Ultrafast time-resolved photoluminescence from novel metal–dendrimer nanocomposites

We report the first results of ultra-fast enhanced light emission from gold– and silver–dendrimer nanocomposites. There is a fast (70 fs) fluorescence decay component associated with the metal nanocomposites. Anisotropy measurements show that this fast component is depolarized. The enhanced emission is suggestively due to local field enhancement in the elongated metal–dendrimer nanoparticles. © 2001 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71043/2/JCPSA6-114-5-1962-1.pd

Two-Photon Fluorescence Spectroscopy and Imaging of 4-Dimethylaminonaphthalimide Peptide and Protein Conjugates

We report detailed photophysical studies on the two-photon fluorescence processes of the solvatochromic fluorophore 4-DMN as a conjugate of the calmodulin (CaM) and the associated CaM-binding peptide M13. Strong two-photon fluorescence enhancement has been observed which is associated with calcium binding. It is found that the two-photon absorption cross-section is strongly dependent on the local environment surrounding the 4-DMN fluorophore in the CaM conjugates, providing sensitivity between sites of fluorophore attachment. Utilizing time-resolved measurements, the emission dynamics of 4-DMN under various environmental (solvent) conditions are analyzed. In addition, anisotropy measurements reveal that the 4-DMN–S38C–CaM system has restricted rotation in the calcium-bound calmodulin. To establish the utility for cellular imaging, two-photon fluorescence microscopy studies were also carried out with the 4-DMN-modified M13 peptide in cells. Together, these studies provide strong evidence that 4-DMN is a useful probe in two-photon imaging, with advantageous properties for cellular experiments.German Science Foundation (SO 1100/1-1

Bostonia: The Boston University Alumni Magazine. Volume 34

Founded in 1900, Bostonia magazine is Boston University's main alumni publication, which covers alumni and student life, as well as university activities, events, and programs

Isolation and Characterization of Precise Dye/Dendrimer Ratios

Fluorescent dyes are commonly conjugated to nanomaterials for imaging applications using stochastic synthesis conditions that result in a Poisson distribution of dye/particle ratios and therefore a broad range of photophysical and biodistribution properties. We report the isolation and characterization of generation 5 poly(amidoamine) (G5 PAMAM) dendrimer samples containing 1, 2, 3, and 4 fluorescein (FC) or 6‐carboxytetramethylrhodamine succinimidyl ester (TAMRA) dyes per polymer particle. For the fluorescein case, this was achieved by stochastically functionalizing dendrimer with a cyclooctyne “click” ligand, separation into sample containing precisely defined “click” ligand/particle ratios using reverse‐phase high performance liquid chromatography (RP‐HPLC), followed by reaction with excess azide‐functionalized fluorescein dye. For the TAMRA samples, stochastically functionalized dendrimer was directly separated into precise dye/particle ratios using RP‐HPLC. These materials were characterized using 1 H and 19 F NMR spectroscopy, RP‐HPLC, UV/Vis and fluorescence spectroscopy, lifetime measurements, and MALDI. High definition : Two approaches for the formation of generation 5 PAMAM samples containing precise dye/dendrimer ratios are presented. The first approach, using direct separation based on dye hydrophobicity, generated a set of TAMRA‐containing dendrimers, and the second, using click chemistry, generated a set of fluorescein‐containing dendrimer (see figure).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106970/1/chem_201304854_sm_miscellaneous_information.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/106970/2/4638_ftp.pd

Heteroatom and side chain effects on the optical and photophysical properties: ultrafast and nonlinear spectroscopy of new Naphtho[1,2-b:5,6-b ']difuran donor polymers

The photophysical and electronic properties of four novel conjugated donor polymers were investigated to understand the influence of heteroatoms (based on the first two member chalcogens) in the polymer backbone. The side chains were varied as well to evaluate the effect of polymer solubility on the photophysical properties. The donor–acceptor polymer structure is based on naptho[1,2-b:5,6-b′]difuran as the donor moiety, and either 3,6-di(furan-2-yl)-1,4-diketopyrrolo[3,4-c]pyrrole or 3,6-di(thiophen-2-yl)-1,4-diketopyrrolo[3,4-c]pyrrole as the acceptor moiety. Steady-state absorption studies showed that the polymers with the furan moiety in the backbone displayed a favorable tendency of capturing more solar photons when used in a photovoltaic device. This is observed experimentally by the higher extinction coefficient in the visible and near-infrared regions of these polymers relative to that of their thiophene counterparts. The excitonic lifetimes were monitored using ultrafast dynamics, and the results obtained show that the type of heteroatom π-linker used in the backbone affects the decay dynamics. Furthermore, the side chain also plays a role in determining the fluorescence decay time. Quantum chemical simulations were performed to describe the absorption energies and transition characters. Two-photon absorption cross sections (TPA-δ) were analyzed with the simulations, illustrating the planarity of the backbone in relation to its torsional angles. Because of the planarity in the molecular backbone, the polymer with the furan π-linker showed a higher TPA-δ relative to that of its thiophene counterpart. This suggests that the furan compound will display higher charge transfer (CT) tendencies in comparison to those of their thiophene analogues. The pump–probe transient absorption technique was employed to probe the nonemissive states (including the CT state) of the polymers, and unique activities were captured at 500 and 750 nm for all of the studied compounds. Target and global analyses were performed to understand the dynamics of each peak and deduce the number of components responsible for the transient behavior observed respectively. The results obtained suggest that the furan π-linker component of a donor and acceptor moiety in a conjugated polymer might be a more suitable candidate compared with its more popular chalcogenic counterpart, thiophene, for use as donor materials in bulk heterojunction photovoltaic devices.Support for this investigation is provided by the National Science Foundation (DMR-1709005) Polymers (TGIII) and (DMR 1410088/1640297) Polymers (MJE). (DMR-1709005 - National Science Foundation; DMR 1410088/1640297 - National Science Foundation)Accepted manuscrip

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Second and third order nonlinear optical properties of organic polymeric materials

The importance of induced orientational dipolar order is investigated by considering its connection to the dynamic poling process. The temporal stability studies showed a non-Arrhenius temperature dependence for the relaxation of the poled order measured by second harmonic generation, and that the dipolar orientational relaxation time was dependent upon the dopant level, with increasing relaxation times with larger dopant levels. The orientational order parameters were also shown to depend on dopant level; however the dependence was nonlinear. The thermal stability of the induced order was enhanced by a photocrosslinked NLO epoxy functionalized system that was synthesized, and characterized. This polymer was stable at high temperatures (100\sp\circC) and appeared not to degrade upon photolysis. Electrochromism was also used to characterize the temporal stability in the guest/host system. It was shown that the activation energy obtained from the temperature dependent curves was affected by the dopant level. The increase in activation energy as a function of concentration was explained in terms of orientational pair correlation. Second and third order NLO effects were investigated by linear and quadratic electro-optic effects. The increase in the linear electro-optic coefficient upon increasing dopant level was shown to be nonlinear. A novel technique called electro-absorption was developed for the investigation of the imaginary part of the Pockels and Kerr coefficients. With this novel technique the complete dispersion of the second and third order effects could be obtained. The quadratic electro-absorption measurement gave information concerning the mechanism of the third order effect. A proposed elastic model depicting the mechanism of the third order effect in polymers was tested for a guest/host system. At low temperature there was an electronic, but no orientational, contribution to the total mechanism. However, at temperatures above the glass transition, orientational effects dominated the mechanism. In both cases (Pockels and Kerr), the correct expressions of the NLO coefficients were presented for the first time