Surface Modification Of Quantum Dots Research Articles

Sol–gels doped with polymer-coated ZnS/CdSe quantum dots for the detection of organic vapors

A novel luminescent sensing material for the detection and discrimination of different organic vapors has been developed and characterized. For such purpose, colloidal polymer surface-modified ZnS/CdSe semiconductor quantum dots (QDs) were synthesized and trapped into sol–gel inorganic matrices following a simple and friendly procedure. It was observed that the QDs entrapped into the sol–gels maintain invariable optical properties. Moreover, rapid and reversible quenching of the fluorescence from the immobilized QDs upon exposure of the doped sol–gel materials to several organic vapors was observed, with the onset of the quenching process being dependent on the target gas type and on its concentration. After a necessary previous photoactivation, the luminescence of the immobilized quantum dots was found to exhibit a distinct behavior when exposed to different organic vapors at atmospheric pressure. The sensing response from the surface-modified quantum dots was also dependent upon the porous sol–gel matrix composition. Two different active materials were prepared using the same colloidal polymer-coated ZnS/CdSe QDs but changing the composition of the precursors used during the sol–gel preparation and doping process. After exposing the synthesized materials to the different organic analytes gaseous samples, the measured luminescence responses were processed, by multivariate analysis and a dynamic pattern recognition method. Results obtained demonstrated the analytical potential of ZnS/CdSe doped sol–gels as luminescent sensing materials for the rapid detection of organic vapors in contaminated atmospheres.

Quantum Dot-Based OFF/ON Probe for Detection of Glutathione

A simple strategy for detection of glutathione (GSH) in physiologically relevant concentrations is reported by manipulating the electron transfer pathways of surface-modified quantum dots. The probe consisted of fluorescent CdS:Mn/ZnS core/shell quantum dots (Qdot) properly conjugated to dopamine through CS2-assisted zero-length covalent coupling. Qdots exhibited bright yellow-orange emission at ∼ 592 nm, which could be attributed to the 4T1 → 6A1 transition of Mn2+ ions in Qdot core. The fluorescently dark Qdots (OFF state) was obtained by modifying the Qdot surface with an electron rich dopamine molecule. The fluorescence of the probe was restored (ON state) when the disulfide bond was cleaved by the reducing GSH.

RETRACTED: l-Cysteine-capped ZnS quantum dots based fluorescence sensor for Cu2+ ion

Abstract This paper describes the investigation of surface modified quantum dots (QDs) as a sensing receptor for Cu 2+ ion detection by optical approach. Water-soluble l -cysteine-capped ZnS QDs have been synthesised in aqueous medium. These functionalised nanoparticles were used as a fluorescence sensor for Cu (II) ion, involved in the fluorescence quenching. The optimum fluorescence intensity was found to be at pH 5.0 with a nanoparticle concentration of 2.5 mg L −1 . The effect of foreign ions on the intensity of ZnS QDs showed a low interference response towards other metal ions except Ag + and Fe 3+ ions. The quenching mechanism was studied and the results show the existence of both static and dynamic quenching processes. However, static quenching is more prominent of the two. The limit of detection of this system was found to be 7.1 × 10 −6 M. When compared with single organic fluorophores, l -cysteine-capped ZnS QDs are brighter and more stable against photobleaching. This method is not only simple, sensitive and low cost, but also reliable for practical applications.

Quantum Dots for Cancer Diagnosis and Therapy: Biological and Clinical Perspectives

Quantum dots (QDs) are semiconductor nanocrystals that emit fluorescence on excitation with a light source. They have excellent optical properties, including high brightness, resistance to photobleaching and tunable wavelength. Recent developments in surface modification of QDs enable their potential application in cancer imaging. QDs with near-infrared emission could be applied to sentinel lymph-node mapping to aid biopsy and surgery. Conjugation of QDs with biomolecules, including peptides and antibodies, could be used to target tumors in vivo. In this review, we summarize recent progress in developing QDs for cancer diagnosis and treatment from a clinical standpoint and discuss future prospects of further improving QD technology to identify metastatic cancer cells, quantitatively measure the level of specific molecular targets and guide targeted cancer therapy by providing biodynamic markers for target inhibition.

PEG-ylated cationic CdSe/ZnS QDs as an efficient intracellular labeling agent

Quantum dots (QDs) have size-tunable optical properties, such as photostability, strong photoluminescence and a large Stokes-shift, which make it possible to adapt them to various biological applications. In many cases, surface modification of QDs by carboxylate ligands has been extensively studied. However, there have been few applications on QDs modified with a potential cationic ligand such as amine. In this study, we synthesized robust amine-functionalized QDs and modified their surface with poly(ethylene glycol) for long-term stability. These QDs showed an excellent stability over a broad pH-range and remarkable internalization efficiency into living cells.

Fluorescence millisecond oscillation in polar solvents regulates fluorescence intensity of colloidal quantum dots' solution

Quantum Dots (QDs) have been used in life science study because of their higher emission and photostability. Although physicochemical and biological properties of QDs were varied dramatically by the surface modification of QDs, little is known about the reason why the photoluminescence intensity (PLI) of QDs was changed by surface modification. We report the millisecond-span change of PLI of QD's collective fluorescence oscillation. QDs covered with carboxylic acid and hydroxyl groups show enhanced PLI by adding NaN3, whereas QDs with amine showed less. Removal of NaN3 from QD solution abrogated the enhanced PLI. In addition, observation evanescent field revealed that addition of antioxidants induced enhanced oscillation of QDs. Furthermore, the blinking count at one millisecond was also increased by addition of antioxidants. However the oscillation enhancement is observed in both aqueous solution and polar organic solvents but not in nonpolar organic solvents, indicating that PLI of QD was varied by the interaction between QDs and their environmental solvents. These millisecond oscillation mechanism was independent of on and off events which were conventionally known as blinking. Taken together, the fluorescent emission of colloidal QDs is affected by both surface-covered colloidal molecules and external solvents around at millisecond span interaction.

Are quantum dots ready for in vivo imaging in human subjects?

Nanotechnology has the potential to profoundly transform the nature of cancer diagnosis and cancer patient management in the future. Over the past decade, quantum dots (QDs) have become one of the fastest growing areas of research in nanotechnology. QDs are fluorescent semiconductor nanoparticles suitable for multiplexed in vitro and in vivo imaging. Numerous studies on QDs have resulted in major advancements in QD surface modification, coating, biocompatibility, sensitivity, multiplexing, targeting specificity, as well as important findings regarding toxicity and applicability. For in vitro applications, QDs can be used in place of traditional organic fluorescent dyes in virtually any system, outperforming organic dyes in the majority of cases. In vivo targeted tumor imaging with biocompatible QDs has recently become possible in mouse models. With new advances in QD technology such as bioluminescence resonance energy transfer, synthesis of smaller size non-Cd based QDs, improved surface coating and conjugation, and multifunctional probes for multimodality imaging, it is likely that human applications of QDs will soon be possible in a clinical setting.

Surface-functionalized CdSe quantum dots for the detection of hydrocarbons

CdSe semiconductor quantum dots (QDs) were synthesized with surface modifying groups to enhance their response towards the detection of aromatic hydrocarbons. The sensing characteristics of unmodified QDs using trioctyl phosphine oxide (TOPO) plus stearic acid (SA) surface groups were compared with QDs with additional benzoic (BA) or pentafluorobenzoic acid (FBA) surface modifying groups. The unmodified and surface-modified QDs were encapsulated into poly(methyl methacrylate) (PMMA) thin films by drop coating QD-PMMA solutions onto silicon substrates. Reversible enhancement and quenching of the photoluminescence (PL) upon film exposure to toluene and xylene vapors were both observed for the QD-SA, BA and FBA systems. PL enhancement was observed at low target gas concentrations, with the onset of the quenching process for each of the films being dependent on the target gas type and its concentration. Unmodified QD/PMMA films had detection limits for xylenes and toluene of 250 and 500 ppm, respectively in a balance of nitrogen. While detection limits of 15 ppm xylenes and 50 ppm toluene in a balance of nitrogen were achieved with the FBA- and BA-modified QD/PMMA films. The surface-modified QDs were found to provide a factor of 16 and 10 sensing enhancement, respectively, for the detection of xylenes and toluene, over the unmodified QDs.

Photoluminescence dynamics of energy transfer between CdS quantum dots prepared by a colloidal method

We have investigated the energy transfer process in CdS quantum dots (QDs) prepared by a colloidal method. By applying a surface-modification method, the band-edge photoluminescence (PL) is intensely observed as a main PL band. The surface-modified QDs were dispersed in polyvinyl alcohol films, where the QD solutions were variously concentrated by a factor from 1 to 250. The change of the degree of concentration corresponds to the change of a mean distance between QDs. In the 1-, 10-, and 75-times concentrated samples, the decay profiles of the band-edge PL do not depend on detection energies and exhibit a slow decay in the order of hundreds of nanosecond. On the other hand, the PL-decay profiles in the 250-times concentrated sample exhibit faster decays as compared with the dilute samples. The faster decay suggests a new decay channel due to an effective energy transfer process between CdS QDs.

Physicochemical Properties and Cellular Toxicity of Nanocrystal Quantum Dots Depend on Their Surface Modification

Nanocrystal quantum dots (QDs) have been applied to molecular biology because of their greater and longer fluorescence. Here we report the potential cytotoxicity of our characterized QDs modified with various molecules. Surface modification of QDs changed their physicochemical properties. In addition, the cytotoxicity of QDs was dependent on their surface molecules. These results suggested that the properties of QDs are not related to those of QD-core materials but to molecules covering the surface of QDs.