Biomedical subjects

Robert M Dickson

Publications and source records attributed to Robert M Dickson.

12 recordsLinked to original sources

PubMed2005

Nanoparticle-free single molecule anti-stokes Raman spectroscopy.

In the absence of large, plasmon-supporting nanoparticles, biocompatible dendrimer- and peptide-encapsulated few-atom Ag nanoclusters produce scaffold-specific single molecule (SM) Stokes and anti-Stokes Raman scattering. The strong SM vibrational signatures are enhanced by the Agn transitions in nanoparticle-free samples and cannot arise from plasmon enhancement. Characteristic SM-Raman intermittency is observed, with antibunching of the underlying Agn emission directly confirming the SM nature of the emissive species.

Coated Materials, Biocompatible↗

PubMed2005

Single-molecule optoelectronics.

With discrete states, several-atom Ag(n) nanoclusters exhibit molecule-like behavior with strong visible fluorescence and robust optical properties. This new class of single-molecule fluorophores has been created and electrically contacted in thin films to produce the first electroluminescent single molecules. A direct reporter of nanoscale charge injection and transport through discrete energy levels, bright Ag(n) electroluminescence has been harnessed to create single-molecule light-emitting diodes (LEDs) and optoelectronic logic gates and even to demonstrate full addition operations. These experiments utilizing the small size and quantum behavior of individual Ag nanoclusters usher in the new field of single-molecule optoelectronics.

Journal Article↗

PubMed2004

Quantum mechanical single-gold-nanocluster electroluminescent light source at room temperature.

Electrically contacted gold-nanocluster arrays formed within electromigration-induced break junctions exhibit bright, field-dependent electroluminescence in the near infrared (650-800 nm). Intensity autocorrelation of spatially isolated individual nanocluster emission driven at high electrical frequency (f(ac)= approximately 200 MHz) reveals antibunched electroluminescence at room temperature. These results demonstrate the single quantum nature of several-atom gold molecules and suggest their use as room-temperature electrically driven single-photon sources.

Journal Article↗

PubMed2004

Highly fluorescent, water-soluble, size-tunable gold quantum dots.

Highly fluorescent, water-soluble, few-atom Au quantum dots have been created that behave as multielectron artificial atoms with discrete, size-tunable electronic transitions throughout the visible and near IR. Correlation of nanodot sizes with emission energies fits the simple relation, EFermi/N1/3, predicted by the jellium model. Providing the "missing link" between atomic and nanoparticle behavior in noble metals, these emissive, water-soluble Au nanoclusters open new opportunities for biological labels, energy transfer pairs, and light emitting sources in nanoscale optoelectronics.

Journal Article↗

PubMed2004

DNA-templated Ag nanocluster formation.

The high affinity of Ag+ for DNA bases has enabled creation of short oligonucleotide-encapsulated Ag nanoclusters without formation of large nanoparticles. Time-dependent formation of cluster sizes ranging from Ag1 to Ag4/oligonucleotide were observed with strong, characteristic electronic transitions between 400 and 600 nm. The slow nanocluster formation kinetics enables observation of specific aqueous nanocluster absorptions that evolve over a period of 12 h. Induced circular dichroism bands confirm that the nanoclusters are associated with the chiral ss-DNA template. Fluorescence, absorption, mass, and NMR spectra all indicate that multiple species are present, but that their creation is both nucleotide- and time-dependent.

Circular Dichroism↗

PubMed2004

Photon antibunching from oriented semiconducting polymer nanostructures.

Fluorescence intensity correlation measurements reveal that z-oriented nanostructures from single chains of a cyano-substituted polyphenylene vinylene (CN-PPV) polymer act as single-quantum emitters. Photon antibunching is observed for the first time on individual polymer nanostructures with a modulation depth exceeding 90%, providing definitive proof that radiative recombination of molecular excitons occurs at a single localized site within the folded polymer chain.

Journal Article↗

PubMed2003

High quantum yield blue emission from water-soluble Au8 nanodots.

Prepared within biocompatible poly(amidoamine) dendrimer hosts, blue emitting Au8 nanodots were prepared with fluorescence quantum yields more than 100 times larger than any previously prepared. The strong size-dependent blue emission from these from monodisperse Au8 nanodots was measured to be 41% in aqueous solution and 52% in methanol. These easily prepared, water-soluble, and high quantum yield gold nanodots lend insight into the molecular nature of small metal nanoclusters and may find application as novel biocompatible fluorophores.

Journal Article↗

PubMed2003

Size-correlated spectroscopy and imaging of rare-earth-doped nanocrystals.

Isolated europium-doped metal-oxide nanoparticles were probed by size-correlated high-numerical-aperture (far-field) imaging techniques. A modified Digital Instruments Bioscope atomic force microscope mounted upon a Nikon TE300 inverted microscope was used to interrogate (dry) particles ranging in size from 2 to 150 nm on the surface of a glass or quartz coverslip. These experiments revealed several interesting features of doped-nanoparticle luminescence such as Poissonian occupation statistics, size-dependent luminescence efficiency enhancement for particle sizes of <10 nm, and correlation of interesting transient behavior at particle sizes of <5 nm.

Journal Article↗

PubMed2003

Discrete two-terminal single nanocluster quantum optoelectronic logic operations at room temperature.

Readily formed at nanoscale break junctions, arrays of individual spatially isolated, strongly electroluminescent Ag(2)-Ag(8) nanoclusters perform complex logic operations within individual two-terminal nanoscale optoelectronics devices. Simultaneous electrical excitation of discrete room-temperature nanocluster energy levels directly yields AND, OR, NOT, XOR, and even full addition logic operations with either individual nanoclusters or nanocluster pairs as the active medium between only two electrodes. Imaged in parallel, noncontact electroluminescent readout obviates the need for electrically isolating individual features. This gated, pulsed, two-terminal device operation will likely drive future nano and molecular electronics advances without complicated nanofabrication.

Journal Article↗

PubMed2002

Individual water-soluble dendrimer-encapsulated silver nanodot fluorescence.

Easily observed on the single molecule level, highly fluorescent and photostable silver nanoclusters have been photochemically prepared within poly(amidoamine) dendrimer hosts in aqueous solutions. The dendrimer cage stabilizes and solubilizes the nanoclusters to yield highly stable, photoactivated single nanodots ranging in size from 2 to 8 silver atoms. These multicolored, highly fluorescent species are extremely photostable and readily observed on the single molecule scale with weak mercury lamp excitation. Such easily created, bright, photoactivated water-soluble fluorophores are likely to greatly expand the impact of single molecule labeling studies in a wide variety of systems.

Fluorescent Dyes↗

PubMed2002

Strongly enhanced field-dependent single-molecule electroluminescence.

Individual, strongly electroluminescent Ag(n) molecules (n = 2 approximately 8 atoms) have been electrically written within otherwise nonemissive silver oxide films. Exhibiting characteristic single-molecule behavior, these individual room-temperature molecules exhibit extreme electroluminescence enhancements (>10(4) vs. bulk and dc excitation on a per molecule basis) when excited with specific ac frequencies. Occurring through field extraction of electrons with subsequent reinjection and radiative recombination, single-molecule electroluminescence is enhanced by a general mechanism that avoids slow bulk material response. Thus, while we detail strong electroluminescence from single, highly fluorescent Ag(n) molecules, this mechanism also yields strong ac-excited electroluminescence from similarly prepared, but otherwise nonemissive, individual Cu nanoclusters.

Journal Article↗

PubMed2002

Three-dimensional single molecule rotational diffusion in glassy state polymer films.

Measuring three-dimensional orientational motions of many individual molecules within glassy state poly(methyl methacrylate) has enabled nanoscopic probing of bulk-obscured polymer dynamics. Complementing bulk studies, the measured distributions of nanoscale barriers to rotational motion afforded by our single molecule orientational methods directly probe the spatial heterogeneity and nanoscopic alpha-relaxation dynamics deep within the glassy state.

Journal Article↗