Three-Dimensional Colloidal Controlled Growth of Core-Shell Heterostructured Persistent Luminescence Nanocrystals.

Persistent luminescence nanoparticles (PLNPs) are an emerging photonic nanomaterial that possesses uniquely persistent luminescence properties after excitation ceases. They can be repeatedly recharged in vitro and in vivo and hold great promise for numerous areas and applications. Unfortunately, none of the existing synthesis methods can control their composition to grow core-shell structured PLNPs with desirable shapes and enhanced functionalities.

Efficient sub-15 nm cubic-phase core/shell upconversion nanoparticles as reporters for ensemble and single particle studies.

Single particle imaging of upconversion nanoparticles (UCNPs) has typically been realized using hexagonal (β) phase lanthanide-doped sodium yttrium fluoride (NaYF) materials, the upconversion luminescence (UCL) of which saturates at power densities (P) of several hundred W cm under 980 nm near-infrared (NIR) excitation. Cubic (α) phase UCNPs have been mostly neglected because of their commonly observed lower UCL efficiency at comparable P in ensemble level studies. Here, we describe a set of sub-15 nm ytterbium-enriched α-NaYbF:Er@CaF core/shell UCNPs doped with varying Er concentrations (5-25%), studied over a wide P range of ∼8-10 W cm, which emit intense UCL even at a low P of 10 W cm and also saturate at relatively low P.

Optical Temperature Sensing With Infrared Excited Upconversion Nanoparticles.

Upconversion Nanoparticles (UCNPs) enable direct measurement of the local temperature with high temporal and thermal resolution and sensitivity. Current studies focusing on small animals and cellular systems, based on continuous wave (CW) infrared excitation sources, typically lead to localized thermal heating. However, the effects of upconversion bioimaging at the molecular scale, where higher infrared intensities under a tightly focused excitation beam, coupled with pulsed excitation to provide higher peak powers, is not well understood.

Motor-like DNA motion due to an ATP-hydrolyzing protein under nanoconfinement.

We report that long double-stranded DNA confined to quasi-1D nanochannels undergoes superdiffusive motion under the action of the enzyme T4 DNA ligase in the presence of necessary co-factors. Inside the confined environment of the nanochannel, double-stranded DNA molecules stretch out due to self-avoiding interactions. In absence of a catalytically active enzyme, we see classical diffusion of the center of mass.

DNA Methylation Detection Using Resonance and Nanobowtie-Antenna-Enhanced Raman Spectroscopy.

We show that DNA carrying 5-methylcytosine modifications or methylated DNA (m-DNA) can be distinguished from DNA with unmodified cytosine by Raman spectroscopy enhanced by both a bowtie nanoantenna and excitation resonance. In particular, m-DNA can be identified by a peak near 1000 cm and changes in the Raman peaks in the 1200-1700 cm band that are enhanced by the ring-absorption resonance. The identification is robust to the use of resonance Raman and nanoantenna excitation used to obtain significant signal improvement.

Interference of ATP with the fluorescent probes YOYO-1 andYOYO-3 modifies the mechanical properties of intercalator-stained DNA confined in nanochannels.

Intercalating fluorescent probes are widely used to visualize DNA in studies on DNA-protein interactions. Some require the presence of adenosine triphosphate (ATP). We have investigated the mechanical properties of DNA stained with the fluorescent intercalating dyes YOYO-1 and YOYO-3 as a function of ATP concentrations (up to 2 mM) by stretching single molecules in nanofluidic channels with a channel cross-section as small as roughly 100×100 nm.

Optical investigation of gold shell enhanced 25 nm diameter upconverted fluorescence emission.

We enhance the efficiency of upconverting nanoparticles by investigating the plasmonic coupling of 25 nm diameter NaYF4:Yb, Er nanoparticles with a gold-shell coating, and study the physical mechanism of enhancement by single-particle, time-resolved spectroscopy. A three-fold overall increase in emission intensity, and five-fold increase of green emission for these plasmonically enhanced particles have been achieved. Using a combination of structural and fluorescent imaging, we demonstrate that fluorescence enhancement is based on the photonic properties of single, isolated particles.

Enhancement of single particle rare earth doped NaYF4: Yb, Er emission with a gold shell.

Upconversion of infrared light to visible light has important implications for bioimaging. However, the small absorption cross-section of rare earth dopants has limited the efficiency of these anti-Stokes nanomaterials. We present enhanced excitation absorption and single particle fluorescent emission of sodium yttrium fluoride, NaYF4: Yb, Er based upconverting nanoparticles coated with a gold nanoshell through surface plasmon resonance.

Probing transient protein-mediated DNA linkages using nanoconfinement.

We present an analytic technique for probing protein-catalyzed transient DNA loops that is based on nanofluidic channels. In these nanochannels, DNA is forced in a linear configuration that makes loops appear as folds whose size can easily be quantified. Using this technique, we study the interaction between T4 DNA ligase and DNA.

Chromatin modification mapping in nanochannels.

We report the simultaneous mapping of multiple histone tail modifications on chromatin that has been confined to nanofluidic channels. In these channels, chromatin is elongated, and histone modification can be detected using fluorescently tagged monoclonal antibodies. Using reconstituted chromatin with three distinct histone sources and two histone tail modification probes (H3K4me3 and H3K9ac), we were able to distinguish chromatin from the different sources.

Near-field enhanced ultraviolet resonance Raman spectroscopy using aluminum bow-tie nano-antenna.

An aluminum bow-tie nano-antenna is combined with the resonance Raman effect in the deep ultraviolet to dramatically increase the sensitivity of Raman spectra to a small volume of material, such as benzene used here. We further demonstrate gradient-field Raman peaks for several strong infrared modes. We achieve a gain of [Formula: see text] in signal intensity from the near field enhancement due to the surface plasmon resonance in the aluminum nanostructure.

Fluctuation modes of nanoconfined DNA.

We report an experimental investigation of the magnitude of length and density fluctuations in DNA that has been stretched in nanofluidic channels. We find that the experimental data can be described using a one-dimensional overdamped oscillator chain with nonzero equilibrium spring length and that a chain of discrete oscillators yields a better description than a continuous chain. We speculate that the scale of these discrete oscillators coincides with the scale at which the finite extensibility of the polymer manifests itself.

DNA methylation profiling in nanochannels.

We report the profiling of the 5-methyl cytosine distribution within single genomic-sized DNA molecules at a gene-relevant resolution. This method linearizes and stretches DNA molecules by confinement to channels with a dimension of about 250×200 nm(2). The methylation state is detected using fluorescently labeled methyl-CpG binding domain proteins (MBD), with high signal contrast and low background.

Density fluctuations dispersion relationship for a polymer confined to a nanotube.

DNA confined to rigid nanotubes shows density fluctuations around its stretched equilibrium conformation. We report an experimental investigation of the length-scale dependent dynamics of these density fluctuations. We find that for highly elongated molecules a Rouse description is consistent with observations at sufficiently large length scales.

Particle size dependence of the dynamic photophysical properties of NaYF4:Yb, Er nanocrystals.

The effects of the nanocrystal size on the emission spectra and decay rates of upconverting hexagonal NaYF(4):Yb,Er nanocrystals are investigated. The influence of nanocrystal size is represented in terms of the surface area/volume ratio (SA/Vol). Our results show that a small nanocrystal size, or large SA/Vol ratio increases the decay rate, in particular, the green luminescence decay rate varies linearly with the SA/Vol ratio.

Stretching chromatin through confinement.

We present a method for the stretching of chromatin molecules in nanofluidic channels width a cross-section of about 80 x 80 nm(2), and hundreds of microns long. The stretching of chromatin to about 12 basepairs/nm enables location-resolved optical investigation of the nucleic material with a resolution of up to 6 kbp. The stretching is based on the equilibrium elongation that polymers experience when they are introduced into nanofluidic channels that are narrower than the Flory coil corresponding to the whole chromatin molecule.

Upconverting nanophosphors for bioimaging.

Upconverting nanoparticles (UCNPs) when excited in the near-infrared (NIR) region display anti-Stokes emission whereby the emitted photon is higher in energy than the excitation energy. The material system achieves that by converting two or more infrared photons into visible photons. The use of the infrared confers benefits to bioimaging because of its deeper penetrating power in biological tissues and the lack of autofluorescence.

The Sackler Colloquium on promises and perils in nanotechnology for medicine.

The Sackler Colloquium entitled "Nanomaterials in Biology and Medicine: Promises and Perils" was held on April 10-11, 2007. We have been able to assemble a representative sampling of 17 of the invited talks ranging over the topics presented. Any new technology carries with it both a promise of transforming the way we do things and the possibility that there are unforeseen consequences.

In vivo and scanning electron microscopy imaging of up-converting nanophosphors in Caenorhabditis elegans.

We show here that upconversion phosphors can be imaged both by infrared excitation and in a scanning electron microscope. We have synthesized and characterized for this work up-converting phosphor nanoparticles nonaggregated nanocrystals of size range 50-200 nm. We have investigated the optical properties of 50-200 nm nanoparticles and found a square dependence of the emitted visible fluorescence on the infrared excitation and verified that under electron excitation similar narrow band emission spectra can be obtained as is seen with IR upconversion.

Restriction mapping in nanofluidic devices.

We have performed restriction mapping of DNA molecules using restriction endonucleases in nanochannels with diameters of 100-200 nm. The location of the restriction reaction within the device is controlled by electrophoresis and diffusion of Mg2+ and EDTA. We have successfully used the restriction enzymes SmaI, SacI, and PacI, and have been able to measure the positions of restriction sites with a precision of approximately 1.