Daniel L. Akins

Raman, fluorescence, and time-resolved light scattering as optical diagnostic techniques to separate diseased and normal biomedical media

Studies of Raman scattering, fluorescence and time-resolved light scattering were conducted on cancer and normal biomedical media. Fourier transform Raman spectroscopic measurements were performed on human normal, benign and cancerous tissues from gynecological (GYN) tracts. A comparison of the intensity differences between various Raman modes as well as the number of Raman lines, enables one to distinguish normal GYN tissues from diseased tissues. Fluorescence spectroscopic measurements on human breast tissues show that the ratio of fluorescence intensity at 340 nm to that at 440 nm can be used to distinguish between cancerous and non-cancerous tissues. Separate studies on normal and cancerous breast cell lines show spectral differences. The measurements of back-scattered ultrafast laser pulses from human breast tissues show differences in the scattered pulse profiles for different tissues. These studies show that various optical techniques have the potential to be used in medical diagnostic applications.

Energy Transfer in Monochromatically‐Excited Hydrogen (B 1Σ u+). I. Excitation Processes, Electronic Quenching, and Vibrational Energy Transfer

Excitation of HD molecules into specific vibrational and rotational levels of the B  1Σ u+ electronic state by absorption of the 1048 and 1066 A argon resonance lines has been studied under various experimental conditions by observing the steady‐state fluorescence spectra of the (B  1Σ u+→ X 1Σg+) Lyman bands. Strong excitation of the (v′ = 3, J′= 2), (v′ = 5 , J′=2), and (v′ = 6 , J′ = 5) levels was achieved. The HD (B 1Σ u+ → X 1Σg+) electronic fluorescence from v′=3 was found to be quenched by HD, 3He, 4He, and Ne with effective collision cross sections of 79, 8.8, 9.9, and 3.5 A2 at 297°K. Vibrational energy transfer processes HD(B  1Σ u+ ; v′=3, J′) + M→ HD(B  1Σ u+; v′=2, J′ + Δ J′ ) + M+ Δ E were studied for the collision partners 3He, 4He, and Ne. Large effective cross sections of 0.89, 0.76, and 0.81 A2 were found at 303°K. Rotationally‐resolved spectra for Ne show that vibrational energy is transferred into both rotation and translation. All energetically accessible values of ΔJ′ were observed. ...

A covalently linked phenanthridine–ruthenium(II) complex as a RNA probe

A phenanthridine derivative covalently linked to a ruthenium complex yields an imaging probe whose fluorescence intensity and lifetime change substantially in the presence of RNA.

Diameter-selective dispersion of single-walled carbon nanotubes using a water-soluble, biocompatible polymer

One-step diameter-selective dispersion of HiPco single-walled carbon nanotubes has been accomplished through noncovalent complexation of the nanotubes with a water-soluble, biocompatible polymer chitosan at room temperature.

High Methanol Tolerance of Carbon-Supported Pt-Cr Alloy Nanoparticle Electrocatalysts for Oxygen Reduction

The electrocatalytic reduction of oxygen on carbon-supported Pt-Cr (1:1) alloy nanoparticle catalysts with two different metal loadings prepared via a carbonyl route was investigated based on the porous thin-film rotatingdisk-ring electrode technique and compared with that on E-TEK Pt/C catalyst in pure and methanol-containing electrolytes. The as-prepared Pt-Cr alloy nanoparticles, which have single-phase disordered structures, are well dispersed on the surface of carbon with a narrow size distribution even at 40 wt % metal loading. Such catalysts are stable in air up to 600°C. As compared to the Pt/C catalyst, the alloy catalysts showed slightly enhanced activity for the oxygen reduction reaction in pure acid electrolyte and significantly enhanced activity in the presence of methanol, and the ring-current measurements on the homemade catalysts showed a reduction in peroxide yield in pure acid solution. The enhanced activity could be ascribed to the effect of alloying on the initiation and extent of surface oxide formation. Oxygen reduction kinetic analysis indicated a potential dependence of the apparent number of electrons transferred per oxygen molecule during the reduction in methanol-containing solution. High methanol tolerance of Pt-Cr alloy catalysts during the oxygen reduction could be explained well by the lower reactivity of methanol oxidation, which may originate from the composition effect and the disordered structure of the alloy catalysts.

Methanol Oxidation on Carbon-Supported Pt-Os Bimetallic Nanoparticle Electrocatalysts

The electrocatalytic oxidation of methanol on carbon-supported bimetallic Pt-Os nanoparticle catalysts has been investigated. The as-prepared Pt-Os nanoparticles, which are single-phase disordered structures and well dispersed on the surface of carbon with a narrow size distribution, exhibit, respectively, significantly enhanced and slightly enhanced activities for methanol oxidation when compared to commercial Pt/C and Pt-Ru (1:1)/C catalysts. The maximum activity of our Pt-Os based catalysts for methanol oxidation was at a Pt/Os atomic ratio of 3:1. Such an enhanced activity can be rationalized by a combination of a bifunctional mechanism and an electronic effect.

Energy transfer in reactions f electrogenerated aromatic anions and benzoyl peroxide. Chemiluminescence and its mechanism

Abstract Experiments reported herein have shown that steady-state chemiluminescences occur with fluoranthene, anthracene, 9,10-DPA and rubrene solutions containing benzoyl perxide when the systems are potentiostated at a potential sufficiently negative t produce the aromatic radical anin. These emissions are identical to the fluorescence spectra of the hydrocarbons. Mixed systems of DPA-rubrene, fluoranthene-anthracene have shown fluorescence from the molecule with the lowest first excited singlet state. It is advanced that it is not necessary in electrochemical systems of homogeneous oxidant and electrogenerated aromatic hydrocarbon anions to postulate the direct formation of the singlet state from oxidation of the anion. A detailed discussion is given of mechanistic steps leading to the indirect formation of first excited singlet molecules.

Superradiant lasing from J-aggregated molecules adsorbed onto colloidal silver

The picosecond time-resolved emission spectrum of the cyanine dye 1,1′-diethyl-3,3′bis-(3-sulfopropyl)-5,5′,6,6′-tetrachlorobenzimidazolocarbocyanine (also known as BIC) adsorbed onto colloidal silver was examined as a function of laser pulse energy at room temperature. BIC is found to aggregate on colloidal silver, and the number of coherently responding molecules involved in the one-exciton state (i.e., the coherence length) was estimated to involve 8–9 molecules. Lasing at a remarkably low incident pulse energy threshold was found for this system and explained in terms of a mechanism involving superradiant states created in coherently coupled adsorbed molecules that emit photons which stimulate emission from other spatially distributed superradiant states.

Resonance-enhanced Raman scattering by aggregated 2,2′-cyanine on colloidal silver

The Raman scattering spectrum of 2,2′-cyanine on colloidal silver metal particles is discussed. Preliminary assignments of some of the vibrational Raman bands to the motions of specific chromophoric units are presented and multiplet character of some bands is discussed. Enhanced Raman scattering of 2,2′-cyanine occurs when the laser radiation is tuned to the J-aggregate absorption feature at 575 nm. The enhancement in Raman intensity is the result of a diminution of fluorescence intensity, as well as a quantitative increase in Raman scattering intensity, and is distinct from other types of enhancement phenomena (e.g., resonance Raman of monomeric solution dye, and surface-enhanced Raman scattering (SERS)). The resonance Raman enhancement, due to excitation at the frequency corresponding to the J-aggregate absorption, is found to be 2 × 10+3.

Extremely low excitation threshold, superradiant, molecular aggregate lasing system

An extremely low threshold for lasing from a specially formulated system involving self-assembled, aggregated molecules enables the system to function as a mirrorless laser. Superradiant energy states created in coherently coupled aggregated molecules emit photons that stimulate emission from other spatially distributed superradiant states. This study focuses on a cyanine dye (specifically, 1,1′-3,3′-tetraethyl-5,5′,6,6′-tetrachlorobenzimidazolocarbocyanine iodide) adsorbed onto silica colloid on which the dye aggregates, forming excitonic states involving coherent domains in which a finite number of molecules act cooperatively in the process of emitting photons. It is found that lasing from such a system is induced at a threshold of ca. 39 pJ/pulse, which corresponds to a factor of 3×10+4 times smaller than the lowest lasing threshold reported in the literature.