Effect of alum on methamphetamine screening tests.

The editorial by Diamandis [1] in Janu-ary discussed a report by Walker et al. [2], who used strand displacement amplification and fluorescence polarization (FP) to detect Mycobacterium tuberculosis. The editorial placed particular emphasis on the homogeneous format of the assay. However, this aspect deserves to be expanded by an outline of the significance and evolution of combining DNA ampli-flcationlhybridization with FP. Walker et al. did not attain the reported results with FP in its traditional format but rather used a radically new fluorometric technology. The use of FP in binding assays is not a recent event. This technology has been known for >20 years [3], and its use in DNA ampliflcation!hybridization procedures has been reported earlier [4]. Traditional FP with fluorescein and steady-state fluorometric instrumentation has been used successfully as a format for assays not requiring high sensitivity, e.g., monitoring the circulating concentrations of therapeutic drugs, for which it has practically displaced most other technologies. Despite its homogeneous format , however, traditional FP has not been able to compete successfully with enzyme-linked immunodiagnostic procedures for the great majority of other assays, and it has not established itself as a viable option for DNA hybridization! amplification procedures either. The reason for this inability is that, in its traditional format, fluorometry has been plagued by substantial background interference , resulting in low sensitivity. Walker et al. report the use of the new fluorescent dye, La Jolla Blue, and the new detection technique, transient-state fluorometry, both engineered to dramatically reduce background interference and improve signal-to-noise ratio. La Jolla Blue fluoresces at 705 nm, near the infrared region, where intrinsic fluores-cence from other serum components is substantially less. Compounding this reduction of autofluorescence is the transient state detection technique, which performs the excitation by short pulses of a laser diode and measures the decaying fluorescence in the intervals between the pulses. The background noise caused by light-scattering is thus eliminated from the excitation beam. In comparison with traditional fluorometric methods that use fluorescein and steady-state detection, either of the two components of the new technique can improve the signal-to-noise ratio by-10-fold, and the two together improve the sensitivity by-100-fold. Earlier, Devlin et al. [5] already reported the use of La Jolla Blue and transient-state fluorometry in connection with another DNA amplification procedure known as 3SR. It is this recent quantum leap in the sensitivity of fluoro-metric detection and quantification-provided by the combination of La …