Biomedical subjects

Sean J Hart

Publications and source records attributed to Sean J Hart.

4 recordsLinked to original sources

PubMed2006

Discovery of a significant optical chromatographic difference between spores of Bacillus anthracis and its close relative, Bacillus thuringiensis.

A significant difference between two closely related Bacillus spores has been discovered using optical chromatography. This difference can be harnessed for the separation of microscopic particles using opposing laser and fluid flow forces. Particles of different size, composition, and shape experience different optical and fluid forces and come to rest at unique equilibrium positions where the two forces balance. Separations in excess of 600 mum have been observed between Bacillus anthracis Sterne strain and its genetic relative, Bacillus thuringiensis. These findings open new possibilities for detection and characterization of the biological warfare agent, B. anthracis, the causative agent of anthrax, the deadly mammalian disease. The large optical separation between these species is surprising given their close genetic relationship but may be explained by differences in their shape and exosporium morphology, which may result in differences in fluid drag force. The observation of large differences due to less common variables indicates the complex nature of the force balance in optical chromatography, which may in the future be used to separate and characterize microbiological samples. In general, the discovery of such large differences between such closely related biological species suggests new possibilities for the separation and characterization of microorganisms using the full range of emerging techniques that employ radiation pressure (optical filtering, laser tweezers, optical chromatography, etc.).

Bacillus anthracis↗

PubMed2002

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.

Journal Article↗

PubMed2002

Light emitting diode excitation emission matrix fluorescence spectroscopy.

An excitation emission matrix (EEM) fluorescence instrument has been developed using a linear array of light emitting diodes (LED). The wavelengths covered extend from the upper UV through the visible spectrum: 370-640 nm. Using an LED array to excite fluorescence emission at multiple excitation wavelengths is a low-cost alternative to an expensive high power lamp and imaging spectrograph. The LED-EEM system is a departure from other EEM spectroscopy systems in that LEDs often have broad excitation ranges which may overlap with neighboring channels. The LED array can be considered a hybrid between a spectroscopic and sensor system, as the broad LED excitation range produces a partially selective optical measurement. The instrument has been tested and characterized using fluorescent dyes: limits of detection (LOD) for 9,10-bis(phenylethynyl)-anthracene and rhodamine B were in the mid parts-per-trillion range; detection limits for the other compounds were in the low parts-per-billion range (< 5 ppb). The LED-EEMs were analyzed using parallel factor analysis (PARAFAC), which allowed the mathematical resolution of the individual contributions of the mono- and dianion fluorescein tautomers a priori. Correct identification and quantitation of six fluorescent dyes in two to six component mixtures (concentrations between 12.5 and 500 ppb) has been achieved with root mean squared errors of prediction (RMSEP) of less than 4.0 ppb for all components.

Electronics↗

PubMed2001

A laser-induced fluorescence dual-fiber optic array detector applied to the rapid HPLC separation of polycyclic aromatic hydrocarbons.

A multi-channel detection system utilizing fiber optics has been developed for the laser-induced fluorescence (LIF) analysis of chromatographic eluents. It has been applied to the detection of polycyclic aromatic hydrocarbons (PAH) in a chromatographically overlapped standard mixture and to a complex soil sample extract obtained during fieldwork. The instrument utilizes dual-fiber optic arrays, one to deliver multiple excitation wavelengths (258-342 nm) generated by a Raman shifter, and the other to collect fluorescence generated by the sample at each excitation wavelength; the collected fluorescence is dispersed and detected with a spectrograph/CCD combination. The resulting data were arranged into excitation emission matrices (EEM) for visualization and data analysis. Rapid characterization of PAH mixtures was achieved under isocratic chromatographic conditions (1.5 mL min(-1) and 80% acetonitrile in water), with mid microg L(-1) detection limits, in less than 4 minutes. The ability of the instrument to identify co-eluting compounds was demonstrated by identifying and quantifying analytes in the rapid analysis of a 17 component laboratory-prepared PAH mixture and a soil extracted sample. Identification and quantification were accomplished using rank annihilation factor analysis (RAFA) using pure component standards and the EEMs of mixtures measured during the rapid high-performance liquid chromatography (HPLC) method as the unknowns. The percentage errors of the retention times (RTs) determined using RAFA compared to the known RTs measured with a standard absorbance detector were between 0 and 11%. For the standard PAH mixture, all 17 components were identified correctly and for the soil extracted sample, all 8 analytes present were correctly identified with only one false positive. Overall, the system achieved excellent qualitative performance with semi-quantitative results in the concentration predictions of both the standard mixture and the real-world sample. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s00216-001-1125-6.

Journal Article↗