ion selectivity. Conversely, thioglycerol-capped CdS QDs were sensitive to only copper and iron ions. Similar concentrations of physiologically relevant cations, such as zinc, sodium, potassium, calcium, and magnesium ions did not affect the luminescence of thioglycerol-capped CdS QDs. On the other hand, L-cysteine-capped CdS QDs were sensitive to zinc ions and insensitive to other physiologically important cations, such as copper, calcium, and magnium ions. To demonstrate the detection capability of these new ion probes, L-cysteine and thioglycerol-capped CdS QDs were used to detect zinc and copper ions in physiological buffer samples. The detection limits were 0.8 microM for zinc (II) and 0.1 microM for copper (II) ions. The emission enhancement of the QDs by zinc (II) is attributed to activation of surface states, whereas the effective reduction of copper (II) to copper (I) may explain the emission decrease of the thioglycerol-capped CdS QDs when charged with copper ions. Unlike organic fluorescent dyes, the thioglycerol-capped luminescent CdS QDs discriminate between copper and zinc ions and are therefore suitable for the analysis of copper ions in biological samples in the presence of physiological concentrations of zinc ions. The interference of iron ions with zinc and copper ion detection is attributed to an inner filter effect, which is eliminated by adding fluoride ions to form the colorless complex FeF6(3-). To the best of our knowledge, this is first use of luminescent semiconductor quantum dots as selective ion probes in aqueous samples.

The Composites of Cationic Polyelectrolyte and Glutathione‐capped Quantum Dots for Selective Fluorescence Detection of Cu2+

“…Besides, fluorescence resonance energy transfer from the fluorophore to the quencher has been applied to sensing of Cu 2+ with high sensitivity and selectivity. [17][18][19] Recently, colloidal semiconductor nanocrystals (quan- 22 The same phenomenon has been discovered in the case of 2-mercaptioethane sulfonic acid-modified CdSe QDs. 23 The addition of F -to a solution of QDs can further improve the selectivity of QDs owing to the formation of the colorless complex FeF 6 3-.…”

Recent developments on nanomaterials-based optical sensors for Hg2+ detection

“…This behavior provides the basis for developing fluorescent sensor with QDs. Generally, the interaction of metal ions with QDs leads to a fluorescence quenching which can be explained by electron transfer process, ion binding interaction, inner filter effect and non radiative recombination pathway [66]. In some cases, fluorescence enhancement, which is usually attributed to the passivation of trap states or defects on the QDs surfaces, can also be observed.…”

“…Since Chen and Rosenzweig [66] 2+ were the most studied. Nowadays, different Cd-chalcogenide QDs (CdS, CdSe, CdTe) coated with thiol-containing organic molecules such as L-cysteine (L-Cys), mercaptoacetic acid (MAA), mercaptopronionic acid (MPA), denatured bovine serum albumin (dBSA), cysteamine (CA) and thioglycolic acid (TGA) were synthesized and used as fluorescent probes to detect Hg 2+ [67][68][69][70][71][72].…”

Determination of Silver Ion with Cadmium Sulfide Quantum Dots Modified by Bismuthiol II as Fluorescence Probe

“…Due to quantum confinement effects, when the size of quantum dots is close to or smaller than that of the Bohr exciton, quantum dots exhibit special physical and chemical properties greatly different from those of their corresponding bulks 10,11 . The intense interest in quantum dots (QDs) gives rise to their potential use in a variety of fields, e.g., optoelectronics 12,13 , lasers 14,15 , biological immunoassays 16 , biosensors 17 , technical applications such as light-emitting devices [18][19][20] , and fluorescent labels 21 . Surface functionalized nanoparticles can be attached to larger particles 22 or modified to suit a particular environment or application.…”

“…The use of QDs as selective chemo-sensors for metal ions has been an active research field in recent years. After Chen and Rosenzweig first demonstrated the luminescent quantum dots probes for copper and zinc ions by utilizing functionalized CdS QDs modified by different organic ligands in aqueous medium 17 , Myung et al showed and discussed the photoluminescence enhancement effect of CdSe nanoparticles dispersed in CHCl 3 by oxygen passivation of surface states 29 . Recently, Sanz-Medel et al reported surface-modified CdSe quantum dots as luminescent probes for cyanide determination 30,31 .…”