A Novel luminescence analyser for europium chelates using solid-state excitation and a gated photomultiplier

Signal detection can present a major challenge for fluorescence based detection modalities when target is encountered together with intrinsically fluorescent (autofluorescent) components. Luminophores with long emission lifetimes (eg lanthanide chelates) afford a means to discriminate signal from short-lived autofluorescence through the use of Time-Gated Luminescence (TGL). We have recently synthesized a number of novel europium chelates and required an instrument to accurately compare luminescence lifetime, spectral output and emission intensity. The photophysical response of the chelates was captured using a lab-built time-gated luminescence analyser employing pulsed UV (360 nm) excitation from a high-power (~200 mW) LED. Chelate luminescence was detected using a R928 photomultiplier tube gated electronically into conduction shortly after the excitation pulse had ceased. The photomultiplier dynodes were configured in a novel switching arrangement using high-voltage field effect transistor (FET) devices driven by an optically isolated signal. Using this arrangement, the photomultiplier was gated off until LED excitation had fully extinguished whereon the tube was switched to full-gain within less than a microsecond. In the prototype instrument the strongly emitting europium line (⁵D₀→⁷F₂) was collected with high efficiency using epifluorescence optics. We used the instrument to compare two intensely luminescent europium chelates (BTOT and BHHT) using the analyser and report key photophysical parameters for both compounds