However, little attention has been paid to exploiting the chemical reactions performed on the surface of Qdots after their synthesis. I have submitted this dissertation to the Department of Chemistry, Indian Institute of Technology, Guwahati, for the award of the degree of Doctor of Philosophy.
Acknowledgements
Role of Surface Ion in the Emission Characteristics of Quantum Dots 17
Double Channel Emission from a Redox Active Single Component Quantum
Surface Complexation Based Biocompatible Magnetofluorescent Nanoprobe
Introduction
Quantum Dots
- The Definition
- The History
- Types
- The Unique Optical Properties Qdots and Their Tailoring
- Size
- Incorporation of Impurity
- Surface
- The Applications
Schematic representation of the quantum confinement effect resulting in the discretization of energy levels based on the reduced dimension of the bulk semiconductor. Schematic representation of the electronic band structure of (A) direct and (B) indirect semiconductors in their lowest transitions.
Chemical Functionalization of Qdots
- Ligand Exchange
- Conjugate Formation
- Other strategies
Therefore, the ligand exchange has become an important and popular strategy for changing the properties of the Qdots and thus for their specific applications. Apart from the ligand exchange strategy, there is another way to modify the surface of the Qdots in which no replacement of existing stabilizer is required.
Chemical Reactions
- Ion Exchange Reaction
- Cation exchange resin Bead (CB)
- Complexation Reaction
Further study in this area should continue to synthesize a library of Qdots and mechanistic understanding of the role of the surface (mostly the surface ions) in the optical properties of Qdots after their synthesis. This thesis will describe the formation of the metal quinolate complexes on the surface of Qdots and the consequences in terms of changes in optical characteristics and solubility of Qdots.
Role of Surface Ion in the Emission Characteristics of Quantum Dots
Experimental Section
To monitor the spectroscopic properties of the NCs, dispersions of the NCs were prepared in hexane.162-163. Then, 30.0 µL of 12 M HCl was added to each of the dried samples, followed by sonication and finally the volume of each added HCl sample was adjusted to 10.0 mL with Milli-Q water.
Results and Discussion
Dependence of (A) NBE/DLE intensity ratio and shifts of DLE max on the amount of CB beads added to NC dispersion (in hexane) and (B) quantum yield (%) of the NCs on CB amount. The results also imply that surface ions played an important role in the emission characteristics of the NCs.
Conclusion
Complexation on the Surface of Quantum dot
Experimental Section
The same procedure was followed to synthesize uncapped ZnS Qdots instead of using cysteine (except that the mixture was refluxed at 100 °C for half an hour to avoid much agglomeration). The details of this are described in Figure A.3.1, Appendix. The optimal amount of ligand and complex added to 2.0 ml of Qdots dispersion was 30.0 l and 100.0 l, respectively.
Results and Discussion
The significant blue shift observed in the emission spectrum in the presence of Qdots may be due to the presence of S2 ions on the surface of the Qdots. The formation of Zn2+–quinolato complex on the surface of the Qdots was further substantiated by FTIR spectroscopic results.
Conclusion
The stability of the complex on the surface was achieved through the inclusion of dangling sulfide bonds. Furthermore, the transferred hydrophilic Qdots—termed here quantum dot complexes (QDCs)—exhibited novel and superior optical properties compared to the bare inorganic complexes by retaining the dimension and core structure of the Qdots.
Experimental Section
Briefly, 5 mL of oleate-capped ZnxCd1−xS Qdots (2.0 mg/10 mL) in hexane was mixed with an equal volume of solution containing 4.0 mL of Milli-Q water and 1 mL of methanol, at varying concentrations of HQ. In addition, we performed a phase transfer reaction where the aqueous phase contains both complexes at equal concentrations (i.e., 1.0 mL methanolic solution containing 0.05 mM ZnQ2 + 0.05 mM CdQ2).
Results and Discussion
In addition, the surface complexation reaction for Qdots with HQ or with MQ2 (M = Zn or Cd) resulted in quenching of the Qdots emission. Further evidence for the transfer of Qdots came from transmission electron microscopy (TEM) and X-ray diffraction measurements. The average Qdot size (value) was also preserved (Figure 4.2 A, B).174 High-resolution TEM (HRTEM) and Inverse Fast Fourier Transform (IFFT) images of a sample prepared from water.
In general, the reaction of the Qdots with HQ led to the formation of surface complexes that quenched the emission of the Qdots.
Conclusion
The change has been attributed to the binding of the complex with dangling sulfide ion on the surface of the Qdots.175 We call this new species as quantum dot complex (QDC), where an inorganic complex is formed on the surface of a quantum dot resulting in distinct optical properties. Schematic representation of quantum dot complex (QDC) formation on the surface of hydrophobic oleate capped ZnxCd1-xS Qdots involving surface Cd2+ and Zn2+ ions and organic ligand (HQ) after phase transfer reaction from hexane to water.
Double Channel Emission from a Redox Active Single Component Quantum Dot Complex
Experimental Section
Briefly, to 2.0 mL of differently capped dispersions of 5.0−6.0% Mn2+ doped ZnS Qdots in water, an excess (100.0 μL) of 5.0 mM HQ (in methanol) was added separately and the resulting mixtures were centrifuged. The obtained pellet was resuspended in the same amount of solvent and used to observe changes in fluorescence. The pellet was resuspended in the same amount of solvent and used to monitor spectroscopic changes in fluorescence.
The pellet was resuspended in the same amount of solvent and the resuspension was used to monitor.
Results and Discussion
The extent of quenching was limited to the concentration of ZnQ2 present on the Qdot surface. This clearly indicates the formation of a metal-oxanate complex on the Qpik surface. Furthermore, it seemed important to identify the excitation source associated with the emission at 500 nm due to the ZnQ2 complex on the Qdot surface.
Thermogravimetric analysis (TGA) of Qdots and QDCs showed similar types of weight loss (15−20%) up to 90 °C due to the removal of adsorbed water from the surface.
Conclusion
Surface Complexation Based Biocompatible
Magnetofluorescent Nanoprobe for Targeted Cellular Imaging
Experimental Section
Unbound ZnS Qpikes were removed using a magnetic field and the particles accumulated towards the magnet were collected. The emission spectrum (ex-365 nm) of the synthesized Fe3O4-ZnS in the presence of HQ was used to monitor and confirm the completeness of the complexation reaction. The solid form of the pellet was used for optical microscopy, Fourier transform infrared (FTIR) and X-ray diffraction (XRD).
The cells were similarly incubated with SPION-QDC in the absence of the magnet and processed as above for other analyses.
Results and Discussion
Powder X-ray diffraction (XRD) pattern of solid HQ-treated Fe3O4-ZnS. A) High resolution TEM (HRTEM; scale bar- 5 nm) and (B) corresponding inverse fast Fourier transform (IFFT) images and (C) selected area electron diffraction (SAED) pattern (scale bar: 5 nm-1) of aqueous dispersion of HQ-treated Fe3O4-ZnS. Moreover, the stability of the luminescence (at ex-365 nm and em-500 nm) of SPION-QDC in human blood serum (measured for 24 h) indicated its clinical application potential (Figure 6.8B). A small magnet was placed under the petri dish and closer to one of the coverslips (Figure 6.10).
Digital image of the setup used for magnet-driven cellular imaging of HeLa cells using HQ-treated Fe3O4-ZnS composite.
Conclusion
Summary and Future Prospects
Summary
Future Prospects
Appendix
A2: Chapter 2
Interplanar distances of as-prepared ZnxCd1-xS NCs measured from HRTEM image (reported) and observed.
A3: Chapter 3
Spectra were recorded with an LED (308 nm). B) Time-resolved photoluminescence spectra of (a) ZnQ2; (b) HQ-doped ZnS Qpikes and (c) ZnQ2-doped ZnS Qpikes. Microscopic images of cysteine-capped ZnS Qpikes in the presence of (A) white and (B) UV light (ex = 350 nm). Complexation decay parameters between cysteine-capped ZnS Qdots and 8-HQ or ZnQ2 monitored at 375 nm (using LASER).
Tabulated FTIR wavenumber versus functional groups of (a) ZnQ2, (b) cysteine-capped ZnS Qdots, (c) HQ-doped ZnS Qdots, and (d) ZnQ2-doped ZnS Qdots.
A4: Chapter 4
Details of the phase transfer systems for the transfer of oleate-capped ZnxCd1-xS Qdots form the hexane phase to the aqueous phase after complexation with different amounts of HQ. Details of the phase transfer systems for the transfer of oleate-capped ZnxCd1-xS Qdots form the hexane phase to the aqueous phase after complexation with MQ2. Dependence of % depletion (or transfer efficiency) on the amount of HQ used for the surface complexation reaction during the transfer of oleate-capped ZnxCd1-xS Qdots from the hexane phase to the aqueous phase.
The dependence of % of depletion (or transfer efficiency) on different complexes used for surface complexation reaction during transfer of oleate-coated ZnxCd1-xS Qdots from hexane phase to aqueous phase.
A5: Chapter 5
Mn2+ doped ZnS Qdots with different capping environments: (A) no capping agents, (B) citrate-capped and (C) chitosan-capped and (D, E and F) of their respective product after complexation with HQ. Presence (P) and absence (A) of the above functional groups in the product after complexation between HQ and 5.0-6.0% Mn2+ doped ZnS Qdots with different capping agents. Tabulated FTIR wavenumber versus functional groups of the product after complexation between HQ and 5.0-6.0% Mn2+ doped ZnS Qdots with different capping agents.
Tabulated intensity ratio of 3333 cm-1 band to 1110 cm-1 band of the product after complexation between HQ and 5.0-6.0% Mn2+ doped ZnS Qdots with different coating environments.
A6: Chapter 6
Decay profiles (using 340 nm LED as excitation source) of the aqueous dispersion of HQ-treated Fe3O4-ZnS (em = 500 nm) which were fitted by tri-exponential function. Microscopic images of solid samples of HQ-treated Fe3O4-ZnS in the presence of (A) white and (B) UV light ex = 350 nm). The solids of the particles were placed on a slide and then imaged under a fluorescence microscope. Fluorescence images (scale bar – 100 m) of HeLa cells – which were grown in a petridis containing two slides (A and B) – after 4 hours of incubation with HQ-treated Fe3O4/ZnS.
FE/UN ratio in a water dispersion table (a) Fe3O4-ZNS and (b) Fe3O4-ZNS treated with HQ.
Instruments
Redox-tuned tricolor emission in doubly (Mn and Cu) doped zinc sulfide quantum dots J. Phys. Klimov, V. I.; Pietryga , J. M. Highly Efficient Surface Passivation of PbSe Quantum Dots by Reaction with Molecular Chlorine J. Am. Chem. Fuji, F.; Yamada, E.; Nodasaka, Y.; Kinjo , M. Controlling the Optical Properties of Quantum Dots by Surface Coating with Calix[n]arene Carboxylic Acids J.
Zhan, N.; Pan, F.; Gray, D.; Alabugin, I.; Mattoussi , H. Photoinduced Phase Transfer of Luminescent Quantum Dots to Polar and Aqueous Media J. Am. Chem.
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![Figure 1.8. Schematic representation of (A) polymer encapsulation of CdSeS/ZnS Qdots making them extremely high bright for two-photon cellular and deep-tissue imaging (Reprinted with permission from Reference [131]](https://thumb-ap.123doks.com/thumbv2/azpdfnet/10509777.0/25.893.105.718.118.445/schematic-representation-encapsulation-extremely-cellular-reprinted-permission-reference.webp)
