We report a "smart" gold nanoparticle that is designed to aggregate in mild acidic intracellular environments by its hydrolysis-susceptible citraconic amide surface. With a relatively small size of 10 nm, the "smart" gold nanoparticles can be efficiently internalized into cancerous cells. Triggered by pH change, the nanoparticle surfaces are engineered to have both positive and negative charges. Electrostatic attractions between the nanoparticles can rapidly form aggregates inside the cells, and the aggregates accumulate as the exocytosis is blocked by the increased size. Endocytosis of gold nanoparticles and the aggregation are monitored real-time by dark field optical microscopy. The pH-induced formation of aggregates shifts the absorption to far-red and near-infrared. The absorption shift to longer wavelength is used for photothermal cancer therapy as it guarantees maximal tissue penetration for potential therapeutic applications. The gold nanoparticles show selective and efficient destruction of cancerous cells with an intensity threshold of 5 W/cm(2) to induce the thermal destruction. In the intensity range 5-13 W/cm(2), the circular area of damaged cells increases linearly with the irradiation power density. This shows a new proof-of-concept for photothermal cancer therapy that exploits collective plasmon modes of metal nanoparticles.

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A novel rhodamine-based fluorogenic and chromogenic probe for Ag(+) ions in aqueous media is developed, which can be also used for the detection of AgNPs. The sensing mechanism is based on irreversible tandem ring-opening and -forming processes promoted by Ag(+)-coordination to the iodide of the probe, which is accompanied by both color and turn-on type fluorescence changes. The probe shows remarkably high selectivity over other metal ions and detects silver ions up to 14 ppb.

A new type of quantum dot (QD) ligand chemistry is introduced that can provide positive, negative, or zwitterionic surface QDs. CdSe/CdZnS coreshell QDs are decorated with ligands, and the non-specifi c and specifi c interactions of the QDs through their surface charge are investigated with the focus on cellular adsorptions and endocytosis. Zwitterionic QDs are compact with a ligand hydrodynamic thickness of less than 2 nm, they are colloidally very stable over a broad pH range and even in saturated NaCl solution, and they show minimal non-specifi c adsorptions. Positive and negative QDs show a very different behavior for cellular adsorption and subsequent incorporation, suggesting mostly energy-independent pathways for positive QDs and exclusively adenosine triphosphate (ATP)-dependent pathways for negative QDs. The zwitterionic QD surface ligands can also be used in conjunction with other functional groups, which allows simple conjugations for highly specifi c targeting whereas retaining the advantages of a zwitterionic QD surface. This QD surface chemistry can provide highly specifi c and very sensitive imaging with very low background level. Using the mixed QD surface ligand system, we demonstrated streptavidin and antibody QD conjugates that show a signal-to-noise ratio that is over 4000 times higher than the unconjugated mixture, which was used as a control case. The QD chemistry reported herein can be easily extended to other functional groups, such as alkynes, azides, or other amines, and can be further used in many future applications, including single-QD level experiments, sensitive assays, or in vivo applications using anti-fouling QD probes. FULL PAPERwww.afm-journal.de www.MaterialsViews.com

Synthesis of a size series of colloidal ZnTe/ZnSe (core/shell) quantum dots (QDs) is reported. Because of the unique Type-II characters, their emission can range over an extended wavelength regime, showing photoluminescence (PL) from blue to amber. The PL lifetime measures as long as 77 ns, which clearly indicates the Type-II characteristics. ZnTe/ZnSe (Core/Shell) QDs can be further passivated by ZnS layers, rendered in water, while preserving the optical and chemical stabilities and thus proved their potentials toward “nontoxic” biological or medical applications that are free from concerns regarding heavy-metal leakage. ZnTe/ZnSe Type-II QD/polymer hybrid organic solar cells are also showcased, promising environmentally friendly photovoltaic devices. ZnTe/ZnSe Type-II QD incorporated photovoltaic devices show 11 times higher power conversion efficiency, when compared to that of the control ZnSe QD devices. This results from the Type-II characteristic broad QD absorption up to extended wavelengths and the spatially separated Type-II excitons, which can enhance the carrier extractions. We believe that ZnTe/ZnSe-based Type-II band engineering can open many new possibilities as exploiting the safe material choice.

Supersized pores: A new mesoporous metal–organic framework that is mainly composed of Tb3+ ions and tripodal carboxylate ligands has cages of 3.9 and 4.7 nm in diameter (see picture). The evacuated framework is robust and can accommodate gases or ferrocene molecules, as verified by gas‐sorption measurements and luminescence studies.

A challenge in using plasmonic nanostructure-drug conjugates for thermo-chemo combination cancer therapy lies in the huge size discrepancy; the size difference can critically differentiate their biodistributions and hamper the synergistic effect. Properly tuning the plasmonic wavelength for photothermal therapy typically results in the nanostructure size reaching ∼100 nm. We report a new combination cancer therapy platform that consists of relatively small 10 nm pH-responsive spherical gold nanoparticles and conjugated doxorubicins. They are designed to form aggregates in mild acidic environment such as in a tumor. The aggregates serve as a photothermal agent that can selectively exploit external light by their collective plasmon modes. Simultaneously, the conjugated doxorubicins are released. The spatiotemporal concertion is confirmed at the subcellular, cellular, and organ levels. Both agents colocalize in the cell nuclei. The conjugates accumulate in cancer cells by the rapid phagocytic actions and effective blockage of exocytosis by the increased aggregate size. They also effectively accumulate in tumors up to 17 times over the control because of the enhanced permeation and retention. The conjugates exhibit a synergistic effect enhanced by nearly an order of magnitude in cellular level. The synergistic effect is demonstrated by the remarkable reductions in both the therapeutically effective drug dosage and the photothermal laser threshold. Using an animal model, effective tumor growth suppression is demonstrated. The conjugates induce apoptosis to tumors without any noticeable damage to other organs. The synergistic effect in vivo is confirmed by qRT-PCR analysis over the thermal stress and drug-induced growth arrest.

A simple and novel electrostatic coupling method is reported, which provides a hyaluronic acid-quantum dot conjugate (HA-QD) that is colloidally stable and size-tunable from 50 to 120 nm. The HA-QDs show cancer targeting efficiency, which suggests diagnostic and imaging applications. The conjugates are also demonstrated for the fluorescence staining capability for lymphatic vessels in vitro and in vivo. Using the HA-QDs in a small animal model, lymphatic vessels are visualized real-time in vivo for days. Comprehensive cytotoxicity evaluations are made for the conjugates and the unconjugated counterpart. The HA-QDs showcase the potentials toward cancer imaging and real-time visualization of changes in lymphatic vessels such as lymphangiogenesis.