Multiple Excitation Sources Research Articles

Fluorescence-enhanced optical imaging of large phantoms using single and simultaneous dual point illumination geometries.

Fluorescence-enhanced optical tomography is typically performed using single point illumination and multiple point collection measurement geometry. Single point illumination is often insufficient to illuminate greater volumes of large phantoms and results in an inadequate fluorescent signal to noise ratio (SNR) for the majority of measurements. In this work, the use of simultaneous multiple point illumination geometry is proposed for acquiring a large number of fluorescent measurements with a sufficiently high SNR. As a feasibility study, dual point excitation sources, which are in-phase, were used in order to acquire surface measurements and perform three-dimensional reconstructions on phantoms of large volume and/or significant penetration depth. Measurements were acquired in the frequency-domain using a modulated intensified CCD imaging system under different experimental conditions of target depth (1.4-2.8 cm deep) with a perfect uptake optical contrast. Three-dimensional reconstructions of the fluorescence absorption from the dual point illumination geometry compare well with the reconstructions from the single point illumination geometry. Targets located up to 2 cm deep were located successfully, establishing the feasibility of reconstructions from simultaneous multiple point excitation sources. With improved excitation light rejection, multiple point illumination geometry may prove useful in reconstructing more challenging domains containing deeply embedded targets. Image quality assessment tools are required to determine the optimal measurement geometry for the largest set off imaging tasks.

Complex NAPL Site Characterization Using Fluorescence Part 3: Detection Capabilities for Specific Excitation Sources

Non-aqueous phase liquid (NAPL) contaminants comprised of polycyclic aromatic hy drocarbons (PAHs) can be detected using fluorescence spectroscopic methods. Dense non-aqueous phase liquid (DNAPL) contaminant source zones can be delineated us ing commercially available cone penetrometer (CPT)devices by detecting commingled oils fuels, and naturally occurring organic materials entrained by DNAPLs and carried to depths below the water table. It has been demonstrated that commercially avail able CPT based fluorescence detection systems can be ranked based on how effectively their excitation source wavelengths induce fluorescence using excitation emission ma trices (EEMs). Several neat NAPLs and dilutions with selected DNAPLs were analyzed for specific fluorescence characteristics to determine the optimal excitation source for site characterization efforts. A comprehensive spectral library and corresponding opti mization matrix were generated for complex petroleum mixtures. Based onfield results documenting successful indirect CPT fluorescence detection of a DNAPL source zone, aviation and dieselfuels were selected from this library, diluted with chlorinated sol vents, and evaluated for fluorescence characteristics. Dilution of these complex NAPL mixtures led to changes in the corresponding EEMs. The optimal excitation source for aviationfuel remained relatively constantf or each dilution. However, sensitivityf or each of the commercially available CPT excitation sources was strongly dependent on diesel concentration, whereby higher energy (lowerwavelength) sources yielded improved sen-sitivityfor lower concentrations. Since field concentrations can be highly variable, these observations support the need for multiple wavelength excitation sources for optimal detection capabilities, particularly when diesel fuel ispresent.

A simple, low-cost, remote fiber-optic micro volume fluorescence flowcell for capillary flow-injection analysis.

A small volume flowcell for fluorescence detection in capillary flow injection (CFI) analysis has been created by using a low cost, commercially available fluidic device. Fluorescence detection is achieved using an optical fiber to deliver excitation light to the sample flowing through the device and another optical fiber to collect fluorescence emission. The flowcell is a standard fluidic cross with a swept volume of 721 nL. Optical fibers were oriented at right angles using standard sleeves and ferrules to set their position near the cross intersection. Multiple excitation sources were used including a low power UV laser and blue and UV light emitting diodes (LED). The full emission spectrum detection limits, using the laser, for fluorescein and bovine serum albumin (BSA) were 0.30 ppb and 2.1 x 10(-4)% (w/w), respectively. Two fluidic crosses were used in series for multi-wavelength fluorescence excitation using fiber-optically coupled LED.

Description and performance of a highly versatile, low-cost fiber-optic confocal Raman microscope

A versatile fiber-optic confocal Raman microscope has been developed. Fiber optics provide remote capabilities for the microscope and the ability to use multiple excitation sources and detection schemes. The horizontal and vertical resolutions of the instrument have been determined by monitoring spectral changes while scanning known interfaces and microparticles. The mini- mum detectable particle size has been determined via the spectroscopic analysis of calibrated polystyrene microspheres. The horizontal resolution has additionally been tested in the imaging of a 10 μm glass fiber embedded in an epoxy matrix.

Chapter 36 Phase-Sensitive Detection Methods for Resolving Fluorescence Emission Signals and Directly Quantifying Lifetime

This chapter discusses phase-sensitive detection methods for resolving fluorescence emission signals and directly quantifying lifetime. A new flow cytometry (FCM) approach, based on phase-resolved fluorescence spectroscopy methods that provides unique capabilities for separating signals from multiple overlapping emissions in fluorochrome-labeled cells as they pass across a modulated excitation source, has been developed. The measurement of fluorescence lifetime also is of importance because it provides additional information about fluorochrome/cell interactions. An important advantage of lifetime measurements is that lifetimes in some cases can be considered as absolute quantities. However, the lifetime of dye molecules bound to cellular macromolecules can be influenced by physical and chemical factors near the binding site, such as solvent polarity, cations, pH, energy transfer, excited-state reactions, and quenching. Spectroscopic methods also have been developed to record fluorescence emission spectra on each cell in real time and to resolve multiple emission spectra signals using computational methods. If fluorochromes cannot be resolved by these means, but have separated excitation spectra, multiple excitation sources can be employed to sequentially excite cells and spatially resolve the spectrally overlapping fluorescence signals.

Acoustic radiation from pipes, excited by internal turbulent flow: Comparison of experimental results with theory

The analysis of acoustic radiation from piping systems is complicated by the presence of multiple excitation sources; for example, mechanical valve vibration, acoustic near- and farfields, and the random pressure field of fully-developed turbulent flow will normally act together. This latter pressure field is well defined, and was chosen as the excitation for an initial parametric investigation of the response of and radiation from piping systems. An intermittent induced-flow pipe facility, mounted across an anechoic chamber, was used to obtain extensive measurements of the radiation from steel and P.V.C. pipes for a wide range of flow speeds and several pipe wall thicknesses. Theoretical predictions compare favourably with experimental measurements. The main conclusions are: the acoustic power radiation is resonant and well-described by considering only acoustically fast pipe vibration modes; this radiation is proportional to the modal loss factors and to the fifth power of flow Mach number. Comparisons between excitation by fully developed flow and propagating acoustic fields are given, which demonstrate their relative importance.