Surface modification of colloidal semiconductor nanocrystal quantum dots

Current quantum dot surface modification strategies rely heavily on ligand exchange that removes the nanocrystal\u27s native ligands originated from its synthesis. This can cause etching and introduce surface defects, affecting the nanocrystal\u27s optical properties. In addition, common ligand exchange method fails to control the degree of functionalization or the number of functional groups introduced per nanocrystal. We describe our work on surface modification of semiconductor nanocrystal quantum dots investigating a new approach that not only bypasses ligand exchange and introduces native active ligands with original optical properties, but also is able to control the degree of surface loading, called valence , in semiconductor nanocrystal quantum dots. We show that surface doped quantum dots capped with chemically-active native ligands can be prepared directly from a mixture of ligands with similar chain lengths. Initial ratio between chemically active and inactive ligands is retained on the nanocrystal surface, allowing to control the extent of surface modification. The extent of surface coverage by a particular functional group will have a large impact on a nanocrystal affinity and permeability to a variety of biological structures. It also affects nanocrystal\u27s ability to localize, penetrate, and transport across specific tissues, cellular and subcellular structures. We show that we are able to control the loading of cholestanone per quantum dot nanocrystal. We observed that samples with higher steroid loading infuse themselves more with the lipid membrane compare to those with no or little steroid. To further investigate the surface ligand packing, structure and reactivity, we apply advanced solution NMR techniques to determine surface ligand organization and chemistry. Two-dimension ROESY studies show that ligands with the same chain length tend to homogeneously distribute themselves onto the nanocrystal\u27s surface however ligands with the different chain length tend to form islands. Furthermore, we demonstrate that surface ligand organization can affect the reactivity of quantum dots. Formation of rafts as a result of packing ligands of a same length, increase the local concentration of reactive terminal group and facilitate the chemical reactivity at the surface of quantum dots. We also synthesize multifunctional multidentate polymeric ligand via ADMET. Varying the total dienes-to-Ru catalyst ratio allows us to control the extent of ADMET, which enables us to achieve an accurate control over polydentate ligand size. We use the synthetic polymer as a linkage for constructing gold-QD heterostructure. We hope that this study can provide a new avenue to understand the organic/inorganic boundary of other and more complex nanoparticle/ligand systems

Distribution and Fate of Per- and Polyfluorinated Alkyl Substances (PFAS) in Wastewater Treatment Plants Discharging to Great Bay

Per-and polyfluoroalkyl substances (PFAS) represent a major class of emerging contaminants composed of nearly 5000 human-made chemicals. PFAS have been used since the 1950s as surfactants in industrial and consumer products due to their unique water and oil repellency, high surface activity, and thermostability. These compounds can bioaccumulate and pose human and ecological health concerns; for example, PFAS intensive exposure can affect the liver, reproduction and development in humans and wildlife. Ubiquitous presence of these compounds in different environmental matrices, high persistency, and potential threats to human and environmental health, have made it critical to develop an understanding of how they are distributed in different matrices and how people get exposed. Previous studies have provided some understanding of how environmental conditions, chemical structures and properties affect PFAS distribution, fate, and their biotransformation. In addition, PFAS environmental exposure studies have been completed or are underway; and while it is clear that exposures are occurring, the effects associated with exposure are not fully understood and therefore there is significant uncertainty associated with evaluation of risks associated with PFAS in environment. Wastewater treatment facilities (WWTFs) are a conduit of PFAS which are not originally designed for the removal of these low level and diverse contaminants. In this study, PFAS distribution and fate in six WWTFs discharging their effluent into Great Bay Estuary in March and July 2019 were investigated. PFAS were detected in influent and effluent of WWTFs with up to 12 detected constituents out of 24 measured by standard analytical method (LC/MS/MS). In general, PFAS concentrations increased in effluent after biological treatment which supports the presence of unknown PFAS precursors in influent not measured during standard analytical method. Seasonal changes exhibited a significant influence on PFAS concentrations in effluent. Higher PFAS concentrations were detected in the warmer season, indicating the effect of temperature and higher microbial activities on PFAS precursor degradation. In addition, PFAS precursors were indirectly quantified by oxidizing precursors into terminal PFAAs compounds using the total oxidizable precursor assay (TOP assay). Higher perfluoroalkyl acids (PFAA) concentrations after oxidation compared to unoxidized samples confirmed the presence of PFAS precursors in WWTFs

Clonidine Versus Chloral Hydrate for Recording Sleep EEG in Children

ObjectiveOne of the difficulties for conduct electroencephalography (EEG) in pediatric patient population is that they are not always cooperative during the procedure. Different medications have been used to induce sedation during EEG recording. In order to find a medication with least adverse effects and high efficacy, we aimed to compare clonidine and chloral hydrate as a premedication prior EEG performing in pediatric population. Materials & MethodsA prospective, randomized, single-blinded, controlled trial was carried out over 198 children (9 to 156 months) to investigate the sedative and adverse effects of clonidine and chloral hydrate. Patients, partially sleep-deprived the night before, were randomly divided in two groups of clonidine (100 patients) and chloral hydrate (98 patients), on an alternative day basis.Results The average sleep onset latency was significantly longer in the clonidine group than chloral hydrate group (Mann-Whitney test, p < 0.0001). Sleep duration ranged between 15-150 minutes and it was not significantly different between two groups (Mann-Whitney test p = 0.2). Drowsiness with chloral hydrate terminated faster than with clonidine. Drowsiness after arousal was seen in 58% and 26.1% of patients in the clonidine and chloral hydrate groups respectively that was  significant  (Mann-Whitney test, p = 0.058). EEG results were reported normal in 77 subjects in the chloral hydrate group (77%) and in 69 subjects (69%) in the clonidine group (p = 0.161). Generalized epileptiform discharges  reported significantly  in the clonidine group  (Mann-Whitney test , p = 0.006).ConclusionThe results of this study showed that both chloral hydrate 5% (one ml/kg)and clonidine (4 μg/kg)could be administered as a pre medication agent for EEG recording in children , although drowsiness after arousal of clonidine is greater than chloral hydrate . However, the yield of generalized epileptiform discharges in the clonidine group was more than the chloral hydrate group.

Surface Doping Quantum Dots with Chemically Active Native Ligands: Controlling Valence without Ligand Exchange

One remaining challenge in the field of colloidal semiconductor nanocrystal quantum dots is learning to control the degree of functionalization or valence per nanocrystal. Current quantum dot surface modification strategies rely heavily on ligand exchange, which consists of replacing the nanocrystal\u27s native ligands with carboxylate- or amine-terminated thiols, usually added in excess. Removing the nanocrystal\u27s native ligands can cause etching and introduce surface defects, thus affecting the nanocrystal\u27s optical properties. More importantly, ligand exchange methods fail to control the extent of surface modification or number of functional groups introduced per nanocrystal. Here, we report a fundamentally new surface ligand modification or doping approach aimed at controlling the degree of functionalization or valence per nanocrystal while retaining the nanocrystal\u27s original colloidal and photostability. We show that surface-doped quantum dots capped with chemically active native ligands can be prepared directly from a mixture of ligands with similar chain lengths. Specifically, vinyl and azide-terminated carboxylic acid ligands survive the high temperatures needed for nanocrystal synthesis. The ratio between chemically active and inactive-terminated ligands is maintained on the nanocrystal surface, allowing to control the extent of surface modification by straightforward organic reactions. Using a combination of optical and structural characterization tools, including IR and 2D NMR, we show that carboxylates bind in a bidentate chelate fashion, forming a single monolayer of ligands that are perpendicular to the nanocrystal surface. Moreover, we show that mixtures of ligands with similar chain lengths homogeneously distribute themselves on the nanocrystal surface. We expect this new surface doping approach will be widely applicable to other nanocrystal compositions and morphologies, as well as to many specific applications in biology and materials science

Surface modification of colloidal semiconductor nanocrystal quantum dots

Current quantum dot surface modification strategies rely heavily on ligand exchange that removes the nanocrystal's native ligands originated from its synthesis. This can cause etching and introduce surface defects, affecting the nanocrystal's optical properties. In addition, common ligand exchange method fails to control the degree of functionalization or the number of functional groups introduced per nanocrystal. We describe our work on surface modification of semiconductor nanocrystal quantum dots investigating a new approach that not only bypasses ligand exchange and introduces native active ligands with original optical properties, but also is able to control the degree of surface loading, called "valence", in semiconductor nanocrystal quantum dots. We show that surface doped quantum dots capped with chemically-active native ligands can be prepared directly from a mixture of ligands with similar chain lengths. Initial ratio between chemically active and inactive ligands is retained on the nanocrystal surface, allowing to control the extent of surface modification. The extent of surface coverage by a particular functional group will have a large impact on a nanocrystal affinity and permeability to a variety of biological structures. It also affects nanocrystal's ability to localize, penetrate, and transport across specific tissues, cellular and subcellular structures. We show that we are able to control the loading of cholestanone per quantum dot nanocrystal. We observed that samples with higher steroid loading infuse themselves more with the lipid membrane compare to those with no or little steroid. To further investigate the surface ligand packing, structure and reactivity, we apply advanced solution NMR techniques to determine surface ligand organization and chemistry. Two-dimension ROESY studies show that ligands with the same chain length tend to homogeneously distribute themselves onto the nanocrystal's surface however ligands with the different chain length tend to form islands. Furthermore, we demonstrate that surface ligand organization can affect the reactivity of quantum dots. Formation of rafts as a result of packing ligands of a same length, increase the local concentration of reactive terminal group and facilitate the chemical reactivity at the surface of quantum dots. We also synthesize multifunctional multidentate polymeric ligand via ADMET. Varying the total dienes-to-Ru catalyst ratio allows us to control the extent of ADMET, which enables us to achieve an accurate control over polydentate ligand size. We use the synthetic polymer as a linkage for constructing gold-QD heterostructure. We hope that this study can provide a new avenue to understand the organic/inorganic boundary of other and more complex nanoparticle/ligand systems.</p