A new method to detect bacterial endospores and determine their concentration was demonstrated by the addition of a solution of terbium chloride to a suspension of bacterial endospores. The terbium chloride reacted with the calcium dipicolinate in the spore case to form terbium(III) dipicolinate anion. Solid particles, including residual bacterial particles, were removed by filtering. The photoluminescence from the solution was measured as a function of excitation wavelength, emission wavelength, and bacterial endospore concentration. The photoluminescence from terbium(III) dipicolinate anion in the solution was easily identified.

A determination of the viability of an endospore detection technique using terbium dipicolinate photoluminescence in the presence of other chemical and biological materials was performed. The compounds and organisms examined, possible environmental constituents, covered three broad categories:  organic compounds, inorganic compounds, and biological materials. Each substance was tested for a false positive, which occurs if the intrinsic terbium photoluminescence is enhanced in the absence of a bacterial endospore. The detection technique was also investigated for false negatives, which occur if a known positive endospore signal is inhibited significantly. Although several materials may give rise to false negative signals, none caused a false positive signal to be observed.

A novel technique in time resolved luminescence spectroscopy called population mixing using a subpicosecond cw mode-locked dye laser has been developed and applied to p-type GaAs at low temperatures. Using this technique the relaxation lifetime for electron recombination was measured to be 39±7 ps for p-type GaAs with Zn at 6×1018 cm−3 hole concentration. This is comparable to the relaxation time measured by a streak camera.

Time-resolved photoluminescence was studied as a function of chelation number in terbium dipicolinate. We excited the ligand (dipicolinate) with UV (250 to 330 nm) and collected the emission from the cation (terbium) in the visible region (450 to 700 nm). The luminescence of Tb(dpa)n3–2n followed a monoexponential decay, with a lifetime (0.66 to 2.0 ms) that decreased continuously as the terbium chloride concentration increased. The luminescence lifetime of Tb(dpa)+ was 0.66 ms. We measured the luminescence decay time, the peak intensity, and the total time-integrated intensity as a function of terbium chloride concentration at two dipicolinic acid concentrations and fitted the results to functions of terbium dipicolinate concentration. We used a model with rapid ligand exchange and rapid back-transfer of energy to fit the data to first order. We also present molar absorptivity spectra of complexes with different chelation numbers.

Light scattered from optically active spheres was theoretically analyzed for biodetection. The circularly polarized signal of near-forward scattering from circularly dichroic spheres was calculated. Both remote and point biodetection were considered. The analysis included the effect of a circular aperture and beam block at the detector. If the incident light is linearly polarized, a false signal would limit the sensitivity of the biodetector. If the incident light is randomly polarized, shot noise would limit the sensitivity. Suggested improvements to current techniques include a beam block, precise angular measurements, randomly polarized light, index-matching fluid, and larger apertures for large particles.

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A determination of the viability of an endospore detection technique using terbium dipicolinate photoluminescence in the presence of other chemical and biological materials was performed. The compounds and organisms examined, possible environmental constituents, covered three broad categories: organic compounds, inorganic compounds, and biological materials. Each substance was tested for a false positive, which occurs if the intrinsic terbium photoluminescence is enhanced in the absence of a bacterial endospore. The detection technique was also investigated for false negatives, which occur if a known positive endospore signal is inhibited significantly. Although several materials may give rise to false negative signals, none caused a false positive signal to be observed.

No abstract