Visualizing resonance energy transfer in supramolecular surface patterns of β-CD-functionalized quantum dot hosts and organic dye guests by fluorescence lifetime imaging

Multicompartment dendrimicelles with binary, ternary and quaternary core composition

Hierarchically built-up multicompartment nanoaggregate systems are of interest for, e.g., novel materials and medicine. Here we present a versatile strategy to generate and unambiguously characterize complex coacervate-core micelles by exploiting four different dendrimeric subcomponents as core-units. The resulting mesoscale structures have a hydrodynamic diameter of 50 nm and a core size of 33 nm, and host about thirty 6th generation polyamidoamine (PAMAM) dendrimers. We have used FRET (efficiency of ∼0.2) between fluorescein and rhodamine moieties immobilized on separate PAMAM dendrimers (G6-F and G6-R, respectively) to prove synchronous encapsulation in the micelle core. Tuning the proximity of the FRET pair molecules either by varying the G6-F : G6-R ratio, or by co-assembling non-functionalized dendrimer (G6-E) in the core, reveals the optimal FRET efficiency to occur at a minimum of 70% loading with G6-F and G6-R. Additional co-encapsulation of 6th generation gold dendrimer-encapsulated nanoparticles (G6-Au) in the micelle core shows a dramatic reduction of the FRET efficiency, which can be restored by chemical etching of the gold nanoparticles from within the micellar core with thiols, leaving the micelle itself intact. This study reveals the controlled co-assembly of up to four different types of subcomponents in one single micellar core and concomitantly shows the wide variety of structures that can be made with a well-defined basic set of subcomponents. It is straightforward to design related strategies, to incorporate inside one micellar core, e.g., even more than 4 different dendrimers, or other classes of (macro)molecules, with different functional groups, other FRET pairs or different encapsulated metal nanoparticles.

Construction of dual nanomedicines for the imaging and alleviation of atherosclerosis

Magnetic resonance imaging (MRI) is an essential tool for the diagnosis of atherosclerosis, a chronic cardiovascular disease. MRI primarily uses superparamagnetic iron oxide (SPIO) as a contrast agent. However, SPIO integrated with therapeutic drugs has rarely been studied. In this study, we explored biocompatible paramagnetic iron-oxide nanoparticles (NPs) in a complex with low pH-sensitive cyclodextrin for the diagnostic imaging and treatment of atherosclerosis. The NPs were conjugated with profilin-1 antibody (PFN1) to specifically target vascular smooth muscle cells (VSMCs) in the atherosclerotic plaque and integrated with the anti-inflammatory drug, rapamycin. The PFN1-CD-MNPs were easily binded to the VSMCs, indicating their good biocompatibility and low renal toxicity over the long term. Ex vivo near-infrared fluorescence (NIRF) imaging and in vivo MRI indicated the accumulation of PFN1-CD-MNPs in the atherosclerotic plaque. The RAP@PFN1-CD-MNPs alleviated the progression of arteriosclerosis. Thus, PFN1-CD-MNPs served not only as multifunctional imaging probes but also as nanovehicles for the treatment of atherosclerosis.

Visualizing Oxidative Cellular Stress Induced by Nanoparticles in the Subcytotoxic Range Using Fluorescence Lifetime Imaging

Nanoparticles hold a great promise in biomedical science. However, due to their unique physical and chemical properties they can lead to overproduction of intracellular reactive oxygen species (ROS). As an important mechanism of nanotoxicity, there is a great need for sensitive and high-throughput adaptable single-cell ROS detection methods. Here, fluorescence lifetime imaging microscopy (FLIM) is employed for single-cell ROS detection (FLIM-ROX) providing increased sensitivity and enabling high-throughput analysis in fixed and live cells. FLIM-ROX owes its sensitivity to the discrimination of autofluorescence from the unique fluorescence lifetime of the ROS reporter dye. The effect of subcytotoxic amounts of cationic gold nanoparticles in J774A.1 cells and primary human macrophages on ROS generation is investigated. FLIM-ROX measures very low ROS levels upon gold nanoparticle exposure, which is undetectable by the conventional method. It is demonstrated that cellular morphology changes, elevated senescence, and DNA damage link the resulting low-level oxidative stress to cellular adverse effects and thus nanotoxicity. Multiphoton FLIM-ROX enables the quantification of spatial ROS distribution in vivo, which is shown for skin tissue as a target for nanoparticle exposure. Thus, this innovative method allows identifying of low-level ROS in vitro and in vivo and, subsequently, promotes understanding of ROS-associated nanotoxicity.

Formation and characterization of β-cyclodextrin (β-CD) - polyethyleneglycol (PEG) - polyethyleneimine (PEI) coated Fe3O4 nanoparticles for loading and releasing 5-Fluorouracil drug

In this work, β-cyclodextrin (β-CD) - polyethyleneglycol (PEG) - polyethyleneimine (PEI) coated iron oxide nanoparticles (Fe3O4-β-CD-PEG-PEI) were developed as drug carriers for drug delivery applications. The 5- Fluorouracil (5-FU) was chosen as model drug molecule. The developed nanoparticles (Fe3O4-β-CD-PEG-PEI) were characterized by various techniques such as Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating sample magnetometry (VSM). The average particles size range of 5-FU loaded Fe3O4-β-CD, Fe3O4-β-CD-PEG and Fe3O4-β-CD-PEG-PEI nanoparticles were from 151 to 300nm and zeta potential value of nanoparticles were from -43mV to -20mV as measured using Malvern Zetasizer. Finally, encapsulation efficiency (EE), loading capacity (LC) and in-vitro drug release performance of 5-FU drug loaded Fe3O4-β-CD, Fe3O4-β-CD-PEG and Fe3O4-β-CD-PEG-PEI nanoparticles was evaluated by UV-vis spectroscopy. In-vitro cytotoxicity tests investigated by MTT assay indicate that 5-FU loaded Fe3O4-β-CD-PEG-PEI nanoparticles were toxic to cancer cells and non-toxic to normal cells. The in-vitro release behavior of 5-FU from drug (5-FU) loaded Fe3O4-β-CD-PEG-PEI composite at different pH values and temperature was studied. It was found that 5-FU was released faster in pH 6.8 than in the acidic mediums (pH 1.2), and the released quantity was higher. Therefore, the newly prepared Fe3O4-β-CD-PEG-PEI carrier exhibits a promising potential capability for anticancer drug delivery in tumor therapy.

Immobilization of multivalent glycoprobes on gold surfaces for sensing proteins and macrophages

A non-covalent host–guest strategy to immobilize heptavalent glyco-β-cyclodextrin on gold-coated glass slides to study multivalent carbohydrate–protein interactions is described.

MMP-2/9-Specific Activatable Lifetime Imaging Agent

Optical (molecular) imaging can benefit from a combination of the high signal-to-background ratio of activatable fluorescence imaging with the high specificity of luminescence lifetime imaging. To allow for this combination, both imaging techniques were integrated in a single imaging agent, a so-called activatable lifetime imaging agent. Important in the design of this imaging agent is the use of two luminophores that are tethered by a specific peptide with a hairpin-motive that ensured close proximity of the two while also having a specific amino acid sequence available for enzymatic cleavage by tumor-related MMP-2/9. Ir(ppy)3 and Cy5 were used because in close proximity the emission intensities of both luminophores were quenched and the influence of Cy5 shortens the Ir(ppy)3 luminescence lifetime from 98 ns to 30 ns. Upon cleavage in vitro, both effects are undone, yielding an increase in Ir(ppy)3 and Cy5 luminescence and a restoration of Ir(ppy)3 luminescence lifetime to 94 ns. As a reference for the luminescence activation, a similar imaging agent with the more common Cy3-Cy5 fluorophore pair was used. Our findings underline that the combination of enzymatic signal activation with lifetime imaging is possible and that it provides a promising method in the design of future disease specific imaging agents.

Glyco-β-cyclodextrin capped quantum dots: synthesis, cytotoxicity and optical detection of carbohydrate-protein interactions

Highly fluorescent water soluble glyco-quantum dots were synthesized using a sonochemical procedure. The synthetic approach is based on specific host-guest interactions between β-cyclodextrin (β-CD) and trioctylphosphine oxide (TOPO) surfactant on quantum dots. The modified QDs were analyzed by a combination of FT-IR, (1)H-NOESY NMR spectroscopy and by TEM. The high sugar density on QDs resulted in selective colloidal aggregation with ConcanavalinA (ConA), Galanthus nivalis lectin (GNA) and Peanut agglutinin (PNA) lectins. Subsequently, in vitro studies indicated that β-CD modification of QDs enabled good cell viability of human hepatocellular carcinoma cell line (HepG2) cells. Finally, flow cytometry and confocal imaging studies revealed that βCDgal capped QDs undergo preferential binding with HepG2 cells. These results clearly demonstrate that β-CD capped QDs could be a promising candidate for further carbohydrate-based biomedical applications.

Synchronized energy and electron transfer processes in covalently linked CdSe-squaraine dye-TiO2 light harvesting assembly

Manipulation of energy and electron transfer processes in a light harvesting assembly is an important criterion to mimic natural photosynthesis. We have now succeeded in sequentially assembling CdSe quantum dot (QD) and squaraine dye (SQSH) on TiO(2) film and couple energy and electron transfer processes to generate photocurrent in a hybrid solar cell. When attached separately, both CdSe QDs and SQSH inject electrons into TiO(2) under visible-near-IR irradiation. However, CdSe QD if linked to TiO(2) with SQSH linker participates in an energy transfer process. The hybrid solar cells prepared with squaraine dye as a linker between CdSe QD and TiO(2) exhibited power conversion efficiency of 3.65% and good stability during illumination with global AM 1.5 solar condition. Transient absorption spectroscopy measurements provided further insight into the energy transfer between excited CdSe QD and SQSH (rate constant of 6.7 × 10(10) s(-1)) and interfacial electron transfer between excited SQSH and TiO(2) (rate constant of 1.2 × 10(11) s(-1)). The synergy of covalently linked semiconductor quantum dots and near-IR absorbing squaraine dye provides new opportunities to harvest photons from selective regions of the solar spectrum in an efficient manner.