Gold Nanorod/Titanium Dioxide Hybrid Nanoparticles for Plasmon-Enhanced Near-Infrared Photoproduction of Hydroxyl Radicals and Photodynamic Therapy

Gold nanoparticles, such as nanorods (AuNRs), present exceptionally high absorption cross sections that can be tuned to the near-infrared (NIR), the optimal window for light penetration in biological tissues. This makes them valuable photosensitizers for the treatment of cancer using photothermal therapy, where absorbed light energy is converted into heat. In addition, there is a strong interest in using hot electron carriers generated in AuNRs by NIR irradiation to produce cytotoxic radical oxygen species in order to enhance the efficiency of the phototherapy. Here, we show that hybrid nanoparticles composed of AuNRs with TiO2 deposited at their extremities are efficient sensitizers to produce hydroxyl radical species under NIR irradiation. We attribute this phenomenon to the transfer of hot electrons generated from the plasmon excitation in AuNR to the TiO2 tips, followed by reduction of dioxygen. We then functionalize these hybrid AuNR/TiO2 nanoparticles with block poly­(ethylene glycol)-phosphonate polymer ligands to stabilize them in a physiological medium. We finally demonstrate that the photodynamic effect induces cell death upon irradiation with a greater efficiency than the photothermal effect alone

pH-Sensitive Visible or Shortwave Infrared Quantum Dot Nanoprobes Using Conformation-Switchable Copolymeric Ligands

Intracellular and extracellular pH are key parameters in many physiological processes and diseases. For example, the extracellular pH of the tumor micro-environment is slightly more acidic than in healthy tissue. In vivo mapping of the extracellular pH within the tumor would therefore improve our understanding of the tumor physiology. Fluorescent semiconductor quantum dots (QDs) represent interesting probes for in vivo imaging, in particular in the shortwave infrared (SWIR) range. Here, pH-sensitive QD nanoprobes are developed using a conformation-switchable surface chemistry. The central fluorescent QD is coated with a copolymer ligand and conjugated to gold nanoparticle quenchers. As the pH decreases from physiological (7.5) to slightly acidic (5.5–6), the copolymer reversibly shrinks, which increases the energy transfer between the QD and the gold quenchers and modulates the QD fluorescence signal. This enables the design of ratiometric QD probes for biological pH range emitting in the visible or SWIR range. In addition, these probes can be easily encapsulated and remain functional within ghost erythrocyte membranes, which facilitate their in vivo application

Micropatterning of Quantum Dots for Biofunctionalization and Nanoimaging

Micron-scale patterning of colloidal quantum dots (QDs) is extremely important for the fabrication of high-performance Quantum dot Light-Emitting Diode (QLED) displays, biosensing, and super-resolution imaging. Thus, several nondestructive methods have been recently proposed, such as spatial self-organization. However, none of them can be useful for biofunctionalization or nanoimaging. To address this limitation, we propose a method to create micropatterns of QDs of any shape and size. UV photolithography assisted by a digital micromirror device (DMD) and silanization allow creating an adhesive layer, on which QDs micropatterns can be assembled with a 2 μm resolution. The patterns are composed of a monolayer of CdSe/CdS/CdZnS/ZnS core/multishell QDs (7 ± 1 nm in diameter, emitting at 590 nm) with a high surface density (typically 4000 QDs/μm2). We also demonstrate that it is possible to reversibly bind any kind of His-Tagged proteins on the QDs surface. This is highlighted by measuring FRET (Förster Resonance Energy Transfer) with a dedicated polymer exhibiting on one end Alexa Fluor 647 (AF647) and on the other end eight imidazole cycles, allowing chelation on the quantum dots’ surface. Therefore, this patterning protocol provides a path to combine nanoimaging with cell patterning through a relevant biofunctionalization

Binding and Neutralization of Lipopolysaccharides by Plant Proanthocyanidins

Proanthocyanidins (PACs), polyphenolic metabolites that are widely distributed in higher plants, have been associated with potential positive health benefits including antibacterial, chemotherapeutic, and antiatherosclerotic activities. In this paper, we analyze the binding of PACs from cranberries, tea, and grapes to lipopolysaccharide (LPS), a major component of the outer membrane of Gram-negative bacteria and the cause of several human illnesses. We demonstrate that in the case of cranberries, the most potent LPS-binding activity is contained within a PAC fraction composed of polymers with an average degree of polymerization of 21. The PAC fraction modestly inhibits the binding of LPS to the surface of HEK 293 cells expressing the full complement of LPS receptors (TLR4/MD2 and CD14), while it significantly abrogates the endocytosis of LPS. This PAC fraction also inhibits LPS-induced nuclear factor-κB activation in a manner that is not readily overcome by excess LPS. Such an effect is mediated through the inhibition of LPS interaction with TLR4/MD2 and the partial abrogation of LPS interaction with CD14. Importantly, PAC concentrations that mediate effective LPS neutralization elicit minimal in vitro cytotoxicity. Our results identify PACs as a new class of LPS-binding compound and suggest that they have potential utility in applications that necessitate either the purification and removal of LPS or the in vivo neutralization of LPS

<i>In Vivo</i> Imaging of Single Tumor Cells in Fast-Flowing Bloodstream Using Near-Infrared Quantum Dots and Time-Gated Imaging

Whereas in vivo fluorescence imaging of cells immobilized within tissues provides a valuable tool to a broad range of biological studies, it still lacks the sensitivity required to visualize isolated cells circulating fast in the bloodstream due, in particular, to the autofluorescence from endogenous fluorophores. Time-gated imaging of near-infrared emitting ZnCuInSe/ZnS quantum dots (QDs) with fluorescence lifetimes in the range of 150–300 ns enables the efficient rejection of fast autofluorescence photons and the selection of QD fluorescence photons, thus significantly increasing sensitivity. We labeled model erythrocytes as well as lymphoma cells using these QDs coated with a stable zwitterionic polymer surface chemistry. After reinjection in the bloodstream, we were able to image and count individual QD-labeled cells circulating at mm·s–1 velocities in blood vessels

<i>In Vivo</i> Imaging of Single Tumor Cells in Fast-Flowing Bloodstream Using Near-Infrared Quantum Dots and Time-Gated Imaging

Whereas in vivo fluorescence imaging of cells immobilized within tissues provides a valuable tool to a broad range of biological studies, it still lacks the sensitivity required to visualize isolated cells circulating fast in the bloodstream due, in particular, to the autofluorescence from endogenous fluorophores. Time-gated imaging of near-infrared emitting ZnCuInSe/ZnS quantum dots (QDs) with fluorescence lifetimes in the range of 150–300 ns enables the efficient rejection of fast autofluorescence photons and the selection of QD fluorescence photons, thus significantly increasing sensitivity. We labeled model erythrocytes as well as lymphoma cells using these QDs coated with a stable zwitterionic polymer surface chemistry. After reinjection in the bloodstream, we were able to image and count individual QD-labeled cells circulating at mm·s–1 velocities in blood vessels

Solution-Phase Single Quantum Dot Fluorescence Resonance Energy Transfer

We present a single particle fluorescence resonance energy transfer (spFRET) study of freely diffusing self-assembled quantum dot (QD) bioconjugate sensors, composed of CdSe−ZnS core−shell QD donors surrounded by dye-labeled protein acceptors. We first show that there is direct correlation between single particle and ensemble FRET measurements in terms of derived FRET efficiencies and donor−acceptor separation distances. We also find that, in addition to increased sensitivity, spFRET provides information about FRET efficiency distributions which can be used to resolve distinct sensor subpopulations. We use this capacity to gain information about the distribution in the valence of self-assembled QD−protein conjugates and show that this distribution follows Poisson statistics. We then apply spFRET to characterize heterogeneity in single sensor interactions with the substrate/target and show that such heterogeneity varies with the target concentration. The binding constant derived from spFRET is consistent with ensemble measurements

Strong Modulation of Two-Photon Excited Fluorescence of Quadripolar Dyes by (De)Protonation

Two quadripolar dyes have been designed and synthesized that present large cross sections for two-photon excitation and whose fluorescence responds strongly to (de)protonation. These dyes are considered as prototypes of molecular pH probes for multiphoton fluorescence microscopy

<i>In Vivo</i> Imaging of Single Tumor Cells in Fast-Flowing Bloodstream Using Near-Infrared Quantum Dots and Time-Gated Imaging

Whereas in vivo fluorescence imaging of cells immobilized within tissues provides a valuable tool to a broad range of biological studies, it still lacks the sensitivity required to visualize isolated cells circulating fast in the bloodstream due, in particular, to the autofluorescence from endogenous fluorophores. Time-gated imaging of near-infrared emitting ZnCuInSe/ZnS quantum dots (QDs) with fluorescence lifetimes in the range of 150–300 ns enables the efficient rejection of fast autofluorescence photons and the selection of QD fluorescence photons, thus significantly increasing sensitivity. We labeled model erythrocytes as well as lymphoma cells using these QDs coated with a stable zwitterionic polymer surface chemistry. After reinjection in the bloodstream, we were able to image and count individual QD-labeled cells circulating at mm·s–1 velocities in blood vessels

Synthesis of Near-Infrared-Emitting, Water-Soluble CdTeSe/CdZnS Core/Shell Quantum Dots

Applications of near-infrared (NIR) emitting CdTe-based QDs have been hampered by their sensitivity to oxidation. Here, we describe a synthetic method for the growth of CdTeSe/CdZnS core/shell QDs emitting in the NIR range (700−800 nm). We first synthesize high-quantum-yield zinc-blende CdTeSe cores with gradient composition and tunable emission up to 800 nm. The CdZnS shell growth is performed with cadmium and zinc carboxylate and trioctylphosphine sulfur precursors in trioctylamine solvent, and yields thick shell with controlled zinc blende crystalline structure. The presence of a high-band-gap, oxidation-resistant shell considerably improves the quantum yield and stability of these QDs when solubilized in saline buffers, making them promising fluorescence probes for NIR biological imaging