Wavelength pair selection for bacterial endospore detection by use of terbium dipicolinate photoluminescence

Two regression techniques, a multivariate technique and a subtracted component technique, were applied to two-wavelength response functions of mixtures of terbium (III) dipicolinate and insoluble bacterial particles. Two wavelength pairs were analyzed: a pair of neighboring wavelengths (450/490 nm) and a pair of widely spaced wavelengths (490/622 nm). The analysis shows that two emission-wavelength spectra from terbium-treated endospores can be distinguished from the vegetative bacteria spectrum above a limit of detection for endospores, which depends on the regression algorithm used to analyze the spectra. The subtracted component method for the neighboring wavelength pair had far lower limits of detection than the other methods.